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Impact of a moderate/high-severity prescribed eucalypt forest fire on soil phosphorous stocks and partitioning
Abstract
This study examines the direct impact of a moderate/high-severity prescribed fire on phosphorous (P) stocks and partitioning in oligotrophic soils of a dry eucalypt forest within Sydney's water supply catchments, Australia. We also quantify and characterize the P present in the ash produced in this fire, and explore its relationships with the maximum temperatures recorded in the litter layer during the burn.
In these oligotrophic soils, P concentrations were already relatively low before the fire (< 130 mg kg− 1, mainly in organic forms). The fire consumed the entire litter layer and the thin Oa soil horizon, creating 6.3 ± 3.1 t ha− 1 of ash, and resulted into direct net P losses of ~ 7 kg ha− 1. The P lost was mostly organic and there was a moderate net gain of inorganic and non-reactive P forms. Importantly, only a small proportion of the post-fire P was bioavailable (equivalent to ~ 3% of the total P lost during fire). Higher total P concentrations in ash corresponded with higher maximum temperatures (> 650 °C) recorded in the burning litter layer, but effects of fire temperature on ash P partitioning were not significant.
Fire not only transformed P chemically, but also physically. Our results show that, immediately after fire, up to 2 kg ha− 1 of P was present in the ash layer and, therefore, highly erodible and susceptible to be transported off-site by wind- and water erosion. Even if most of this P was, initially, of low bioavailability, its transfer to depositional environments with different geochemical conditions (e.g. anoxic sediments in water reservoirs) can alter its geochemical forms and availability. Further investigation of potential P transformations off-site is therefore essential, particularly given that SE-Australian water supply catchments are subject to recurrent perturbation by prescribed fire and wildfires. The latter have already resulted in major algal blooms in water supply reservoirs.
... Prescribed burning is gradually being adopted in Mediterranean countries as an important tool for fuel management, to limit the risk and to reduce impacts and negative consequences of large, severe wildfires 3,4 . Although the implementation of PB remains limited, different technical studies have assessed the effects on overland flow 5 and soil erosion 6 as well as the short-and long-term dynamics of soil properties, including soil organic matter (SOM) 4,7-10 and soil phosphorus 11 . ...
... favours soil P depletion via solubilization and mobilization with run-off and eroded sediments 54 , which can be detrimental to the maintenance of long-term P supply in the system 28 . Beyond a certain pH threshold, P availability may also be reduced due to physical trapping phenomena (occlusion) in carbonates 11,28 . ...
... In the present study, soils affected by low SBS, as in the Doñana site, produced a short-term orthophosphate peak in the organic layer, possibly due to the mineralization of monoesters and diester 38 . In soils affected by higher SBS, as in the Cartaya and Bermeja sites, the clear dominance of orthophosphate and the disappearance of the remaining P forms was consistent with previous findings in sites affected by high SBS 11 . Along with the orthophosphate dominance, the clear trend of diminishing P-diester with increasing fire severity was another notable effect in our study and elsewhere 27,28 . ...
Soil phosphorus (P), which is essential for ecosystem functioning, undergoes notable changes after fire. However, the extent to which fire characteristics affect P dynamics remains largely unknown. This study investigated the impact of type of fire (prescribed burning and natural wildfires) of different levels of severity on P dynamics in Mediterranean soils. Soil P concentrations in the organic layers were strongly affected by fire severity but not fire type. Low severity fire did not have any observable effect, while moderate fire increased soil P levels by 62% and high severity decreased soil P concentration by 19%. After one year, the soil P concentration remained unchanged in the low severity fires, while rather complex recovery was observed after moderate and high severity fires. In the mineral layers, P concentration was reduced (by 25%) immediately after the fires and maintained for one year (at 42%). ³¹P-NMR spectroscopy revealed almost complete post-fire mineralization of organic P forms (mono- and diesters), large increases in inorganic orthophosphate and a decrease in the organic:inorganic P ratio (Po:Pi). After one year, di-esters and orthophosphate recovered to pre-fire levels at all sites, except those where parent material composition (high pH and Fe concentration) had an enduring effect on orthophosphate retention, and thus, on the total soil P. We showed that fire severity and soil pH (and hence, soil mineralogy) played an essential role in soil P dynamics. These findings are important for reliable assessment of the effects of fire on soil P conservation and for improving the understanding the impact of prescribed burning.
... Several plants were shown to acquire P through dust that settled on their leaves, as the leaf surface chemical environment favours conditions that enhance dust P solubility with pH that ranges between 3-6 and exudation of organic acids by the leaf (Gross et al., 2021). P in ash from biomass fire is derived mainly from organic compounds that were oxidised during biomass burning and supposedly converted into readily solubilised inorganic P compounds (Bauters et al., 2021;Gabet & Bookter, 2011;Santín et al., 2018). Yet, the effects of pH and organic exudates on fire ash P are harder to predict as the role of ash as a P source received less attention in the literature. ...
... Error bars represent standard deviations (n = 4) fractionation in fire ash is scarce and highly variable. Several studies reported that the dominant P fraction is Ca-P (Masto et al., 2013;Qian et al., 2009) while other shows low Ca-P or Fe-P (Tan & Lagerkvist, 2011) but high Al-P highly insoluble non-reactive P (Santín et al., 2018). All of these P fractions could be sensitive to pH and organic acids and explain our results. ...
... All of these P fractions could be sensitive to pH and organic acids and explain our results. Fire temperature and the type of the burning biomass were associated with the high variability found in ash P fractionation due to differences in the combustion efficiency of the burned biomass (Gabet & Bookter, 2011;Santín et al., 2018). At moderate temperatures (~200 C), P condensation to form polyphosphate is feasible, while high temperatures promote polymerisation and decrease solubility . ...
Atmospheric deposition of desert dust and ash from wildfires are recognised as major suppliers of phosphorus (P) to soils in many terrestrial ecosystems. The biological effects of desert dust and fire ash P depend on their interactions with the receiving soils. However, the chemical processes and environmental conditions that control dust and ash P bioavailability post deposition are unknown. Soil and rhizospheric pH and organic exudates are acknowledged as central parameters that control soil P bioavailability. Here we performed a series of in‐vitro incubation experiments to study their effects on P solubility of various desert dust and fire ash samples. Then, we tested the dust and ash P solubility that were added to acidic and alkaline soils. Our results show that dust P solubility gradually increases by a few orders of magnitude as pH decreases from 7 to 2.5 and also with increased concentrations of oxalic and malic acids, two ubiquitous P solubilising organic exudates in soils. In both cases, the increase in dust P solubility occurs mainly by dissolving P from insoluble Ca‐P minerals such as apatite, the major P bearing mineral in desert dust. P solubility of fire ash was dramatically higher than that of desert dust but showed the same pattern of a gradual increase with decreasing pH or with increasing concentrations of oxalic and malic acids. When the dust was suspended with soils, extractable P level was ~10 times higher in alkaline soil than acidic soil despite the lower pH of the later, probably due to the strong P sorption capacity of the acidic soils. On the contrary, when fire ash was suspended, extractable P in the acidic soil was higher than that of the alkaline soil indicating substantial variation in P forms. Overall, our results indicate that the bioavailability of P from desert dust and fire ash is largely controlled by environmental and chemical factors in the receiving soils.
Highlights
Atmospheric deposition from desert dust and fire ash is a major phosphorus source to soils.
However, the actual bioavailability of dust and ash P post deposition is unknown.
Soil pH, organic acids concentrations and P sorption capacity controls dust and ash bioavailability.
The bioavailability of atmospheric P is controlled by environmental factors in the receiving soils.
... This contrast between the ash and topsoil layer could reflect the fast mineralization of organic matter during the combustion of aboveground vegetation and litter (Caon et al., 2014;Kutiel and Inbar, 1993;Santín et al., 2018). The present results differed, however, from those of Ferreira et al. (2016a) who reported higher Pav contents in the topsoil than in the ash layer of a burnt eucalypt plantation on schist in the same study area. ...
... Noteworthy, the temporal patterns in nutrient concentrations varied markedly between the two elements (Fig. 8). In the case of dissolved as well as total P concentrations, the highest peaks coincided with the first significant post-fire rainfall events, likely due to the detachment and transport of the P-enriched easily-erodible ash layer (Ferreira et al., 2005;Lane et al., 2008;Thomas et al., 1999;Santín et al., 2018). By contrast, the major peaks in dissolved and total N concentrations, occurred all over the monitoring period, suggesting that the availability of N forms for export may be dependent on an interplay of biogeochemical processes such as N mineralization and nitrification (Lane et al., 2008). ...
... The comparison of the observed TN and TP levels in post-fire overland flow with the Portuguese quality standards for multi-purpose surface waters (SNIRH, 2019: TN ≈ 52 mg L -1 , TP -0.4 mg L -1 ) suggested that P is more likely to cause water quality problems than N. Phosphorus concentrations in overland flow exceeded the quality threshold levels at several occasions, especially during the first 4 months after fire, reinforcing the need for timely application of postfire erosion mitigation measures. This risk of P contamination has also been referred in other studies dealing with other forest types and water quality standards (Blake et al., 2009a(Blake et al., , b, 2010Burd et al. 2018;Burke et al., 2005;Santín et al., 2018;Santos et al., 2015;Silins et al., 2014;Stein et al., 2012). ...
Wildfires affect vast areas of Mediterranean forests, thereby triggering changes in hydrological and geomorphological processes that can negatively affect both terrestrial and aquatic ecosystems. Although several studies have evaluated the post-fire hydrological and erosive response in burnt forest areas, an important knowledge gap remains with respect to nutrient mobilization by overland flow. To address this gap, a recently burnt area was selected near the Ermida village (north-central Portugal). The study area was instrumented shortly after a wildfire that occurred in July 2010, to evaluate the export of dissolved (nitrate - NO3-N and orthophosphate - PO4-P) and total nitrogen (TN) and phosphorus (TP) forms by overland flow. This was done in two burnt eucalyptus plantations due to their contrasting slope aspects (south-east vs. north-west). Bounded micro-plots were installed in August 2010 and monitored over two years. During this period, overland flow samples were collected on a 1- to 2-weekly basis, depending on the occurrence of rain. Results showed that the north west-facing slope (BE-N) presented higher nutrient losses than the south east-facing slope (BE-S), contradicting the findings of previous studies in the Mediterranean region. A logging operation that had taken place at the BE-N site shortly before the fire might account for these findings, by causing soil compaction and/or reducing the protective vegetation and litter cover. TN and TP exports were particularly pronounced during the first four months following the wildfire. After this initial period, further peaks in TN and TP exports occurred sporadically, mainly associated to intense rainfall events. The observed mid-term post-fire nutrient losses not only suggested a threat to the soil nutrient balance of Mediterranean eucalypt forests but also a potential risk of eutrophication of downstream water bodies.
... The P dynamics are particularly critical in shifting cultivation, as the tropical and subtropical regions where this practice is prevalent are limited in P (Du et al., 2020;Heinimann et al., 2017). Additionally, recent concerns over a global P shortage caused by soil erosion (Alewell et al., 2020) highlight the potential for fires to exacerbate this issue by accelerating erosion (Santín et al., 2018;Schaller et al., 2015). Therefore, comprehending the effects of fire on soil P dynamics is essential and requires proper fire-based land management strategies. ...
... Soil P primarily exists as inorganic phosphate (P i ) and organic phosphate (P o ) (Darch et al., 2014). Although previous studies have reported that fire increases bioavailable P i through the thermal mineralization of P o , ash incorporation and dissolution of stable P with pH change, the changes are highly variable (García-Oliva et al., 2018;Santín et al., 2018;Schaller et al., 2015) and not always statistically significant (Alcañiz et al., 2018). Understanding the effects of fire on soil P dynamics in the field remains challenging due to the interaction between fire spread and soil properties with high spatial heterogeneity, as described above (Alcañiz et al., 2018;Gimeno-Garcıá et al., 2004;Vega et al., 2013). ...
This study demonstrates that phosphate oxygen isotope (δ¹⁸OPO4) analysis effectively detects and monitors fire‐induced transformation in soil phosphorus (P). Fires increase bioavailable P, potentially limiting primary production in terrestrial ecosystems. However, understanding the effects of fire on soil P dynamics in the field remains challenging due to the interaction between fire spread and soil properties with high spatial heterogeneity. Soil burning experiments were conducted using a surface soil sample collected in central Japan. The soil was burned in an electric furnace from 50 to 550°C for 3 h, and P concentrations and δ¹⁸OPO4 values were determined. The results revealed that high temperatures (>350°C) depleted the soil of organic P (Po) and increased labile and stable inorganic P (Pi) concentrations while significantly decreasing δ¹⁸OPO4 values. By contrast, low temperatures (150°C) increased labile Pi and Po concentrations without isotopic shift, indicating that low‐intensity fires could increase bioavailable P while conserving soil organic matter. These findings indicate that δ¹⁸OPO4 analysis can provide insight into the relationship between P transformations and fire intensity and track subsequent changes in P dynamics over time. Our research highlights the potential of δ¹⁸OPO4 in predicting and managing postfire ecological and agricultural impacts.
... Exposure to high temperatures can also transform crystalline minerals, which regulate the sorption capacity of soils for phosphorus, resulting in a lower phosphorus content in soils and/or reduced bioavailability of soil phosphorus following fires. In the study of a prescribed moderate-high severity burn, a loss of approximately 7 kg/ha of phosphorus was observed in oligotrophic soil (Santín et al. 2018). The majority of the organic and bioavailable forms of phosphorus were removed from the soil, with implications for vegetation recovery and capacity in ecosystem support, as well as reduced resilience of soils to future stresses (Santín et al. 2018). ...
... In the study of a prescribed moderate-high severity burn, a loss of approximately 7 kg/ha of phosphorus was observed in oligotrophic soil (Santín et al. 2018). The majority of the organic and bioavailable forms of phosphorus were removed from the soil, with implications for vegetation recovery and capacity in ecosystem support, as well as reduced resilience of soils to future stresses (Santín et al. 2018). Short-term increases in post-fire soil microorganism biomass result from rapid growth of fire-resistant microorganism communities that utilise nutrients from dead microorganisms and labile carbon. ...
Geodiversity elements contribute significantly to local and global hydrological, biogeochemical and ecosystem services and as such, fire is a potentially disruptive force with long-term implications. from limiting karstic speleothems formation, to compounding impacts of peat-fire-erosion cycles. Geodiversity elements additionally possess important cultural, aesthetic, and environmental values, including the support of ecosystem services. Hence, assessments of potential fire damage should consider implications for land users, society, and culture, alongside the geomorphic impacts on geodiversity elements. With a view to providing a concise set of descriptors of the response of geodiversity elements to fire, we qualify and in places, quantify, how fire may degrade geosystem function. Where possible, we highlight the influence of fire intensity and frequency gradients, and cumulative fire, in the deterioration of geodiversity values. Geoconservation is integral to protected areas with implications from fire effected geodiversity functions and values presenting issues for management, with potential consequences extending through to delisting, degazetting, and resizing of protected areas. Future research in reserve systems should concentrate on understanding the synergistic and compounding effects of fire on the geophysical landscape.
... For example, variable P molecular structures (e.g. pyrophosphates and organophosphates) were identified in fire residues (García-Oliva et al. 2018;Santín et al. 2018), but thermochemical reactions and factors controlling their formation and abundance remain unknown. Second, although P mobility of fire residues has been evaluated, mechanisms underlining the rate and extent of P release are not well understood (Qian et al. 2009;Galang et al. 2010). ...
... Pyrophosphate was also inconsistently detected in natural fire residues. For example, pyrophosphate accounts for about 0.2-2.8% of total extractable P in fire residues from a pine forest fire but is absent in the residue from a eucalypt forest fire (García-Oliva et al. 2018;Santín et al. 2018). Without information on the biomass composition and fire conditions, causes of this variation were unknown. ...
Background
Vegetation fire may change Phosphorus (P) cycling in terrestrial ecosystems through converting biomass into fire residues.
Aim
The aim of this study was to understand the chemistry and mobility of P in fire residues to help reveal P thermochemistry during biomass burning and post-fire P cycling.
Methods
A combination of sequential extraction, liquid ³¹P NMR and P K-edge XANES was used to obtain quantitative P speciation and explain P solubilisation behaviours of charcoal.
Key results
Despite varying diverse P species existing in raw biomass, only two P structural moieties – orthophosphate and pyrophosphate – were identified in charcoal. However, relative abundance of pyrophosphate differs greatly among charcoal samples from different biomass types, ranging between 0 and 40% of total extractable P. Although P K-edge XANES data indicates abundant soluble phosphate minerals, most P (70–90%) is likely occluded physically in the charcoal. The bicarbonate-extractable P (the Olsen-P) varies significantly and cannot be explained by surface P concentration or elemental stoichiometry alone.
