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Environmental controls on carbon sequestration, sediment accretion, and elevation change in the Ebro River Delta: Implications for wetland restoration
Abstract
Delta wetlands are increasingly recognized as important sinks for ‘blue carbon,’ although this and other ecosystem services that deltas provide are threatened by human activities. We investigated factors that affect sediment accretion using short term (3 years using marker horizons) and longer-term measures (∼50 year using ¹³⁷ Cs soil core distribution and ∼100 year using ²¹⁰ Pb distribution), the associated carbon accumulation rates, and resulting changes in surface elevation in the Ebro River Delta, Catalonia, Spain. Fifteen sites were selected, representing the geomorphological settings and range of salinities typical of the delta's wetlands. Sediment accretion rates as measured by ¹³⁷ Cs distribution in soil cores ranged from 0.13 to 0.93 cm yr ⁻¹ . Surface elevations increased at all sites, from 0.10 to 2.13 cm yr ⁻¹ with the greatest increases in natural impoundments with little connection to other surface waters. Carbon accumulation rates were highly spatially variable, ranging from 32 to 435 g C m ⁻¹ yr ⁻¹ with significantly higher rates at bay sites (p = 0.02) where hydrologic connectivity is high and sediment resuspension more intense. Sites with high connectivity had significantly higher rates of carbon accumulation (averaging 376 ± 50 g C m ⁻¹ yr ⁻¹ ) compared to sites with moderate or low connectivity. We also found high rates of carbon accumulation in brackish sites where connectivity was low and biomass production was characteristically higher than in saline sites. A stepwise regression model explained 81% of variability in carbon accumulation rates across all sites. Our data indicate deltaic wetlands can be important sinks for blue carbon, contributing to climate change mitigation.
... Fluvial sediment input in deltas plays an important role in soil accretion and SOC sequestration through burial of organic matter, and both processes are key for maintaining the elevation of soil in relation to sea level (Day et al., 1995;Fennessy et al., 2019). One main cause of coastal erosion of deltas is construction of dams along rivers, which traps sediment and prevents its deposition in deltas, which decreases the resilience of deltas in the face of sea level rise (SLR) (Brown et al., 2018;Syvitski et al., 2005). ...
... Since rice fields were created in different wetland habitats, the initial amount of SOM was set using field data to consider heterogeneity in SOM content. Based on data from Fennessy et al. (2019) for wetland soils in the Ebro Delta, within the range of the initial SOM content of the parent soil (1 -30 %), the lowest SOM contents (1 -7 %), which correspond to mineral soils, were related to converted marshes and riparian ecosystems, while higher SOM contents (15 -30 %) were related to converted lagoon or peatland ecosystems. The organic fraction was estimated as loss on ignition (Table 2, Eq. ...
... In this sense, the initial SOM content is important since it influences the vertical accretion rate and SOC stock. Thus, initial SOM content is related to the productivity and soil properties of the habitats that were converted into rice fields; thus, SOM content is higher in rice fields converted from peatlands, salt meadows and coastal lagoons, and lower in those converted from riparian vegetation and salt marshes (Fennessy et al., 2019;Morant et al., 2020). During model calibration, the initial SOM contents selected for the parent soils were consistent with the pre-existing reclaimed ecosystems, with lower contents selected for rice fields close to the river and in marshes (R1, R2 and S1) than for those in grasslands, coastal lagoons or peatlands (M2, L1 and P1). ...
Rice cultivation is popular in low-lying areas such as deltas, but climate change threatens the viability of the crop. In recent decades, the resilience of deltas to sea level rise (SLR) has been influenced by the reduction of sediment load from rivers due to the construction of dams, disrupting natural deposition in deltaic plains. Sediment and organic matter accumulation in wetlands are key to vertical accretion in the face of SLR and soil organic carbon (SOC) sequestration. In this sense, deltaic rice fields can retain sediments as well as wetlands and promote SOC sequestration, which is effective in adapting to SLR. In the Ebro Delta, the sediments that reached the fields through irrigation channels were used to build up and form rice fields in the wetlands of the area. We hypothesize that this sedimentation has been key to vertical accretion and SOC sequestration in rice fields. These processes were simulated by developing a process-based cohort model inspired by accretion in marsh equilibrium models (MEM). The model was able to simulate the soil carbon profile of rice fields in the Ebro Delta, based on the soil-accretion concept and considering the spatial heterogeneity of the area. Its predictions of vertical accretion and carbon content were more accurate for mineral and clay-like soils than for organic and sandy soils. Topsoil decomposition rate and organic matter content were the parameters that most influenced predictions of total vertical accretion and final soil organic carbon stock. Simulations were carried out according to future climate change scenarios, considering restoration of river sediment flux, to evaluate effects on SOC sequestration and vertical accretion in rice fields. Results showed that only with
significant river sediment restoration did rice fields show positive vertical accretion, which facilitates SOC sequestration.
... The capacity of wetlands to sequester carbon is ultimately a function of environmental and human factors operating at different scales including landscape level (e.g., location, watershed, land use), ecosystem level (water and sediment inputs and retention, hydroperiod) and ecosystem features such as soil redox potential (Trepel & Palmeri, 2002). In a study of 15 natural wetlands (9 brackish and 6 salt marshes) carried out in the Ebro Delta to quantify C sequestration rates, differences in C sequestration were found to be a result of landscape (geomorphological) position and their degree of hydrological connectivity (Fennessy et al. 2019). Reflecting the diversity of ecosystems in the Ebro Delta, C sequestration was highly spatially variable, ranging from 32 to 435 g C/m 2 /yr (Table 15.1). ...
... In a comprehensive review of coastal wetlands, Chmura et al. (2003) found that C sequestration rates ranged from 18 to 1,713 g C/ m 2 /yr with a global average of 210 g C/m 2 /yr, whereas Ouyang and Lee (2014) found a slightly higher mean of 245 g C/m 2 /yr. Both values are close to the mean carbon sequestration rate of 205 g C/m 2 /yr found by Fennessy et al. (2019) for the Ebro Delta sites. No significant difference was found between rates in brackish and salt marshes (due to the high variability within types), contrary to many studies of coastal wetlands that report significantly higher rates of C sequestration under brackish conditions (e.g., Loomis & Craft, 2010). ...
... mm/yr, which is lower than those estimated by Ibañez et al. (1997) (4.7-7.4 mm/ yr) and those estimated for natural wetlands (1.0-21.3 mm/yr) by Fennessy et al. (2019). In a related study, Calvo-Cubero et al. (2013; assessed vertical accretion in abandoned rice fields receiving different water sources (irrigation versus runoff water from rice fields) and found vertical accretion rates of 11.5 ± 0.8 and 15.5 ± 0.6 mm/yr, respectively. ...
Coastal and deltaic wetlands are among the most effective ecosystems for climate regulation through carbon sequestration and storage. The Ebro Delta is an example of a landscape that attempts to integrate nature protection with economic development that is threatened by global change. The functionality of Ebro Delta wetlands is deteriorating due to sea‐level rise, subsidence, sediment starvation, limited hydrological connectivity and direct impacts caused by human activities (i.e., agriculture). Here we review studies on natural and agricultural wetlands (i.e., rice fields) with a focus on drivers of carbon (C) dynamics. The evidence supports that natural wetlands keep functioning as C sinks despite the impact of anthropogenic activities in the Delta, while rice fields act as net carbon sources to the atmosphere. Rates of C sequestration are mainly related to hydrological connectivity and salinity that modulate metabolic rates. In coastal lagoons (lower connectivity, lower salinity), autochthonous primary productivity is the main C sequestering process, whereas in salt marshes (higher connectivity, higher salinity) with lower metabolic rates, deposition of allochthonous material dominates. We discuss management options that promote C sequestration and greenhouse gas (GHG) emission reduction under a changing climate. Integrated management both at the local level – mainly of rice fields and adjacent wetlands – and at the regional level – the whole river basin and the delta – is essential to enhance fundamental ecosystem services such as carbon sequestration provided by the Ebro Delta, in order to increase its capacity to mitigate climate change.
... These deltaic areas support high levels of biodiversity and generate a wide variety of ecosystem services [7]. They are also among the most productive ecosystem types [8] and usually function as natural carbon (C) sinks [9][10][11]. However, due to their location in highly productive areas, they experience a sort of direct and indirect impacts that makes them among the most endangered systems due to human threats [12]. ...
... Primary production and decomposition rates were in the same magnitude order than other studies done in similar deltaic wetlands in the Mediterranean region [27,49]. Annual rates of C-retention were also in the rage of C-accretion rates in delta marshes found by Fennessy et al. [11] based on 137 Cs (32-435 g C m -2 yr -1 ). However, these authors found higher C-accumulation in salt marshes, meanwhile our results suggested that coastal lagoons were slightly more productive. ...
... As important as the ecological features for the metabolic C-balance, is the conservation status of the wetlands [18]. Carbon sequestration has been found to be negatively related with human disturbances [11]. The influence of some factors such as changes in salinity, and increases of trophic level, were already noted as huge threats for the deltaic wetland conservation in previous studies [49]. ...
