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Patterns of Nitrate Loss From a Chronosequence of Clear-Cut Watersheds
Abstract
Three clear-cuts at the Hubbard Brook Experimental Forest (NH) have resulted in a chronosequence of forest watersheds in close proximity. Following clear-cutting, the stands, now 12, 21, 27, and 78 years old, have different species composition, nutrient capital, and biogeochemistry. In this study, we compared seasonal patterns of NO3
– in streamwater, changes in N capital, and N retention in watersheds of differing stand age. All of the watersheds showed elevated losses of NO3
–, H+ and nutrient cations (Ca2+, Mg2+, K+) during the first few years following clear-cutting. Increased retention of N occurred during vegetation regrowth compared to the reference watershed (W6). Nitrate concentrations were low during the summer growing season, increased in the late fall and peaked in March during spring snowmelt. Concentrations of NO3
– were lower in the regrowing watersheds than in W6 during all months. In W6, there was considerable year-to-year variability in N retention, which was not initially observed in the manipulated watersheds. However, two cut watersheds exhibited higher export of NO3
– in 1989 and 1990, corresponding to a 10-year high value in annual NO3
– loss in W6. These results demonstrate the importance of land use and cutting history in assessments of N saturation and loss from forest watersheds.
... and also in watersheds affected by clear-cut harvest (Pardo et al., 1995). The temporal evolution of the processes regulating and exporting N, however, remain poorly quantified. ...
... When kt r was near zero across the sites, the production and removal of NO 3 in the near-surface layer were of comparable rates so the in-stream NO 3 concentration did not show a seasonal pattern. Such disappearance or even reversal of the seasonal pattern after severe dieback due to increased NO 3 production has frequently been observed in forest catchments (Kaňa et al., 2015;Pardo et al., 1995;Yeakley et al., 2003). ...
The ecosystem function of vegetation to attenuate export of nutrients is of substantial importance for securing water quality. This ecosystem function is at risk of deterioration due to an increasing risk of large-scale forest dieback under climate change. The present study explores the response of the nitrogen (N) cycle of a forest catchment in the Bavarian Forest National Park, Germany, in the face of a severe bark beetle (Ips typographus Linnaeus) outbreak and resulting large-scale forest dieback using top-down statistical-mechanistic modeling. Outbreaks of bark beetle killed the dominant tree species Norway spruce (Picea abies (L.) H.Karst.) in stands accounting for 55% of the catchment area. A Bayesian hierarchical model that predicts daily stream NO3 concentration (C) over three decades with discharge (Q) and temperature (T) (C-Q-T relationship) outperformed alternative statistical models. A catchment model was subsequently developed to explain the C-Q-T relationship in top-down fashion. Annually varying parameter estimates provide mechanistic interpretations of the catchment processes. Release of NO3 from decaying litter after the dieback was tracked by an increase of the nutrient input parameter cs0. The slope of C-T relation was near zero during this period, suggesting that the nutrient release was beyond the regulating capacity of the vegetation and soils. Within a decade after the dieback, the released N was flushed out and nutrient retention capacity was restored with the regrowth of the vegetation.
... At higher ratios nitrogen is immobilized and nitrification is inhibited [36]. In addition, high nitrate leaching rates were observed after strong disturbances such as tree cutting [37]. ...
... Analysis of the temporal variation in N leaching showed a significant contribution of relative mortality or tree removal, that can be detected up to three years after the event. This is in line with previous studies that found an increase in N leaching after clear cutting in a catchment area [37] or after tree removal [69]. In contrary other findings [35], the C:N ratio was not a significant predictor Table 4. ...
Soil solution chemistry is influenced by atmospheric deposition of air pollutants, exchange processes with the soil matrix and soil-rhizosphere-plant interactions. In this study we present the results of the long-term Intercantonal Forest Observation Program in Switzerland with soil solution measurements since 1998 on a current total of 47 plots. The forest sites comprise two major forest types of Switzerland including a wide range of ecological gradients such as different nitrogen (N) deposition and soil conditions. The long-term data set of 20 years of soil solution measurements revealed an ongoing, but site-specific soil acidification. In strongly acidified soils (soil pH below 4.2), acidification indicators changed only slowly over the measured period, possibly due to high buffering capacity of the aluminum buffer (pH 4.2–3.8). In contrast, in less acidified sites we observed an increasing acidification rate over time, reflected, for example, by the continuous decrease in the ratio of base cations to aluminum (BC/Al ratio). Nowadays, the main driver of soil acidification is the high rate of N deposition, causing cation losses and hampering sustainable nutrient balances for tree nutrition. Mean nitrate leaching rates for the years 2005–2017 were 9.4 kg N ha⁻¹ yr⁻¹, ranging from 0.04 to 53 kg N ha⁻¹ yr⁻¹. Three plots with high N input had a remarkable low nitrate leaching. Both N deposition and nitrate leaching have decreased since 2000. However, the latter trend may be partly explained due to increased drought in recent years. Nonetheless, those high N depositions are still affecting the majority of the forest sites. Taken together, this study gives evidence of anthropogenic soil acidification in Swiss forest stands. The underlying long-term measurements of soil solution provides important information on nutrient leaching losses and the impact climate change effects such as droughts. Furthermore, this study improves the understanding of forest management and tree mortality regarding varying nitrate leaching rates.
... Increased post-harvest NO 3 -N concentrations and loads have been noted in previous studies (e.g. Gravelle et al., 2009;Henriksen and Kirkhusmo, 2000;Martin et al., 2000;Pardo et al., 1995;Tremblay et al., 2009). The importance of increased nitrification after clear-fell harvesting (due to increased levels of soil microorganisms, increased decomposition of organic matter and soil mineralisation) has been considered important by many previous authors (e.g. ...
... Effect of forestry management activities on nitrate/TN concentrations/loads from selected previous studies. Increased concentrations of stream nitrate and TN following planting of a loblolly pine plantationQuinn and Ritter (2003) Central North Island, New Zealand Nitrate leaching decreased in the five years following planting a P. radiata forestHarvestPardo et al. (1995) New Hampshire, USA Elevated nitrate losses during the first few years following clear-fell harvestingHenriksen and Kirkhusmo (2000) Southern Norway Immediate increase in groundwater nitrate concentrations following clear-fell harvest of Norway SpruceMartin et al. (2000) New Hampshire, USA Increase in concentrations of stream nitrate immediately following harvesting. The concentrations return close to preharvest levels within 3-5 yearsGravelle et al. (2009) Northern Idaho, USA Nitrate concentrations increased significantly following clear-fell harvestTremblay et al. (2009) Quebec, Canada Stream nitrate concentrations increased by up to 6000% after clear-fell harvestThinningBäumler and Zech (1999) Southern Germany Nitrate concentrations increased by ∼20% following thinning of a mixed species forestGravelle et al. (2009) Northern Idaho, USA Nitrate concentrations increased significantly following partial harvestTian et al. (2012) North Carolina, USA No significant change in nitrate loads following thinning of an intensively managed loblolly pine forest ...
Many long-term forestry water quality studies focus on the impact of the harvesting phase of forestry operations. As a result, the water quality impacts of other activities such as forest (re)planting, thinning and fertilising are less well understood. Here we report the results from 23 years of monthly water quality monitoring from a steep headwater catchment within the Waikato region, New Zealand. Three experimental sub-catchments were planted in different proportions of Pinus radiata (PW2 = 100%, K-Pine 57%; PW3 = 36%). PW2 and PW3 were historical pastoral sites in the first rotation of plantation forestry and K-Pine was harvested and subsequently planted in a second rotation of forestry. All sites underwent two phases of stand thinning six and eight years after planting. The most significant effect of forestry was the increase in nitrate-N (NO 3 -N) and total nitrogen (TN) concentrations in response to both stand planting and stand thinning operations. Planting resulted in significant increases in NO 3 -N, TN and DRP over a four-year planting period at PW2. Significant increases in NO 3 -N and TN were detected over a four-year thinning period, at all three experimental sites. We propose that stream NO 3 -N and TN concentrations increased in response to stand planting at PW2 because of the change in physical conditions (e.g. increased stream shading, proliferation of nitrogen fixing weeds and decreased spatial extent of seepage wetlands) caused by the change in land use. Increasing nitrogen concentrations due to decreasing stream runoff could also be contributing a factor. Any decrease in NO 3 -N and TN concentrations in response to increased uptake by the rapidly growing P. radiata appears to have been masked by these other factors. However, the increase in NO 3 -N and TN concentrations in response to stand thinning at all three experimental sites suggests that NO 3 -N uptake by growing trees is an important process. Over the entire forestry period, median NO 3 -N concentrations at PW2 (first rotation site) increased by a factor four (400–1590 µg l ⁻¹ ). The median NO 3 -N during the post-thinning period was also one order of magnitude higher than those measured at K-Pine (second rotation site) during the post-thinning period. We attribute these differences to the NO 3 -N legacy within soil and/or groundwater of the previous sheep and beef cattle grazing land use. Long-term use of the PW2 catchment for forestry may eventually reduce NO 3 -N concentrations to the lower levels measured at K-Pine. Therefore, while NO 3 -N concentrations and loads may increase in response to the establishment of plantation forestry we envisage that these will decline if plantation forestry continues beyond the first rotation. This research highlights: (i) the complex nature of the response of stream water quality to catchment land use changes, and (ii) the value of studies that monitor the impact of land use/cover change over the long-term.