Conclusion and implications
The results suggest the importance of starting biomass P speciation (i.e. molecular structure and complexation environment) and thermal conditions in controlling P speciation and availability in charcoal. The different P chemistry between charcoal and ash suggests the importance of fire types and severity in disturbing the P cycle.
... The combustion of nutrients bound to vegetation and SOM adds inorganic forms of K, Ca, Mg, P, and N to the soil (Alcañiz et al., 2016;Schlesinger et al., 2016). Studies by Tomkins et al. (1991) and Santín et al. (2018) reported an increase in soil exchangeable Ca one month after a fire on a Eucalyptus plantation. However, the increase of soil exchangeable Ca was almost gone six months later. ...
... Chungu et al. (2020) found results similar to those of our study, and the increase in Ca concentration persisted for one to two years after a fire event. Tomkins et al. (1991), Santín et al. (2018) and Chungu et al. (2020) also found an increase in soil exchangeable K, differing from our results. However, Bridges et al. (2019) found a reduction in K concentrations under burned soils when compared to unburned soils. ...
Field fires can modify soil nutrient cycling and alter soil microbial communities (SMC), although the latter is not well understood. In the southern region of Puerto Rico, field fires have become a significant problem during the dry season. To mimic the effects of a field fire, we performed prescribed fires on a hillside at the Juana Díaz Agricultural Experiment substation in October 2015 and March 2017. A complete randomized block design was established in Yauco soil (Typic calciustolls) that included the following treatments: negative control (unburned), positive control (burned plots, no remediation), mulching treatment (burned plots remediated with Leucaena spp. mulch), and surfactant treatment (burned plots remediated with a surfactant). In the first burning (2015), soil samples were collected before burning and at 30, 180, and 420 days after burning (DAB). In the second burning (2017), soil samples were collected at 30, 90, and 270 DAb. soil physicochemical properties and microbial community structure were assessed using phospholipid fatty acid (PLFA) analysis. Overall, burning increased soil exchangeable Ca2+ (except after 30 DAB in the second burning) and decreased exchangeable K+ when compared to unburned soils. compared to unburned plots, total fungal PLFA was significantly lower in burned plots with or without mulch and surfactant treatments, and total bacterial PLFA did not differ between burned and unburned plots after 30 days. Total microbial biomass was significantly (P<0.05) higher in mulch and surfactant treated burned soil compared to unburned and burned plots without treatment after 90 DAB (2017) and 420 (2015) DAB. The use of mulch and surfactant treatments in prescribed burning fields increased microbial communities 90 DAB. This study emphasizes short-term changes in microbial communities and suggests they are highly resilient to disturbances after prescribed fires.
... The wind event that occurred shortly after fire, deposited ash and charcoal particles rich in OM (and consequently C, N and P), on both untreated and mulched plots ( Table 1). The C contents of the wind-blown sediments were within the range of values reported in other studies for the ash layer (227-345 g kg −1 ; Campos et al., 2016;Gómez-Rey et al., 2013;Santín et al., 2018), but the N and P contents were about one order of magnitude higher (Santín et al., 2018;Serpa et al., 2020), which can explain the higher P exports found in the present study, especially during the first post-fire year (Table 4). ...
... The wind event that occurred shortly after fire, deposited ash and charcoal particles rich in OM (and consequently C, N and P), on both untreated and mulched plots ( Table 1). The C contents of the wind-blown sediments were within the range of values reported in other studies for the ash layer (227-345 g kg −1 ; Campos et al., 2016;Gómez-Rey et al., 2013;Santín et al., 2018), but the N and P contents were about one order of magnitude higher (Santín et al., 2018;Serpa et al., 2020), which can explain the higher P exports found in the present study, especially during the first post-fire year (Table 4). ...
The quick implementation of emergency stabilization measures is vital for minimizing post-fire soil erosion and the associated fertility loss. Mulching has proven to be highly effective in minimizing post-fire soil erosion, however few studies have investigated its impacts on organic matter (OM) and nutrient mobilization from burned forest areas. This study evaluates the effectiveness of forest residue mulching at reducing OM, N and P losses within the sediments after a moderate-severity wildfire over a period of 5 years (Ermida, North-central Portugal). Untreated and mulched plots of ca. 100 m2 were bounded with geotextile fabric and sediments were collected from silt fences after a total of 29 periods. During the first five years after the fire, the accumulated OM, N and P exportations in the untreated plots were, respectively, 199, 5.2 and 0.38 g m-2; and mulch significantly reduced these figures in, respectively, 91 %, 94 % and 95 % (p < 0.05). The overall OM content in the sediments of the untreated plots (45 %) was not different from the OM content of the mulched plots (34 %, p = 0.16). However, the N (8.9 g kg-1) and Pav contents (0.62 g kg-1) in the untreated plots were significantly higher than the N (5.6 g kg-1; p < 0.05) and Pav contents (0.36 g kg-1; p < 0.05) in the mulched plots. This effect was especially noticeable in the first year after fire. OM and TN contents in the sediments were highly variable throughout the study period, whereas Pav contents declined sharply in the first post-fire rainfall events, maintaining low values afterwards. The main factors driving nutrient exports were ash and litter cover, whereas no significant relationship was observed for OM exports. The present work has shown that forest residues application can be a sustainable strategy for the conservation of soil carbon and nutrients in fire-affected areas.
... Similarly, forest treatments and wildfire have the potential to increase P concentrations in forested ecosystems mainly through increases in soil erosion and increased availability of ash that has an elevated P concentration (Santín et al., 2018). However, studies have found little effects from thinning or from a combination of thinning and prescribed fires on P delivery (Kaye et al., 2005;Martin and Harr, 1989). ...
... However, studies have found little effects from thinning or from a combination of thinning and prescribed fires on P delivery (Kaye et al., 2005;Martin and Harr, 1989). Since forest wildfires, especially those that result in high soil burn severity, affect soil properties, there is more evidence that P concentrations post-wildfire increase (Lane et al., 2008;Murphy et al., 2006;Santín et al., 2018;Smith et al., 2011). However, because this information is limited in the research literature, we did not attempt to include in the model any temporal changes in phosphorus concentrations with treatment. ...
... For example, the Balmoral fire of October 2013 which burned almost 13, 000 ha of Sydney's (Australia) forested water supply catchment produced substantial ash loads that increased with burn severity, with 6, 16 and 34 T/ha found in areas affected by low, high and extreme burn severity, respectively (Santín et al., 2015). Similarly, Santín et al. (2018) reported that fire in dry sclerophyll eucalypt forest of south-eastern Australia produced an average of 6.3±3.1 T/ha of ash, with higher quantities in the areas subjected to high burn severity (6.9±3.3 T/ha) than in the areas of moderate burn severity (4.9±1.6 T/ha). ...
... However, records of actual temperature profile in the soil, and duration of heating (Bodi et al. 2014) attained in the organic layer during fire event are limited and highly variable. For example, a maximum temperature of 890 • C was recorded in a litter layer during prescribed burns conducted in dry eucalypt forest within Sydney's water supply catchments (Santín et al., 2018), and 250 • C was measured in the top 1 cm of soil for 27 min during an experimental burn in Banksia-Eucalypt by Tangney (2018) in urban woodland forest in Perth, Australia. Thus, monitoring of temperatures may be useful to improve our understanding of the underlying processes that lead to spatio-temporal variability of the OM stock and composition. ...
Fires in forested catchments pose a water contamination risk from fire-derived dissolved organic matter (DOM). Fire events are expected to increase under a projection of warmer and drier climatic conditions; therefore, understanding the consequences of fire-derived DOM is critical for water supply and management of drinking water and catchments. This paper addresses how fire regime - the intensity, severity and frequency of fires - influences DOM quantity and composition in surface waters in forested catchments, and how long it takes for water quality to recover to pre-fire levels. A review of post-fire studies in Mediterranean regions reporting on DOM related parameters has been conducted. The literature shows that post-fire DOM composition and reactivity is different from DOM generated under processes of biological degradation, and hence our reliance on DOM 'bulk properties' and surrogate DOM bulk parameters may not provide sufficient information to deal with the potential complexity of the organic compounds produced by a catchment fire. Appropriate measures are important to adequately operate conventional water treatment facilities, for example. Critical parameters for the effects of burning include the alteration of DOM composition, aromaticity, and the relative amounts of labile/recalcitrant organic components. The literature shows mixed information for the influence of both burn severity and fire intensity, on these parameters, which indicates DOM response to fire is highly variable. For fire frequency, the evidence is more unequivocal, indicating that frequent fires change the composition of DOM to components that are less bioavailable, and elevate the degree of aromaticity, which may be detrimental to water quality. In addition, and in general terms, the more recent the fire, the more aromatic and humified DOM components are found, and vice versa. The recovery of surface water quality to pre-fire conditions was variable, with no safe temporal thresholds suggested in the literature. In some cases, fire-induced changes in DOM composition were observable up to 16 years post-fire. The lack of clearly observed trends in post-fire DOM with fire regimes could be attributed to numerous factors such as limited long-term and event-based observations, experimental design challenges, and site-specific biological, physical and hydrological factors. The application of terminologies used to describe fire regimes such as burn severity and fire intensity also creates challenges in comparing the outcomes and results from numerous studies.
... In more severe fires where the soil can experience substantial heating (>200-300 C), decreases in soil organic carbon (SOC) have been observed. For example, for a moderate-high severity fire in eucalyptus forest over sandy soils near Sydney, complete combustion of the Oa horizon (maximum temperature: $400 C), was observed, whereas the C concentration in the Ah horizon (maximum temperature: $50 C) was not altered ( Fig. 2; Santín et al., 2018). A study examining SOC at 0-5-cm soil depth after different severities of soil burn in pine forest and shrublands in NW Spain showed that the lowest severities of soil burn did not translate into a significant decrease of SOC, but the highest resulted in SOC losses of up to 86% (Vega et al., 2013). ...
... This fertilizing effect has long been taken advantage of in agriculture, such as slash and burn in shifting cultivation in tropical forest regions or stubble burning following harvesting in croplands (Maass, 1995). This fertilization effect, however, is rather transient and postfire erosion processes can lead to a substantial net loss of nutrients in the longer term (Caon et al., 2014;Santín et al., 2018). ...
Fires affect many landscapes whether ignited by lightning or humans. They can affect soil physical, chemical and biological characteristics directly through heating and combustion, or indirectly through modified biological, pedological and hydrological processes after the fire. Direct effects include changes in organic matter, nutrients, biota, water repellency, aggregate stability, and an increased susceptibility to erosion. Indirect effects arise from incorporation of ash and from changes in vegetation cover, the water balance, organic matter inputs or protection from erosion. These effects can last from months to years and, in fire-adapted ecosystems, fire can be considered a key factor in soil formation.
... Similarly, forest treatments and wildfire have the potential to increase P concentrations in forested ecosystems mainly through increases in soil erosion and increased availability of ash that has an elevated P concentration (Santín et al., 2018). However, studies have found little effects from thinning or from a combination of thinning and prescribed fires on P delivery (Kaye et al., 2005;Martin and Harr, 1989). ...
... However, studies have found little effects from thinning or from a combination of thinning and prescribed fires on P delivery (Kaye et al., 2005;Martin and Harr, 1989). Since forest wildfires, especially those that result in high soil burn severity, affect soil properties, there is more evidence that P concentrations post-wildfire increase (Lane et al., 2008;Murphy et al., 2006;Santín et al., 2018;Smith et al., 2011). However, because this information is limited in the research literature, we did not attempt to include in the model any temporal changes in phosphorus concentrations with treatment. ...
Suspended sediment and nutrients following forest management activities or wildfires are transported to streams and lakes via surface runoff and are a major threat to water quality. Land and water managers resort to hydrologic models to test hypotheses that can help them make informed decisions to minimize disturbances and protect water resources. We present applications of an online interface, WEPPcloud, for the Water Erosion Prediction Project (WEPP) model as a pre- and post-disturbance management tool to various gauged and ungauged forested watersheds throughout the western U.S. We compare simulated streamflow, sediment, and phosphorus to observations at USGS gauging stations and assess the accuracy of the online interface with minimal or no calibration. Specifically, we present modeling results from 28 relatively undisturbed forested watersheds in the states of California, Nevada, Oregon, Washington, and Idaho. Across all watersheds, the NSEs based on the daily streamflow values, were in the range of 0.43 to 0.64 indicating satisfactory agreement between modeled and observed values. Similarly, annual average NSE for sediment yield was 0.61, while for phosphorus it was 0.75, 0.71, and 0.66, for total, particulate, and soluble reactive phosphorus, respectively. Additionally, we demonstrate the utility of the WEPPcloud interface as a tool to compare model results for ungauged watersheds from various disturbed conditions including prescribed fire, thinning, and wildfire to undisturbed model results to better understand the effects of forest management and wildfires on water quality and quantity.
... Whether or not these increases in nutrient concentrations constitute eutrophication and negatively affect stream ecosystems is still questionable due to the magnitude and limited duration of increased concentrations (Table 2). Additionally, several studies also reported reduced soil solution nutrient concentrations immediately after prescribed fire, suggesting that burning removes nutrients from a system before they can be transported into water bodies (Douglass & Van Lear, 1983;Elliott & Vose, 2005;Santín et al., 2018;Smith et al., 2010). As such, it is difficult to establish a causal relationship between fireinduced changes to terrestrial or subsurface nutrient pools and elevated surface water concentrations. ...
... Battle & Golladay (2003) reported that intense burning (>300 • C) of bunchgrass fuel beneath longleaf pine conferred greater PO 4 3− concentrations in runoff, though this observed increase was likely ecologically insignificant due to the limited mobility of PO 4 3− either above-or belowground. The low-severity nature of prescribed fire in many forested environments likely does not affect P availability, as intense heating (>650 • C) is necessary to reduce organic P pools (Santín et al., 2018). As such, although litter combustion can increase terrestrial SRP, inorganic PO 4 3− exports after prescribed are unlikely to differ from unburned areas due to the inherent immobility of PO 4 3− and high energy needed to mobilize large quantities. ...
This review examines the impact of prescribed fire on the water quality variables (a) sediment load and (b) limiting macronutrients in forested environments globally. We aim to characterize the forested environments subject to prescribed fire, to discuss factors of the fire regime that contribute to water quality concerns, and to offer insight into the effect of precipitation timing and study scale on constituent exports. High fuel consumption during fire increases the risk of erosion and constituent export during precipitation, though high fuel consumption during prescribed fire is uncommon in forested environments. Small‐scale studies examining sediment yield after prescribed fire may fail to capture the effect of landscape‐scale spatial variability, and watershed‐scale studies accounting for such variability are lacking. Although small‐plot studies confirm that prescribed fire can alter hydrologic inputs, the environmental impact of these increases is minimal, particularly when compared with other land‐use systems. Generally, prescribed fire is a beneficial and low‐impact disturbance that likely improves fire‐adapted forest health. However, gaps in knowledge exist at various spatial and temporal scales; this review suggests two avenues of future research, including (a) greater understanding of fire regime interactions that control surface runoff and erosion at the watershed scale, and (b) monitoring forest health and ecological function after prescribed fire rather than direct nutrient exports.
... Rapid mineralization of SOM via burning and ash production can temporarily offset this effect by increasing P availability in burned soils (Butler et al., 2018). Typically, P does not easily volatilize, and so P concentrations tend to increase or remain constant following fires (Alcañiz et al., 2018;Butler et al., 2018), which is also reflected the ratio of inorganic to organic P pools (Butler et al., 2018;Santín et al., 2018). Once in the ash component, P loss from the system can happen by water and wind erosion (Santín et al., 2018). ...
... Typically, P does not easily volatilize, and so P concentrations tend to increase or remain constant following fires (Alcañiz et al., 2018;Butler et al., 2018), which is also reflected the ratio of inorganic to organic P pools (Butler et al., 2018;Santín et al., 2018). Once in the ash component, P loss from the system can happen by water and wind erosion (Santín et al., 2018). In fact, we found lower soil P availability in burned surface soils, suggesting that fire can aggravate P limitation in tropical soils. ...