Deltaic wetlands are highly productive ecosystems, which characteristically can act as C-sinks. However, they are among the most threatened ecosystems, being very vulnerable to global change, and require special attention towards its conservation. Knowing their climate change mitigating potential, conservation measures should also be oriented with a climatic approach, to strengthen their regulatory services. In this work we studied the carbon biogeochemistry and the specific relevance of certain microbial guilds on carbon metabolisms of the three main types of deltaic wetlands located in the Ebro Delta, north-eastern Spain, as well as how they deal with human pressures and climate change effects. We estimated the metabolic rates of the main carbon-related metabolisms (primary production and respiration) and the resulting carbon and global warming potential balances in sites with a different salinity range and trophic status. With the results obtained, we tried to define the influence of possible changes in salinity and trophic level linked to the main impacts currently threatening deltaic wetlands, on the C-metabolisms and GHG emissions, for a better understanding of the mitigating capacity and their possible enhancement when applying specific management actions. Metabolic rates showed a pattern highly influenced by the salinity range and nutrients inputs. Freshwater and brackish wetlands, with higher nutrient inputs from agricultural runoff, showed higher C-capture capacity (around 220–250 g C m⁻² y⁻¹), but also higher rates of degradative metabolisms (aerobic respiration and CH4 emissions). Contrastingly, the rates of C-related metabolisms and C-retention of Salicornia-type coastal salt marshes were lower (42 g C m⁻² y⁻¹). The study of the microbial metacommunity composition by the16S RNA gene sequencing revealed a significant higher presence of methanogens in the salt marsh, and also higher metabolic potential, where there was significantly more organic matter content in sediment. Salinity inhibition, however, explained the lower respiration rates, both aerobic and anaerobic, and prevented higher rates of methanogenesis despite the major presence of methanogens. Conservation measures for these wetlands would require, overall, maintaining the sediment contributions of the river basin intending to overcome the regression of the Delta and its salt marshes in a climate change scenario. Particularly, for reducing degradative metabolisms, and favour C-retention, nutrient inputs should be controlled in freshwater and brackish wetlands in order to reduce eutrophication. In salt marshes, the reduction of salinity should be avoided to control increases in methanogenesis and CH4 emissions.
... below mean sea level (MSL)), particularly on major deltas like the Po, Rhone, Ebro and Nile deltas 60,61 , and densely populated coastal zones (also driven by the seasonal influx of tourists). However, focussed studies on the response of Mediterranean coastal wetlands to SLR are limited to selected areas in the North-West 23,27,29,62,63 , while very few studies are available for other parts (i.e. Eastern 64 , and Southern Mediterranean 65 ), all highlighting the threat of reduced sediment availability to Mediterranean coastal wetlands. ...
... Due to their high sensitivity to human impacts and climate change, and their high ecological importance, this study focuses on coastal marshes. It complements previous local 23,29,33,62,63 and global-scale studies 17,18 to provide a more detailed vulnerability assessment for one of the key global hotspots of coastal wetland loss. ...
Mediterranean coastal wetlands account for important biodiversity and ecosystem services. But climate-change induced sea-level rise poses a critical risk to their survival. Here, we assess these risks for Mediterranean coastal marshes, one key type of Mediterranean coastal wetlands, and identify main drivers for future coastal marsh change for the Mediterranean and comparable coastlines. We apply an integrated modelling approach that accounts for future sea-level rise, sediment accretion, coastal management and marsh inland migration processes. Depending on climate mitigation scenarios, widespread coastal marsh loss is projected, ranging from 8% to 92% of current extents. For Egypt, France, and Algeria, we predict (near) total loss of coastal marshes by 2100 for current coastal management and sediment supply scenarios. Overall, losses could at least be halved if additional inland migration space were created, e.g. through passive or active habitat restoration. Bold climate mitigation and local adaptation are needed to preserve existing coastal marshes.
... Consequently, the ability of coastal wetlands to mitigate climate change through carbon sequestration may be, at least partially, offset by GHG emissions (Holm et al., 2016). Despite the paramount role of wetlands in climate regulation, numerous studies have only separately evaluated GHG emissions (Holm et al., 2016;Keshta et al., 2023) and carbon sequestration (Choi and Wang, 2004;Fennessy et al., 2019), with fewer (e.g., Arias-Ortiz et al., 2021) investigating both aspects within the same study. ...
... The organic carbon stocks in the upper meter in the Camargue are low (17 to 90 Mg OC ha − 1 ) and comparable to those found in other coastal wetlands (Serrano et al., 2019;Vaughn et al., 2021;Bai and Cotrufo, 2022). Similarly, the range of carbon accumulation rates over the last 40 years (21 to 64 g OC m − 2 yr − 1) were slightly lower than the 55 ± 2 Mg OC ha − 1 yr − 1 in tidal marshes in Australia (Macreadie et al., 2017;Serrano et al., 2019), and fall within the lower range (14-435 g OC m − 2 yr − 1 ) of those reported in the US-North Carolina (Miller et al., 2022) and in Spain, in the Ebro Delta (Fennessy et al., 2019). There are several plausible reasons for these relative low carbon sequestration rates and SOC stocks. ...
... Previous studies have reported that mangroves sequester approximately 13.5 Gt C year −1 [14], most of which is captured in their soils (49-98% of the ecosystem C content is stored in the soil) [14,15]. The large C storage and sequester capacity of mangrove forests and other coastal ecosystems (e.g., mangroves) have led to the creation of the term "Blue Carbon sinks" [16][17][18][19]. ...
... The stored carbon in mangrove soils exists in living (roots) and non-living biomass (litter and deadwood), as well as in the organic matter incorporated into the soil [15,[20][21][22][23]. Soil organic matter (SOM) can remain stored for a millennial scale or be mineralized in the short term (within years or decades) [21,[24][25][26]. The high C content in coastal wetland soils occurs because of the specific biogeochemical conditions resulting from the combination of the high primary productivity of the plants and the soil characteristics, such as high salinity, circumneutral pH, mineral interactions, and low availability of oxygen, which compromises organic matter decomposition [18,19]. ...
Mangroves are among the most relevant ecosystems in providing ecosystem services because of their capacity to act as sinks for atmospheric carbon. Thus, restoring mangroves is a strategic pathway for mitigating global climate change. Therefore, this study aimed to examine the organic matter dynamics in mangrove soils during restoration processes. Four mangrove soils under different developmental stages along the northeastern Brazilian coast were studied, including a degraded mangrove (DM); recovering mangroves after 3 years (3Y) and 7 years (7Y) of planting; and a mature mangrove (MM). The soil total organic carbon (CT) and soil carbon stocks (SCSs) were determined for each area. Additionally, a demineralization procedure was conducted to assess the most complex humidified and recalcitrant fractions of soil organic matter and the fraction participating in organomineral interactions. The particle size distribution was also analyzed. Our results revealed significant differences in the SCS and CT values between the DM, 3Y and 7Y, and the MM, for which there was a tendency to increase in carbon content with increasing vegetative development. However, based on the metrics used to evaluate organic matter interactions with inorganic fractions, such as low rates of carbon enrichment, C recovery, and low C content after hydrofluoric acid (HF) treatment being similar for the DM and the 3Y and 7Y—this indicated that high carbon losses were coinciding with mineral dissolution. These results indicate that the organic carbon dynamics in degraded and newly planted sites depend more on organomineral interactions, both to maintain their previous SCS and increase it, than mature mangroves. Conversely, the MM appeared to have most of the soil organic carbon, as the stabilized organic matter had a complex structure with a high molecular weight and contributed less in the organomineral interactions to the SCS. These results demonstrate the role of initial mangrove vegetation development in trapping fine mineral particles and favoring organomineral interactions. These findings will help elucidate organic accumulation in different replanted mangrove restoration scenarios.
... Additionally, relevant literature pertaining to these ESS and their association with the targeted habitats in the Ebro delta, published within the last five years, was referenced. Examples include works by Fennessy et al. (2019), Matamoros et al. (2020), Morant et al. (2020), andBerenguer-Manzanedo et al. (2021), among others, to ensure a comprehensive understanding of the ecosystem's potential in delivering these services. ...
This deliverable presents the generation of EUNIS habitat maps for Europe as a whole and for each of the pilot areas in REST-COAST. Subsequently, it presents the assignment of semi-quantitative scores for the contribution of each EUNIS (sub)habitat to the five key ecosystem services applying the rank scale 0 (none), 1 (very low contribution), 2 (low contribution), 3 (medium contribution), 4 (high contribution) to 5 (very high contribution). It also describes the assignment of the IUCN Red List of Habitats to each of the depicted EUNIS (sub)habitats in the pilot areas. And finally, to assess coastal system behaviour and restoration effects on ecosystem services and biodiversity gains under climate change, a homogenised score card methodology is presented to overcome the problem of comparing minor changes (some percents) with major changes (tens of percents) in the total scores for ESS or BDV in each pilot area.
... The fastest rate of increase of surface elevation (13 ± 5.6 mm y −1 ) was about twice that of natural wetlands, and the average OC accumulation rate increased from 96 ± 33 to 197 ± 64 g C m −2 y −1 (Eagle et al., 2022). Previous investigations have revealed that good hydrological conditions can strengthen the rate of burial of blue carbon in restored wetlands and significantly reduce greenhouse gas emissions (Fennessy et al., 2019;Kroeger et al., 2019). After the restoration of tidal currents in the reclaimed wetlands of New Wales (Australia), Negandhi et al. (2019) reported an increase in the reduction of greenhouse gas emissions in low-elevation restored wetlands, from 264 g m −2 yr −1 CO 2 to 351 g m −2 yr −1 CO 2 . ...