... Following the perturbation, marked increases in drainage water NO 3 À concentrations were observed in the extensive crown damage zone relative to both nonimpacted areas and pre-disturbance data. This pattern of elevated NO 3 À loss agrees with observations of both natural and anthropogenic disturbances in temperate forest ecosystems (Swank et al. 1981; Pardo et al. 1995; Likens and Bormann 1995; Mitchell et al. 1996; Eshleman et al. 199819981999) the ice storm are shown. Error bars reflect standard deviations dissipation in the Bs horizon at the HBEF (Fig. 31.3); the upper soil (0–12 cm) was the source of elevated N. Two processes – either separate or in combination – can explain the response (1) enhanced solar radiation to the forest floor (due to newly created gaps in forest over-story) stimulating microbial decomposition (mineralization ) and subsequent nitrification; supplying a source of N in excess of biotic requirements, and/or (2) decreased uptake of N. ...
... Finally, transiently high losses of N associated with natural and anthropogenic disturbances probably contribute to N limitations of CO 2 uptake in Northern Hardwood ecosystems. Explanations for widespread occurrence of N limitation in temperate ecosystems have focused on fire and harvesting of annual crops (Seastedt et al. 1991),Houlton et al. 2003) d Pardo et al. (1995) e Likens et al. (1978) energetic constraints to growth or colonization of N fixers, disproportionate P (or other element) limitation to fixers as opposed to nonfixers, and disproportionately high rates of herbivory on fixers as opposed to nonfixers (Vitousek and Howarth 1991). Other studies have identified the importance of long-term losses of organically bound forms of N, which are generally unavailable to plants (Hedin et al. 1995; Vitousek et al. 1998). ...
A critical challenge of biogeochemical research is to distinguish between the effects of natural and anthropogenic disturbances
on nutrient cycles. Natural agents of disturbance – particularly wind and ice storms, insect defoliation episodes, and fire
– are stochastic and highly variable; hence, it is difficult to develop broad generalizations about the effects of such exogenous
perturbations on ecosystem pattern and process (Waring and Schlesinger 1985). Nonetheless, examples of disturbance effects
are apparent (Lemon 1961; Mattson and Addy 1975; Bormann and Likens 1979a; Whitney and Johnson 1984; Bruederle and Stearns
1985), pointing to their importance in the regulation of biogeochemical cycles in general, nitrogen (N) cycles in particular
(Swank et al. 1981; Likens and Bormann 1995; Mitchell et al. 1996; Eshleman et al. 1998). Here, we review the impact of ice
storms on N cycling in forest ecosystems, also reviewing (and comparing) disturbance effects on N cycling more generally.
... Vitousek and Melillo, 1979;Burns andMurdoch, 2005 NO 3 Likens et al., 1970;Dahlgren and Driscoll, 1994;Pardo et al., 1995 S e θ θ r / θ s θ r { [1 | αΨ | n ] m Ψ 0 2 θ s Ψ 0 S e θ cm 3 cm 3 Ψ cm θ s cm 3 cm 3 θ r cm 3 cm 3 α cm 1 n m , m 1 1/n van Genuchten-Mualem van Genuchten, 1980;Mualem, 1976 K S e { K s S e 1/2 [1 1 S e 1/m m ] 2 Ψ 0 3 K s Ψ 0 K cm d 1 K s cm d 1 θ s θ r α n 0Changes of NO 3 concentration in soil water and streamwater and water discharge before and after cutting., 5 cm; , 15 cm; , 50 cm; , 80 cm; , Streamwater; , Monthly water discharge. Likens et al., 1970;Pardo et al., 1995;Fukuzawa et al., 2006Likens et al., 1969Corbett et al., 1978 NO , Soil water in 80 cm depth observed value ;, Streamwater observed, monthly average ; , Simulated value without NO 3 adsorption capacity;, Simulated value with NO 3 adsorption capacity. ...
... , 5 cm; , 15 cm; , 50 cm; , 80 cm; , Streamwater; , Monthly water discharge. Likens et al., 1970;Pardo et al., 1995;Fukuzawa et al., 2006Likens et al., 1969Corbett et al., 1978 NO , Soil water in 80 cm depth observed value ; ...
Long-term changes in the water quality of soil water and streamwater were monitored before and after cutting at the lower slope position in a small forested watershed composed of artificial stands of old aged Japanese cedar and cypress in the northern Kanto region in Japan. The NO3-concentration in soil water directly reflected the N dynamics, i.e., the reduced nutrient uptake and accelerated nitrogen mineralization in the surface soil layer immediately after the cutting, and the increased nutrient uptake induced by regenerated trees several years after the practice. In contrast, the NO3-concentration in streamwater maintained higher level than before cutting in the sixth year after the practice. The NO3-concentrations in high and low discharge, which is dominated by direct flow and base flow, respectively, were calculated from the relationships between discharge rates and the NO3- concentration in streamwater. The results suggested that the NO3-distribution in soil affects the NO3-concentration in streamwater. Changes in the NO3-concentration in the subsoil were calculated using the HYDRUS-1D model, and these changes were consistent with previously measured seasonal and long-term changes in the NO3-concentration in streamwater. This finding implies that NO3-adsorption characteristics of the volcanic ash subsoil affects NO3-leaching into streamwater. In order to clarify the effects of the aging of artificial forests, the method of cutting, and environmental changes on N dynamics in soil and streamwater, it is necessary to consider the NO3-adsorption characteristics of volcanic ash soil.
... When forest primary productivity is Nlimited, net nitrification and nitrate (NO 3 2 ) leaching rates from forests should be low because either (1) plants out-compete nitrifying bacteria for ammonium (NH 4 + ) thereby leading to lower gross nitrification rates; or (2) gross nitrification rates are equally high under N-limited conditions, but microbial assimilation of NO 3 2 reduces net nitrification rates and NO 3 2 leaching losses (Fenn et al. 1998). Several studies have corroborated that nutrient retention decreases as forests mature (Vitousek and Reiners 1975, Leak and Martin 1975, Peet 1992, Pardo et al. 1995, Perakis and Hedin 2001, while others have not (e.g., Martin 1979, Fisk et al. 2002. In particular, recent research has suggested that greater detrital biomass pools (primarily due to greater amounts of coarse woody debris) in old-growth forests result in greater microbial N immobilization compared to second-growth forests (Fisk et al. 2002). ...
... Discussion. Past research suggests that oldgrowth forests display lower ecosystem N retention than aggrading and mature forests, due to elevated rates of canopy tree mortality and subsequent reduced phyto-autotrophic N demand (e.g., Vitousek and Reiners 1975, Leak and Martin 1975, Peet 1992, Pardo et al. 1995, Perakis and Hedin 2001. However, others have found that accumulations of recalcitrant woody detritus and/or foliar litter with high C:N and lignin:N ratios lead to greater microbial immobilization of N in woody debris and the forest floor, thereby leading to reduced nitrification rates, and lower NO 3 2 leaching rates in old-growth forests (Gower et al. 1996, Fisk et al. 2002. ...
We conducted a biogeochemical analysis of four Adirondack northern hardwood forests (two old-growth and two maturing second-growth) to elucidate correlations among stand age, site conditions and several nutrient cycling processes. One each of the old-growth and maturing forests were located on base-rich sites, while the other two were on base-poor sites. At each site we analyzed soil solution chemistry and estimated nutrient flux rates; measured annual litter production, and nutrient and lignin content; measured annual N mineralization and nitrification rates; and characterized herb- and canopy-layer vegetation, and coarse woody debris volumes. Vascular plant communities of the two base-rich sites were dominated by several rich-site indicator species, while such indicators were lacking at the base-poor sites. Tree basal areas and annual litter production did not differ among the study sites, but the old-growth stands contained 3-fold more coarse woody debris than the maturing stands. Foliar litter N concentrations did not differ among the study sites, but foliar litter from the base-rich sites had higher Ca2+ and lower lignin concentrations than the base-poor sites. Differences in foliar litter quality among the sites were due, in part, to intraspecific variation in litter chemistry. There were no consistent differences between the old-growth and maturing stands in soil solution nutrient concentrations or fluxes. Soil solution H+ concentrations were higher and Ca:Al ratios lower at the two base-poor sites. Annual, net N mineralization rates did not differ among the sites, but net nitrification rates in the organic soil horizons at the rich old-growth site were more than twice those at the other sites. High levels of net nitrification and N leaching were observed only in the base-rich old-growth site. Our data suggest that net forest nutrient retention may be a function of interacting mechanisms associated with forest developmental stage, community composition and site conditions.
... This unclear seasonality of Forellenbach after forest disturbance was not an exception. This phenomenon has also been observed in other forested catchments, where large amounts of IN from dead tree residues alter the soil nitrogen balance and complicate the magnitude and temporal relationship between nitrogen mineralization and consumption year round (Ge et al., 2014;Pardo et al., 1995). Hence, drawing general conclusions is difficult due to the large variability between different catchments. ...
Forest status is crucial for catchment hydrology and water quality but is increasingly disturbed by human activities and climatic factors. Therefore, it is urgently necessary to develop water quality models that can adapt to these changes. This study used a new dynamic Hydrological Predictions for the Environment (HYPE) model to assess the effect of rapid and continuous forest changes on catchment hydrology and nitrogen export. The modified HYPE model was implemented for the 25 years period in the Große Ohe catchment in Germany, which has experienced severe forest dieback and recovery. Due to the stochastic nature of infestation events, data covering the entire process of forest change are rare. The modified HYPE model performed well at different scales for discharge and dissolved inorganic nitrogen (DIN) export. It was able to (a) capture the timing of peak flows and the seasonal DIN concentration dynamics and (b) reflect the initial increase and subsequent decrease trend in discharge and DIN export in accordance with forest dieback and regeneration. The increase in nitrogen export after forest dieback primarily resulted from reduced forest uptake and increased soil nitrogen availability from tree residues. The difference in runoff and nitrogen export increment with or without regeneration highlights the importance of forest regeneration in restoring catchment hydrology and water quality. Additionally, a decrease in DIN export after residue removal implies the impact of sound post‐disturbance management strategies. The dynamic modeling under changing catchment forests can enhance the analysis of catchment water quality and effectively support forest management.