In this study, we investigate the biogeochemical consequences of fire in seasonally flooded Amazon forests, where recent declines in forest cover have been linked to increases in fire frequency and severity. Previous studies have hypothesized that a quasi‐permanent state‐shift transition from typical Amazon forests to open savannas can occur when fire results in further depletion of already impoverished soil nutrient pools. Asymbiotic N2 fixation (ANF) is an essential pathway for fire‐affected forests to acquire nitrogen (N) after disturbance, but ANF response to fire has yet to be quantified in Amazonia. Here, we quantify ANF through field sampling and laboratory incubations using ¹⁵N‐labeled dinitrogen (¹⁵N2) and measurement of 14 biogeochemical parameters in surface (0–10 cm) and subsurface (10–30 cm) soils. Our data represent burned and unburned replicated sampling sites, across five stands, spanning a gradient from infrequent (once in 13 years) to frequent (five times in 13 years) fire occurrences. ANF did not vary with fire frequency but was, on average, 24% lower in burned than in unburned surface soils across all stands. Burned and unburned subsurface soils had similar ANF rates. About 58% of ANF variance was explained by the joint effect of carbon (C):N ratio and available phosphorus (P) in burned and unburned soils. ANF increased linearly with C:N and P availability in unburned soils, but a highly non‐linear relationship was observed in burned soils. Our findings show that fire alters soil C‐to‐nutrient stoichiometry, which resulted in lower N inputs via ANF into burned relative to unburned tropical forest soils.
... Only a few recent studies have characterized the speciation of P in ash from a particular fire, using nuclear magnetic resonance (NMR) spectroscopy and sequential extraction. 21,22 Regarding smoke from wildland fires, although extensive studies have characterized its chemical composition, 23,24 the speciation of macronutrients and the effects of fuel sources and fire conditions remain largely unexplored. With respect to question #3, previous studies have observed variation in the aqueous solubility and mobility of macronutrients among fire ash, while the causes were not clear. ...
This study investigated the speciation and aqueous dissolution of macronutrients in fire ash from diverse ecosystems and speciation of ash and smoke from laboratory burning, exploring the variations and their causes. The speciation of phosphorus (P), calcium (Ca), and potassium (K) in fire ash from five globally distributed ecosystems was characterized by using X-ray absorption spectroscopy and sequential fractionation. Aqueous dissolution of the macronutrients was measured by batch experiments at acidic and alkaline pHs. The results showed that P existed mainly as Ca phosphates, Ca as double carbonates, calcite, and sulfates, and most K was associated with Ca carbonates. Mineralogy and the relative abundance of the species were primarily controlled by elemental stoichiometry and fire temperature. Differences in Ca and P speciation existed between ash and smoke from laboratory burning, possibly caused by the temperature difference and/or mass fractionation during burning. The rates, extents, and pH dependencies of macronutrient dissolution differed among macronutrients and depended on their speciation, with K being highly soluble and the P and Ca regulated by solution pH. The variability in ash macronutrient chemistry and ecosystem-specific fire ash loads resulted in varying loads and availability of individual macronutrient from fire among ecosystems. This study provides a mechanistic understanding of how fires transform the chemistry of macronutrients and affect macronutrient returns to soils across different ecosystems, which is essential for evaluating the disturbance to ecosystem nutrient cycling by fires.
... Mean values are shown, and the error bars represent the standard deviation (N = 3). Lowercase letters for a given variable indicate significant differences (P < 0.05) before and after prescribed burning based on one-way ANOVA, followed by Tukey's HSD test carbon storage (Merino et al. 2019;Santín et al. 2018). Thus, by managing fuel loads and carrying on prescribed burnings, may reduce the risk of wildfires in the future and retain carbon stock in the soil. ...
Prescribed burning is commonly used to maintain forest ecosystem functions and reduce the risk of future wildfires. Although many studies have investigated the response of microbial community to wildfires in forest ecosystems, the effects of prescribed burnings on soil microbial community structure are less studied. It is also unclear that how post-fire soil physiochemical properties changes affected soil microbial communities. Here, we studied the impacts of prescribed burning on soil microbiome in three typical temperate forests of northern China by collecting soil physicochemical and high-throughput sequencing for 16S rRNA and 18S rRNA was applied to analyze the diversity and community composition of soil microbes (bacteria and fungi). Compared with pre-fire condition, prescribed burning significantly decreased Chao1 index and altered soil bacterial communities (P < 0.05), whereas it had no significant effect on fungal diversity and community structure of the (P > 0.05). Planctomycetes and Actinobacteria made the greatest contributions to the bacterial community dissimilarity between the pre-fire and post-fire conditions. The main variables influencing the post-fire soil microbial community structure are soil pH, available phosphorus, total nitrogen, and the ratio of soil total carbon to soil total nitrogen, which could account for 73.5% of the variation in the microbial community structure in these stands. Our findings demonstrated a great discrepancy in the responses of bacteria and fungi to prescribed burning. Prescribed burning altered the soil microbial structure by modifying the physicochemical properties. Our results pointed that it is essential to evaluate the impact of prescribed burnings on forest ecosystem functions. These findings provide an important baseline for assessing post-fire microbial recovery in the region and offer critical guidance for restoration efforts.
... Ash deposition from combusted biomass burning following fire adds P in the bioavailable form of orthophosphate to the soil (Cade-Menun et al. 2000;Wang et al. 2015). The process of N and P liberation from biomass and redistribution to the soil as ash is crucial in the post-fire landscape, especially where P is in scarce supply such as for coastal scrub vegetation (Wright et al. 2001;Santin et al. 2018). Vegetation that was previously P-limited can experience a transient increase in P after burning, leading to enhanced plant productivity during recovery (Dijkstra and Adams 2015) and accelerated regrowth. ...
Fire-prone landscapes experience frequent fires, disrupting above-ground biomass and altering below-ground soil nutrient availability. Augmentation of leaf nutrients or leaf water balance can both reduce limitations to photosynthesis and facilitate post-fire recovery in plants. These modes of fire responses are often studied separately and hence rarely compared. We hypothesised that under severe burning, woody plants of a coastal scrub ecosystem would have higher rates of photosynthesis (Anet) than in unburned areas due to a transient release from leaf nutrient and water limitations, facilitating biomass recovery post-burn. To compare these fire recovery mechanisms in regrowing plants, we measured leaf gas exchange, leaf and soil N and P concentrations, and plant stomatal limitations in Australian native coastal scrub species across a burn sequence of sites at one year after severe fi, seven years following a light controlled fire, and decades after any fire at North Head, Sydney, Australia. Recent burning stimulated increases in Anet by 20% over unburned trees and across three tree species. These species showed increases in total leaf N and P as a result of burning of 28% and 50% for these macronutrients, respectively, across the three species. The boost in leaf N and P and stimulated leaf biochemical capacity for photosynthesis, alongside species-specific gs increases, together contributed to increased photosynthetic rates after burning compared to the long-unburned area. Photosynthetic stimulation after burning occurred due to increases in nutrient concentrations in leaves, particularly nitrogen, as well as stomatal opening for some species. The findings suggest that changes in species photosynthesis and growth with increased future fire intensity or frequency may be facilitated by changes in leaf physiology after burning. On this basis, species dominance during regrowth depends on nutrient and water availability during post-fire recovery.
... Because of incomplete combustion of organic matter, breakdown of incompletely burned biomass, and ash accumulation, low-intensity fires are linked to higher SOC [82,83,84]. Black carbon (BC) is the term used to describe the ash and carbon that are produced during low-intensity forest fires [85,86]. ...
The present study highlights forest fire effects on soil properties. One of the most
harmful challenges to our forest is fire. Forest fires may have an impact on a
combination of vegetation cover, structure, composition, density, and productivity
leading to deforestation, population decline, consequences of the forest edge,
and exotic animal immigration species. The impact of forest fires on soil physical
properties had an emphasis on texture, bulk density, porosity, aggregate stability,
and water content and repellency. Following the fire, the surface soil of the
burned region had higher soil pH, total nitrogen, accessible phosphorus,
potassium, calcium, and magnesium levels than the unburned area. Because of
the low fire intensity, the organic matter in the soil and the litter burned,
increasing the amount of nutrients available and encouraging the growth of the
post-fire community and herb regeneration. Higher-intensity fires totally burn out
secondary minerals like magnesium and micronutrients like manganese at
extremely high temperatures. They also volatilize nitrogen, phosphate, and
potassium in the soil and kill microorganisms. Some nutrients were more readily
available by the burning of soil organic matter (OM), such as N, P, and S, while
others were volatilized. Controlled fire did not result in any significant changes to
the nutrients or physico-chemical composition of soil and can be utilized as an
efficient management technique to reduce the harm caused by wildfires to soil.
Remote sensing and GIS technology are the highly advanced tools used to
detect forest fires, calculate burned areas and determine of changes in land use.
As a tool for predicting fires, remote sensing, and GIS are highly essential.
Hence it is important to understand how fire affects the physical, chemical, and
biological aspects of forest ecosystems.
... loosely attached to Ca, Fe, or Al that prevents its utilization (Masto et al., 2013;Qian et al., 2009;Tan and Lagerkvist, 2011;Santín et al., 2018). Another reason for the roots' impairment in P uptake might be the insufficient physical contact between fire ash particles and the roots, even though the tested plants exhibited an extensive root system, with an average root-to-shoot ratio of 50 : 50; the pH of the substrate was around 7, in the range of most alkaline soils. ...
Atmospheric particles originating from combustion byproducts (burned biomass or wildfire ash) are highly enriched in nutrients such as P, K, Ca, Mg, Fe, Mn, and Zn. Over long timescales, deposited wildfire ash particles contribute to soil fertility by replenishing soil nutrient reservoirs. However, the immediate nutritional effects of freshly deposited fire ash on plants are mostly unknown. Here, we study the influence of fire ash on plant nutrition by applying ash separately on a plant's foliage or to its substrate around the roots. We conducted experiments on chickpea model plants under ambient and elevated CO2 levels, which reflect current and future climate scenarios. We found that plants can utilize fire ash P and Ni through their leaves by direct nutrient uptake from particles captured on their foliage but not via their roots, both under ambient and elevated CO2 levels. These results indicate that over a short timescale, plants effectively uptake P from fire ash only via the foliage rather than the root pathway, which is possibly due to low bioavailability or limited contact between fire ash particles and the roots. According to many previous studies, elevated levels of CO2 will reduce the ionome of plants due to the partial inhibition of the key root uptake mechanism, thus increasing the significance of foliar nutrient uptake in a future climate. Furthermore, the role of fire ash is expected to increase in the future world, thus giving a competitive advantage to plants that can utilize fire ash P from the foliar pathway, as fire ash P is a particularly efficient and important source of P.
... In 2020, more than 100 wildfires raged in Oregon, California, and Washington, USA, affecting nearly 2 million ha, burning more than 1.3 million ha of land, and causing losses of up to US $12 billion in the economy (Filonchyk et al., 2022). Most existing studies on environmental pollution caused by wildfires focus on the changes in soil structure and physical and chemical properties caused by wildfires (Santín et al., 2018;Dymov et al., 2021a;Baieta et al., 2022). Carrà et al. (2022) and Cerdà and Doerr (2008) reported that wildfires in Mediterranean regions could change soil structure and reduce the stability of aggregates, increasing runoff coefficients and soil loss, making the soil more vulnerable to erosion. ...
... This study results are in line with the outcome of Gluns and Toews (1989), that there are no significant effects on stream water quality in terms of the orthophosphorus level a few years after burning. Furthermore, Santín et al. (2018) also observed that low-intensity prescribed fire does not affect the availability of phosphate in water bodies. This could be due to low ash that accompanied the prescribed fire intensities as ash is part of the ingredients that enhance nutrient in waterbodies (Bladon et al., 2014). ...
The experiment was conducted at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria to investigate the influence of prescribed fire intensity on soil erosion and runoff, a situation that occur regularly in the study area. The experimental site is within the rainforest ecosystem of the Southwest Nigeria, and usually experiences a significant amount of rainfall every year. This encourages rainfed farming around the study area with most farmers using prescribed fire for land preparation before planting. It is presumed that bush burning causes erosion and degradation of other soil properties. The study therefore investigated the influence of prescribed fire of two intensities and mulching on runoff and soil loss, runoff coefficient, phosphate and nitrate contents of the runoff water. The treatments consisted of fire intensities of 200 ◦C (with effect correspondingly felt at a maximum of 2 cm soil depth) and 500 ◦C (with effect correspondingly felt at a maximum of 5 cm soil depth), grass mulch, and control (bare soil without vegetation or plant residue). Each treatment was imposed on a plot of 1 m2 arranged in a randomized complete block design with triplicates, for three cropping seasons, and prescribed burning at the start of each cropping season. The first season was from May to August 2019, second season was from September to December 2019 while the third season was from September to December 2020. Runoff volume, soil loss, phosphate and nitrate contents in runoff were measured using bounded erosion plots of polyvinyl chloride (PVC) materials with a harvesting container (25 L) installed at about 1 m deep. The 200 ◦C prescribed fire plots had higher soil loss than that of 500 ◦C. The runoff in the 200 ◦C prescribed fire plot were 13.36 mm, 10.80 mm and 12.78 mm during the first, second and third seasons respectively, while those of the 500 ◦C prescribed fire were 12.88 mm, 7.63 mm and 11.96 mm in the same order. Soil loss from the 200 ◦C prescribed fire plot was an average of 2.46, 3.40, 1.77 Mg ha− 1 in the first, second and third seasons respectively, while the 500 ◦C prescribed fire plot lost an average of 1.70, 1.23 and 2.17 Mg ha− 1 in the same order. The Average concentration of nitrates in the runoff under 200 ◦C prescribed fire were an average of 0.14, 0.21, and 0.38 mg L− 1 while for 500 ◦C, they were 0.18, 0.19, 0.81 mg L− 1 in the first, second and third seasons respectively. Nitrate and phosphate contents of the runoff were not significantly influenced by prescribed fire. The fire intensities did not have a significant impact on the total runoff and soil loss under maize in the prescribed fire plots. The slash and pack plots without burning experienced the highest runoff and soil loss. However, grass mulch plot reduced total runoff and soil loss. Therefore, grass mulching of soil is encouraged to mitigate soil erosion in maize fields.
... -2617 Preprint. Qian et al., 2009;Tan and Lagerkvist, 2011;Santín et al., 2018). Another reason for the roots impairment in P uptake might be the insufficient physical contact between fire ash particles and the roots. ...
Atmospheric particles originating from combustion byproducts (burned biomass or wildfire ash) are highly enriched in nutrients such as P, K, Ca, Mg, Fe, Mn, Zn, and others. Over long timescales, deposited wildfire ash particles contribute to soil fertility by replenishing soil nutrient reservoirs. However, the immediate nutritional effects of freshly deposited fire ash on plants are mostly unknown. Here we study the influence of fire ash on plant nutrition by applying particles separately on a plant’s foliage or onto its roots. We conducted experiments on chickpea model plants under ambient and elevated CO2 levels, 412 and 850 ppm, that reflect current and future climate scenarios. We found that plants can uptake fire ash P only through their leaves, by a direct nutrient uptake from particles captured on their foliage, but not via their roots. In a future climate scenario, foliar nutrient uptake pathway may be even more significant for plants, due to the partial inhibition of key root uptake mechanism. Our findings highlight the effectiveness of the foliar nutrient uptake mechanism under both ambient and elevated CO2 levels, with fire ash P being the sole nutrient absorbed by the foliage. These findings demonstrate the substantial contribution of fire ash to the nutrition of plants. Furthermore, the role of fire ash is expected to increase in the future world, thus giving a competitive advantage to plants that can utilize fire ash P from the foliar pathway.
... The P loss rate may have been amplified through the elevated proportions of P i dissolved in the "aqueous phase" of frequently burned sites (Fig. 5b). Merino et al. (2019) and Santin et al. (2018) demonstrated the appreciable shift of the extractable P from organic P to inorganic P probably due to mineralization with burning, which could accelerate P loss from soil. However, fire did not significantly affect WDC-Ca, -Si, -Al, -Fe or -Mg concentrations in soils beneath any of the three vegetation types (Fig. 2a). ...
... The combination of environmental factors such as (1) burn temperature, (2) topography, (3) rainfall and its chemistry, (4) vegetation and soils, (5) the area affected by a burn, (6) the volume of ash generated, and (7) the hydrological conditions must then explain why increased concentrations for low-severity burns are rarely identified in field conditions. In a field study, Santín et al. (2018) who compared unburnt sites with low-, medium-and high severity burns found that only Ca and Cu were elevated for low severity burn. ...