... Generally, mangrove sediments have a pH range of 6,5 -7,2 [25] and an ORP mostly less than 100 mV [26]. Low pH and ORP values, especially in the landward and middle zones, indicate high organic matter decomposition processes supported by the sediment type and high organic sediment carbon [27,28]. Salinity also gradually increased from landward to seaward zones due to tidal movement and freshwater inputs [29]. ...
Beside their role as carbon sinker, mangrove soil can also emit greenhouse gases (GHG) through microbial metabolism. However, their emission was scarce in every mangrove zone. We measured the CO2 and N2O concentrations in Ngurah Rai Grand Forest Park, Bali, which experienced anthropogenic pressure. Rhizophora mucronata and Sonneratia alba dominated the mangrove vegetation in this area and have a characteristic zonation across the intertidal (landwards, middle, and seaward zone). Gas samples were taken above a height of 25 cm from mangrove soil during the wet season of 2020 at the three mangrove zones within three sites. Gas concentrations ranged from 303.09-330.57 ppm for CO2 and 0.51-0.53 ppm for N2O. CO2 and N2O concentrations were similar across mangrove zones, with a decreasing trend from the land toward the sea. A high density of mangrove trees was negatively associated with N2O; meanwhile, no soil and porewater parameters were significantly correlated with the gas concentrations. The result revealed that N2O concentration had exceeded the average value of the earth's atmospheric N2O concentration. This information is essential for complementing previous research variations on GHG emissions and helps support the inventory of GHG emissions from the forestry sector.
... The lower average SAR found compared to the recent estimates in Mediterranean saltmarshes could be explained by differences in geomorphological characteristics across sites. The saltmarshes of our study are located in Atlantic macrotidal estuaries whereas saltmarshes studied in Fennessy et al. (2019) are located in a Mediterranean delta system (i.e., Ebro Delta) under a microtidal regime where hydrodynamic processes allow a higher deposition of inorganic and organic particles (Jiménez et al., 1997). In addition, the lower average SAR and C org burial rates found in the saltmarshes of this study compared to previous European and global assessments might be due to an uneven distribution of data across high marshes and low marshes in the latter. ...
The implementation of climate change mitigation strategies based on the conservation and restoration of Blue Carbon ecosystems requires a deep understanding of the magnitude and variability in organic carbon (Corg) storage across and within these ecosystems. This study explored the variability in soil Corg stocks and burial rates across and within intertidal estuarine habitats of the Atlantic European coast and its relation to biotic and abiotic drivers. A total of 136 soil cores were collected across saltmarshes located at different tidal zones (high marsh, N = 45; low marsh, N = 30), seagrass meadows (N = 17) and tidal flats (N = 44), and from the inner to the outer sections of five estuaries characterized by different basin land uses. Soil Corg stocks were higher in high-marsh communities (65 ± 3 Mg ha-1) than in low-marsh communities (38 ± 3 Mg ha-1), seagrass meadows (40 ± 5 Mg ha-1) and unvegetated tidal flats (46 ± 3 Mg ha-1) whereas Corg burial rates also tended to be higher in high marshes (62 ± 13 g m-2 y-1) compared to low marshes (43 ± 15 g m-2 y-1) and tidal flats (35 ± 9 g m-2 y-1). Soil Corg stocks and burial rates decreased from inner to outer estuarine sections in most estuaries reflecting the decrease in the river influence towards the estuary mouth. Higher soil Corg stocks were related to higher content of silt and clay and higher proportion of forest and natural land within the river basin, pointing at new opportunities for protecting coastal natural carbon sinks based on the conservation and restoration of upland ecosystems. Our study contributes to the global inventory of Blue Carbon by adding data from unexplored regions and habitats in Europe, and by identifying drivers of variability across and within estuaries.
... Cs 137 is usually used as a soil marker, and the sediment accretion rate could be calculated by the relationship between its peak value and half-life. Pb 210 could estimate sediment accretion rates by calculating based on the constant initial concertation model [41]. Sea level change rate, elevation change rate, and shallow subsidence rate were taken from the same publication that contained sediment accretion rate. ...
An accelerating rate of sea level rise (SLR) is causing huge inundation pressure on coastal wetlands worldwide. Vegetation of coastal wetlands plays a key role in stabilizing the coast and accreting sediment in order to mitigate the negative impact of SLR. The ability to accrete sediment is influenced by individual species traits; however, there are insufficient information and indicators to identify differences in the adaptability of various coastal vegetations to SLR at a regional or global scale. Here, the potential adaptation of 27 plant populations in coastal wetlands subject to SLR was evaluated using a compiled global dataset and a marsh equilibrium model. Sediment accretion efficiency differed among plant populations, but most coastal marsh populations and a few mangrove populations had relatively high accretion rates; habitats with high accretion rates will have a better potential to deal with the threat of SLR. These results showed that latitude and efficiency shared a nonlinear relationship, and plant stem density and root structure were among the important factors that influenced the efficiency. Fibrous root plant populations had a greater sediment accretion efficiency than tap root plant populations, and perennial populations had a greater sediment accretion efficiency than annual plant populations. These findings can provide key parameters relating to the sediment accretion efficiency of hydrological and geomorphic models on a global scale. This study offers some novel insights into the dynamic changes in coastal wetlands following SLR that will be particularly useful in devising appropriate strategies for the protection and management of coastal wetlands.
... In addition to hydroperiod, physicochemical properties such as soil redox potential, pH and the distribution and availability of nutrients are important drivers of plant diversity, vegetation structure and wetland dynamics (Seybold et al. 2002, Boomer & Bedford 2008, Thomas et al. 2009, Foster et al. 2011, Torres et al. 2018. Wetlands on large floodplains and in deltaic areas are highly productive due to the availability of nutrient-rich sediments brought down from the entire watershed (Fennessy et al. 2019), and soil exchangeable cations point towards an effect from the main water source (Infante-Mata et al. 2011). Thus, in order to characterise and understand these systems, it is necessary to know the chemical properties of the soil as well as to monitor the flooding regime. ...
Stored carbon varies among wetlands, yet they rank among the highest carbon accumulating ecosystems. Leaf litter production and aboveground carbon storage are frequently used as proxies for estimating primary productivity, which can be affected by flooding, salinity and other environmental factors. The objective of this study was to quantify leaf litter production and soil carbon density in two coastal tropical wetland types, namely mangrove swamps and forested freshwater wetlands. Water and soil physicochemical properties, together with leaf litter production, were measured bimonthly between 2007 and 2009 in wetlands of both types, located on the coast of the Gulf of Mexico. The soils ranged from entirely mineral to entirely organic in the top metre. Mangrove sites had relatively uniform hydroperiods and moderately reductive soils, whereas forested freshwater wetlands had reducing conditions. Electrical conductivity was lower and pH less acidic in forested freshwater wetland soils. Litterfall was around 1000 g m-2 yr-1 and annual production did not differ significantly between wetlands, despite the presence of acidic soils with prolonged flooding and high salinity in the mangrove swamps. Also, there were no consistent differences in soil carbon density between the two wetland types. Some forested freshwater wetlands had low litter production and high soil carbon density, whereas some mangrove swamps had high litter production and low soil carbon density. We present information regarding aboveground biomass turnover and belowground carbon storage in coastal tropical forested wetlands
which is greatly needed to support us in understanding, valuing and conserving these neglected ecosystems.
... Assessment of available published and unpublished soil organic carbon accumulation rate (CAR) data from locations where wetlands have been created due to restrictions to tidal flows (tidal-restricted wetlands, Fennessy et al., 2019) were used to estimate soil CAR in tidallyrestricted wetlands in Australia (Table S2). These values were derived from estimates of soil CAR in hydrologically modified mangrove forests, saltmarshes, and other herbaceous communities, and are therefore applicable to a range of baseline tidally-restricted wetland scenarios. ...
Restoration of coastal wetlands has the potential to deliver both climate change mitigation, called blue carbon, and adaptation benefits to coastal communities, as well as supporting biodiversity and providing additional ecosystem services. Valuing carbon sequestration may incentivise restoration projects, however, it requires development of rigorous methods for quantifying blue carbon sequestered during coastal wetland restoration. We describe the development of a blue carbon abatement model (BlueCAM) used within the Tidal Restoration of Blue Carbon Ecosystems Methodology Determination 2022 of the Emissions Reduction Fund (ERF), which is Australia's voluntary carbon market scheme. The new BlueCAM uses Australian data to estimate abatement from carbon and greenhouse gas sources and sinks arising from coastal wetland restoration (via tidal restoration) and aligns with the Intergovernmental Panel for Climate Change guidelines for national greenhouse gas inventories. BlueCAM includes carbon sequestered in soils and biomass and avoided emissions from alternative land uses. A conservative modelled approach was used to provide estimates of abatement (as opposed to on‐ground measurements); and in doing so, this will reduce the costs associated with monitoring and verification for ERF projects and may increase participation in blue carbon projects by Australian landholders. BlueCAM encompasses multiple climate regions and plant communities and therefore may be useful to others outside Australia seeking to value blue carbon benefits from coastal wetland restoration. This article is protected by copyright. All rights reserved.