... Since enzymatic activity is temperature-sensitive, experiments were conducted in 2019 and 2020 to quantify the relationship between NRA and incubation temperature [47]. Based on simultaneously incubating foliage at ambient (~20 • C) and elevated temperature (23,25,27,29,31, and 33 • C) of sugar maple, red maple, common greenbrier, blackberry, violets, and hay-scented fern, a mean NRA correction of 0.0086 for each 1 • C was applied to normalize all 2018 NRA values to 27 • C. ...
Forest plants that can assimilate nitrate may act as nitrate sink and, consequently, reduce nitrate losses from watershed ecosystems through leaching. This study, conducted at the Fernow Experimental Forest in West Virginia, quantified via nitrogen reductase activity (NRA) the nitrate assimilation of two tree species, red maple and sugar maple, and surrounding common herb-layer species at the tissue (foliage, roots) and plot level. NRA measurements were conducted in summer and spring. Furthermore, NRA was quantified under varying levels of soil nitrate availability due to fertilization, different stages in secondary forest succession, and watershed aspect. This study confirmed that NRA of mature maples does not respond to varying levels of soil nitrate availability. However, some herb-layer species’ NRA did increase with nitrogen fertilization, and it may be greater in spring than in summer. Combined with biomass, the herb layer’s NRA at the plot-level (NRAA) comprised 9 to 41% of the total (tree + herb-layer) foliar NRAA during the growing season. This demonstrates that the herb layer contributes to nitrate assimilation disproportionally to its small biomass in the forest and may provide a vernal dam to nitrate loss not only by its early presence but also by increased spring NRA relative to summer.
... While spatial variation in the stream NO 3 − concentration is frequently attributed to land use (van Breemen et al. 2002) and/or geology (Holloway et al. 1998) in the watershed, the effect of such variables was not significant in our watersheds. In addition, other factors affecting the NO 3 − concentration such as climatic condition (Watmough et al. 2004), nitrogen deposition (Nishina et al. 2017;Amos et al. 2018), and forest age (Pardo et al. 1995;Tokuchi and Fukushima 2009) are almost the same within the range of our study watersheds. While the excretion of nitrogen from benthos was in the form of NH 4 + , we assume that NH 4 + Content courtesy of Springer Nature, terms of use apply. ...
Animals affect element cycling in ecosystems by consumption and excretion. Amphidromous shrimps frequently dominate low-mid altitude streams, where downstream connectivity to oceans is sustained. Although shrimps’ direct influence on benthic communities has been studied, little is known about their influences on nutrient cycling. Here, we hypothesized that the dominance of shrimps alters nutrient mineralization by benthic macroinvertebrates in streams due to the difference in the quality and quantity of excretion between shrimps and aquatic insects. We tested this hypothesis through a field manipulative experiment, excretion measurements of animals, and field surveys. In the field manipulative experiment, the presence of shrimps slightly decreased the biomass of aquatic insects but tripled total benthic macroinvertebrate biomass directly through their own biomass. The mass-specific NH4+ excretion rate by shrimps was similar to aquatic insects, and the areal NH4+ excretion by benthic macroinvertebrates was increased by 2.5 times in the presence of shrimps. In contrast, shrimps excreted significantly less soluble reactive phosphorus (SRP) than aquatic insects, and the presence of shrimps did not affect areal SRP excretion by benthic macroinvertebrates. The field survey showed a positive correlation of NO3− concentration with the shrimp density, inferring the excess NH4+ was nitrified. Although the nutrient concentration of stream water is frequently attributed to watershed conditions, the results of this study indicate that downstream connectivity to oceans may also influence nutrient dynamics of the stream through the density of amphidromous shrimps.
... We observed seasonal patterns of low summer nitrate-N concentration followed by higher concentration during fall high flows similar to those seen in western, conifer-forested watersheds (Lajtha et al. 1995;Pardo et al. 1995;Williams et al. 1996;Stottlemyer and Toczydlowski 1999;) and in watersheds draining young forest stands with elevated stream nitrate-N concentrations (Cairns and Lajtha 2005). In studies of watersheds with low N exports (<1 to 2 kg/ha/yr), the opposite pattern (i.e., higher summer concentrations) was observed (Swank and Vose 1997;Edmonds et al. 1998). ...
... Past experiments have shown that nitrogen and phosphorus export increases after the clear felling of a forest (Likens et al., 1970in Molles, 2005, Pardo et al., 1995. The amount of sediment from eroded soil is also found highest in sites with less vegetation cover, and increase as vegetation cover increases (Heartsill-Scalley and Aide, 2003). ...
... Several studies carried out in boreal forests indicate that logging affects the retention of inorganic nitrogen in the forest soil, so that nitrate leaching in the runoff water increases (e.g. Emmet et al., 1991b;Futter et al., 2010;Gundersen et al., 2006;Kreutzweiser et al., 2008;Pardo et al., 1995;Rosén et al., 1996). The soil conditions of clear-cut areas are warmer and moister than in growing forests, due to decreased transpiration and increased sun exposure when the trees have been removed (Kreutzweiser et al., 2008). ...
... The most affected medium catchment showed maximum nitrate concentrations equivalent to the highest concentrations found in studies of clear-cuts in Europe (Didons-Lescot et al. 1993) and North America (Likens et al. 1970;McHale et al. 2007). Nevertheless, concentrations were three times lower than those recorded in the "herbicide without biomass removal" treatment in the Hubbard Brook Experiment (Likens et al. 1978), underscoring the important role of undisturbed residual and regenerating vegetation for nitrate retention (Pardo et al. 1995). In contrast, maximum nitrate concentrations of the small and large catchments were considerably lower. ...
Increasing natural disturbances in conifer forests worldwide complicate political decisions about appropriate land management. In particular, allowing insects to kill trees without intervention has intensified public debate over the dual roles of strictly protected areas to sustain ecosystem services and to conserve biodiversity. Here we show that after large scale bark beetle Ips typographus infestation in spruce Picea abies forests in south-eastern Germany, maximum nitrate concentrations in runoff used for drinking water increased significantly but only temporarily at the headwater scale. Moreover, this major criterion of water quality remained consistently far below the limit recommended by the World Health Organization. At the same time, biodiversity, including numbers of Red-listed species, increased for most taxa across a broad range of lineages. Our study provides strong support for a policy to allow natural disturbance-recovery processes to operate unimpeded in conifer-dominated mountain forests, especially within protected areas.This article is protected by copyright. All rights reserved.
... Nevertheless, concentrations were three times lower than those recorded in the ‗herbicide without biomass removal' treatment in the Hubbard Brook Experiment (Likens et al. 1978), underscoring the important role of undisturbed residual and regenerating vegetation for nitrate retention (Pardo et al. 1995). In contrast, maximum nitrate concentrations of the small and large catchments were considerably lower. ...
Increasing natural disturbances in conifer forests worldwide complicate political decisions about appropriate land management. In particular, allowing insects to kill trees without intervention has intensified public debate over the dual roles of strictly protected areas to sustain ecosystem services and to conserve biodiversity. Here we show that after large scale bark beetle Ips typographus infestation in spruce Picea abies forests in south-eastern Germany, maximum nitrate concentrations in runoff used for drinking water increased significantly but only temporarily at the headwater scale. Moreover, this major criterion of water quality remained consistently far below the limit recommended by the World Health Organization. At the same time, biodiversity, including numbers of Red-listed species, increased for most taxa across a broad range of lineages. Our study provides strong support for a policy to allow natural disturbance-recovery processes to operate unimpeded in conifer-dominated mountain forests, especially within protected areas.This article is protected by copyright. All rights reserved.
... A particularly large increase in sediment loads likely occurred during and after the American Revolution, as tobacco markets tilted in favor of grains and more land was cleared and ploughed (Curtin et al. 2001). Elevated NO 3 and sediment losses have been reported for recent clearcuts in experimental forests (Pardo et al. 1995;Eshleman et al. 2000), and nutrient and sediment loads to the Patuxent likely increased during this period, although the elevated N loads were probably of brief duration. However, commercial fertilizers were not yet in use, so nutrient loads probably did not increase enough to produce a substantial trophic response in the river at this point in time. ...
Located at the interface between estuaries and surrounding uplands, tidal marshes are in position to receive and transform material from both adjacent systems. Of particular importance in eutrophic estuarine systems, tidal marshes permanently remove nutrients via two mechanisms -denitrification and long-term burial. Denitrification was measured (monthly) in two marshes in a Chesapeake Bay tributary for 7 months, using the MIMS technique. Burial of nitrogen (N) and phosphorus (P) was measured using 210 Pb techniques. Strong spatial and temporal patterns emerged, and there was a Michaelis-Menten type response in denitrification rates to experimentally elevated nitrate levels. Denitrification rates measured may account for removal of 22% of N inputs to the upper estuary on an annual basis. Burial rates could account for 30% of N inputs and 60% of P inputs. Based on the cost of nutrient control technologies, Patuxent marsh nutrient removal may be valued at $10 to 30 million yr -1 .
... Conditions on clearcuts are completely different from those in growing forests, since net mineralization continues at the same or an even higher rate, while there is no uptake by trees. This causes increased N leaching from clearcuts, as has been shown in several studies in Europe (Adamson and Hornung, 1990;Wiklander et al., 1991;Ahtiainen, 1992;Rosén et al., 1996;Ahtiainen and Huttunen, 1999) and in the United States (Dahlgren and Driscoll, 1994;Pardo et al., 1995;Hermann et al., 2001). In a study of clearcuts in southern Sweden, N concentrations in soil water were found to be positively related to N deposition . ...
Akademisk avhandling för avläggande av teknologie doktorsexamen vid tekniska fakulteten, Lunds universitet. Avhandlingen kommer att försvaras offentligt onsdagen den 4 maj kl 13:15 i Stora hörsalen, Ingvar Kamprad Designcentrum (IKDC), Sölve-gatan 26, Lund. Fakultetens opponent: Professor Martin Forsius, Finnish Environment Institute, Helsinki, Finland.