As wildfires are of increasing concern in a warming world, there is a need to understand how fire temperatures affect solute concentrations of forest litter and soils in drinking water catchments. In addition, the concentrations are expected to be affected by time since the previous fire. We sampled soil and litter from recently (2 months) and less recently (4.5 years) burnt sites from jarrah forest in SW Australia. The samples were heated at 250 • C, 350 • C, and 500 • C for 30min followed by leaching to determine solute compositions at these temperatures and in unburnt samples. At 250 • C-350 • C, we found increased concentrations of manganese (Mn), arsenic (As), total phosphorus (TP), phosphate (PO 3− 4), ammonia (NH + 4), potassium (K), calcium (Ca), mangesium (Mg), cobalt (Co), barium (Ba), sulphate (SO 2− 4), alkalinity and dissolved organic carbon in soils, as well as of zinc (Zn), As, Ca, Ba, alkalinity, aluminium (Al) and chromium (Cr) in litter. At 350 • C-500 • C, divalent cations and organic carbon declined, while soils generated very high Al and Cr concentrations. The time following the fire was important, with the more recent fire generating higher concentrations. The elevated concentrations in 250 • C-350 • C were attributed to a decomposition of organic matter and mineral transformations, including CaCO 3 formation. Based on thermodynamics, we propose a couple of burn severity indicators: activities of calcium and carbonates that are calculated from pH, alkalinity and Ca concentration. The indicators do not only show the degree of post-fire transformations, but they also inform on CaCO 3 formation. Further studies include: (1) application to field data, (2) association with organic contaminants, and (3) validation in other geographical locations.
... The P loss rate may have been amplified through the elevated proportions of P i dissolved in the "aqueous phase" of frequently burned sites (Fig. 5b). Merino et al. (2019) and Santin et al. (2018) demonstrated the appreciable shift of the extractable P from organic P to inorganic P probably due to mineralization with burning, which could accelerate P loss from soil. However, fire did not significantly affect WDC-Ca, -Si, -Al, -Fe or -Mg concentrations in soils beneath any of the three vegetation types (Fig. 2a). ...
Soil colloids (diameter < 1000 nm) are comprised mainly of clay minerals and organic matter, and play major roles in determining ion exchange capacity and in regulating key biogeochemical processes. Consequently, it is important to understand how soil colloids and their functions are influenced by land cover and anthropogenic disturbances. In grasslands, savannas, and other dryland ecosystems across the globe, woody plants are encroaching due to livestock grazing, fire suppression, elevated CO2 concentrations, and climate change. These major land cover changes could influence soil colloidal properties, with implications for soil C, N, and P cycles. We assessed how woody encroachment, livestock grazing, and fire interact to influence soil colloidal properties in a juniper-oak savanna. Surface soils (0–10 cm) from the southern Great Plains (Texas, USA) were collected from long-term treatments differing in grazing intensity (none, moderate, and heavy) and fire history. Within each treatment, soil samples were taken under grass, juniper, and oak canopies. Water dispersible soil colloids (WDC, d < 500 nm) were isolated and analyzed by asymmetric flow field-flow fractionation and their P species by liquid-state ³¹P-nuclear magnetic resonance spectroscopy (³¹P NMR). Soil beneath oak and juniper canopies had smaller WDC and elevated colloidal organic carbon (OC) and P concentrations, especially in nanocolloid (<30 nm) and fine colloid (30–160 nm) size fractions. Woody encroachment enriched Ca, Fe, Al, Si and Mg in WDC in the ungrazed control, but not in any of the other grazed or burned areas. Colloidal soil P mainly occurred as orthophosphate and orthophosphate diesters, and was present as OC-Ca-P complexes in fine and medium colloid fractions (30–500 nm), while P in the nanocolloid fraction (<30 nm) was in direct association with Ca. Moderate grazing did not affect the retention of colloidal P, while heavy grazing potentially increased the loss risk of colloidal P. Fire accelerated soil P loss from colloid fractions only in woody areas. Our findings highlight that woody encroachment strengthens the retention of OC and P by soil colloids, consequently increasing overall C and P pools in savanna soils.
... In terms of stoichiometric changes, studies have shown that the decomposition of litter after a fire will cause high sensitivity to stoichiometric imbalances on local scales [22]. Under nutrient-sufficient conditions, the hydrolysis of C drives the decomposition of litter, microbial N restriction (high litter C:N or low litter N:P) and P restriction (high litter C:P or N:P) appear, and the driving effect of N and P on decomposition is enhanced [35][36][37][38]. Frequent fire disturbance reduces the coupling relationship between litter C:N:P stoichiometry, the N:P ratio of microbial biomass, and enzyme activity, and the forest tends toward an N-restricted ecosystem [39]. ...
Fire disturbance can affect the function of the boreal forest ecosystem through litter decomposition and nutrient element return. In this study, we selected the Larix gmelinii forest, a typical forest ecosystem in boreal China, to explore the effect of different years (3 years, 9 years, 28 years) after high burn severity fire disturbance on the decomposition rate (k) of leaf litter and the Carbon:Nitrogen:Phosphorus (C:N:P) stoichiometry characteristics. Our results indicated that compared with the unburned control stands, the k increased by 91–109% within 9 years after fire disturbance, but 28 years after fire disturbance the decomposition rate of the upper litter decreased by 45% compared with the unburned control stands. After fire disturbance, litter decomposition in boreal forests can be promoted in the short term (e.g., 9 years after a fire) and inhibited in the long term (e.g., 28 years after a fire). Changes in litter nutrient elements caused by the effect of fire disturbance on litter decomposition and on the C, N, and C:N of litter were the main litter stoichiometry factors for litter decomposition 28 years after fire disturbance. The findings of this research characterize the long-term dynamic change of litter decomposition in the boreal forest ecosystem, providing data and theoretical support for further exploring the relationship between fire and litter decomposition.
... Elsewhere, Alcañiz et al. (2016) for a P. halepensis forest in Spain and Liu et al. (2018) for grasslands in China, recorded a 19.4% and 11.2% increase in SOC after a low intensity prescribed fire and a wildfire, respectively. Thus, low-intensity fires are associated with increased SOC due to increased pyrogenic C resulting from incomplete combustion of organic matter, decomposition of incomplete burnt biomass, and the addition of ash (Sánchez Meador et al. 2017;Santín et al. 2018;Hu et al. 2020). The combustion of C and the ash produced during low-intensity forest fires are referred to as black carbon (BC) (Thomas et al. 2017;Gao et al. 2018). ...
Forest fires are key ecosystem modifiers affecting the biological, chemical, and physical attributes of forest soils. The extent of soil disturbance by fire is largely dependent on fire intensity, duration and recurrence, fuel load, and soil characteristics. The impact on soil properties is intricate, yielding different results based on these factors. This paper reviews research investigating the effects of wildfire and prescribed fire on the biological and physico-chemical attributes of forest soils and provides a summary of current knowledge associated with the benefits and disadvantages of such fires. Low-intensity fires with ash deposition on soil surfaces cause changes in soil chemistry, including increase in available nutrients and pH. High intensity fires are noted for the complete combustion of organic matter and result in severe negative impacts on forest soils. High intensity fires result in nutrient volatilization, the break down in soil aggregate stability, an increase soil bulk density, an increase in the hydrophobicity of soil particles leading to decreased water infiltration with increased erosion and destroy soil biota. High soil heating (> 120 °C) from high-intensity forest fires is detrimental to the soil ecosystem, especially its physical and biological properties. In this regard, the use of prescribed burning as a management tool to reduce the fuel load is highly recommended due to its low intensity and limited soil heating. Furthermore, the use of prescribed fires to manage fuel loads is critically needed in the light of current global warming as it will help prevent increased wildfire incidences. This review provides information on the impact of forest fires on soil properties, a key feature in the maintenance of healthy ecosystems. In addition, the review should prompt comprehensive soil and forest management regimes to limit soil disturbance and restore fire-disturbed soil ecosystems.
... Higher sediment fluxes from burned watersheds can increase phosphate inputs to water bodies (Coombs and Melack, 2013;Emelko et al., 2016). Along with increased longitudinal connectivity that limits detention and microbial processing of nitrate, this can result in algal blooms in lakes and reservoirs (McEachern et al., 2000;Santin et al., 2018). As a warming climate drives more intense and frequent wildfires in drylands around the world (Westerling et al., 2006), it becomes increasingly important to understand the characteristics that foster resilience to the wildfire disturbance cascade. ...
We examine a 9.4-km-long portion of a montane river corridor in the Southern Rockies, the upper 8 km of which burned in 2020. We focus on sediment storage in logjam backwaters and how spatial heterogeneity in the river corridor attenuates downstream fluxes of material following the wildfire. Wider portions of river corridor exhibit greater spatial heterogeneity, as reflected in multithread channel planform and more closely spaced abandoned beaver dams and channel-spanning logjams. Logjams in multithread reaches have greater volumes of backwater storage and store finer sediment than logjams in single-thread reaches. Despite substantial turnover of sediment in backwater storage during the first runoff season after the wildfire, the cumulative volume of sediment stored at 11 monitored logjams following the 2021 runoff season was 71% of the cumulative sediment volume at the logjams immediately after the fire. Floodplain vegetation regrowth was also faster and more complete at multithread reaches. Vegetation recovery contributed to overbank deposition in these reaches, in contrast to the bank erosion observed in single-thread reaches. More spatially heterogeneous portions of the river corridor appear to be disproportionately important in attenuating enhanced inputs of sediment following wildfire, and the cumulative effect of this attenuation across a river network likely enhances watershed-scale resilience to wildfire disturbance.
... The occurrence of post-fire debris flows and shallow landslides is closely related to the status of the soil after the fire (Bodí et al., 2012;Cui et al., 2015;Cui et al., 2019;Santín et al., 2018). Previous studies have mostly investigated the physical, chemical, and biological properties of soil shortly after a fire (DeBano, 2000;González-Pérez et al., 2004;Lucas-Borja et al., 2020b;Rodríguez et al., 2017;Rodríguez et al., 2018). ...
Plant roots generally enhance soil strength and stabilize slopes through hydro-mechanical effects, especially in forested areas prone to shallow slope failure. Forest fires can severely weaken the hydro-mechanical contribution of roots to slopes, however, the hydro-mechanical characteristics of soil–root systems (SRS) affected by wildfire remain poorly understood. To obtain insight into the post-fire hydro-mechanical characteristics of SRS, a subalpine conifer forested area in Sichuan Province, China that suffered a wildfire on March 30, 2019 was continuously monitored over two consecutive years. Samples from zones with different degrees of burn severity were collected and tests both for roots and SRS were performed. The results revealed a substantial decline in root number, which decreased by 46%–58% two years after the wildfire in the medium- and high-severity areas. The tensile strength tests indicated a reduction of root tensile strength by 36%–47% for roots with diameters less than 2 mm. The shear strength of the SRS determined from saturated direct shear tests strongly and had degraded by 55%–82% two years after the wildfire because of root death and reduced root reinforcement. The results of hydraulic conductivity tests over the same time period indicated an abrupt reduction of SRS hydraulic conductivity within several months after the fire owing to ash clogging and the formation of a hydrophobic layer. After more time had elapsed, however, hydraulic conductivity had increased unexpectedly by a factor of 2.2–3.2 greater than that of unburned soil. We attribute this observation to the formation of macropore flow pathways from decayed roots, which was observed by scanning electron microscopy. The findings presented here provide important insight into the temporal changes of the hydro-mechanical characteristics of SRS in burned areas and their associated mechanisms and could be a useful reference to better evaluate post-wildfire stability of subalpine conifer forest in similar environmental conditions.
... The specific responses of vegetation after fire are partially conditioned by fire-driven changes in environmental conditions such as nutrient availability, soil temperature, surface albedo, and soil water content (Bret-Harte et al., 2013;Andrieux et al., 2018;Santin et al., 2018;Stirling et al., 2019). In wet meadows, fire during the early growing season has been seen to promote flowering of Muhlenbergia capillaris, Paspalum monostachyum and Schizachyrium rhizomatum in the following growing season (Main and Barry, 2002). ...
Fire is an important disturbance in many wetlands, which are key carbon reservoirs at both regional and global scales. However, the effects of fire on wetland vegetation biomass and plant carbon dynamics are poorly understood. We carried out a burn experiment in a Calamagrostis angustifolia wetland in Sanjiang Plain (Northeast China), which is widespread wetland type in China and frequently exposed to fire. Using a series of replicated experimental annual burns over a three-year period (spring and autumn burns carried out one, two or three times over three consecutive years), together with a control unburned treatment, we assessed the effect of burn seasonality and frequency on aboveground biomass, stem density, and carbon content of aboveground plant parts and ground litter. We found that burning promoted plant growth and hence plant biomass in burned sites compared to the unburned control, with this effect being greatest after three consecutive burn years. Autumn burns promoted higher stem density and more total aboveground biomass than spring burns after three consecutive burn years. Burning increased stem density significantly, especially in twice and thrice burned plots, with stem densities in September over 2000 N/m², which was much higher than in the control plots (987 ± 190 N/m²). Autumn burns had a larger effect than spring burns on total plant biomass and litter accumulated (e.g. 1236 ± 295 g/m² after thrice autumn burns compared 796.2 ± 66.6 g/m² after thrice spring burns), except after two burn treatments. With time since burning, total biomass loads increased in spring-burned plots, while autumn-burned plots showed the opposite trend, declining towards values found at unburned plots in year three. Our results suggest that, at short fire return intervals, autumn burns lead to a more pronounced increase in aboveground biomass and carbon accumulation than spring burns; however, the effects of spring burns on biomass and carbon accumulation are longer lasting than those observed for autumn burns.
... Fire intensity is strongly associated with the alterations in the amount and availability of soil nutrients due to the severe influence of fire on the biological, chemical, and physical properties of soils (James et al., 2018). Resembling the findings by Tomkins et al. (1991) and Santín et al. (2018), our results show a high availability of nutrients in years closer to the fire events (i.e., 2015; Table 3) than in later years, as an outcome of the combustion of residues and organic matter (Certini, 2005). The similar Ca 2+ , Mg 2+ , K + , and Na + levels in control and more-recently burned plots (i.e., Sta. ...
We performed a five-year assessment of the natural vegetation restoration capacity following the 2012 fires in Valdemaqueda (Madrid, Spain) via the characterization of the post-fire and residual vegetation and the analysis of soil physico-chemical characteristics. Six pilot-plots were established in the affected site. Forest species, representative of the potential natural vegetation of the area (Juniperus oxycedrus subsp. lagunae and Quercus rotundifolia woodlands) and broom shrubs (Cytisus scoparius, Retama sphaerocarpa) were planted to assess the relationship among the stages of ecological succession, competition, and soil restoration processes following devastating fire events.
The fire-driven alteration of the soil’s physico-chemical properties was evident, given the increased pH and reduced C/N ratio in the first years of the study. However, we observed an increased soil enrichment in the last years of study, accompanied by the propagation of herbaceous species, su[1]pporting our seed bank findings, showing a clear difference in the sprouting rate between burnt and control plots (80% vs. 20%, respectively). The establishment of robust, pyrophyte shrub species (Cistus ladanifer, C. laurifolius, Rosmarinus officinalis) rather than natural succession evidenced the clear conversion of the vegetation in burnt areas. These findings in the pilot-plots allowed evidencing the high vulnerability of the natural vegetation to the settling of pyrophytes, given their low survival rate under the strong competitive pressure of these pyrophytic species. The proliferation of these pyrophytes could translate into changes in soil macro- and microbiota, nutrient dynamics, species diversity, and interaction, added to the alteration of fire regimes in the area. Overall, these results highlight the risk for soil impoverishment and possible erosion of the fire-affected sites. Moreover, they underline the importance of the establishment and regeneration of Genisteae species to outcompete pioneer pyrophytic species, favoring the restoration of the area’s potential natural vegetation
... Previous studies in the area Previous collaborative work between Swansea University and WaterNSW produced datasets on the contaminant content in ash and burnt soil resulting from fires in this particular ecosystem. Contaminant data were collected following the 2013 Balmoral Fire, which affected another of the WaterNSW's catchments, and from a research burn in the Warragamba catchment in 2014 (Santín et al. 2018). This previous collaboration provided likely ash loads under different burn severities. ...