... Wetlands in the Ebro River delta are being affected by the construction of dams and the adaptation of rice crops, bringing with it an alteration of the accumulation of allochthonous carbon transported in the sediments. Furthermore, there are alterations in the soil level, showing that where there is greater connectivity, there will be greater results of organic carbon accumulation [148]. On the other hand, Sánchez-Espinosa and Schröder [4], affirm that agriculture expansion has led to changes in land use in recent decades within and around the limits of water resources by modifying water level. ...
Despite occupying an area no greater than 8% of the earth’s surface, natural wetland
ecosystems fulfill multiple ecological functions: 1. Soil formation and stabilization support, 2. Food,
water, and plant biomass supply, 3. Cultural/recreational services, landscape, and ecological tourism,
4. Climate regulation, and 5. Carbon sequestration; with the last one being its most important
function. They are subject to direct and indirect incident factors that affect plant productivity and the
sequestration of carbon from the soil. Thus, the objective of this review was to identify the incident
factors in the loss of area and carbon sequestration in marine, coastal, and continental wetlands that
have had an impact on climate change in the last 14 years, globally. The methodology consisted of
conducting a literature review in international databases, analyzing a sample of 134 research studies
from 37 countries, organized in tables and figures supported by descriptive statistics and content
analysis. Global results indicate that agriculture (25%), urbanization (16.8%), aquaculture (10.7%),
and industry (7.6%) are incident factors that promote wetlands effective loss affecting continental
wetlands more than coastal and marine ones. Regarding carbon sequestration, this is reduced
by vegetation loss since GHG emissions raise because the soil is exposed to sun rays, increasing
surface temperature and oxidation, and raising organic matter decomposition and the eutrophication
phenomenon caused by the previous incident factors that generate wastewater rich in nutrients in
their different activities, thus creating biomass and plant growth imbalances, either at the foliage
or root levels and altering the accumulation of organic matter and carbon. It is possible to affirm in
conclusion that the most affected types of wetlands are: mangroves (25.7%), lagoons (19.11%), and
marine waters (11.7%). Furthermore, it was identified that agriculture has a greater incidence in the
loss of wetlands, followed by urbanization and industry in a lower percentage.
Keywords: anthropogenic activities; climate change; terrestrial ecosystems; environmental impacts;
greenhouse gases
... Natural processes that impact ecosystem structure, function, and land cover may or may not be directly influenced by anthropogenic activities. They include coastline erosion (Sapkota & White, 2019;Theuerkauf et al., 2015), saltwater intrusion (Wen et al., 2019), submergence by global sea-level rise and local subsidence (DeLaune & White, 2012;Edwards et al., 2019), expansion of invasive plants Chen et al., 2015;Yang et al., 2017), changes in vegetation structure (Owers et al., 2018) and variations in hydrogeological settings (DeLaune et al., 2016;Fennessy et al., 2019;Saintilan et al., 2013). Carbon sequestration in large estuarine deltas has been found to be particularly sensitive to direct anthropogenic interventions such as hydrological engineering (causing reductions in sediment supply, see Chmura et al., 2003;Syvitski et al., 2009), land-use change (farming and oil exploration, e.g., Nahlik & Fennessy, 2016;Ma et al., 2019), and contamination and eutrophication of coastal waters (McLeod et al., 2011). ...
Five 20–30 m long boreholes recovered from the modern Yellow River Delta (MYRD) were analyzed for sedimentary characteristics, grain sizes, foraminiferal species, and ages determined by accelerator mass spectrometry (AMS) 14 C, bulk density, and carbon content to document the variation of carbon sequestration in several distinct wetlands and aquatic units of the MYRD during the Holocene. Eight units have been identified since the early Holocene, namely, riverine wetland, ancient tidal wetland, neritic‐sea aquatic system, pro‐delta aquatic system, interdistributary bay wetland, delta‐front wetland, modern tidal wetland, and upper delta plain wetland. Our results revealed that the highest apparent sedimentation rate (ASR) was in the delta‐front wetland (up to 85 cm/yr) in the MYRD, while the lowest value range (only 0.04~0.05 cm/yr) occurred in the neritic‐sea aquatic system. Accordingly, the average carbon accumulation rates (CAR) were up to 1020.35 g C/m 2 /yr for organic carbon, and 5202.24 g C/m 2 /yr for inorganic carbon in the delta‐front wetland, nearly 350 times and 640 times higher than those in the neritic‐sea system, respectively. The ASRs dominated the variations of CARs in the various wetlands and aquatic environments. Therefore, the MYRD is likely a highly significant carbon sink during the past 2000 years, even under the condition of very low carbon contents due to dilution processes. Management activities including coastline protection and wetland restoration, freshwater and sand discharge to deltaic wetlands, and reducing and limiting human activities, which may all be effective ways of managing for carbon sequestration and storage in the MYRD.
... 134 However, runoff of nutrients and sediments can also lead to increased vertical accretion of the sediment surface, which can enhance carbon stocks and reduce vulnerability to sea level rise, as observed in the mineral sediment saltmarshes of Spain. 135,136 The effects of nutrient enrichment on saltmarsh and mangrove sediment carbon stocks are likely to be dependent on levels of nutrient enrichment and sedi-ment characteristics, with highly organic sediments being more susceptible to decomposition and subsidence. 133 Allocation of biomass to roots, whose detritus is a large component of sediment carbon and which can contribute significantly to accretion of soil volume, 7 varies in sensitivity to nutrient enrichment among species 25 and thus adds further complexity to the effects of nutrient enrichment on sediment carbon stocks. ...
Blue carbon provides opportunities to mitigate climate change while increasing ecosystem services for coastal communities, including climate change adaptation; however, blue carbon ecosystems are vulnerable to climate change, leading to uncertainties in the future efficacy of these ecosystems. In this review, we assess the potential impacts of climate change on blue carbon. Despite uncertainties, carbon sequestration in coastal ecosystems is enhanced by landward migration of blue carbon habitats, maintenance of sediment supply, restoration, and improved water quality. As an example, landward migration of mangroves could result in carbon sequestration of 1.5 Pg by 2100. Mudflats, seaweed beds, and coastal swamp forests could also contribute to climate change mitigation, although there are large data gaps. Achieving the full potential of blue carbon requires protection and restoration of ecosystems and facilitation of changes in ecosystem distributions with climate change, actions that will also deliver adaptation benefits. Conversely, in the worst-case coastal squeeze scenario, losses of 3.4 Pg of sequestered carbon by 2100 could occur.
Bu çalışmanın temel amacı, Bursa Karacabey subasar ormanlarında, iki farklı ortamdaki (sulak ve karasal) doğal kızılağaç (Alnus glutinosa L.) Kzc3 (d1,3=20-35,9 cm) ve Kzd3 (d1,3=36,0-51,9 cm) meşcere gelişim çağlarında, ağaç bileşenlerinin (yaprak, dal, tohum ve diğer) yıllık döküm miktarı ve döküm ile ölü örtüye ulaşan karbon ve makro (N, P, K, Ca, Mg ve S) ve mikro (Fe, Mn, Na, Cu, Zn, Cl, Ni ve Co) besin elementi miktarını belirlemektir. Çalışma 2021, 2022 ve 2023 yıllarında yürütülmüştür. Bulgulara göre, yıllık ortalama döküm miktarı, sulak ortamdaki Kzc3 için hektarda 10407 kg, Kzd3 için 7678 kg iken, karasal ortamdaki Kzc3 ve Kzd3 için bu değerler daha düşük olup sırasıyla 8157 ve 5907 kg olarak tespit edilmiştir. Toplam döküntüye, yaprak miktarının katkı oranı, sulak ortamdaki Kzc3 ve Kzd3 meşcerelerinde sırasıyla %45 ve %47 iken, bu oranlar karasal ortamda %37 ve %41 olarak belirlenmiştir. Döküntü miktarı meşcere tipine göre farklılık göstermiş ve genel olarak meşcere yaşı ve ortalama çapı arttıkça döküntü miktarı azalmıştır. Sulak ortamda, döküntü ile ekosisteme giren yıllık ortalama karbon ve diğer makro ve mikro besin maddesi miktarları, genel olarak karasal ortamdan daha yüksek bulunmuştur. Örneğin, sulak ortamda Kzc3 için C, N, P, K, Ca, Mg ve S girdileri sırasıyla 4154; 130; 15; 48; 244; 48 ve 24 kg/ha/yıl olarak hesaplanırken, karasal ortamda bu değerler sırasıyla 3051; 104; 27; 49; 202; 38 ve 32 kg/ha/yıl olarak hesaplanmıştır. Çalışma ile kızılağaç meşcerelerinin döküntü üretimi ve besin maddesi girişinin sulak ve karasal ortam ile meşcere gelişim çağlarına göre farklılık gösterdiği ortaya konulmuştur.