... At BBWM the most common damage was cankers. The cankers occurred primarily on F. grandifolia, one of Foliar Chemical Analyses at Acadia The initial effects of fire and harvesting on biogeochemical cycling in forest ecosystems include elevated losses of some nutrients from the system, e.g., N (Clinton et al. 1996), Ca 2+ , Mg 2+ , and K + (Pardo et al. 1995). The extent of the loss in relation to fires varies depending on the intensity of the fires (Vose et al. 1999). ...
The goal of this report is to present the results of the vegetation component of the PRIMENet study at Acadia. The results include a classification of vegetation types and their locations within Cadillac Brook and Hadlock Brook watersheds; a synthesis of the primary and meta tree, sapling, and seedling data from the two study watersheds; and foliar chemical analyses using Acer rubrum and Picea rubens from Cadillac Brook and Hadlock Brook watersheds. This report provides the baseline information for long-term forest vegetation monitoring in the deciduous and coniferous forests in Cadillac Brook and Hadlock Brook watersheds. Ongoing interest and studies on the status of the natural resources within Acadia National Park makes availability of information from previous work, such as the baseline data in this report, very important.
... Human impacts on ecological systems are widespread and have been observed to alter soil nutrient cycling and availability (Vitousek and Walker, 1989;Aber et al., 1989;Harrison et al., 1995), with profound effects on ecosystem structure and function (Rusek, 1993;Carreira et al., 1997). Anthropogenic factors known to alter nutrient cycling and availability include atmospheric pollutants (Aber et al., 1989;Harrison et al., 1995), heavy metals (Berg et al., 1991), exotic invasive species (Vitousek and Walker, 1989), and human disturbance (Pardo et al., 1995;Weston and Attiwill, 1996). Although these anthropogenic factors typically occur together in human-dominated ecosystems (Breitberg et al., 1998), we know relatively little about their combined effects on soil nutrient availability. ...
We compared soil N and P availability in similar oak forest stands located in either an urban or a rural area. To compare N and P availability in the urban and rural soils, we measured: (1) net N-mineralization potential and extractable inorganic P; (2) plant demand for NH4+, NO3− and PO43− using a root nutrient uptake bioassay; and (3) N and P acquisition by red oak (Quercus rubra L.) seedlings grown in the contrasting soils. Although net N-mineralization potential did not differ between the urban and rural soils, we found a 5-fold increase in net nitrification in urban compared to rural soils. Despite an apparent trend toward lower labile inorganic P in the urban versus the rural soils, the treatment means did not differ statistically. Root nutrient uptake bioassays indicated that demand for NH4+ was higher (i.e. availability lower) in the urban than in the rural soils in 1995, but did not differ in 1996. A trend toward greater root demand for NO3− in the rural than the urban soils was observed but the means did not differ significantly. We also found that demand for PO43− was significantly higher in oak roots collected from the urban compared to the rural soils in both 1995 and 1996. Total seedling N content (mg N in tissue) and leaf N concentration were significantly lower in Q. rubra seedlings grown in urban compared to rural soils, with decreased N content associated with lower leaf, stem and tap root nitrogen. Leaf and stem P contents were also significantly lower in urban-grown Q. rubra seedlings compared to rural-grown seedlings. We found no differences in tissue P concentration between urban and rural seedlings. Together our results suggest that soil P and, to a lesser degree, N availability is lower in the urban than the rural stands and that these differences are associated with anthropogenic impacts. We discuss the potential for differences in litter quality, exotic earthworms and N deposition between the urban and rural soils to lower soil N and P availability in the urban forest stands.
... The availability of DON from humic watersheds may be further promoted by photochemical transformations induced by solar radiation, as suggested by Bushaw et al. (1996). Rivers at temperate latitudes tend to have high nitrate concentrations during high discharge periods in autumn–spring, whereas DIN concentrations are low during summer (Pardo et al. 1995). Depending on hydrological conditions in the coastal areas, nitrogen brought by rivers in winter may be transported to the open ocean and may have less of an impact on coastal summer blooms. ...
Access to bioavailable nitrogen often limits primary production in marine and freshwater ecosystems. Around 70% of nitrogen transported by rivers worldwide consists of dissolved organic nitrogen (DON), but its bioavailability has been poorly investigated. To assess the potential bacterial growth on DON, we developed a bioassay employing natural DON and bacterial inocula in medium manipulated to make N the limiting nutrient. We analyzed the bacterial utilization of the high-molecular-weight fraction of DON isolated by ultrafiltration from three wetlands in South Sweden throughout the year. The bioavailability of low-molecular-weight and bulk DON was also analyzed in one of the wetlands, where inorganic nitrogen concentration was sufficiently low and did not interfere with bioassays. The bioavailability of bulk DON in the latter wetland varied from 2% to 16%, suggesting that DON is an important nitrogen source for the biota of coastal waters. DON may be the dominant input of bioavailable nitrogen during summer, when nitrate concentrations in rivers decrease and DON bioavailability increases. Marine bacterioplankton assimilated a substantially larger fraction of DON than did freshwater bacterioplankton, on average by a factor of 2.4. This finding indicates that the susceptibility of DON to bacterial mineralization increases as it is transported from freshwaters into saline environments.
... Our initial hypothesis for the increase in δ 15 N in the Oie horizon after clear-cutting was that increased nitrification and nitrate loss were responsible for 15 N enrichment of the total forest floor nitrogen. Nitrate loss during the first 3 years after clear-cutting increased by 1500 mol·ha -1 ·year -1 (Pardo et al. 1995). In our calculations, we attribute this nitrate loss to nitrification. ...
Export of microbially produced nitrate from an ecosystem is expected to increase δ15N in the remaining soil organic matter and NH4+. To test the hypothesis that nitrification and nitrate loss induced by clear-cutting cause an increase in soil and foliar δ15N, we measured δ15N in a clear-cut watershed at the Hubbard Brook Experimental Forest, New Hampshire. δ15N ranged from 0.02 in the Oie horizon to 7.7 in the Bs2 horizon prior to clear-cutting and increased significantly by 1.3 in the Oie horizon and 0.9 in the Oa horizon 3 years after clear-cutting. Fifteen years after clear-cutting, δ15N in both O horizons decreased to near-initial values. No significant temporal changes in the Bs2 and C horizons δ15N were observed. Foliar δ15N was highest (1.7) the first 2 years after clear-cutting and was significantly higher than in the reference watershed (mean δ15N = 1.2), decreasing to 0.0 35 years after clear-cutting and to 1.3 911 years after clear-cutting. Increased foliar δ15N coincided with increased stream-water nitrate concentration, suggesting that the increased nitrification responsible for elevated stream-water nitrate may also have caused an enrichment of the plant-available ammonium pool. The response observed in this catchment also suggests that sampling of soil or foliar δ15N may provide a practical alternative to long time series of stream chemistry for evaluating nitrogen saturation of forested ecosystems.
... Chronic N deposition may lead to N saturation, which is N availability in excess of plant and microbial demand, accompanied by elevated nitrification and NO 3 losses ( Aber et al. 1989, Stoddard 1994. Field measurements have demonstrated that N losses do not necessarily increase directly with N inputs (Van Miegroet et al. 1992, Dise et al. 1998b), and northern hardwood forests with similar N inputs can have vastly different N outputs ( Pardo et al. 1995, Hornbeck et al. 1997, Lovett et al. 2000). These authors and others have inferred that land-use history may influence nitrate output. ...
Nearly all northeastern U.S. forests have been disturbed by wind, logging, fire, or agriculture over the past several centuries. These disturbances may have long-term impacts on forest carbon and nitrogen cycling, affecting forests' vulnerability to N saturation and their future capacity to store C. We evaluated the long-term (80-110 yr) effects of logging and fire on aboveground biomass, foliar N (%), soil C and N pools, net N min- eralization and nitrification, and NO3 2 leaching in northern hardwood forests in the White Mountain National Forest, New Hampshire. Historical land-use maps were used to identify five areas each containing previously logged, burned, and relatively undisturbed (old- growth) forests. Aboveground biomass averaged 192 Mg/ha on the historically disturbed sites and 261 Mg/ha on the old-growth sites, and species dominance shifted from early- successional and mid-successional species (Betula papyrifera and Acer rubrum) to late- successional species (Fagus grandifolia and particularly A. saccharum). Forest floors in the old-growth stands had less organic matter and lower C:N ratios than those in historically burned or logged sites. Estimated net N mineralization did not vary by land-use history (113 kg·ha 21 ·yr 21 ); mean (6 1 SE) nitrification rates at old-growth sites (63 6 4.3 kg·ha 21 ·yr 21 ) doubled those at burned (34 6 4.4 kg·ha 21 ·yr 21 ) and logged (29 6 4.7 kg·ha 21 ·yr 21 ) sites. Across all plots, nitrification increased as forest floor C:N ratio decreased, and NO3 2 concentrations in streamwater increased with nitrification. These results indicate that forest N cycling is affected by century-old disturbances. The increased nitrification at the old-growth sites may have resulted from excess N accumulation relative to C accu- mulation in forest soils, due in part to low productivity of old-aged forests and chronic N deposition.
... This is consistent with predictions from successional theory that plant uptake should keep soil inorganic N pools low, leading to minimal leaching losses from successional ecosystems (Gorham et al. 1979). Research also indicates that ecosystem N retention is high during succession (Vitousek 1977, Pardo et al. 1995. ...