The 2019/2020 Australian bushfires (or wildfires) burned the largest forested area in Australia's recorded history, with major socio-economic and environmental consequences. Among the largest fires was the 280 000 ha Green Wattle Creek Fire, which burned large forested areas of the Warragamba catchment. This protected catchment provides critical ecosystem services for Lake Burragorang, one of Australia's largest urban supply reservoirs delivering ~85% of the water used in Greater Sydney. Water New South Wales (WaterNSW) is the utility responsible for managing water quality in Lake Burragorang. Its postfire risk assessment, done in collaboration with researchers in Australia, the UK, and United States, involved (i) identifying pyrogenic contaminants in ash and soil; (ii) quantifying ash loads and contaminant concentrations across the burned area; and (iii) estimating the probability and quantity of soil, ash, and associated contaminant entrainment for different rainfall scenarios. The work included refining the capabilities of the new WEPPcloud-WATAR-AU model (Water Erosion Prediction Project cloud-Wildfire Ash Transport And Risk-Australia) for predicting sediment, ash, and contaminant transport, aided by outcomes from previous collaborative postfire research in the catchment. Approximately two weeks after the Green Wattle Creek Fire was contained, an extreme rainfall event (~276 mm in 72 h) caused extensive ash and sediment delivery into the reservoir. The risk assessment informed on-ground monitoring and operational mitigation measures (deployment of debris-catching booms and adjustment of the water supply system configuration), ensuring the continuity of safe water supply to Sydney. WEPPcloud-WATAR-AU outputs can prioritize recovery interventions for managing water quality risks by quantifying contaminants on the hillslopes, anticipating water contamination risk, and identifying areas with high susceptibility to ash and sediment transport. This collaborative interaction among scientists and water managers, aimed also at refining model capabilities and outputs to meet managers' needs, exemplifies the successful outcomes that can be achieved at the interface of industry and science. Integr Environ Assess Manag 2021;17:1151–1161. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).
KEY POINTS
The extreme wildfires of 2019/20 burned 35% of the slopes that surround Sydney's main drinking water reservoir, Lake Burragorang, raising concerns about the viability of maintaining the supply of water to the Sydney area due to the risk of contamination from post-fire erosion of soil and ash. We applied the newly developed WEPPcloud-WATAR tool (Water Erosion Prediction Project cloud model—Wildfire Ash Transport And Risk estimation tool) to this catchment to predict risks to water quality from contaminants contained in eroded soil and wildfire ash. This collaboration between scientists and managers served as a test bench and helped in improving model capabilities and in adapting its outputs to water managers' needs. The tool now predicts spatial distribution of ash and pollutants on the hillslopes, loads of ash, soil, and pollutants reaching water assets for single rain events; probabilities of water contamination in the medium term; and location of hotspots for soil, ash, and contaminant transport.
... The current evidences about the temporal element trends after fires are controversial for some elements, such as Ca, Mg, K, Na and lacking for others, such as Cu, Ni, Pb (Enoki et al., 1996;Griffiths, et al., 2009;Kong et al., 2018). In fact, Santìn et al. (2018) and Chungu et al. (2019) report an increase of soil Ca, Mg and K availability, respectively, one month and one year after fire. By contrast, Francos et al. (2019) report a decrease of their availability one year after fire; whereas, Kong et al. (2018) found that eleven years after fire, the soil still not recovered its pre-fire Ca, Mg and K availability. ...
The increasing frequency and extent of forest fires cause severe temporal effects on soil properties, which knowledge about is controversial or lacking. So, the research aimed to evaluate changes in Mediterranean Andosol properties (pH, water and organic matter contents, C and N concentrations) and total and available Ca, Cu, Fe, K, Mg, Na, Ni and Pb concentrations 1 and 2 years after fire occurrence, comparing them to the pre-fire ones. The results underline that, in the investigated Mediterranean Andosols, fire caused significant decrease in water and organic matter contents, C, Fe and Mg total concentrations as well as significant increase in pH, total Ca, K, Fe, Na concentrations and available Cu and Pb fractions. After fire, temporal changes of soil element concentrations occurred at different speeds, as Ca, Cu, Fe, Mg and Ni total concentrations changed already 1 year after fire occurrence; whereas, K and Na total concentrations changed only after two years. Finally, 2 years after fire none of the investigated soil properties reached the pre-fire values, suggesting a whole worsening of soil conditions. The early responses of soils to fire are useful to predict the evolution of the system, the relationships between below and above ground and to provide useful tools for management practices.
... Such a narrative has profound implications for conservation management of eucalypts and the use of prescribed burning in eucalypt communities (Gosper et al., 2016;Bradshaw et al., 2018;Barker & Price, 2018;Santín et al., 2018), especially given the prevalence of speculation that eucalypts have traits specifically adapted to fire (Gill, 1981;Burrows et al., 2010;Crisp et al., 2011;Keeley et al., 2011;Burrows, 2013). Given that this speculation was rigorously critiqued from a modern evolutionary perspective (Hopper, 2003;Bradshaw et al., 2011), some authors have been more cautious in routinely invoking adaptation to fire in plants such as eucalypts (Clarke et al., 2013;Midgley, 2013;Bowman et al., 2014;Miller & Dixon, 2014;Hill et al., 2016;Hopper et al., 2016;Poulos et al., 2018). ...
OCBIL theory is a multi-hypothesis formulation aimed towards an understanding of the evolution, ecology and conservation of biological and cultural diversity on old, climatically buffered, infertile landscapes (OCBILs). OCBILs have been in existence contemporaneously with rainforest since Gondwanan times. Such landscapes are common in areas of eucalypt species richness embraced by Australia’s two Global Biodiversity Hotspots, the Southwest Australian Floristic Region and the Forests of East Australia. Here, I summarize evidence pertaining to the eucalypts in the context of a recent reformulation of OCBIL theory into 12 evolutionary, ecological and cultural hypotheses and ten conservation management hypotheses. A compelling argument emerges for a new interpretation of the eucalypts evolving out of the OCBILs, rather than out of the rainforests as traditionally interpreted. This calls for a significant reinterpretation of best conservation management of the eucalypts. For example, traditional ideas on application of fire in eucalypt communities regarded as well adapted to this disturbance need to give way to a more nuanced and cautious view. This review of eucalypts seen as evolving out of the OCBILs helps in understanding the group from several new perspectives. Interpretation of other sedentary plant and animal groups as out of the OCBILs is commended for further study.
... The organic phosphorus directly turned into inorganic phosphorus forms by fire, which increased degree of conversation rate to inorganic phosphorus with the increasing burning temperature. As a consequence, most of the organic phosphorus were lost and the availability of phosphorus was increased (Santín et al., 2018;Wang et al., 2015). The concurrent decline in P accumulation rates and P o /P i were used as indicators of fire event occurrence in this article. ...
To investigate the connection of phosphorus (P) forms with peatland succession and history of fire in Tuqiang peatland, a 57 cm peat core was sampled with high-resolution (1-cm intervals) in the north of the Great Khingan mountain (Northeast China). AMS 14 C dating techniques combined with sequential chemical extraction was used to determine and calculate the accumulation rates of phosphorus fractions. Phosphorus forms were mainly composed with NaOH-P o , hot concentrated HCl-P (conc. HCl-P) and residual-P. Active phosphorus pools were enriched in the top 8-10 cm of the peat surface. The concentrations of organic phosphorus forms and residual-P were generally high during 1200 to 500 cal yr BP, and the accumulation rate of that gradually decreased since 1600 cal yr BP. Both of concentration and accumulation of organic phosphorus decreased after 600 cal yr BP. The accumulation rate of organic phosphorus forms significantly corresponded with peat development frequency, pollen records and other paleo evidence. The concentration and accumulation of organic phosphorus, especially NaOH-P o, was positively connected with concentration of pollen and Cyperaceae, and decreased when relative abundance of moss or shrubs occurred. Fire changed the vegetation community, decreased the concentration and accumulation of P o , and reduced inactive P o /P i at the same time. Fire events could also leave geochemical evidence on peat. It is necessary to consider the both changes of inactive P o /P i and organic phosphorus accumulation rate when reflected the fire history by phosphorus in core.
... 8 Forest Science • XXXX 2020 of burning on soil P, and those that have posit that moderate-to high-severity fire causes P loss from a forest system by means of volatilization or off-site transport, which can affect surface water (Stephens et al. 2004, Son et al. 2015, Santín et al. 2018. In this study, postfire P loss was likely caused by complexion of mobilized inorganic orthophosphate to soil metal cations in acidic soils (pH < 6), rather than direct off-site transport in runoff, leachate, or via volatilization. ...
Burn severity, commonly assessed as the amount of fuel consumed during fire, is an indicator of postfire sediment yield and erosion. This study examined the effect of burn severity on sediment and nutrient response in three different fire-adapted forest types of the Southeast. Soil and litter samples were experimentally burned to achieve increasing levels of fuel consumption. Simulated rainfall was applied to burned litter samples collected from pine, hardwood, and mixed hardwood-pine forests in the Clemson Experimental Forest. Runoff and leachate samples were collected and analyzed for sediment yield (kilograms per hectare) and total suspended solids (grams per liter); both runoff and leachate samples were analyzed for ammonium (NH4–), nitrate (NO3–), and orthophosphate (PO43–). Sediment yield and total suspended solids increased at only the highest burn severity treatment in all three forest types, with pine litter samples yielding significantly greater sediment in surface runoff than both mixed and hardwood samples. Burn treatment did not readily affect soluble nutrient concentrations in either runoff or leachate, but the data suggest that high-severity burning increases the availability of PO43– bound to sediment. This study suggests that high-severity burn patches function as sediment sources, but overall sediment and nutrient response to burning was minimal.
Study Implications
This study suggests that low-to-moderate burn severity, in terms of litter removal, is not an important indicator of sediment and nutrient exports from southeastern forests; precipitation in the immediate aftermath of fire (<48 hours) is not an effective transport mechanism for biologically available macronutrients; and that even at the highest burn severity treatment, sediment yield was relatively low.
... Nitrogen plays a vital role for all watershed organisms (Wilhelm, 2009), but increased nutrients (i.e., N, P) in downstream water bodies can cause adverse effects, such as eutrophication and harmful algal blooms (Bladon et al., 2014;Emelko et al., 2016;Santín et al., 2018). During the first post-fire rainy season, TDN consisted mainly (98%, 92% and 90% in the reference, Rocky and Wragg Fire samples, respectively) of organic nitrogen. ...
We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years' post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year's initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH4⁺/NH3), and specific ultraviolet absorbance (SUVA254) were significantly higher (67 ± 40%, 418 ± 125%, 192 ± 120%, and 31 ± 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br⁻) concentrations (up to 8.7 μM]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (≤1 year).
Shifting phosphorus (P) dynamics after wildfires can have cascading impacts from terrestrial to aquatic environments. However, it is unclear if post-fire responses are primarily driven by changes to the molecular composition of the charred material or from the transport of P-containing compounds. We used laboratory leaching experiments of Douglas-fir forest and sagebrush shrubland chars to examine how the potential mobility of P compounds is influenced by different burn severities. Burning produced a 6.9- and 29- fold increase in particulate P mobilization, but a 3.8- and 30.5- fold decrease in aqueous P released for Douglas-fir forest and sagebrush shrubland, respectively. P compound mobilization in the particulate phase was controlled by solid char total P concentrations while the aqueous phase was driven by solubility changes of molecular species. Nuclear magnetic resonance and X-ray absorption near edge structure on the solid chars indicated that organic orthophosphate monoester and diester species were thermally mineralized to inorganic P moieties with burning in both vegetation types. This coincided with the production of calcium- and magnesium-bound inorganic P compounds. With increasing burn severity there were systematic shifts in P concentration and composition— higher severity chars mobilized P compounds in the particulate phase, although the magnitude of change was vegetation specific. Our results indicate a post-fire transformation to both the composition of the solid charred material and to how P compounds are mobilized, which may influence its environmental cycling and fate.
Despite growing interest in nutrient cycling genes, the influence of fire and clipping on soil microbes, phosphorus (P) and sulfur (S) cycling genes in Karst landscape remain unclear yet are critical for soil fertility in vegetation restoration landscape. Microorganisms have developed various adaptive mechanisms to improve nutrient availability in the soil in response to various landscape disturbances. In this study, we analyzed soil microbial communities and their role in mediating 90 P and 46 S genes under five fire and clipping management practices including: high-intensity fire (HIF), low-intensity fire (LIF), clipping and fire (CF), clipping (CP), and undisturbed control (CK) in Jianshui research station, Yunan province, China. The results indicated no significant (p < 0.05) differences in the predominant bacterial and fungal genera among the treatments. For bacterial compositions such as Sphingomonas, the relative abundance was highest (0.069 %) in LIF. In contrast, the relative abundance of Micromonospora was lowest (0.012 %) in LIF compared to CK. In the case of the fungal genus, Rhizophagus and Trichophyton were highest (0.187, 0.128 %) in CP and LIF respectively compared to control. Bacterial diversity was highest in CF (4.69) following the CK (4.71) while Fungal diversity was highest in CP (3.33) following the CK. P cycling genes increased in LIF, particularly those related to organic phosphoester hydrolysis and transporters, while the other treatments showed no considerable changes. S cycling genes related to S mineralization and assimilation increased in HIF and LIF, respectively, with CF showing a higher presence of sulfide cycling genes. Network analysis of P and S cycling genes indicated that S interactions formed tighter clusters under fire and clipping treatments, while P interactions had more extensive connectivity among genes. These findings underscore the distinct roles and network behaviours of P and S and provide valuable insights into the microbial mechanisms that regulate P availability and S cycling in Karst soils treated with fire and clipping. This also sheds light on the taxonomy of the microbes involved in informed decision-making in karst landscape management.
Soil represents long-term interactions between the ground (mineral material and organic soil matter), climate, trees, ground vegetation, soil animals, and microbial communities. These interactions modify the structure and functioning of soil, including the physical and chemical properties related to its stocks of water, nutrients, and organic matter with carbon. In natural succession, wildfires and the uprooting of trees disturb the surface and even deeper layers of soil through the rooting zone. Disturbance of forest soils maintains their long-term fertility based on changes in primary and secondary production over space and time. The response of soil carbon is also affected by the different impacts of forest management on the structure and dynamics of carbon stocks in the ecosystem. Soil management can be divided into prescribed burning and mechanical management. Both of these processes affect the soil carbon bound in ground vegetation, soil litter, soil detritus, and mineral soil affecting the release of nutrients and carbon bound in soil organic matter. The consequent mixture of soil layers with patches of open mineral soil provides seedbeds for germination of seeds and rooting of initial seedlings improving the success of natural regeneration. Soil management also makes manual seeding and planting in reforestation easier, thus reducing the required workforce and enhancing regeneration success.
Bush burning, whether the result of a wildfire or a controlled burn, has been shown to affect not only the appearance of the landscape, but the quality of the soil as well. Uncontrolled bush fires impact the soil in a variety of ways with the magnitude of the disturbance largely dependent upon the fire intensity, duration and recurrence, fuel load, and soil characteristics. The impact on soil properties is intricate, yielding different results based on these factors. Whereas burning off the vegetation during land clearing for cultivation is a common farming practice among farmers in many parts of the tropics, yet little is known by perpetrators of this practice about its impacts on the soil and its dwellers. This paper reviews research findings from a number of works conducted across the globe with the aim of gaining an insight the effects of wildfire and prescribed fire on the soil chemical and biological attributes. The knowledge of soils response in terms of these two properties to fire events can help in proper implementation of rehabilitation and restoration strategies at the short term, medium term, and long term.
Z Orman yangınlarının birçok çalışmada olumsuz etki gösterdiği ifade edilse de kontrollü yakma uygulamalarının hem yangınlarla mücadelede hem de ekolojik bir araç olarak kullanıldığını ifade eden birçok çalışma mevcuttur. Özellikle ayrışmanın yavaş olduğu ekosistemlerde, örtü yangını uygulamaları yapılarak bu konunun olumlu tarafları olduğu gösterilmektedir. Bu çalışma kapsamında karaçam meşcerelerinde kontrollü yakma uygulamalarının bazı toprak özellikleri üzerine etkisi araştırılmıştır. Bu çalışma kapsamında karaçam alanlarından 10x10 m büyüklüğünde 9 örnekleme noktasından ibre, humus ve toprak örneklemesi yapılmıştır. Kontrollü yakma uygulaması yapıldıktan sonra aynı alanlardan yangın şiddetine göre düşük, orta ve yüksek şiddetli olan yerlerden kül ve toprak örneklemesi yapılmıştır. Toprak reaksiyonu (pH), Elektriksel iletkenlik (EC), karbon (C), azot (N) ve karbon/azot oranı (C/N) analizleri ibre, humus, kül ve toprak örneklerinde yapılırken, tekstür, kireç ve agregat stabilitesi analizleri ise sadece toprak örneklerinde yapılmıştır. Çalışma sonucunda, ölü örtü, humus ve kül örnekleri üzerinde yapılan analizler bakımından kontrollü yakma uygulamasının farklılığın önemli düzeyde olduğu tespit edilmiştir. Genel itibari ile kül örneklerinde pH, EC değerlerinde artma, karbon ve azot değerlerinde ise bir azalma söz konusudur. Toprak örneklerinde ise kum, pH ve azot değerlerinde artma diğer özelliklerde ise anlamlı bir azalma görülmüştür. Çalışma sonucu verilerine göre hem ölü örtünün ortamdan uzaklaşması hem de ölü örtünün yakma sonucunda kül olarak toprağa besin maddesi kazandırması gibi özellikler düşünüldüğünde kontrollü yakma uygulamalarının bir yönetim aracı olarak önemli bir potansiyele sahip olduğu söylenebilir. Anahtar Kelimeler: Yangın, yangın şiddeti, karbon, azot Determination of the effects of prescribed burning applications on some soil properties in Anatolian Black pine (Pinus nigra ssp. pallasiana) stand ABSTRACT Although many studies show that forest fires have negative effects, there are also many studies that show that prescribed burning is used both for fire management and as an ecological tool. Especially in ecosystems where decomposition is slow, the use of prescribed burns has been shown to have positive aspects. In this study, the effects of prescribed burning practices on some soil properties were investigated in Anatolian black pine stands. Within the scope of this study, needle, humus and soil samples were taken from black pine stands at 9 sampling points, each 10x10 m, before the fire. After prescribed burning, ash and soil samples were taken from the same areas at low, medium and high burn severity. While soil reaction (pH), electrical conductivity (EC), carbon (C), nitrogen (N) and carbon/nitrogen ratio (C/N) were analyzed on needle, humus, ash and soil samples, texture, lime and aggregate stability were analyzed on soil samples. Only soil samples were analyzed. As a result of the study, it was found that the difference in the application of prescribed burning was significant in terms of the analyses carried out on the litter, humus and ash samples. In general, there was an increase in pH and EC and a decrease in carbon and nitrogen in the ash samples. In the soil samples, an increase in sand, pH and nitrogen values and a significant decrease in other properties were observed. According to the result of the study, it can be said that prescribed burning practices have an important potential as a management tool, considering the features such as the removal of litter from the environment and the provision of nutrients to the soil as ash as a result of burning.