A century ago, measuring elevation in tidal wetlands proved difficult, as survey leveling of soft marsh soils relative to a fixed datum was error prone. For 60 years, vertical accretion measures from marker horizons were used as analogs of elevation change. But without a direct measure of elevation, it was not possible to measure the total influence of surface and subsurface processes on elevation. In the 1990s, the surface elevation table (SET) method, which measures the movement of the wetland surface relative to a fixed point beneath the surface (i.e., the SET benchmark base), was combined with the marker horizon method (SET-MH), providing direct, independent, and simultaneous measures of surface accretion and elevation and quantification of surface and shallow subsurface process influences on elevation. SET-MH measures have revealed several fundamental findings about tidal wetland dynamics. First, accretion [A] is often a poor analog for elevation change [E]. From 50–66% of wetlands experience shallow subsidence (A > E), 7–10% shallow expansion (A < E), 7% shrink-swell, and for 24–36% A is an analog for E (A = E). Second, biological processes within the root zone and physical processes within and below the root zone influence elevation change in addition to surface processes. Third, vegetation plays a key role in wetland vertical dynamics. Plants trap sediment and increase resistance to erosion and compaction. Soil organic matter accumulation can lead to shallow expansion, but reduced plant growth can lead to subsidence, and plant death to soil collapse. Fourth, elevation rates are a better indicator of wetland response to sea-level rise than accretion rates because they incorporate subsurface influences on elevation occurring beneath the marker horizon. Fifth, combining elevation trends with relative sea-level rise (RSLR) trends improves estimates of RSLR at the wetland surface (i.e., RSLRwet). Lastly, subsurface process influences are fundamental to a wetland’s response to RSLR and plant community dynamics related to wetland transgression, making the SET-MH method an invaluable tool for understanding coastal wetland elevation dynamics.
Blue carbon has been proposed as a nature-based solution for climate change mitigation; however, a limited number of published works and data and knowledge gaps hinder the development of small island developing states' (SIDS) national blue carbon resources globally. This paper reviews the blue carbon ecosystems of Seychelles as a case study in the context of SIDS, comparing estimations by the Blue Carbon Lab and recent blue carbon (mangrove and seagrass) evaluations submitted to the Seychelles national government. Mangroves (2195 ha, 80% in Aldabra Atoll) and seagrasses (142,065 ha) dominate in Seychelles, with coral reefs having the potential for carbon sequestration (169,000 ha). Seychelles is on track to protecting its blue carbon, but these systems are threatened by rising sea levels, coastal squeeze, erosion, severe storms, and human activities. The importance of carbon inventories, accounting institutions, and continuous monitoring of blue carbon systems is discussed. Blue accounting is necessary for accurate accounting of carbon sequestration and carbon storage, generating carbon credits, and representing impactful reductions in greenhouse gases for NDCs. Challenges and opportunities include policy legislation regarding ownership rights, accreditation and certification for carbon credits, sustainable financing mechanisms like natural asset companies and blue tokens, local engagement for long-term success, and carbon market dynamics following COP27. The restoration and regulation of blue carbon resources for optimal ecosystem services delivery, carbon inventories, and blue carbon policy are recommended development priorities. Blue carbon ecosystems have the potential to contribute to NDCs of SIDS while simultaneously offering sustainable development pathways for local communities through the multiple ecosystem services they provide.
Coastal saltmarshes are found globally, yet are 25%–50% reduced compared with their historical cover. Restoration is incentivised by the promise that marshes are efficient storers of ‘blue’ carbon, although the claim lacks substantiation across global contexts. We synthesised data from 431 studies to quantify the benefits of saltmarsh restoration to carbon accumulation and greenhouse gas uptake. The results showed global marshes store approximately 1.41–2.44 Pg carbon. Restored marshes had very low greenhouse gas (GHG) fluxes and rapid carbon accumulation, resulting in a mean net accumulation rate of 64.70 t CO2e ha−1 year−1. Using this estimate and potential restoration rates, we find saltmarsh regeneration could result in 12.93–207.03 Mt CO2e accumulation per year, offsetting the equivalent of up to 0.51% global energy- related CO2 emissions—a substantial amount, considering marshes represent <1% of Earth's surface. Carbon accumulation rates and GHG fluxes varied contextually with temperature, rainfall and dominant vegetation, with the eastern coasts of the USA and Australia particular hotspots for carbon storage. While the study reveals paucity of data for some variables and continents, suggesting need for further research, the potential for saltmarsh restoration to offset carbon emissions is clear. The ability to facilitate natural carbon accumulation by saltmarshes now rests principally on the action of the management-policy community and on financial opportunities for supporting restoration.
Paddy farming can potentially sequester carbon. However, agricultural practices may alter the stability of the soil organic carbon (SOC) stocks and thereby increase carbon mobilization in the topsoil and subsoil. We hypothesize that both agricultural practices and soil physical–chemical characteristics, mostly those related to the type of the parental soil where the paddy is established, play an important role in SOC stabilization and sequestration. To test this, we profiled the biochemical characteristics of soil organic matter (SOM) and the SOC concentrations in sediment cores of 10 rice fields from the Ebro Delta (Northeast Spain) representing former reclaimed habitats (i.e., peatlands, meadows, coastal lagoons, riverbanks and salt marshes). The effects of physical–chemical soil properties on SOM content were tested with Generalized Linear Models and the best models were selected using information-theoretic approach. The optical characteristics of SOM extracts were analyzed by UV–Visible and fluorescence spectrophotometry, and six fluorescence components were identified by Parallel Factor Analysis (PARAFAC). Higher clay and lower sand content explained the greater SOM presence in topsoil while higher clay content and salinity prevailed as the main explanatory factors in the subsoil showing a positive correlation with SOM content. The results revealed a correlated gradient of SOM quantity and quality where in SOM-rich soils both the aromaticity and the humification degree were higher while in soils with lower SOM content it was fresher and more microbially derived. Current agricultural practices favored SOM humification in the topsoil while the variability in SOM quality in subsoil is attributed to the combination of soil physical–chemical characteristics (pH, conductivity and clay content) and the previous habitat’s influence. This study represents a comprehensive empirical analysis on the carbon stocks in rice fields and the identification of soil physical–chemical factors, related to prior land uses, favoring soil carbon accumulation. These results may have major implications in decision-making process for climate change mitigation in vulnerable Mediterranean coastal paddies.
Pialassa Baiona is a shallow temperate coastal lagoon influenced by a variety of factors, including regional climate change and local anthropogenic disturbances. To better understand how these factors influenced modern organic carbon (OC) sources and accumulation rates, we measured OC as well as stable carbon isotopes (δ13C) in ²¹⁰Pb-dated sediments within a vegetated saltmarsh habitat and a human impacted habitat. Relative Sea Level (RSL) at the nearby tide gauge station data and four different Sea Surface Temperature (SST) data sets were analyzed starting from 1900 to assess the potential effect of sea ingression and warming on the coastal lagoon sedimentary processes. The source contribution calculated from the MixSIAR Bayesian model revealed a mixed composition of sedimentary OC, dominated by an increase in marine-derived OC after the 1950s, matching with a decrease from autochthonous saltmarsh vegetation (Juncus spp.) in the saltmarsh habitat, and from riverine/estuarine-derived OC in the impacted habitat. RSL rise in the area (8.7 ± 0.5 mm yr −1 in the period 1900–2014) has been mainly driven by the land subsidence, especially during the central decades of the last century, enhancing the sea ingression into the lagoon. RSL rise influenced changes in sedimentary OC sources and accumulation at different level within the two habitats from the 1950s onward; conversely, no direct effect of SST was detected.
The Everglades Stormwater Treatment Areas (STAs) are a complex of large constructed wetlands that are an integral component of the State and Federal efforts to restore the Everglades ecosystem. The overall objective of this study was to determine the accumulation rates of macro‐elements including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and associated secondary elements including calcium (Ca), magnesium (Mg), aluminum (Al), and iron (Fe) in two Everglades STAs over their periods of operation. The study was conducted in STA‐2 with parallel flow‐ways consisting of emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) and the Western flow‐way of STA‐3/4 with EAV and SAV cells operated in series. Elemental accumulation rates were determined in the unconsolidated surficial sediments (floc) and recently accreted soil (RAS) that have accumulated on top of the antecedent soil over the 14‐ and 10‐yr periods of operation for STA‐2 and STA‐3/4, respectively. Flow‐ways with SAV were more efficient than EAV in accreting mineral matter, resulting in increased bulk density and higher accumulation rates of elements. Average C accumulation in the floc and RAS of SAV flow‐ways was 320 g·m−2·yr−1 with approximately equal proportions of inorganic and organic C, while in the EAV flow‐ways accumulation rates of C ranged from 116 to 147 g·m−2·yr−1 with mostly organic C. Phosphorus accumulation rates were approximately 2–3 times higher in SAV than in EAV flow‐ways. Differences in accumulation of elements between SAV and EAV were largest for Ca with 17–42 times more Ca in SAV than EAV systems. This suggests that in the SAV systems, possible occlusion of macro‐elements and metals during CaCO3 precipitation facilitated accretion of material with high mineral content. In EAV, biomass turnover and associated biotic processes regulated organic matter accumulation rates. The spatial accumulation patterns of P, C, and N in the EAV areas of STA‐2 and STA‐3/4 were similar to those observed in the EAV areas of the natural wetlands in Water Conservation Areas, suggesting that constructed wetland systems function similarly to natural wetlands dominated by EAV areas in retaining and storing macro‐ and secondary elements.