... Nitrate leaching can increase after timber harvesting because of loss of vegetative uptake of nitrogen and enhanced microbial nitrification rates because of increased soil moisture, temperature, and physical disturbance (Vitousek and Melillo 1979, Huttl and Schaaf 1995). Most harvesting studies showed short-term increases in stream nitrate , with nitrate exports returning to preharvest levels in 3– 4 years because of uptake by regrowing vegetation and soil nitrification returning to predisturbance rates (Hornbeck et al. 1986, Lynch and Corbett 1991, Pardo et al. 1995). Arthur et al. (1998) found nearly identical nitrate exports with and without BMPs after harvesting (Table 3). ...
Quantifying the effects of forestry best management practices (BMPs) on sediment and nutrient loads is a critical need. Through an exhaustive literature search, three paired forested watershed studies in the eastern United States were found that permitted the calculation of BMP efficiencies—the percent reduction in sediment or nutrients achieved by BMPs. For sediment, BMP efficiencies ranged from 53 to 94% during harvest and up to 1 year after harvesting. For nutrients, BMP efficiencies were higher for total nitrogen (60-80%) and phosphorus (85-86%), which included particulate and sediment-bound forms, than for nitrate-nitrogen (12%), which occurs primarily in the dissolved phase. Results indicate forestry BMPs can significantly reduce sediment and nutrient loads; however, BMPs appear to be more effective at reducing pollutants associated with surface runoff than with subsurface flow.
... Terrestrial and aquatic processes affect DIN concentrations in streamwater. Watershed geomorphology (Creed and Band 1998), soil characteristics (Gundersen et al. 1998; Seely et al. 1998), land-use or fire history (Pardo et al. 1995; Johnson et al. 1997), vegetation type or successional stage (Vitousek and Reiners 1975; Wigington et al. 1998), and atmospheric loading (Stoddard 1994) may all affect the quantity of DIN entering a stream from the terrestrial ecosystem. N uptake by vegetation or soil microfauna may also influence seasonal patterns of stream DIN export (Likens and Bormann 1995; Vitousek 1977; Foster et al. 1989). ...
We analyzed long-term organic and inorganic nitrogen inputs and outputs in precipitation and streamwater in six watersheds at the H.J. Andrews Experimental Forest in the central Cascade Moun-tains of Oregon. Total bulk N deposition, averaging 1.6 to 2.0 kg N ha −1 yr −1 , is low compared to other sites in the United States and little influenced by anthropogenic N sources. Streamwater N export is also low, averaging <1 kg ha −1 yr −1 . DON is the predominant form of N exported from all watersheds, fol-lowed by PON, NH 4 -N, and NO 3 -N. Total annual stream discharge was a positive predictor of annual DON output in all six watersheds, suggesting that DON export is related to regional precipitation. In contrast, annual discharge was a positive predictor of annual NO 3 -N output in one watershed, annual NH 4 -N output in three watersheds, and annual PON output in three watersheds. Of the four forms of N, only DON had consistent seasonal concentration patterns in all watersheds. Peak streamwater DON concentrations occurred in November-December after the onset of fall rains but before the peak in the hydrograph, probably due to flushing of products of decomposition that had built up during the dry summer. Multiple biotic controls on the more labile nitrate and ammonium concentrations in streams may obscure temporal DIN flux patterns from the terrestrial environment. Results from this study un-derscore the value of using several watersheds from a single climatic zone to make inferences about controls on stream N chemistry; analysis of a single watershed may preclude identification of geograph-ically extensive mechanisms controlling N dynamics.
... Forest harvesting may alter stream water chemistry, but the effects should not be expected to be consistent across forest types and regions. Any initial increase in NO 3 concentrations in streams following harvesting may be followed by longer term declines as forest regeneration increases ecosystem N retention as observed at Hubbard Brook (Pardo et al., 1995). Fire is a major factor in most forests of the United States, including both wildfires and prescribed management fires (DeBano et al., 1998). ...
Seventy to eighty percent of the water flowing in rivers in the United States originates as precipitation in forests. This project developed a synoptic picture of the patterns in water chemistry for over 300 streams in small, forested watersheds across the United States. Nitrate (NO3−) concentrations averaged 0.31 mg N/L, with some streams averaging ten times this level. Nitrate concentrations tended to be higher in the northeastern United States in watersheds dominated by hardwood forests (especially hardwoods other than oaks) and in recently harvested watersheds. Concentrations of dissolved organic N (mean 0.32 mg N/L) were similar to those of NO3∼, whereas ammonium (NH4+) concentrations were much lower (mean 0.05 mg N/L). Nitrate dominated the N loads of streams draining hardwood forests, whereas dissolved organic N dominated the streams in coniferous forests. Concentrations of inorganic phosphate were typically much lower (mean 12 mg P/L) than dissolved organic phosphate (mean 84 mg P/L). The frequencies of chemical concentrations in streams in small, forested watersheds showed more streams with higher NO3− concentrations than the streams used in national monitoring programs of larger, mostly forested watersheds. At a local scale, no trend in nitrate concentration with stream order or basin size was consistent across studies.
Temporal patterns in stream chemistry provide integrated signals describing the hydrological and ecological state of whole catchments. However, stream chemistry integrates multi-scale signals of processes occurring in both the catchment and stream. Deconvoluting these signals could identify mechanisms of solute transport and transformation and provide a basis for monitoring ecosystem change. We applied trend analysis, wavelet decomposition, multivariate autoregressive state-space modeling, and analysis of concentration–discharge relationships to assess temporal patterns in high-frequency (15 min) stream chemistry from permafrost-influenced boreal catchments in Interior Alaska at diel, storm, and seasonal time scales. We compared catchments that varied in spatial extent of permafrost to identify characteristic biogeochemical signals. Catchments with higher spatial extents of permafrost were characterized by increasing nitrate concentration through the thaw season, an abrupt increase in nitrate and fluorescent dissolved organic matter (fDOM) and declining conductivity in late summer, and flushing of nitrate and fDOM during summer rainstorms. In contrast, these patterns were absent, of lower magnitude, or reversed in catchments with lower permafrost extent. Solute dynamics revealed a positive influence of permafrost on fDOM export and the role of shallow, seasonally dynamic flowpaths in delivering solutes from high-permafrost catchments to streams. Lower spatial extent of permafrost resulted in static delivery of nitrate and limited transport of fDOM to streams. Shifts in concentration–discharge relationships and seasonal trends in stream chemistry toward less temporally dynamic patterns might therefore indicate reorganized catchment hydrology and biogeochemistry due to permafrost thaw.
The chemistry of the soil solution is influenced by atmospheric deposition of air pollutants, by exchange processes between the soil matrix and the soil solution and by processes between the rhizosphere and the soil. At sites of the Intercantonal Long-term Forest Observation Programme in Switzerland the soil solution has been monitored since 1998 in a number of forest plots growing from 9 to 47 sites in a wide range of soil conditions and air pollution impacts. The results show various site-specific developments of soil acidification. At sites with already advanced acidification (pH < 4.2), the acidification indicators remained rather stable at high levels, possibly due to the high buffering capacity of the aluminum buffer (pH 4.2 – 3.8). In contrast, in less acidified sites the acidification still progressed further which is reflected by e.g. the ongoing decrease of the base cation to aluminum ratio. Main driver of the acidification is the high N deposition which provokes cation loss and impedes sustainable nutrient balances for tree nutrition in the majority of plots examined. On an average for the years 2005-2017, N leaching rates were 9.4 kg N ha ?1 yr ?1 , ranging from 0.04 to 53 kg N ha ?1 yr ?1 . Three plots with high N input show very low N leaching, suggesting that N leaching may not always be a good eutrophication indicator. Both N deposition and N leaching have decreased since the year 2000 but the latter trend is partly also due to increased drought.
Forestry best management practices (BMPs) have proven to be very effective in protecting adjacent stream water quality at the plot scale. However, our knowledge is incomplete about the effectiveness of forestry BMPs in large watersheds where industrial forests are intensively managed. In this study, we compared long-term concentrations and loadings of total suspended solids (TSS), nitrate/nitrite nitrogen (NO3NO2–N), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) before (1978–1988) and after extensive implementation of forestry BMPs (1994–2008) at the outlet of a 5000-km² river basin that is predominately covered by intensively managed pine forests in Central Louisiana, USA. Our study shows that after extensive BMP implementation, both concentrations and loads of TSS in the basin outlet decreased significantly from 34 to 25 mg L⁻¹ and from 55,000 to 36,700 t year⁻¹, respectively. However, no significant difference was found in NO3NO2–N, TKN, and TP concentrations between the two periods. The results of nutrient loadings varied, whereby the annual nitrogen loading declined without significant differences (from 1790 to 1600 t year⁻¹ for TKN and from 176 to 158 t year⁻¹ for NO3NO2–N, respectively) but the annual TP loading increased significantly (from 152 to 192 t year⁻¹) after BMP implementation. The increase in TP loading is likely due to an increased application of phosphorus fertilizer, which offset BMPs’ effects especially during high-flow conditions. These results strongly suggest that current forestry BMPs in this region are effective in reducing sediment loading, but current BMP guidelines for fertilization and nutrient management need to be reviewed and improved. [Read full text at http://rdcu.be/F6oZ]
Atmospheric Acid Deposition: Nitrogen Saturation of Forests: Volume weighted annual average wet deposition of nitroge at 33 sites in Korea during 1999-2004 ranged 7.28 to 21.05kgN{\cdot}ha^{-1}{\cdot}yr^{-1} with average 12.78kgN{\cdot}ha^{-1}{\cdot}yr^{-1}, which values are similar level with nitrogen deposition of Europe and North America. The temperate forests that suffered long-term high atmospheric nitrogen deposition are gradually saturated with nitrogen. Such nitrogen saturated forest watersheds usually leach nitrate ion (NO_3^-) in stream water and soil solution. It may be likely that Korean forest ecosystems are saturated by much nitrogen deposition. In leaves with nitrogen saturation ratios of N/P, N/K and N/Mg are so enhanced that mineral nutrient system is disturbed, suffered easily frost damage and blight disease, reduced fine-root vitality and mycorrhizal activity. Consequently nitrogen saturated forests decrease primary productivity and finally become forest decline. Futhermore understory species are replaced the nitrophobous species by the nitrophilous one. In soil with nitrogen saturation uptake of methane (CH_4) is reduced and emission of nitrogen monoxide (NO) and nitrous oxide (N_{2}O) are increased, which gases are greenhouse gas accelerating global warming.