Orman yangınlarının birçok çalışmada olumsuz etki gösterdiği ifade edilse de kontrollü yakma uygulamalarının hem yangınlarla mücadelede hem de ekolojik bir araç olarak kullanıldığını ifade eden birçok çalışma mevcuttur. Özellikle ayrışmanın yavaş olduğu ekosistemlerde, örtü yangını uygulamaları yapılarak bu konunun olumlu tarafları olduğu gösterilmektedir. Bu çalışma kapsamında karaçam meşcerelerinde kontrollü yakma uygulamalarının bazı toprak özellikleri üzerine etkisi araştırılmıştır. Bu çalışma kapsamında karaçam alanlarından 10x10 m büyüklüğünde 9 örnekleme noktasından ibre, humus ve toprak örneklemesi yapılmıştır. Kontrollü yakma uygulaması yapıldıktan sonra aynı alanlardan yangın şiddetine göre düşük, orta ve yüksek şiddetli olan yerlerden kül ve toprak örneklemesi yapılmıştır. Toprak reaksiyonu (pH), Elektriksel iletkenlik (EC), karbon (C), azot (N) ve karbon/azot oranı (C/N) analizleri ibre, humus, kül ve toprak örneklerinde yapılırken, tekstür, kireç ve agregat stabilitesi analizleri ise sadece toprak örneklerinde yapılmıştır. Çalışma sonucunda, ölü örtü, humus ve kül örnekleri üzerinde yapılan analizler bakımından kontrollü yakma uygulamasının farklılığın önemli düzeyde olduğu tespit edilmiştir. Genel itibari ile kül örneklerinde pH, EC değerlerinde artma, karbon ve azot değerlerinde ise bir azalma söz konusudur. Toprak örneklerinde ise kum, pH ve azot değerlerinde artma diğer özelliklerde ise anlamlı bir azalma görülmüştür. Çalışma sonucu verilerine göre hem ölü örtünün ortamdan uzaklaşması hem de ölü örtünün yakma sonucunda kül olarak toprağa besin maddesi kazandırması gibi özellikler düşünüldüğünde kontrollü yakma uygulamalarının bir yönetim aracı olarak önemli bir potansiyele sahip olduğu söylenebilir.
The mobilisation of potentially harmful chemical constituents in wildfire ash can be a major consequence of wildfires, posing widespread societal risks. Knowledge of wildfire ash chemical composition is crucial to anticipate and mitigate these risks.Here we present a comprehensive dataset on the chemical characteristics of a wide range of wildfire ashes (42 types and a total of 148 samples) from wildfires across the globe and examine their potential societal and environmental implications. An extensive review of studies analysing chemical composition in ash was also performed to complement and compare our ash dataset.Most ashes in our dataset had an alkaline reaction (mean pH 8.8, ranging between 6 and 11.2). Important constituents of wildfire ash were organic carbon (mean: 204 g kg−1), calcium, aluminium, and iron (mean: 47.9, 17.9 and 17.1 g kg−1). Mean nitrogen and phosphorus ranged between 1 and 25 g kg−1, and between 0.2 and 9.9 g kg−1, respectively. The largest concentrations of metals of concern for human and ecosystem health were observed for manganese (mean: 1488 mg kg−1; three ecosystems > 1000 mg kg−1), zinc (mean: 181 mg kg−1; two ecosystems > 500 mg kg−1) and lead (mean: 66.9 mg kg−1; two ecosystems > 200 mg kg−1). Burn severity and sampling timing were key factors influencing ash chemical characteristics like pH, carbon and nitrogen concentrations. The highest readily dissolvable fractions (as a % of ash dry weight) in water were observed for sodium (18 %) and magnesium (11.4 %). Although concentrations of elements of concern were very close to, or exceeded international contamination standards in some ashes, the actual effect of ash will depend on factors like ash loads and the dilution into environmental matrices such as water, soil and sediment. Our approach can serve as an initial methodological standardisation of wildfire ash sampling and chemical analysis protocols.
The study investigated the influence of prescribed fire of two different intensities and mulching on runoff and soil loss, runoff coefficient, and phosphate and nitrate contents of the runoff water. The treatments consisted of fire intensities of 200 and 500 o C, grass mulch, and control. Each treatment was imposed on a plot of 9 m 2 arranged in a randomized complete block design and replicated three times, for three cropping seasons. Runoff volume, soil loss, phosphate and nitrate contents in runoff were measured and the data analysed using general linear method for treatment effects at p < 0.05 . Grass-mulched plot had the lowest runoff and soil loss, while the control plot had the highest. Soil loss from the control plot was 3.40, 4.14, 2.58 t ha -1 in the first, second and third seasons respectively, while the mulched plot lost 0.47, 0.62 and 0.91 t ha -1 in the same order. The volumes of runoff in the mulched plot were 5.28, 4.63 and 4.72 L ha -1 during the first, second and third seasons respectively, while those of control were 14.33, 13.43 and 12.29 L ha -1 . Nitrate and phosphate contents of the runoff were not significantly influenced by the treatments. The fire intensities did not have a significant impact on the total runoff. However, mulching reduced the runoff and soil loss. Therefore, grass mulching of soil is encouraged to mitigate soil erosion in agricultural land.
Globally landscape fires produce about 256 Tg of pyrogenic carbon or charcoal each year. The role of charcoal as a source of environmentally persistent free radicals, which are precursors of potentially harmful reactive oxygen species, is poorly constrained. Here, we analyse 60 charcoal samples collected from 10 wildfires, that include crown as well as surface fires in forest, shrubland and grassland spanning different boreal, temperate, subtropical and tropical climate. Using electron spin resonance spectroscopy, we measure high concentrations of environmentally persistent free radicals in charcoal samples, much higher than those found in soils. Concentrations increased with degree of carbonization and woody fuels favoured higher concentrations. Moreover, environmentally persistent free radicals remained stable for an unexpectedly long time of at least 5 years. We suggest that wildfire charcoal is an important global source of environmentally persistent free radicals, and therefore potentially of harmful reactive oxygen species.
The Fraser Island and the Cooloola dune fields are dominated by giant (>20 m deep) podzols, with numerous buried and well-preserved soil B horizons. Due to their cohesive structure and composition, these horizons can provide extensive information on the past weathering and environmental events that contributed to their formation. Previous work has attributed differences in the consistency and appearance of these B horizons to their mode of formation and past environmental setting. However, the role of post-erosional weathering (weathering after the removal of the overlying A and E horizons in response to climate change), such as fire, in altering these properties has not yet been explored. This laboratory study investigated the effects of simulated fire conditions on B horizon samples from Fraser Island and the Cooloola coast, and how fire may affect their efficacy as weathering and soil formation proxies. Fire simulations were found to alter the mineralogy and geochemistry of the B horizons. More than 94% of soil C in all samples was lost through volatilisation upon heating to 500 °C. Key mineral transformations included the dehydroxylation of gibbsite, kaolinite and lepidocrocite, and the formation of hematite when samples were heated to 500 °C and above. Mineral transformations and soil C loss during heating were reflected in the extractable Al, Fe and Si concentrations, indicating decreased Al, Fe, Si-organic complexes and increased poorly crystalline fractions due to additions from newly-formed dehydroxylated minerals. Results indicate that fires have the ability to affect both the geochemistry and mineralogy of B horizons, and therefore the present study recommends preliminary work should be carried out to determine if soils have been fire affected, before measuring for and relying on B horizon properties as markers for past soil formation conditions.
Hernández et al. La mineralogía en la estimación de las temperaturas de los incendios forestales 1 La mineralogía en la estimación de las temperaturas de los incendios forestales y sus efectos inmediatos en Andosoles, Estado de México Mineralogy in the estimation of the temperature of forest fire and their immediate effects in Andosols, State of Mexico Resumen El fuego es un fenómeno natural e indispensable dentro de los ciclos biogeoquímicos de los suelos, sobre todo aquellos que sustentan una vegetación forestal como los Andosoles. No obstante, poco se conoce sobre las temperaturas que se alcanzan en el suelo y su efecto inmediato sobre sus propiedades edáficas. En 2017 se realizaron recorridos de campo en Texcoco, Estado de México, dos días después de que ocurrió un incendio forestal en Quercus sp y Pinus sp. Muestras de suelo compuestas e inalteradas se colectaron en los primeros 5 cm de suelo para el análisis de sus propiedades edáficas y micro-morfológicas. La estimación de la temperatura se realizó a través de un experimento térmico y análisis mineralógico. Con base en la destrucción, formación y dominancia principalmente de óxidos, ferromagnesianos y
Monitoring landscape-scale vegetation responses of resprouter species to wildfire is helpful in explaining post-wildfire recovery. Several previous Australian studies have investigated the temporal recovery of eucalypt obligate- seeder communities (which have a significantly delayed revegetation response), but little research has been conducted for resprouter communities. In this study, we found that eucalypt dominated resprouter communities in Sydney’s drinking water supply catchments (SDWC) have a rapid post-wildfire response and recovery rate. This study was designed to detect inter-annual landscape-scale changes in vegetation response using a 22 yr pre- and post-wildfire time series of Landsat satellite-derived Australian summer images (1990/91 to 2011/12). Four burned subcatchments and three unburned subcatchments were analyzed. The temporal change in eucalypt forest and woodland vegetation communities was examined within the subcatchments using the Normalized Differenced Vegetation Index (NDVI) to assess their health. A new spectral index, differenced Recovery Index (dRI), was developed to quantify the difference between the pre- and post-wildfire NDVI values. We found that, spectrally, at the landscape scale, vegetation communities recovered to near pre-wildfire conditions within five to seven years post wildfire. These results demonstrate the resilience of resprouter vegetation communities in the Sydney Basin to large-area disturbance events at the landscape scale.
Significance
Increased forest fire activity across the western United States in recent decades has contributed to widespread forest mortality, carbon emissions, periods of degraded air quality, and substantial fire suppression expenditures. Although numerous factors aided the recent rise in fire activity, observed warming and drying have significantly increased fire-season fuel aridity, fostering a more favorable fire environment across forested systems. We demonstrate that human-caused climate change caused over half of the documented increases in fuel aridity since the 1970s and doubled the cumulative forest fire area since 1984. This analysis suggests that anthropogenic climate change will continue to chronically enhance the potential for western US forest fire activity while fuels are not limiting.
Bushfires are one of the most frequent natural hazards experienced in Australia.Fires play an important role in shaping the landscape and its ecological dynamics, but may also have devastating effects that cause human injuries and fatalities, as well as broad-scale environmental damage. While there has been considerable effort to quantify changes in the occurrence of bushfire in Australia, a comprehensive assessment of the most extreme bushfire cases, which exact the greatest economic and environmental impacts, is lacking. In this paper
we reflect upon recently developed understanding of bushfire dynamics to consider (i) historical changes in the occurrence of extreme bushfires, and (ii) the potential for increasing frequency in the future under climate change projections. The science of extreme bushfires is still a developing area, thus our conclusions about emerging patterns in their occurrence should be considered tentative. Nonetheless, historical information on noteworthy bushfire events suggests an increased occurrence in recent decades. Based on our best current understanding of how extreme bushfires develop, there is strong potential for them to increase in frequency in the future. As such there is a pressing need for a greater understanding of these powerful and often destructive phenomena.
Wildfire has been an important process affecting the Earth's surface and atmosphere for over 350 million years and human societies have coexisted with fire since their emergence. Yet many consider wildfire as an accelerating problem, with widely held perceptions both in the media and scientific papers of increasing fire occurrence, severity and resulting losses. However, important exceptions aside, the quantitative evidence available does not support these perceived overall trends. Instead, global area burned appears to have overall declined over past decades, and there is increasing evidence that there is less fire in the global landscape today than centuries ago. Regarding fire severity, limited data are available. For the western USA, they indicate little change overall, and also that area burned at high severity has overall declined compared to pre-European settlement. Direct fatalities from fire and economic losses also show no clear trends over the past three decades. Trends in indirect impacts, such as health problems from smoke or disruption to social functioning, remain insufficiently quantified to be examined. Global predictions for increased fire under a warming climate highlight the already urgent need for a more sustainable coexistence with fire. The data evaluation presented here aims to contribute to this by reducing misconceptions and facilitating a more informed understanding of the realities of global fire.
This article is part of themed issue ‘The interaction of fire and mankind’.
Soils are among the most valuable non-renewable resources on the Earth. They support natural vegetation and human agro-ecosystems, represent the largest terrestrial organic carbon stock, and act as stores and filters for water. Mankind has impacted on soils from its early days in many different ways, with burning being the first human perturbation at landscape scales. Fire has long been used as a tool to fertilize soils and control plant growth, but it can also substantially change vegetation, enhance soil erosion and even cause desertification of previously productive areas. Indeed fire is now regarded by some as the seventh soil-forming factor. Here we explore the effects of fire on soils as influenced by human interference. Human-induced fires have shaped our landscape for thousands of years and they are currently the most common fires in many parts of the world. We first give an overview of fire effect on soils and then focus specifically on (i) how traditional land-use practices involving fire, such as slash-and-burn or vegetation clearing, have affected and still are affecting soils; (ii) the effects of more modern uses of fire, such as fuel reduction or ecological burns, on soils; and (iii) the ongoing and potential future effects on soils of the complex interactions between human-induced land cover changes, climate warming and fire dynamics.
This article is part of the themed issue ‘The interaction of fire and mankind’.
The societal risks of water scarcity and water-quality impairment have received considerable attention, evidenced by recent analyses of these topics by the 2030 Water Resources Group, the United Nations and the World Economic Forum. What are the effects of fire on the predicted water scarcity and declines in water quality? Drinking water supplies for humans, the emphasis of this exploration, are derived from several land cover types, including forests, grasslands and peatlands, which are vulnerable to fire. In the last two decades, fires have affected the water supply catchments of Denver (CO) and other southwestern US cities, and four major Australian cities including Sydney, Canberra, Adelaide and Melbourne. In the same time period, several, though not all, national, regional and global water assessments have included fire in evaluations of the risks that affect water supplies. The objective of this discussion is to explore the nexus of fire, water and society with the hope that a more explicit understanding of fire effects on water supplies will encourage the incorporation of fire into future assessments of water supplies, into the pyrogeography conceptual framework and into planning efforts directed at water resiliency.
This article is part of the themed issue ‘The interaction of fire and mankind’.
Ash is generated in every wildfire, but its eco-hydro-geomorphic effects remain poorly understood and quantified, especially at large spatial scales. Here we present a new method that allows modelling the spatial distribution of ash loads in the post-fire landscape, based on a severe wildfire that burnt ~13 600 ha of a forested water supply catchment in October 2013 (2013 Hall Road Fire, 100 km south-west of Sydney, Australia). Employing an existing spectral ratio-based index, we developed a new spectral index using Landsat 8 satellite imagery: the normalised wildfire ash index (NWAI). Before- and after-fire images were normalised and a differenced wildfire ash image (dNWAI) computed. The relationship between dNWAI and ash loads (t ha⁻¹) quantified in situ at nine sampling locations burnt under a range of fire severities was determined using a polynomial regression (R2 = 0.98). A spatially applied model was computed within a geographic information system (GIS) to illustrate the spatial distribution of ash across the area burnt and to estimate ash loads in the five subcatchments affected by the wildfire. Approximately 181 000 tonnes of ash was produced by the wildfire, with specific loads increasing with fire severity. This new tool to model wildfire ash distribution can inform decisions about post-fire land management in future wildfires in the region. It can also be adapted for its application in other fire-prone environments.