Arid zone coastal wetlands provide disproportionally important ecosystem services due to their relatively high levels of productivity relative to adjacent terrestrial systems. However, these wetlands are vulnerable to sea level rise as sediments needed for vertical accretion are limited. In order to assess the processes important for vertical accretion in arid zone coastal wetlands, we assessed vertical accretion across an arid zone wetland landscape in Western Australia. We found that overall coastal wetlands were declining in elevation at −0.18 mm yr−1 (± standard error 0.12 mm yr−1). Vertical accretion in mangroves was evident in years of high mean sea level, but this was insufficient to counteract shallow subsidence. The high intertidal cyanobacterial mat and salt flat zones were eroding, particularly in years of high rainfall. We observed retreat of the seaward mangrove fringe associated with tree mortality caused by cyclones, but we also observed recruitment of mangroves onto the high intertidal cyanobacterial mat zone, attributed to higher sea levels. Our study found complexity in the factors causing landscape change across the intertidal zone, where variation in sea level, intense storms, and other climatic and biotic factors interact.
Wetland soils contain some of the highest stores of soil carbon in the biosphere. However,
there is little understanding of the quantity and distribution of carbon stored in our remaining
wetlands or of the potential effects of human disturbance on these stocks. Here we use field
data from the 2011 National Wetland Condition Assessment to provide unbiased estimates of
soil carbon stocks for wetlands at regional and national scales. We find that wetlands in the
conterminous United States store a total of 11.52 PgC, much of which is within soils deeper
than 30 cm. Freshwater inland wetlands, in part due to their substantial areal extent,
hold nearly ten-fold more carbon than tidal saltwater sites—indicating their importance in
regional carbon storage. Our data suggest a possible relationship between carbon stocks
and anthropogenic disturbance. These data highlight the need to protect wetlands to mitigate
the risk of avoidable contributions to climate change.
For decades, ecosystem scientists have used global warming potentials (GWPs) to compare the radiative forcing of various greenhouse gases to determine if ecosystems have a net warming or cooling effect on climate. On a conceptual basis, the continued use of GWPs by the ecological community may be untenable because the use of GWPs requires the implicit assumption that greenhouse gas emissions occur as a single pulse; this assumption is rarely justified in ecosystem studies. We present two alternate metrics – the sustained-flux global warming potential (SGWP, for gas emissions) and the sustained-flux global cooling potential (SGCP, for gas uptake) – for use when gas fluxes persist over time. The SGWP is generally larger than the GWP (by up to ~40%) for both methane and nitrous oxide emissions, creating situations where the GWP and SGWP metrics could provide opposing interpretations about the climatic role of an ecosystem. Further, there is an asymmetry in methane and nitrous oxide dynamics between persistent emission and uptake situations, producing very different values for the SGWP vs. SGCP and leading to the conclusion that ecosystems that take up these gases are very effective at reducing radiative forcing. Though the new metrics are more realistic than the GWP for ecosystem fluxes, we further argue that even these metrics may be insufficient in the context of trying to understand the lifetime climatic role of an ecosystem. A dynamic modeling approach that has the flexibility to account for temporally variable rates of greenhouse gas exchange, and is not limited by a fixed time frame, may be more informative than the SGWP, SGCP, or GWP. Ultimately, we hope this article will stimulate discussion within the ecosystem science community about the most appropriate way(s) of assessing the role of ecosystems as regulators of global climate.
Sea-level rise and river engineering spell disaster, say Liviu Giosan and colleagues.
Studies on carbon stock in salt marsh sediments have increased since the review by Chmura et al. (2003). However, uncertainties exist in estimating global carbon stor-age in these vulnerable coastal habitats, thus hindering the as-sessment of their importance. Combining direct data and in-direct estimation, this study compiled studies involving 143 sites across the Southern and Northern hemispheres, and pro-vides an updated estimate of the global average carbon ac-cumulation rate (CAR) at 244.7 g C m −2 yr −1 in salt marsh sediments. Based on region-specific CAR and estimates of salt marsh area in various geographic regions between 40 • S to 69.7 • N, total CAR in global salt marsh sediments is esti-mated at ∼10.2 Tg C yr −1 . Latitude, tidal range and elevation appear to be important drivers for CAR of salt marsh sedi-ments, with considerable variation among different biogeo-graphic regions. The data indicate that while the capacity for carbon sequestration by salt marsh sediments ranked the first amongst coastal wetland and forested terrestrial ecosystems, their carbon budget was the smallest due to their limited and declining global areal extent. However, some uncertainties remain for our global estimate owing to limited data avail-ability.
Many of the world’s largest deltas are densely populated and heavily farmed. Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean. The vulnerability is a result of sediment compaction from the removal of oil, gas and water from the delta’s underlying sediments, the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level. Here we present an assessment of 33 deltas chosen to represent the world’s deltas. We find that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of 260,000 km2. We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas.
The risk of flood disasters is increasing for many coastal societies owing to global and regional changes in climate conditions, sea-level rise, land subsidence and sediment supply. At the same time, in many locations, conventional coastal engineering solutions such as sea walls are increasingly challenged by these changes and their maintenance may become unsustainable. We argue that flood protection by ecosystem creation and restoration can provide a more sustainable, cost-effective and ecologically sound alternative to conventional coastal engineering and that, in suitable locations, it should be implemented globally and on a large scale.
Sea-level rise threatens coastal salt-marshes and mangrove forests around the world, and a key determinant of coastal wetland vulnerability is whether its surface elevation can keep pace with rising sea level. Globally, a large data gap exists because wetland surface and shallow subsurface processes remain unaccounted for by traditional vulnerability assessments using tide gauges. Moreover, those processes vary substantially across wetlands, so modelling platforms require relevant local data. The low-cost, simple, high-precision rod surface-elevation table-marker horizon (RSET-MH) method fills this critical data gap, can be paired with spatial data sets and modelling and is financially and technically accessible to every country with coastal wetlands. Yet, RSET deployment has been limited to a few regions and purposes. A coordinated expansion of monitoring efforts, including development of regional networks that could support data sharing and collaboration, is crucial to adequately inform coastal climate change adaptation policy at several scales.
The fragility of the world's deltas is not solely a consequence of rising ocean waters. Human fresh water use is a predominant force behind receding coastlines.
The distribution of belowground biomass within monotypic stands of invasive Phragmites australis (Common Reed) was documented from a series of oligo-, meso-, and polyhaline coastal marshes in New Hampshire. Soil profiles were described, and live biomass was documented growing to a maximum depth of 95 cm for roots and 85 cm for rhizomes. Our data show that invasive P. australis utilizes a greater depth range than na- tive graminoids (90% within the top 70 cm and top 20 cm, respectively). We corroborate prior anecdotal observations and provide further evidence illustrating the potential for this invasive plant to access resources (i.e., water and nutrients) at depths greater than the native species with which it competes.
Tidal wetlands play an important role with respect to climate change because of both their sensitivity to sea-level rise and their ability to sequester carbon dioxide from the atmosphere. Policy-based interest in carbon sequestration has increased recently, and wetland restoration projects have potential for carbon credits through soil carbon sequestration. We measured sediment accretion, mineral and organic matter accumulation, and carbon sequestration rates using 137Cs and 210Pb downcore distributions at six natural tidal wetlands in the San Francisco Bay Estuary. The accretion rates were, in general, 0.2–0.5 cm year−1, indicating that local wetlands are keeping pace with recent rates of sea-level rise. Mineral accumulation rates were higher in salt marshes and at low-marsh stations within individual sites. The average carbon sequestration rate based on 210Pb dating was 79 g C m−2 year−1, with slightly higher rates based on 137Cs dating. There was little difference in the sequestration rates among sites or across stations within sites, indicating that a single carbon sequestration rate could be used for crediting tidal wetland restoration projects within the Estuary.
Inland and transitional aquatic systems play an important role in global carbon (C) cycling. Yet, the C dynamics of wetlands and floodplains are poorly defined and field data is scarce. Air-water [Formula: see text] fluxes in the wetlands of Doñana Natural Area (SW Spain) were examined by measuring alkalinity, pH and other physiochemical parameters in a range of water bodies during 2010-2011. Areal fluxes were calculated and, using remote sensing, an estimate of the contribution of aquatic habitats to gaseous [Formula: see text] transport was derived. Semi-permanent ponds adjacent to the large Guadalquivir estuary acted as mild sinks, whilst temporal wetlands were strong sources of [Formula: see text] (-0.8 and 36.3 [Formula: see text]). Fluxes in semi-permanent streams and ponds changed seasonally; acting as sources in spring-winter and mild sinks in autumn (16.7 and -1.2 [Formula: see text]). Overall, Doñana's water bodies were a net annual source of [Formula: see text] (5.2 [Formula: see text]). Up-scaling clarified the overwhelming contribution of seasonal flooding and allochthonous organic matter inputs in determining regional air-water gaseous [Formula: see text] transport (13.1 [Formula: see text]). Nevertheless, this estimate is about 6 times < local marsh net primary production, suggesting the system acts as an annual net [Formula: see text] sink. Initial indications suggest longer hydroperiods may favour autochthonous C capture by phytoplankton. Direct anthropogenic impacts have reduced the hydroperiod in Doñana and this maybe exacerbated by climate change (less rainfall and more evaporation), suggesting potential for the modification of C sequestration.