Many attempts at balancing ecosystem-level nutrient budgets have been made in the past few decades using a variety of approaches, and for a variety of different purposes. Relatively simple mass balance equations have been used at the level of the watershed that might comprise single forested ecosystems (e.g., Binkley et al. 1982; Stohlgren et al. 1991; Likens and Bormann 1995; Hedin et al. 1995; Stottlemyer and Troendle 1992), or at the level of a larger-scale region (e.g., Gold 1990; Frink 1991; Jaworski et al. 1992; Howarth et al. 1996; Valiela et al. 1997) that might include different land uses and nutrient inputs. These budgets have been developed with varying efforts at measuring, or modeling, internal processes of nutrient retention and release.
We examined the effects of deep percolation on dissolved inorganic nitrogen (DIN) exports from two adjacent weathered granite headwater catchments with different deep percolations of water in the Kiryu Experimental Watershed (KEW), Japan. The DIN output in streamflow was estimated from a regression equation between stream discharge and the DIN load, determined from both monthly sampling data and event-based sampling data. The range of deep percolation of DIN was estimated by multiplying observed DIN concentrations in bedrock groundwater by the deep percolation of water estimated from an annual water budget analysis. We found that the deep percolation of DIN corresponded to 34–76 % and −18 to 8 % of the total DIN output in catchments where the deep percolation of water was 37–45 % and −6 to 3 % of annual precipitation, respectively. This means that the deep percolation of DIN is not negligible when estimating the total output of DIN in the former catchment. Moreover, the fact that deep percolating water from upper catchments discharged into a lower catchment in KEW suggests that deep percolation of DIN affects downstream N budgets. Therefore, it is important to account for the deep percolation of DIN when evaluating N budgets in forested headwater catchments as well as downstream catchments.
Currently, in Europe and North America, as S emissions decrease and N deposition increases (Galloway, 1995), NH4 and NO3 will replace sulphate, as the major soil-acidifying mobile ions and supply nutrient N in excess. This applies especially to those terrestrial ecosystems which historically have been N-limited and are susceptible to vegetation change (Bråckenhielm and Qinghong, 1995). This deposition is now perceived as one of the major threats to the structure and functioning of natural and semi-natural ecosystems (Bobbink and Roelofs, 1995).
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Nearly all northeastern U.S. forests have been disturbed by wind, logging, fire, or agriculture over the past several centuries. These disturbances may have long-term impacts on forest carbon and nitrogen cycling, affecting forests' vulnerability to N saturation and their future capacity to store C. We evaluated the long-term (80-110 yr) effects of logging and fire on aboveground biomass, foliar N (%), soil C and N pools, net N mineralization and nitrification, and NO3- leaching in northern hardwood forests in the White Mountain National Forest, New Hampshire. Historical land-use maps were used to identify five areas each containing previously logged, burned, and relatively undisturbed (oldgrowth) forests. Aboveground biomass averaged 192 Mg/ha on the historically disturbed sites and 261 Mg/ha on the old-growth sites, and species dominance shifted from early-successional and mid-successional species (Betula papyrifera and Acer rubrum) to late-successional species (Fagus grandifolia and particularly A. saccharum). Forest floors in the old-growth stands had less organic matter and lower C:N ratios than those in historically burned or logged sites. Estimated net N mineralization did not vary by land-use history (113 kg·ha-1·yr-1); mean (± 1 SE) nitrification rates at old-growth sites (63 ± 4.3 kg·ha-1·yr-1) doubled those at burned (34 ± 4.4 kg·ha-1·yr-1) and logged (29±4.7 kg·ha-1-yr-1) sites. Across all plots, nitrification increased as forest floor C:N ratio decreased, and NO3- concentrations in streamwater increased with nitrification. These results indicate that forest N cycling is affected by century-old disturbances. The increased nitrification at the old-growth sites may have resulted from excess N accumulation relative to C accumulation in forest soils, due in part to low productivity of old-aged forests and chronic N deposition.
Nitrate leaching to streams is a sensitive indicator of the biogeochemical status of forest ecosystems. Two primary theories predicting long-term (decadal) changes in nitrate loss rates (N saturation theory and the nutrient retention hypothesis) both predict increasing dissolved inorganic nitrogen (DIN) losses for watershed 6 (W6), the biogeochemical reference watershed at the Hubbard Brook Experimental Forest (HBEF). Measured values, however, have declined substantially since measurements began in the mid-1960s. Are these theories wrong, or are there other important controls on DIN losses at the annual to decadal time scale that have obscured the tendency toward higher losses over time? We tested the individual and combined effects of several forms of disturbance on DIN loss rates from northern hardwood forests by comparing predictions from a relatively simple model of forest carbon, nitrogen, and water dynamics (PnET-CN) with the long-term record of annual DIN loss from W6 at HBEF. Perturbations tested include interannual climate variation, changes in atmospheric chemistry (CO2, O3, N deposition), and physical and biotic disturbances (two harvests, a hurricane salvage, and a defoliation event). No single disturbance caused changes in DIN losses to mimic measured values. Only when run with all of the disturbances combined did the model-predicted pattern of interannual change in DIN loss approach the measured record. Single-disturbance simulations allow an estimation of the role of each in the total pattern of DIN loss. We conclude that DIN losses from W6 were elevated in the 1960s by a combination of recovery from extreme drought and a significant defoliation event. N deposition alone, in the absence of other disturbances, would have increased DIN losses by 0.35 g N m-2y-1. These findings indicate that predictions of DIN losses must take into account the full spectrum of disturbance events and changes in environmental conditions impacting the systems examined.
In a study to examine impacts of successional and disturbance history on N export from 20 headwater stream systems in the west central Cascades of Oregon, a region of low anthropogenic N inputs, watersheds of differing ages showed a number of significant difference in nutrient export. In order to determine the mechanistic factors driving these differences, we measured soil solution and mineral soil C and N, forest floor and coarse woody detritus biomass, C and N in 12 plots categorized into 4 different classes of successional development. In streamwater, DON ranged from 24% to 51% of TDN in the youngest and oldest watersheds, respectively. In soil solution, %DON did not vary with succession, and was 40-75% of TDN. Although ammonium concentrations were very low in streamwater, ammonium was 25-59% of TDN in lysimeter samples and also did not vary with time since disturbance. The C content and C:N ratio of the forest floor was significantly higher in the youngest plots, most likely due to post-harvest residue and slash. Although there were 2-fold differences in the C content of the mineral soil, these differences were not related to disturbance history. Even with these sharp differences in both forest floor and mineral soil C contents as well as C:N ratios among plots, no measure of N export -- not soil solution, not stream flow -- was significantly related to forest floor, down wood, or mineral soil characteristics. This is most likely because forest floor C:N ratios (54-126:1) all greatly exceed the C:N ratios reported to allow significant leakage.
The American Geophysical Union sponsored a Chapman Conference on ``Nitrogen Cycling in Forested Catchments'' on September 16-20, 1996. This conference brought together scientists from many disciplines to share recent observations and to discuss advances in the study of nitrogen (N) cycling in forests. Conference presentations and discussions focused on mechanisms controlling the retention and losses of N in forests and on the effects of atmospheric deposition, land use, and climate on watershed N loss. The importance of dissolved organic nitrogen in the biogeochemistry of N was a subject of considerable discussion. Several critical issues were identified for future research on N cycling in forested catchments.
Hope, G. D. 2009. Clearcut harvesting effects on soil and creek inorganic nitrogen in high elevation forests of southern interior British Columbia. Can. J. Soil Sci. 89: 35-44. Responses of both soil and streaminorganic nitrogen (N) after operational clearcut harvesting were explored in two high elevation British Columbia Engelmann spruce-Subalpine fir (ESSF) forests. At one study site, net N mineralization was measured between 1 and 11 yr after harvest. At a second site, for 3 yr after harvesting, available soil ammonium and nitrate were measured using ion exchange resins, and drainage losses of N were estimated using tension lysimeters and soil water balance models. Stream water N concentrations were also measured in one unlogged, and two logged watersheds at the second study area for 12 yr, both pre- and post-clearcut harvesting. Growing season as well as over-winter increases in post-harvest soil nitrate were detected after 3 yr, and the increases were apparent for up to 11 yr. Seasonal losses of N in drainage were greater in clearcut soils than in the forest soils in year 2 for ammonium and in years 2 and 3 for nitrate. A high proportion of the N was lost in drainage during snowmelt. Stream water ammonium in all three streams and nitrate in the unlogged and one harvested creek remained at or below the detection level. In the third creek, the frequency of detection and concentrations of nitrate peaked 2 to 3 yr after 30 to 57% of the watershed was harvested. The annual peak in NO3-N concentrations occurred immediately before the snowmeltdriven streamflow peak. Drainage losses and stream N fluxes were both small, relative to the total soil N content.
In Matsu-zawa catchment, central Japan, nitrate concentrations in stream water increased following a small-scale, natural disturbance involving an outbreak of pine wilt disease that affected similar to 25% of the forested catchment. To clarify nutrient dynamics in soils and their relationship with stream water nitrate, we investigated soil nitrogen dynamics and soil water chemistry in disturbed and undisturbed, water-unsaturated and -saturated plots. The highest values for nitrification rate, nitrate concentration in soil solution, and nitrate exported from the root zone were observed for the disturbed plot. The ratio of nitrification to mineralization in surface soil of the disturbed plot dramatically increased from 1989 (pre-disturbance) to 1997. Root zone leachate from the disturbed area showed gradually increasing groundwater nitrate concentrations in the temporarily saturated zone during lateral, matrix flow. The catchment's deep soils and associated hydrologic processes limited the degree of plant uptake of the nitrate generated in the disturbed area. It was inferred that the persistent high levels of nitrate observed in the stream water resulted largely from the stable high nitrate concentrations observed in the saturated groundwater of this catchment. Stream water nitrate loads discharged following the disturbance were about 16 times greater than prior to it.