It is often stated that the availability of N limits the rate of growth of native forests. We discuss this hypothesis with particular reference to the mountain ash (Eucalyptus regnans) forests of south-eastern Australia. The abundance of 15 N in leaves and soil of mountain ash forest is in accord with data for Northern Hemisphere temperate forests and for tropical forests,and indicates that N availability is relatively high.None of the nutrient elements has limited the rate of growth of mountain ash forest regenerating after major disturbance (clear-felling and intense wild-fire). There is some evidence that P may be limiting to some ecological processes (e.g. the rate of litter decomposition). We conclude that phosphorus is more likely to be limiting than nitrogen in mountain ash forest because nitrogen cycling is conservative and continual inputs of N through biological fixation supplement this conservative N supply, and the stands never become N-deficient. The development of methodologies to determine the rate of N2-fixation in forests should be of high priority in ecological research.
In the subsistence-based, nutrient-poor soils, and fertilizer-limited agriculture of northern Ghana, 45-65 % of land cover is annually burned for purposes of hunting and agricultural land preparation. The effects of burn-season, fractional nutrient losses, combusted plant parts and vegetation type on the fire-mediated nutrient cycling are unclear. We estimate and compare the plant nutrient losses associated with different savanna covers in the early and late burn-seasons and fractionate the losses into actual losses, which should be the cause for concern and the losses due to particulate redistribution. The tissue-moisture and fuel-load elemental concentrations are predominant factors that determine the quantity of fire-induced nutrient losses. About 50 % of total combusted phosphorus, potassium, calcium and magnesium load; and ~99 % of the carbon and nitrogen loads are directly lost from burned sites during burns. Generally, calcium and magnesium are redistributed in particulate forms (~100 and ~90 % respectively) and not lost from the region, phosphorus and potassium are lost in both particulate (~50 and ~75 % respectfully) and non-particulate forms (~50 and ~25 % respectively), whereas the carbon and nitrogen are mostly lost in gaseous forms (~95 %). In the early-burn season high tissue-nitrogen concentration and low phosphorus-concentration renders burn vulnerable to high nitrogen-losses/emissions and low phosphorus-losses per unit burnt biomass. A comparatively high tissue moisture, however, impedes the early burns, resulting in patches of burned and unburned vegetation that reduce the occurrence of late burns and the total losses of plant-nutrients. Early burns reduce the quantity of nutrient losses towards a more secured food production.
Remote sensing observations provide useful spatially explicit and temporally dense information for monitoring post-fire vegetation recovery patterns over large areas. Although large fires are common in Australian eucalypt forests, research on remote sensing of post-fire vegetation recovery in this ecosystem has been limited. In this study, time series (2000-2012) of Normalised Difference Vegetation Index, Enhanced Vegetation Index and Normalised Differenced Infrared Index derived from Moderate Resolution Imaging Spectroradiometer (MODIS) were used to analyse post-fire vegetation recovery in eucalypt forests in Australia. The analysis focused on 11 sites which burned during 2001/02 and 2002/03 fire seasons. Results indicated that spectral recovery in Australian eucalypt forests is particularly rapid after fire as spectral indices values returned to pre-fire levels three to six years after fire. Spectral recovery was particularly rapid during the first year following fire and the influence of severity was limited to the first two years after fire.
Fly ash has increasingly been used as soil amendment. The mobility of the plant nutrient, phosphorus (P), from fly ash into plant roots is limited due to various inherent locking of P in fly ash. Similarly, the phosphatic fertilizer added to acid soils is fixed and is not easily available to plants. The present study is focused on finding some important aspects of P fractions, P fixing capacity, and P adsorption behavior in acid soil and fly ash- soil mixtures to substantiate the beneficial effect of fly ash addition to acid soil in overcoming the P fixation. Fly ash collected from the fluidized bed combustion power plant of Tata Iron and Steel Company, Jamadoba, Dhanbad, India, and acid soil from Jamdoba village was mixed at different ratios for studying the behavior of P in soil and fly ash soil mixtures. In fly ash out of 3,140 mg kg−1 total P, only 2.89% (90.95 mg kg−1) was in loosely bound form, whereas in soil 54.45 mg kg−1 P (10.8%) out of the 504 mg kg−1 total P was in loosely bound form. Most of the P in fly ash (55.0%) was associated with Ca, while it was Fe-P (40.6%) in soil. The P adsorption maximum followed the order: fly ash (9,354 mg kg−1), 7:1 mix (8,850 mg kg−1), 3:1 mix (8,547 mg kg−1), soil alone (8,130 mg kg−1), and 1:1 mix (7,194 mg kg−1). The supply parameter calculated from the equilibrium phosphorus concentrations and adsorption data showed that the supply parameter increased with fly ash addition. Individually, P fixing capacity of the fly ash and soil was 75.6 and 65.68%, respectively, when both were mixed (1:1), the P fixing capacity decreased to 52.94% due to the synergistic interaction between soil and fly ash. Thus, though fly ash and acid soil is having difficulty with P availability, mixing enhanced the availability of P synergistically.
Using pre- and post-fire satellite imagery from SPOT2, we examined the fire severity and intensity of the Christmas 2001 wildfires in the greater Sydney Basin, Australia. We computed a Normalised Difference Vegetation Index (NDVI) from the two satellite images captured before (November 2001) and after (January 2002) the wildfires, then subtracted the later from the former to produce a difference image (NDVIdiff) which was subsequently classified into six fire severity classes (unburnt, low, moderate, high, very high and extreme severity). We then tested the fire severity classification on 342 sample sites within the 225 000ha fire affected area using a qualitative visual assessment guide. We found that the NDVIdiff classification produced an accuracy of at least 88% (K hat = 0.86), with the greatest discrepancy being between the low and moderate classification. Knowledge of rate of spread over some of the affected area, coupled with a complete knowledge of fuel loads, was used to retrospectively model fire intensity, which in areas of extreme fire intensity, produced heat energy levels exceeding 70 000 kW m–1. Importantly, we found no positive effect of topography on fire severity, in fact finding an inverse relationship between slope and fire severity and no effect due to aspect. Further analysis showed that flat to moderate slopes less than 18° across all aspects suffered the greatest vegetal destruction, and there was no relationship between north-westerly aspects and fire severity. We also introduce a relatively simple method for estimating fuel load biomass using a combination of satellite image and rapid field assessment. We found 79% accuracy for this method based on 125 sample sites. It is postulated that this type of analysis can greatly improve our understanding of the spatial impact of fire, how natural areas within the fire ground were impacted, and how remote sensing and GIS technologies can be efficiently used in fire management planning and post-fire analysis.
Skill-selected global climate models were used to explore the effect of future climate change on regional bushfire weather in eastern Australia. Daily Forest Fire Danger Index (FFDI) was calculated in four regions of differing rainfall seasonality for the 20th century, 2050 and 2100 using the A2 scenario from the Special Report on Emissions Scenarios. Projected changes in FFDI vary along a latitudinal gradient. In summer rainfall-dominated tropical north-east Australia, mean and extreme FFDI are projected to decrease or remain close to 20th century levels. In the uniform and winter rainfall regions, which occupy south-east continental Australia, FFDI is projected to increase strongly by 2100. Projections fall between these two extremes for the summer rainfall region, which lies between the uniform and summer tropical rainfall zones. Based on these changes in fire weather, the fire season is projected to start earlier in the uniform and winter rainfall regions, potentially leading to a longer overall fire season.
In this study, ash is analysed as a geological material; in particular, we focus on ash produced by the burning of Ponderosa pine, a conifer that is widespread throughout mountainous landscapes of western North America. One set of ash samples used in the analyses was collected from a wildfire site and another set was created in the laboratory. We found that the median particle size of the ash was in the fine sand to silt range with at least 25–50% of the particle size distribution in the appropriate range for maintaining debris flow behaviour. Measurements of the infiltration capacity of ash found values similar to fine sands, indicating that a layer of ash can reduce the infiltration capacity of coarse soils. The elemental composition of ashes analysed through inductively coupled plasma emission spectrometry was dominated by Ca, K, Mg, P, Mn, Fe and Al. X-ray diffraction analysis revealed the presence of calcite, quartz and feldspars in ashes created from a variety of fuels; fuel type and combustion temperature were found to have a dominant control on ash mineralogy. The results suggest that the elemental and mineral composition of ash could be used to identify dominant fuel sources and combustion temperatures.
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Research into post-wildfire effects began in the United States more than 70 years ago and only later extended to other parts of the world. Post-wildfire responses are typically transient, episodic, variable in space and time, dependent on thresholds, and involve multiple processes measured by different methods. These characteristics tend to hinder research progress, but the large empirical knowledge base amassed in different regions of the world suggests that it should now be possible to synthesize the data and make a substantial improvement in the understanding of post-wildfire runoff and erosion response. Thus, it is important to identify and prioritize the research issues related to post-wildfire runoff and erosion. Priority research issues are the need to: (1) organize and synthesize similarities and differences in post-wildfire responses between different fire-prone regions of the world in order to determine common patterns and generalities that can explain cause and effect relations; (2) identify and quantify functional relations between metrics of fire effects and soil hydraulic properties that will better represent the dynamic and transient conditions after a wildfire; (3) determine the interaction between burned landscapes and temporally and spatially variable meso-scale precipitation, which is often the primary driver of post-wildfire runoff and erosion responses; (4) determine functional relations between precipitation, basin morphology, runoff connectivity, contributing area, surface roughness, depression storage, and soil characteristics required to predict the timing, magnitudes, and duration of floods and debris flows from ungaged burned basins; and (5) develop standard measurement methods that will ensure the collection of uniform and comparable runoff and erosion data. Resolution of these issues will help to improve conceptual and computer models of post-wildfire runoff and erosion processes.
Slash-and-burn clearing of forest typically results in an increase in soil nutrient availability. Throughout the tropics, ash from consumed vegetation has been accepted as the primary nutrient source for this increase. In contrast, soil heating has been viewed as a secondarily important mechanism of nutrient release. Through the use of multiple burn plots and intensive pre-burn and post-burn sampling of mineral soil, this study quantified changes in total P and N, P fractions, and KCl-extractable N in soil during the slash-and-burn conversion of a Mexican dry forest to agriculture. Slash burning resulted in large transformations of non-plant-available P and N in soil into mineral forms readily available to plants. Anion-exchange resin, NaHC3-extractable P, and KCl-extractable N in soil increased by 37 kg P ha-1 and 82 kg N ha-1. Organic and occluded P (sequentially extracted with NaOH, sonication + NaOH, and NaOH fusion) and organic N (total N minus KCl-extractable N) decreased after burning by 25 kg P ha-1 and 150 kg N ha-1. Immediately after burning, ash from consumed aboveground biomass contained 11 kg P ha-1 and 27 kg N ha-1, of which 55 and 74%, respectively, were quickly transported off the site by wind. At this dry forest site, soil heating had a much larger influence on soil P and N availability than inputs of ash.
Research highlights
► Wildfire effects on water quality vary substantially. ► Large post-fire increases to sediment, nutrient and trace element fluxes reported. ► Wildfires may disrupt the supply of potable water from forest catchments.
Soil P composition can be conveniently determined in alkaline extracts using solution 31P nuclear magnetic resonance (NMR) spectroscopy, but spectral assignments are based on fragmentary literature reports of model compounds in various extraction matrices. We report solution 31P NMR chemical shifts of model P compounds, including inorganic phosphates, orthophosphate monoesters and diesters, phosphonates, and organic polyphosphates, determined in a standardized soil P extractant (0.25 M NaOH and 0.05 M EDTA). Signals from nucleic acids (DNA -0.37 ppm, RNA 0.54 ppm) and phospholipids (phosphatidyl choline 0.78 ppm, phosphatidyl serine 1.57 ppm, phosphatidyl ethanolamine 1.75 ppm) could be differentiated in the orthophosphate diester region, and were identified in a sample of cultured soil bacteria. Inorganic and organic polyphosphates could be differentiated by the presence of a signal at -9 ppm from the α phosphate of organic polyphosphates. Some orthophosphate diesters, notably RNA and phosphatidyl choline, degraded rapidly to orthophosphate monoesters in NaOH-EDTA although DNA, other phospholipids, and orthophosphate monoesters were more stable. Changes in probe temperature had a marked influence on signal intensities and the relative magnitude of signals from orthophosphate monoesters and inorganic orthophosphate, and we suggest that solution 31P NMR spectroscopy of soil extracts be performed at 20°C.
Prolonged seasonal drought affects most of the tropics, including vast areas presently or recently dominated by 'dry forests'. These forests have received scant attention, despite the fact that humans have used and changed them more than rain forests. This volume reviews the available information, often making contrasts with wetter forests. The world's dry forest heterogeneity of structure and function is shown regionally. In the neotropics, biogeographic patterns differ from those of wet forests, as does the spectrum of plant life-forms in terms of structure, physiology, phenology and reproduction. Biomass distribution, nutrient cycling, below-ground dynamics and nitrogen gas emission are also reviewed. Exploitation schemes are surveyed, and examples are given of non-timber product economies. It is hoped that this review will stimulate research leading to more conservative and productive management of dry forests.
Wetland ecosystems maintain a fragile balance of soil, water, plant, and atmospheric components in order to regulate water flow, flooding, and water quality. Marginally covered in traditional texts on biogeochemistry or on wetland soils, Biogeochemistry of Wetlands is the first to focus entirely on the biological, geological, physical, and chemical processes that affect these critical habitats. This book offers an in-depth look at the chemical and biological cycling of nutrients, trace elements, and toxic organic compounds in wetland soil and water column as related to water quality, carbon sequestration, and greenhouse gases. It details the electrochemistry, biochemical processes, and transformation mechanisms for the elemental cycling of carbon, oxygen, nitrogen, phosphorus, and sulfur. Additional chapters examine the fate and chemistry of heavy metals and toxic organic compounds in wetland environments. The authors emphasize the role of redox-pH conditions, organic matter, microbial-mediated processes that drive transformation in wetlands, plant responses and adaptation to wetland soil conditions. They also analyze how excess water, sediment water, and atmospheric change relate to elemental biogeochemical cycling. Delivering an in-depth scientific examination of the natural processes that occur in wetland ecosystems, Biogeochemistry of Wetlands comprises a key perspective on the environmental impact of pollutants and the role freshwater and coastal wetlands play in global climate change.
Forest productivity is limited by soil P availability in several forest ecosystems worldwide. Most of the soil available P is probably produced by the mineralization of organic forms of P when these forms dominate in the soil. Severe wildfires lead to loss of soil organic compounds and therefore represent a strong risk of loss of soil P. The objective of the present study was to examine how the temperature reaching during burning affects the P fractions in organic horizons and soil. For this purpose, we conducted experimental burns of intact soil monoliths with their organic horizons. We then used Hedley chemical sequential fractionation and 31P MNR spectroscopy to determine the effects of temperature during burning on soil P fractions. In the unburned organic horizons, the organic P represented 70% of the total P and it was completely mineralized when the temperatures reached above 500 °C. Similarly, in the unburned mineral soil, organic P forms represented 76% of the total P and the organic P was reduced by around 50% in the moderate soil burn severity (SBS) levels. In the highest SBS, the concentration of inorganic P (Pi) with a fast turnover rate (representing available P) was three times higher and the concentration of Pi with a slow turnover rate (representing the sum of inorganic fractions bound to Al and Ca) was eight times higher than in the unburned soil. By contrast, the organic P fractions decreased with the temperature reached during the fire, with 200 °C considered a threshold for the total thermal mineralization of organic P, mainly the labile organic fraction. These findings suggest that high temperatures lead to release of Pi, most of which is precipitated by P forms such as Pi with a slow turnover rate. It appears that the high burn severity associated with temperatures higher than 200 °C strongly disrupts soil P dynamics, increasing the occlusion capacity and decreasing the bioavailability.