Wetlands are among the most important natural resources on earth. They are the sources of cultural, economic and biological diversity. With their wealth of stored carbon, wetlands provide a potential sink for atmospheric carbon, but if not managed properly could become sources of greenhouse gases (GHGs) such as carbon dioxide and methane. Two important long-term uncertainties have initiated much debate in the scientific community. These are global wetland area and the amount of carbon stored in it. Compilation of relevant databases could be useful in setting up a long-term strategy for wetland conservation. It has been difficult to estimate the net carbon sequestration potential of a wetland, because the rate of decomposition of organic matter and the abundance of methanogenic micro-organisms and fluxes from the sediment are extremely complex, and there are often gaps in relevant scientific knowledge. The present discussion on density distribution of soil organic C in global wetlands could well be instrumental in formulating efficient strategies related to carbon sequestration and reduction of GHG emissions in wetland ecosystems. Effective assessment of wetlands will only take place when the available information becomes accessible and usable for all stakeholders.
Organic soil accretion and nutrient accumulation were measured in the northern, central, and southern Everglades to evaluate the effects of anthropogenic nutrient and hydroperiod alterations on organic C and nutrient storage during the past century. Six soil cores (euic, hyperthermic Typic Medisaprists) were collected from nutrient-enriched (Water Conservation Area [WCA] 2A) and unenriched locations. Soil depth increments were analyzed for radionuclides (137Cs, 210Pb, 164C), bulk density, and nutrients (C, N, P, S) to estimate recent (30-yr) and long-term (100-yr) organic soil accretion and nutrient accumulation. Since WCA 2A was completely impounded in the early 1960s, organic soil accretion in northern WCA 2A (5.8-6.7 mm yr-1) increased by three to five times compared with before 1960 (1.9 mm yr-1) or with unenriched areas within and outside of WCA 2A (1.4-1.6 mm yr-1). Nutrient accumulation in the enriched area of WCA 2A since 1960 was two (184-223 g C m-2 yr-1, 13.6-16.6 g N m-2 yr-1) to eight (0.40-0.46 g P m-2 yr-1) times higher than before 1960 (110 g C m-2 yr-1, 6.6 g N m-2 yr-1, 0.06 g P m-2 yr-1) or in unenriched areas (65-90 g C m-2 yr-1, 4.7-6.4 g N m-2 yr-1, 0.06 g P m-2 yr-1). Unenriched areas of the Everglades possess some of the lowest rates of P accumulation of peatlands in North America. Successful restoration of the Everglades will have to include the elimination of anthropogenic nutrient loadings to limit the P enrichment zone from expanding into existing unenriched interior areas and areas downstream of WCA 2A.
Increased recognition of the global importance of salt marshes as 'blue carbon' (C) sinks has led to concern that salt marshes could release large amounts of stored C into the atmosphere (as CO2) if they continue undergoing disturbance, thereby accelerating climate change. Empirical evidence of C release following salt marsh habitat loss due to disturbance is rare, yet such information is essential for inclusion of salt marshes in greenhouse gas emission reduction and offset schemes. Here we investigated the stability of salt marsh (Spartinaalterniflora) sediment C levels following seagrass (Thallasiatestudinum) wrack accumulation; a form of disturbance common throughout the world that removes large areas of plant biomass in salt marshes. At our study site (St Joseph Bay, Florida, USA), we recorded 296 patches (7.5 ± 2.3 m(2) mean area ± SE) of vegetation loss (aged 3-12 months) in a salt marsh meadow the size of a soccer field (7 275 m(2)). Within these disturbed patches, levels of organic C in the subsurface zone (1-5 cm depth) were ~30% lower than the surrounding undisturbed meadow. Subsequent analyses showed that the decline in subsurface C levels in disturbed patches was due to loss of below-ground plant (salt marsh) biomass, which otherwise forms the main component of the long-term 'refractory' C stock. We conclude that disturbance to salt marsh habitat due to wrack accumulation can cause significant release of below-ground C; which could shift salt marshes from C sinks to C sources, depending on the intensity and scale of disturbance. This mechanism of C release is likely to increase in the future due to sea level rise; which could increase wrack production due to increasing storminess, and will facilitate delivery of wrack into salt marsh zones due to higher and more frequent inundation.
Wetland ecosystems provide an optimum natural environment for the sequestration and long-term storage of carbon dioxide (CO2) from the atmosphere, yet are natural sources of greenhouse gases emissions, especially methane. We illustrate that most wetlands, when carbon sequestration is compared to methane emissions, do not have 25 times more CO2 sequestration than methane emissions; therefore, to many landscape managers and non specialists, most wetlands would be considered by some to be sources of climate warming or net radiative forcing. We show by dynamic modeling of carbon flux results from seven detailed studies by us of temperate and tropical wetlands and from 14 other wetland studies by others that methane emissions become unimportant within 300 years compared to carbon sequestration in wetlands. Within that time frame or less, most wetlands become both net carbon and radiative sinks. Furthermore, we estimate that the world’s wetlands, despite being only about 5–8 % of the terrestrial landscape, may currently be net carbon sinks of about 830 Tg/year of carbon with an average of 118 g-C m−2 year−1 of net carbon retention. Most of that carbon retention occurs in tropical/subtropical wetlands. We demonstrate that almost all wetlands are net radiative sinks when balancing carbon sequestration and methane emissions and conclude that wetlands can be created and restored to provide C sequestration and other ecosystem services without great concern of creating net radiative sources on the climate due to methane emissions.
The main goal of the Spanish National Hydrological Plan is the implementation of an inter-basin water transfer of a maximum of 1050 hm 3 /year from the lower Ebro River to the north and south Mediterranean coast. The plan also includes an additional list of public works of about 100 new dams and the infrastructure for new irrigation areas, as well as water treatment plants and river canalizations, etc. Taking into accout that the planned Ebro transfer would take 50 m 3 /s during 8 months, and that river flow is mostly in the interval of 150-250 m 3 /s during this period, the abstraction would repesent between one-third and one-fifth of the Ebro flow. This plan, if implemented, would have a strong negative environmental impact on the fluvial ecosystem, as well as on the estuarine and marine ecosystems, but these impacts have not been properly considered in the environmental assessment. This paper principally deals with the environmental effects of the water transfer on the area that supplies the water, downstream from the diversion point. The impact of an inter-basin water transfer on the mouth area is based on three aspects: (1) there is an increase in salinity in the delta and estuary; (2) there is a decrease in the biological productivity, mostly due to the decrease of nutrient inputs, and there are also changes in the species distribution; and (3) the river carries less sediment, which affects the geomorphology of the system. The possible effects of lower water quality and changes in the fluvial system have also to be considered. The sustainability of deltas can only be guaranteed with the allocation of an appropriate flow regime, which must include not only a liquid flow, but also a solid flow (sediment), given that deltas and coastal systems need sediment inputs (and nutrients) from the river to maintain their structure and dynamics. The classical methods of determining environmental flows in rivers are neither designed nor adequate for the objective of maintaining the deltas and estuaries in a good ecological state. The determination and implementation of an environmental flow regime not only for the river but also for the coastal and marine systems represent a new challenge for scientists and managers.
Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems-marshes, mangroves, and seagrasses-that may be lost with habitat destruction ('conversion'). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this 'blue carbon' can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15-1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3-19% of those from deforestation globally, and result in economic damages of $US 6-42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of land-use conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the well-recognized ecosystem services of coastal habitats.
1] Wetlands represent the largest component of the terrestrial biological carbon pool and thus play an important role in global carbon cycles. Most global carbon budgets, however, have focused on dry land ecosystems that extend over large areas and have not accounted for the many small, scattered carbon-storing ecosystems such as tidal saline wetlands. We compiled data for 154 sites in mangroves and salt marshes from the western and eastern Atlantic and Pacific coasts, as well as the Indian Ocean, Mediterranean Ocean, and Gulf of Mexico. The set of sites spans a latitudinal range from 22.4°S in the Indian Ocean to 55.5°N in the northeastern Atlantic. The average soil carbon density of mangrove swamps (0.055 ± 0.004 g cm À3) is significantly higher than the salt marsh average (0.039 ± 0.003 g cm À3). Soil carbon density in mangrove swamps and Spartina patens marshes declines with increasing average annual temperature, probably due to increased decay rates at higher temperatures. In contrast, carbon sequestration rates were not significantly different between mangrove swamps and salt marshes. Variability in sediment accumulation rates within marshes is a major control of carbon sequestration rates masking any relationship with climatic parameters. Globally, these combined wetlands store at least 44.6 Tg C yr À1 and probably more, as detailed areal inventories are not available for salt marshes in China and South America. Much attention has been given to the role of freshwater wetlands, particularly northern peatlands, as carbon sinks. In contrast to peatlands, salt marshes and mangroves release negligible amounts of greenhouse gases and store more carbon per unit area.
We examine the carbon balance of North American wetlands by reviewing and synthesizing the published literature and soil databases.