We reviewed the research articles to understand the current findings and to suggest the future directions on relationship between biogeochemical cycling and forest practices in Japan. The studies on the effect of forest harvest on the biogeochemical cycling in forest has been mainly conducted using the manipulation experiments in forested basin, indicating that the tree cutting caused the significant nitrate leaching to stream due to the absence of nutrient uptake by trees. However, the unique processes in Japanese forest ecosystems has been also reported such as the role of nutrient uptake by understory vegetation after the tree cutting in northern Hokkaido, nitrate absorption in volcanic ash soil in northern Kanto region, and fluctuation of stream chemistry associated with basin hydrological processes during the last decades. In steeper slopes in southern Kinki region, it was suggested that the land slide after the forest practices has strong impact on the following hydrological processes and stream chemistry. The biogeochemical hot spots in the boundary of each ecosystem such as riparian buffer, nutrient spirals in stream channel, nutrient cycling in "SATOYAMA" region would be great concern for further understandings. It would be necessary to promote the studies on the parameterization in the ecosystem process model under the effect of forest practices with attention to their regional differences.
Ecosystem retention of N is mediated by interactions among plant, soil, and microbial processes. These are likely to change with forest ecosystem development as living plant biomass accumulation slows and detrital biomass increases. We investigated linkages among N storage, N cycling processes, and N leaching losses in a study of replicate mid-successional (80-yr-old) and late-successional (uneven-aged old-growth) northern hardwood forests in the western upper peninsula of Michigan, USA. Our study tested hypotheses that detrital biomass and microbial immobilization of N function as larger N sinks and correspond to greater N retention in old-growth compared to maturing second-growth forests. Aboveground living and detrital biomass pools were greater in old-growth compared to second-growth forest, a difference due largely to coarse woody debris (CWD). The total amount of N in detrital pools was significantly greater in old-growth than second-growth forests. We also found more rapid rates of microbial N immobilization in old-growth forests than in second-growth forests. In situ net N mineralization ranged widely among individual stands and did not differ between old- and second-growth forests. Nitrogen (organic + inorganic) leaching did not differ significantly between old-growth and second-growth forests, and was substantially lower than wet deposition inputs. Nitrate leaching losses were significantly related to soil NO3- pools, litterfall N flux, and fine root biomass across both old- and second-growth forest stands. We conclude that CWD and microbial N uptake and turnover are greater N sinks in old-growth than in second-growth forests. This apparent N sink was not the primary factor influencing N leaching loss, however. Patterns of N dynamics among individual forest ecosystems indicate that N losses correspond to net rates of N mineralization and to litterfall N flux (indicators of plant N cycling), which are independent of forest age, biomass pools, and gross N transformations at the successional stages that we compared.
Effluent organic nitrogen concentrations from seven constructed stormwater wetlands in North Carolina were examined to compare background organic nitrogen (ON) concentrations and the fraction of organic nitrogen relative to total nitrogen discharged. Seasonal influences on organic nitrogen concentrations were also examined. The median ON concentration from the stormwater wetlands was 0.78mgl−1, and despite differences in wetland design and influent ON characteristics, outlet ON concentrations from all but one wetland were not significantly different. ON export from all stormwater wetlands was significantly less than untreated runoff entering the wetlands (p=0.002). In addition, median organic:total nitrogen (ON:TN) ratios from stormwater wetlands (0.75) were significantly greater than from untreated urban runoff (0.66), comparing more closely to ON:TN ratios collected from a naturally occurring wetland and reported in the literature for natural landscapes. Seasonal differences in organic nitrogen concentrations were identified with significantly lower concentrations during the winter. Though stormwater wetlands will not (and perhaps should not be expected to) completely remove total nitrogen loads from runoff, these results suggest constructed wetlands can play a role in restoring the balance between organic and inorganic nitrogen forms closer to that of an undisturbed landscape. The presence of background organic nitrogen concentrations from stormwater wetlands similar to those from a naturally occurring wetland highlights the importance of choosing appropriate metrics (e.g., effluent concentrations) when assessing treatment performance.
In Matsu-zawa catchment, central Japan, nitrate concentrations in stream water increased following a small-scale, natural disturbance involving an outbreak of pine wilt disease that affected ~25% of the forested catchment. To clarify nutrient dynamics in soils and their relationship with stream water nitrate, we investigated soil nitrogen dynamics and soil water chemistry in disturbed and undisturbed, water-unsaturated and -saturated plots. The highest values for nitrification rate, nitrate concentration in soil solution, and nitrate exported from the root zone were observed for the disturbed plot. The ratio of nitrification to mineralization in surface soil of the disturbed plot dramatically increased from 1989 (pre-disturbance) to 1997. Root zone leachate from the disturbed area showed gradually increasing groundwater nitrate concentrations in the temporarily saturated zone during lateral, matrix flow. The catchment's deep soils and associated hydrologic processes limited the degree of plant uptake of the nitrate generated in the disturbed area. It was inferred that the persistent high levels of nitrate observed in the stream water resulted largely from the stable high nitrate concentrations observed in the saturated groundwater of this catchment. Stream water nitrate loads discharged following the disturbance were about 16 times greater than prior to it.
Whole-tree clear-cutting and progressive strip-cutting of northern hardwood forests at the Hubbard Brook Experimental Forest in central New Hampshire resulted in measurable changes in physical and chemical conditions of forest streams. As a result of reduced transpiration and interception, water yield for the first year after whole-tree harvesting increased by >150 mm, the majority of which occurred during the growing season. Peak flows increased only moderately. Water yield and peak flow increases disappeared within 4-6 years as a result of rapidly regrowing vegetation. Sediment yields increased during and after harvesting but can be maintained within normal ranges of reference streams by careful use of best management practices. Stream chemistry changes occurred immediately following harvesting, most notably in the form of increases in concentrations of Ca2+, K+, NO3-, and H+. The concentrations return close to preharvest levels within 3-5 years. The above changes are discussed in terms of their causes and implications for aquatic habitat and fisheries.
Increased losses of nitrate from watersheds may accelerate the depletion of nutrient cations and affect the acidification and trophic status of surface waters. Patterns of nitrate concentrations and losses were evaluated in four forested watersheds (East Bear Brook Watershed, Lead Mountain, ME; Watershed 6, Hubbard Brook Experimental Forest, White Mountains, NH; Arbutus Watershed, Huntington Forest, Adirondack Mountains, NY; Biscuit Brook, Catskill Mountains, NY) located across the northeastern United States. A synchronous pattern was observed in nitrate concentrations of drainage waters from these four sites from 1983 through 1993. Most notably, high concentrations and high drainage water losses followed an anomalous cold period (mean daily temperature −11.4 to −16 °C in December 1989) for all four sites. After high nitrate losses during the snowmelt of 1990, nitrate concentrations and fluxes decreased at all sites. These results suggest that climatic variation can have a major effect on nitrogen flux and cycling and may influence temporal patterns of nitrate loss in a region.
Increased nitrogen leaching from forest soils is a potential environmental problem in areas with high nitrogen deposition. In Sweden nitrogen is strongly retained in the forests, and high nitrogen leaching is not common from growing forests. However, soil water measurements on clearcuts along a deposition gradient in Sweden showed a positive correlation between increased concentration of inorganic nitrogen and the deposition. In this paper nitrogen leaching from clearcuts in southern Sweden was modelled on a municipality level, based on this correlation. Modelled deposition was used as input data together with runoff and forest statistics, e.g. clearcut areas from the municipalities. The calculations showed a clear leaching gradient on clearcuts from west (up to 35 kg ha−1 year−1) to east (less than 5 kg ha−1 year−1). This was in accordance with the deposition gradient. The leaching gradient was reinforced by the higher runoff in the west. The results indicated that, in southwestern Sweden with the highest nitrogen deposition, up to 30–40% of the total leaching of nitrogen from forest soils originates from clearcuts. These high amounts of nitrogen leaching from clearcuts in southwestern Sweden have not been included in previous national calculations of nitrogen leaching to surface waters. The contribution of nitrogen from clearcuts to the total nitrogen leaching from all land use classes varies between 1% in the southernmost part where agricultural land is highly dominating, to 11% in the forested central part of southern Sweden.
This study examined impacts of succession on N export from 20 headwater stream systems in the west central Cascades of Oregon,
a region of low anthropogenic N inputs. The seasonal and successional patterns of nitrate (NO3−N) concentrations drove differences in total dissolved N concentrations because ammonium (NH4−N) concentrations were very low (usually < 0.005 mg L−1) and mean dissolved organic nitrogen (DON) concentrations were less variable than nitrate concentrations. In contrast to
studies suggesting that DON levels strongly dominate in pristine watersheds, DON accounted for 24, 52, and 51% of the overall
mean TDN concentration of our young (defined as predominantly in stand initiation and stem exclusion phases), middle-aged
(defined as mixes of mostly understory reinitiation and older phases) and old-growth watersheds, respectively. Although other
studies of cutting in unpolluted forests have suggested a harvest effect lasting 5 years or less, our young successional watersheds
that were all older than 10 years still lost significantly more N, primarily as NO3−N, than did watersheds containing more mature forests, even though all forest floor and mineral soil C:N ratios were well
above levels reported in the literature for leaching of dissolved inorganic nitrogen. The influence of alder may contribute
to these patterns, although hardwood cover was quite low in all watersheds; it is possible that in forested ecosystems with
very low anthropogenic N inputs, even very low alder cover in riparian zones can cause elevated N exports. Only the youngest
watersheds, with the highest nitrate losses, exhibited seasonal patterns of increased summer uptake by vegetation as well
as flushing at the onset of fall freshets. Older watersheds with lower N losses did not exhibit seasonal patterns for any
N species. The results, taken together, suggest a role for both vegetation and hydrology in N retention and loss, and add
to our understanding of N cycling by successional forest ecosystems influenced by disturbance at various spatial and temporal
scales in a region of relatively low anthropogenic N input.