The large mediatic coverage of recent massive wildfires across the world has emphasized the vulnerability of freshwater resources. The extensive hydrogeomorphic effects from a wildfire can impair the ability of watersheds to provide safe drinking water to downstream communities and high-quality water to maintain riverine ecosystem health. Safeguarding water use for human activities and ecosystems is required for sustainable development; however, no global assessment of wildfire impacts on water supply is currently available. Here, we provide the first global evaluation of wildfire risks to water security, in the form of a spatially explicit index. We adapted the Driving forces-Pressure-State-Impact-Response risk analysis framework to select a comprehensive set of indicators of fire activity and water availability, which we then aggregated to a single index of wildfire-water risk using a simple additive weighted model. Our results show that water security in many regions of the world is potentially vulnerable, regardless of socio-economic status. However, in developing countries, a critical component of the risk is the lack of socio-economic capability to respond to disasters. Our work highlights the importance of addressing wildfire-induced risks in the development of water security policies; the geographic differences in the components of the overall risk could help adapting those policies to different regional contexts.
Forest catchment supply high quality water to a number of communities around the world. • Forest fire release sequestered metals from soil organic matter and vegetation. • Post-fire erosion rapidly transports these metals to downstream soil and water bodies. • Their deposition in the water bodies affects the water quality and aquatic biota. • This metal contamination may reach to human being as a consumer. One of the significant economic benefits to communities around the world of having pristine forest catchments is the supply of substantial quantities of high quality potable water. This supports a saving of around US$ 4.1 trillion per year globally by limiting the cost of expensive drinking water treatments and provision of unnecessary infrastructure. Even low levels of contaminants specifically organics and metals in catchments when in a mobile state can reduce these economic benefits by seriously affecting the water quality. Contamination and contaminant mobility can occur through natural and anthropogenic activities including forest fires. Moderate to high intensity forest fires are able to alter soil properties and release sequestered metals from sediments, soil organic matter and fragments of vegetation. In addition, the increase in post-fire erosion rate by rainfall runoff and strong winds facilitates the rapid transport of these metals downslope and downstream. The subsequent metal deposi-tion in distal soil and water bodies can influence surface water quality with potential impacts to the larger ecosystems inclusive of negative effects on humans. This is of substantial concern as 4 billion hectares of forest catchments provide high quality water to global communities. Redressing this problem requires quantification of the potential effects on water resources and instituting rigorous fire and environmental management plans to mitigate deleterious effects on catchment areas. This paper is a review of the current state of the art literature dealing with the risk of post-fire mobilization of the metals into surface water resources. It is intended to inform discussion on the preparation of suitable management plans and policies during and after fire events in order to maintain potable water quality in a cost-effective manner. In these times of climate fluctuation and increased incidence of fires, the need for development of new policies and management frameworks are of heighted significance.
This perspective article summarizes, from the author's point of view at the beginning of 2016, the major challenges and perspectives in the field of quantitative NMR. The key concepts in quantitative NMR are first summarized, then the most recent evolutions in terms of resolution and sensitivity are discussed, as well as some potential future research directions in this field. A particular focus is made on methodologies capable of boosting the resolution and sensitivity of quantitative NMR, which could open application perspectives in fields where the sample complexity and the analyte concentrations are particularly challenging. These include multi-dimensional quantitative NMR and hyperpolarization techniques such as para-hydrogen induced polarization or dynamic nuclear polarization. Since quantitative NMR cannot be dissociated from the key concepts of analytical chemistry, ie. trueness and precision, the methodological developments are systematically described together with their level of analytical performance.
Over the past decades, wildfires have affected vast areas of Mediterranean ecosystems leading to a variety of negative on- and off-site environmental impacts. Research on fire-affected areas has given more attention to sediment losses by fire-enhanced overland flow than to nutrient exports, especially in the Mediterranean region. To address this knowledge gap for post-fire losses of phosphorus (P) by overland flow, a recently burnt forest area in north-central Portugal was selected and instrumented immediately after a wildfire. Three slopes were selected for their contrasting forest types (eucalypt vs. pine) and parent materials (granite vs. schist). The selected study sites were a eucalypt site on granite (BEG), a eucalypt site on schist (BES) and a maritime pine site on schist (BPS). Micro-plots were monitored over a period of six months, i.e. till the construction of terraces for reforestation obliged to the removal of the plots. During this 6-month period, overland flow samples were collected at 1- to 2-weekly intervals, depending on rainfall. Total P and PO4-P losses differed markedly between the two types of forests on schist, being lower at the pine site than at the eucalypt site, probably due to the presence of a protective layer of pine needle cast. Parent material did not play an important role in PO4-P losses by overland flow but it did in TP losses, with significantly lower values at the eucalypt site on granite than that on schist. These differences in TP losses can be attributed to the coarser texture of granite soils, typically promoting infiltration and decreasing runoff. The present findings provided further insights into the spatial and temporal patterns of post-fire soil nutrient losses in fire-prone forest types during the initial stages of the window-of-disturbance, which can be useful for defining post-fire emergency measures to reduce the risk of soil fertility losses.
The model has 3 components: 1) the reaction between divalent phosphate ions and a variable-charge surface; 2) the assumption that there is a range of values of surface properties and that these are normally distributed; 3) the assumption that the initial adsorption induces a diffusion gradient towards the interior of the particle which begins a solid-state diffusion process. The model closely describes the effects on sorption of phosphate of: concentration of phosphate, pH, temperature, and time of contact. It also reproduces the effects on desorption of phosphate of: period of prior contact, period and temperature of desorption, and soil: solution ratio. The model suggests that phosphate that has reacted with soil for a long period is not 'fixed' but has mostly penetrated into the soil particles. The phosphorus can be recovered slowly if a low enough surface activity is induced. -from Author
Global increases in the occurrence of large, severe wildfires in forested watersheds threaten drinking water supplies and aquatic ecology. Wildfire effects on water quality, particularly nutrient levels and forms, can be significant. The longevity and downstream propagation of these effects, as well as the geochemical mechanisms regulating them remain largely undocumented at larger river basin scales. Here, phosphorus (P) speciation and sorption behavior of suspended sediment were examined in two river basins impacted by a severe wildfire in southern Alberta, Canada. Fine grained suspended sediments (<125 μm) were sampled continuously during ice-free conditions over a two year period (2009-2010), 6 and 7 years after the wildfire. Suspended sediment samples were collected from upstream reference (unburned) river reaches, multiple tributaries within the burned areas, and from reaches downstream of the burned areas, in the Crowsnest and Castle River basins. Total particulate phosphorus [TPP], particulate phosphorus [PP] forms (non-apatite inorganic P [NAIP], apatite P [AP], organic P [OP]), and the equilibrium phosphorus concentration (EPC0 ) of suspended sediment were assessed. Concentrations of TPP and the EPC0 were significantly higher downstream of wildfire-impacted areas compared to reference (unburned) upstream river reaches. Sediments from the burned tributary inputs contained higher levels of bioavailable particulate P (NAIP)-these effects were also observed downstream at larger river basin scales. The release of bioavailable P from post-fire, P-enriched fine sediment is a key mechanism causing these effects in gravel-bed rivers at larger basin scales. Wildfire-associated increases in NAIP and the EPC0 persisted 6 and 7 years after wildfire. Accordingly, this work demonstrated that fine sediment in gravel-bed rivers is a significant, long-term source of in-stream bioavailable P that contributes to a legacy of wildfire impacts on downstream water quality, aquatic ecology, and drinking water treatability. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Fire can have large effects on ecosystems, with phosphorus being highly important in this regard, especially when considering productivity in burned or adjacent ecosystems after fire. Unfortunately, existing data pose contradictions and methodological challenges to assessing P availability. Here, the impact of fire on topsoil available P was estimated using three different types of organic soil layers (raw humus from spruce, humus from beech and peat) and two fire regimes (obtaining black carbon and ash). Our findings suggest a strong fire impact on P-availability, by enhancing available P during burning to black carbon (~10-fold), and to ash (~2 to 7.5-fold) dependent on calcite content. Fire impact on P availability is on a similar order of magnitude as mineral weathering and annual P-cycling/uptake in/by ecosystems. Furthermore, the proportion of available-P in relation to total-P depends on the origin of the organic soil layers. When relating to the remaining mass after burning as commonly done, P-availability can be overestimated by up to 1400%. Results from this study provide a realistic magnitude of shifts in P-release and -availability by fire events of different intensity for widely abundant ecosystem conditions. Taking the importance of P for ecosystem processes into account, these results are highly relevant, since fires for fuel reduction are a common application, and for temperate and boreal ecosystems even moderate climate change scenarios predict an increasing appearance of fires in these regions.
Fire transforms fuels (i.e. biomass, necromass, soil organic matter) into materials with different chemical and physical properties. One of these materials is ash, which is the particulate residue remaining or deposited on the ground that consists of mineral materials and charred organic components. The quantity and characteristics of ash produced during a wildland fire depend mainly on (1) the total burned fuel (i.e. fuel load), (2) fuel type and (3) its combustion completeness. For a given fuel load and type, a higher combustion completeness will reduce the ash organic carbon content, increasing the relative mineral content, and hence reducing total mass of ash produced. The homogeneity and thickness of the ash layer can vary substantially in space and time and reported average thicknesses range from close to 0 to 50 mm. Ash is a highly mobile material that, after its deposition, may be incorporated into the soil profile, redistributed or removed from a burned site within days or weeks by wind and water erosion to surface depressions, footslopes, streams, lakes, reservoirs and, potentially, into marine deposits.
In many parts of the world, forests provide high quality water for domestic, agricultural, industrial, and ecological needs, with water supplies in those regions inextricably linked to forest health. Wildfires have the potential to have devastating effects on aquatic ecosystems and community drinking water supply through impacts on water quantity and quality. In recent decades, a combination of fuel load accumulation, climate change, extensive droughts, and increased human presence in forests have resulted in increases in area burned and wildfire severity - a trend predicted to continue. Thus, the implications of wildfire for many downstream water uses are increasingly concerning, particularly the provision of safe drinking water, which may require additional treatment infrastructure and increased operations and maintenance costs in communities downstream of impacted landscapes. A better understanding of the effects of wildfire on water is needed to develop effective adaptation and mitigation strategies to protect globally critical water supplies originating in forested environments.
Wildfires transform the landscape, leading to changes in surface cover and, potentially, in water quality. The purpose of this study was to assess changes in the chemical composition of soils and surface water as a result of a wildfire that burned in 2006 in the Marão Mountains, NE Portugal, by comparing pre- and post-fire hydrochemical data and burned/unburned soil data, and to examine the recovery of vegetation over time using Landsat TM imagery. Studies that have access to pre-fire data are rare and even fewer studies document changes in biomass as a result of fire and during the postfire recovery period. Samples of ash, soil and water, from within and outside the burned area, were collected 5 months, and one year after the fire, for chemical analyses. Landsat TM Images were downloaded and transformed into a vegetation index, in order to analyze landcover dynamics and to calculate biomass. The wildfire effects on the Marão River water quality, resulted in an increase in the total mineralization of water. Five months after the wildfire the electrical conductivity (E.C.) at the mainstem was about 56% higher than pre-fire values (E.C. increased from 25 to 39 μS/cm) and still higher one year after (36 μS/cm). Cations of Ca, Na, Mg and Mn showed the greatest increase. This increase was probably triggered by the movement of ash to the watercourses. This disturbance had already attenuated one year after wildfire to values closer to pre-fire data except for manganese. Manganese had anomalous concentrations in the water within the burned area. The concentration of Mn in ash samples reached values up to 5 times more than values found in underlying soils. One year after the wildfire, almost all the burned area had recovered with herbaceous vegetation and patches of shrub vegetation. The wildfire burned 1194.7 dry tons of biomass which means, on average, 4.9 dry ton/ha. Based on the mass of burned biomass, we calculated approximately 350 g/ha of Mn were released as a result of the fire. We suggest that this type of calculation can be conducted before a fire to help resource managers understand worst-case scenarios for changes in water quality that have the potential to affect aquatic biotic and the suitability of water for drinking water purposes and agriculture.
Ecohydrological linkages between phosphorus (P) production, stream algae, benthic invertebrate, and fish communities were studied for 4 years after severe wildfire in the Rocky Mountains (Alberta, Canada). Mean concentrations of all forms of P (soluble reactive, total dissolved, particulate, and total) were 2 to 13 times greater in burned and post-fire salvage-logged streams than in unburned streams (p < 0.001). Post-disturbance recovery of P was slow with differences in P-discharge relationships still evident 5 years after the fire (p < 0.001). Coupled P and sediment interactions were likely responsible for slow recovery of P regimes in fire-disturbed watersheds. P loading was associated with strong ecological responses in stream biota. Annual algal productivity was 5 to 71 times greater in streams within burned watersheds than in reference watersheds and persisted for 5 years after the fire (p < 0.001). Elevated algal production was associated with strong differences in benthic invertebrate community structure, including greater invertebrate densities, biomass, species diversity, and shifts in species composition. Monotonic shifts in invertebrate stable carbon and nitrogen isotope ratios indicated increased consumption of autochthonous food sources and effects on energy pathways for invertebrates from fire-affected streams. Wildfire-related changes at lower trophic lead to increases in size (weight and length) and growth rate (weight : age ratios) of cutthroat trout (Oncorhynchus clarki). This cascading series of effects of wildfire on stream productivity (primary production, secondary invertebrate consumers, and fish) may be long-lived legacies of wildfire because of the slow recovery of P regimes.
The concentration of elements in ash from eucalyptus litter varied several-fold depending upon the type of fuel and combustion conditions. In vegetation fires, and where ash is used as a soil amendment, significant amounts of nutrients and heavy metals will be added to soils. Three patterns of dissolution of ash constituents in water were observed: (1) high (> 70% of element content of ash quickly soluble), but with a residual component which was not solubilized by further dilution (elements K, S, and B); (2) relatively insoluble, but where the amount dissolved is related to dilution (Ca, Mg, Si and Fe), and (3) highly insoluble (such as P). The capacity of ash to neutralize acid was well correlated with the total amount of basic cations (K+Ca+Mg) in the ash.Addition of 4–20 t ash ha−1 to a range of forest soils increased pH (KCl) by one to three units depending on soil C content, decreased exchangeable Al and H content, increased exchange sites (variable negative charges) and increased basic-cation levels. Ash addition increased respiration rates in all soils, especially in those with higher organic matter content. Addition of ash increased N mineralization rate and nitrification in most of the soils, although the magnitude of response was not clearly related to assessed soil properties.This study suggests that account must be taken of soil and ash properties when assessing the utility of plant ash for soil amelioration.
Area-based sampling was carried out to investigate the effect of thinning and soil properties on accumulation of forest floor carbon (C), nitrogen (N) and phosphorus (P) in Norway spruce (Picea abies (L.) Karst.) stands in Denmark. Four thinning intensities (unthinned, and about 83%, 67% and 50% of unthinned basal area) were investigated at three sites in Denmark: a calcareous, relatively nutrient rich soil with a sandy loam/loam texture and two soils with low to intermediate nutritional status and sandy loam and loamy sand textures, respectively.
The effect of thinning on accumulated carbon and nitrogen was significant at two of the investigated sites. Accumulated phosphorus was significantly affected by thinning at one of these two sites and at the third site. Accumulated carbon and phosphorus were negatively linearly correlated with thinning intensity. pH tended to be highest and C/N and C/P ratios tended to be lowest in the heaviest thinned plots. It is hypothesized that the differences in accumulation may be due to a more favourable microclimate and substrate for saprophytic organisms in the most heavily thinned plots. However, the differences between sites were greater than differences between thinning intensities. The accumulation of carbon, nitrogen and phosphorus in the forest floors was much higher at the two less fertile sites with loamy sand and sandy loam than at the relatively fertile site with sandy loam/loam. Significant differences in pH and in C/N and C/P ratios at the three sites indicate that the amounts of available nutrients influence the mineralization pattern. In addition, at the site with the greatest forest floor root density, competition for nutrients and moisture between mycorrhiza-infected roots and free-living saprophytic decomposers may be co-responsible for the large amounts of accumulated carbon, nitrogen and phosphorus.
Nine different organic and inorganic soil phosphorus fractions were obtained by a sequential extraction of samples from 168 USDA-SCS benchmark soils, representing eight soil orders of the Soil Taxonomy. The distribution of P across the different fractions (resin, bicarbonate, hydroxide, sonification-2nd hydroxide, acid, and acid-peroxide digest fractions with separate organic and inorganic P determinations) and their relationships to other soil chemical properties were used to evaluate the effects of different soil development on phosphorus composition. Correlation and regression analyses of P distribution and chemical analyses confirmed the partial dependence of organic matter accumulation on available forms of P. Weathering indicators such as base saturation were related to the formation of secondary P forms. The relative proportions of available and stable as well as organic and inorganic P forms were dependent upon soil chemical properties and related to soil taxonomy.