Nitrogen saturation occurs when the supply of nitrogenous compounds from the atmosphere exceeds the demand for these compounds on the part of watershed plants and soil microbes. Several factors predispose forested watersheds to N saturation, including chronically high rates of N deposition, advanced stand age, and large pools of soil N. Many watersheds in the eastern United States exhibit symptoms of N saturation. A sequence of recognizable stages produces characteristic long-term and seasonal patterns of lake-water and stream-water NO3- concentrations that reflect the changes in rates and relative importance of N transformations as these watersheds become more N sufficient. The early stages of N saturation are marked by increases in the severity and frequency of NO3- episodes. The later stages of N saturation are marked by elevated baseflow concentrations of NO3- from groundwater. The most advanced symptoms of N saturation usually occur in regions with the most elevated rates of N deposition. Long-term increases in surface-water NO3- have important implications for surface-water acidification, but probably will not lead to freshwater eutrophication.
The Hubbard Brook Ecosystem Study was designed to evaluate element flux and cycling in a northern hardwood forest and the effects of disturbance on these processes. In the original experiment, an entire watershed was deforested and regrowth was inhibited for three years using herbicides. Initial effects of the treatment included: elevated stream discharge, large increases in streamwater solute concentrations and elevated losses of those ions from the watershed. In contrast, streamwater concentrations and net ecosystem output of sulfate decreased in response to the treatment. During the post treatment period, the concentrations of most dissolved ions declined relative to a reference watershed while, again in contrast, sulfate concentrations increased relative to the reference. In this paper we develop a hypothesis which links acidification and sulfate adsorption processes in the soil to explain the observed trends in sulfate losses from the Hubbard Brook Experimental Forest.
A synthesis of the biogeochemistry of K was conducted during 1963–1992 in the reference and human-manipulated watershed-ecosystems of the Hubbard Brook Experimental Forest (HBEF), NH. Results showed that during the first two years of the study (1963–65), which coincided with a drought period, the reference watershed was a net sink for atmospheric inputs of K. During the remaining years, this watershed has been a net source of K for downstream ecosystems. There have been long-term declines in volume-weighted concentration and flux of K at the HBEF; however, this pattern appears to be controlled by the relatively large inputs during the initial drought years. Net ecosystem loss (atmospheric deposition minus stream outflow) showed an increasing trend of net loss, peaking during the mid-1970s and declining thereafter. This pattern of net K loss coincides with trends in the drainage efflux of SO4
2– and NO3
–, indicating that concentrations of strong acid anions may be important controls of dissolved K loss from the site. There were no long-term trends in streamwater concentration or flux of K. A distinct pattern in pools and fluxes of K was evident based on biotic controls in the upper ecosystem strata (canopy, boles, forest floor) and abiotic controls in lower strata of the ecosystem (mineral soil, glacial till). This biological control was manifested through higher concentrations and fluxes of K in vegetation, aboveground litter, throughfall and forest floor pools and soil water in the northern hardwood vegetation within the lower reaches of the watershedecosystem, when compared with patterns in the high-elevation spruce-fir zone. Abiotic control mechanisms were evident through longitudinal variations in soil cation exchange capacity (related to soil organic matter) and soil/till depth, and temporal and disturbance-related variations in inputs of strong-acid anions. Marked differences in the K cycle were evident at the HBEF for the periods 1964–69 and 1987–92. These changes included decreases in biomass storage, net mineralization and throughfall fluxes and increased resorption in the latter period. These patterns seem to reflect an ecosystem response to decreasing rates of biomass accretion during the study. Clearcutting disturbance resulted in large losses of K in stream water and from the removal of harvest products. Stream losses occur from release from slash, decomposition of soil organic matter and displacement from cation exchange sites. Elevated concentrations of K persist in stream water for many years after clearcutting. Of the major elements, K shows the slowest recovery from clearcutting disturbance.
Replacing biomass and nutrients lost in harvesting northern hardwoods may take 60 to 80 years.
All vegetation on Watershed 2 of the Hubbard Brook Experimental Forest was cut during November and December of 1965, and vegetation regrowth was inhibited for two years by periodic application of herbicides. Annual stream-flow was increased 39% the first year and 28% the second year. Large increases in streamwater concentration were observed for all major ions, except NHâ/sup +/SOâ/sup 2 -/ and HCOââ», approximately five months after the deforestation. Nitrate concentrations were 41-fold higher than the undisturbed condition the first year and 56-fold higher the second. Sulfate was the only major ion in stream water that decreased in concentration after deforestation. An inverse relationship between sulfate and nitrate concentrations in stream water was observed in both undisturbed and deforested situations. Average streamwater concentrations increased for Ca++, Mg++, K+ and Na+ during the two years subsequent to deforestation. 58 references, 8 tables, 15 figures.
From 1975 to 1987 a 19% change in SO2 emissions a 16% change in NOx emissions have occurred over the eastern and mid-western U.S. Six continental precipitation chemistry sites from the MAP3S network, plus the Hubbard Brook Experimental Forest, NH, show a direct relationship between emission levels and precipitation H+ and SO42- concentrations, except for Penn State, PA. MAP3S sites at Illinois and Ohio, located closest to the major SO2 source regions, demonstrates statiscally significant (P <0.05) linear regressions of SO42- concentrations on SO2 emissions. Whiteface Mt., NY, shows a weaker relationship (P <0.01), and Hubbard Brook shows the strongest relationship (P <0.01) between SO2 emissions and SO42- concentration in precipitation. No site shows a significant relationship (P <0.10) for NOx emissions and NO3− concentrations in precipitation. Illinois, Ohio, Ithaca and Hubbard Brook show significant linear regressions of H+ concentrations on emissions of SO2 + NOx (P <0.10, 0.05, 0.01, and 0.01, respectively). Overall, for the entire region examined, decreasing SO2 emissions levels appear to have decreased SO42- concentrations with an efficiency of 74% ± 15% (s.e.). Decreasing SO2 plus NOx emissions (18%) have been accompanied by a decreasing H+ concentrations (18%) suggesting an efficiency of conversion of 100% ± 15% (s.e.) for the study region as a whole. While significant reductions in acid species have occured at Hubbard Brook, further reductions in excess of 50% of present deposition are necessary to protect acid-sensitive ecosystems.
Aluminum chemistry was evaluated in two headwater streams in the White Mountains of New Hampshire. Observed elevational trends in stream aluminum chemistry may be related to spatial variations of vegetation type and mineral soil depth within the watersheds. At the highest elevations maximum densities of spruce and fir vegetation occur and aluminum appears to be mobilized predominantly by transformations involving dissolved organic matter. At the mid-elevations hardwood vegetation predominates and the mechanism of aluminum mobilization shifts to dissolution by strong acids within the mineral soil. At the lowest elevations, relatively thick mineral soil seems to limit aluminum mobility, resulting in low concentrations in streamwater. Comparison of these results with an earlier study of an adjacent watershed, indicates that subtle differences in watershed characteristics such as tree species distribution and topography may cause significant variations in stream aluminum chemistry. Control of aluminum mobility by imogolite minerals was not indicated by the stream chemistry of these watersheds. To determine the relationship between acidic deposition and aluminum mobility, natural variations which occur in the aluminum cycle must be addressed.
The goal of this Third Edition is to update long-term data presented in earlier editions and to generate new syntheses and conclusions about the biogeochemistry of the Hubbard Brook Valley based on these longer-term data. There have been many changes, revelations, and exciting new insights generated from the longer data records. For example, the impact of acid rain peaked during the period of the HBES and is now declining. The longer-term data also posed challenges in that very marked changes in fluxes occurred in some components, such as hydrogen ion and sulfate deposition, calcium and nitrate export in stream water and biomass accumulation, during the almost 50 years of record. Thus, presenting "mean" or "average" conditions for many components for such a long period, when change was so prominent, do not make sense. In some cases, pentads or decades of time are compared to show these changes in a more smoothed and rational way for this long period. In some cases, a single period, often during periods of rapid change, such as acidification, is used to illustrate the main point(s). And, for some elements a unique mass balance approach, allowing the calculation of the Net Ecosystem Flux (NEF), is shown on an annual basis throughout the study. © Springer Science+Business Media New York 2013. All rights are reserved.
Nitrogen saturation, in the sense that nitrogen additions to an ecosystem lead to losses of the same order of magnitude, is analyzed as an interplay between a plant subsystem and a soil subsystem. The plant system is defined by its nitrogen productivity, which allows calculations of the maximum amount of nitrogen that can be held in, and the maximum nitrogen flux density that can be utilized by, the plant subsystem. The most important response of the soil subsystem is a change in the microbial nitrogen concentration, from which the nitrogen absorption capacity can be derived. It is shown that of the two subsystems the soil must always saturate first. The time to reach saturation depends strongly on site history in terms of the sources of litter forming the soil organic matter and on the ratio between the external nitrogen inflows and the litter nitrogen flow.
The Ecosystem Approach: Its Use and Abuse, Excellence in Ecology, Book 3. The Ecology Institute, Oldendorf-Luhe
- G.E. Likens
The Ecosystem Approach: Its Use and Abuse, Excellence in Ecology, Book 3. The Ecology Institute
- G E Likens
- G.E. Likens
- G.E. Likens