North American wetlands contain about 220 Pg C, most of which is in peat. They are a small to moderate carbon sink of about
49 Tg C yr−1, although the uncertainty around this estimate is greater than 100%, with the largest unknown being the role of carbon sequestration
by sedimentation in freshwater mineral-soil wetlands. We estimate that North American wetlands emit 9 Tg methane (CH4) yr−1; however, the uncertainty of this estimate is also greater than 100%. With the exception of estuarine wetlands, CH4 emissions from wetlands may largely offset any positive benefits of carbon sequestration in soils and plants in terms of
climate forcing. Historically, the destruction of wetlands through land-use changes has had the largest effects on the carbon
fluxes and consequent radiative forcing of North American wetlands. The primary effects have been a reduction in their ability
to sequester carbon (a small to moderate increase in radiative forcing), oxidation of their soil carbon reserves upon drainage
(a small increase in radiative forcing), and reduction in CH4 emissions (a small to large decrease in radiative forcing). It is uncertain how global changes will affect the carbon pools
and fluxes of North American wetlands. We will not be able to predict accurately the role of wetlands as potential positive
or negative feedbacks to anthropogenic global change without knowing the integrative effects of changes in temperature, precipitation,
atmospheric carbon dioxide concentrations, and atmospheric deposition of nitrogen and sulfur on the carbon balance of North
American wetlands.
Sediment cores from three lakes were dated with210Pb using a constant rate of supply (CRS) model. We used low-background gamma counting to measure naturally occurring levels of210Pb,226Ra, and137Cs in sediment samples because sample preparation is simple and non-destructive,226Ra activity provides a direct measure of supported210Pb activity for each sample analyzed, and137Cs activity may provide an independent age marker for the 1962–1963 peak in atmospheric fallout of this radionuclide. In one core supported210Pb activity was estimated equally well from226Ra activity of each sampling interval or from the mean total210Pb activity of constant activity samples at depth. Supported210Pb activity was constant with depth in this core. In a short freeze core, determining226Ra activity of every sample proved advantageous in estimating supported210Pb activity because supported210Pb activity could be estimated from210Pb measurements only at the deepest sampling interval. Supported210Pb activity estimated from226Ra activity also yielded more precise estimates of highly variable sedimentation rates. In the third core226Ra activity exceeded210Pb activity at the top of the core and varied 20 fold with depth. This high input of226Ra in disequilibrium with210Pb is attributed to recent erosion of radium-bearing materials in the drainage basin. These data invalidate the assumption that supported210Pb activity is constant in sediment cores and can be estimated from the mean total210Pb activity at depths where210Pb activity is constant. We recommend using gamma counting or another independent assay of226Ra to validate the assumption of constant supported210Pb activity in sediment cores if there is reason to expect that226Ra activity varies with depth.
Recent (6–12 month) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity
of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual
accretion rates in aSpartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent
to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion
in the same salt marsh region for a transect perpendicular to a canal (13 mm yr−1) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr−1). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability
in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment
input from lateral erosion associated with pond enlargement. In a brackishSpartina patens marsh on Louisiana’s Chenier plain, vertical accretion rates were the same along natural and canal waterways (3–4 mm yr−1) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than
the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr−1). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.
The Ebre (Ebro) Delta is one of the most important wetland areas in the western Mediterranean. Ca. 40% of the delta plain is less than 0.5 m above mean sea level and part of the southern margin of the delta is at mean sea level in an area protected by dikes. Both mean rates of secular subsidence in the Ebre Delta and eustatic sea level rise are ca. 1–2 mm/yr. Thus, the present annual relative sea level rise (RSLR) rate in the Ebre Delta may be at least 3 mm/yr. Measured accretion rates in the delta range from 4 mm/yr in the wetlands surrounding the river mouth to <0.1 mm/yr in impounded salt marshes and rice fields. The annual sediment deficit in the delta plain to offset RSLR is close to 1 million m3/yr. Accretion rates in the rice fields prior to the construction of large dams in the Ebre watershed were higher than RSLR rates, from 3–15 mm/yr. At present, > 99% of the riverine sediments are retained in the reservoirs and rice fields are losing ca. 0.2 mm/yr.
Future management plans should take RSLR into account and include control of freshwater and sediment flows from the river in order to offset negative effects from waterlogging and salt intrusion, and maintain land elevation. This will include the partial removal of sediments trapped behind the Ribarroja and Mequinença dams. Stocks and inputs of sediments in the corresponding reservoirs are large enough for land elevation of ca. 50 cm in the whole delta plain.
Advantages of this solution include (1) new sediments to the delta to offset subsidence (via rice fields) and coastal retreat, (2) enhanced functioning of the delta (productivity and nutrient processing), (3) avoidance of accumulation of sediments in the reservoirs. Hence, it is important to manage river discharges at the dams from an integrated viewpoint, whereas currently only hydropower and agricultural requirements are considered. It is also crucial to maintain periods of high discharge, to have enough river energy to transport as much sediments as possible.
We report on a decadal trend of accretionary dynamics in the wetlands of several northwestern Mediterranean deltas and a lagoon
system, all of them with high rates of wetland loss. Wetland vertical accretion and surface elevation change were measured
at 55 riverine, marine, and impounded sites in four coastal systems: the Ebro delta, Spain; the Rhône delta, France; and the
Po delta and Venice Lagoon, Italy. Vertical accretion and elevation change ranged between 0 and 25mmyear−1 and were strongly correlated. The highest rates of elevation gain occurred at riverine sites where vertical accretion was
highest. We conclude that areas with high sediment input, mainly riverine, are the only ones likely to survive accelerated
sea-level rise, especially if recent higher estimates of 1m or more in the twenty-first century prove to be accurate. This
is the first study where the importance of river input on wetland survival has been demonstrated at a decadal time scale over
a broad geographical area.
KeywordsDeltas–Sediment input–Flood pulse–Sea-level rise–Mediterranean wetlands
Soils (n=250) were collected from ten salt and brackish-water marshes of North Carolina and analyzed for organic matter content
by loss on ignition (LOI) and Kjeldahl nitrogen (KN). Total organic carbon and total nitrogen were determined on the same
samples using an elemental CHN analyzer. Regression analyses indicated that LOI and KN were excellent estimators of organic
C (R2=0.990) and total N(R2=0.986), respectively, in low clay content (0–11%) marsh soils containing a wide range of soil organic C (0.1–28%) and total
N (0–1.6%). A quadratic equation best described the relationship between organic C and organic matter (Organic C=0.40 [LOI]
+0.0025 [LOI]2) while a linear model accurately described the relationship between total N and Kjeldahl N (Total N=1.048 [KN]−0.010). The
proportion of organic C in organic matter (C/OM) increased with increasing soil organic matter content, probably as a result
of aging. Young marshes, which are characterized by low soil organic content contain C/OM ratios similar to emergent vegetation
(40–45%). In old organic soils (70–80% organic matter), C/OM increased to 57–60% due to accumulation of reduced organic materials.
River deltas are ecologically and economically valuable coastal ecosystems but low elevations make them extremely sensitive to relative sea level rise (RSLR), i.e. the combined effects of sea level rise and subsidence. Most deltas are subjected to extensive human exploitation, which has altered the habitat composition, connectivity and geomorphology of deltaic landscapes. In the Ebro Delta, extensive wetland reclamation for rice cultivation over the last 150 years has resulted in the loss of 65% of the natural habitats. Here, we compare the dynamics of habitat shifts under two departure conditions (a simulated pristine delta vs. the human-altered delta) using the Sea Level Affecting Marshes Model (SLAMM) under the 4.5 and 8.5 RCP (Representative Concentration Pathways) scenarios for evaluating their resilience to RSLR (i.e. resistance to inundation). Results showed lower inundation rates in the human delta (~10 to 22% by the end of the century, depending on RCP conditions), mostly due to ~4.5 times lower initial extension of coastal lagoons compared to the pristine delta. Yet, inundation rates from ~15 to 30% of the total surface represent the worst possible human scenario, assuming no flooding protection measures. Besides, accretion rates within rice fields are disregarded since this option is not available in SLAMM for developed dry land. In the human delta, rice fields were largely shifted to other wetland habitats and experienced the highest reductions, mostly because of their larger surface. In contrast, in the pristine delta most of the habitats showed significant decreases by 2100 (~2 to 32% of the surface). Coastal infrastructures (dykes or flood protection dunes) and reintroduction of riverine sediments through irrigation channels are proposed to minimize impacts of RSLR. In the worst RCP scenarios, promoting preservation of natural habitats by transforming unproductive rice fields into wetlands could be the most sustainable option.
Human impacts and emerging mega-trends such as climate change and energy scarcity will impact natural resource management in this century. This is especially true for deltas because of their ecological and economic importance and their sensitivity to climate change. The Mississippi delta is one of the largest in the world and has been strongly impacted by human activities. Currently there is an ambitious plan for restoration of the delta. This book, by a renown group of delta experts, provides an overview of the challenges facing the delta and charts - a way forward to sustainable management.
We evaluated the ability of freshwater riparian wetlands along a gradient of ecological condition to act as sinks
for carbon and sediment. We compared rates of carbon accretion and soil accretion across 20 wetlands in the
Lake Erie Drift Plain and the Ridge and Valley ecoregions. Soil cores were collected and analyzed using 137Cs
dating to quantify long-term (∼50 year) rates of sediment and carbon accumulation. Data on hydrology and
floristic quality were used to help explain variability in rates. Sites were classified as being in low, moderate, or
high ecological condition based on a rapid assessment method, which was verified by their floristic quality.
Wetlands of low ecological condition (more human disturbance) had higher mean soil accretion and carbon
accretion rates. Soil accretion averaged 0.24 ± 0.17 cm yr−1 and 0.14 ± 0.04 cm yr−1 in low condition sites
and high condition sites, respectively. Carbon accretion averaged 88 ± 50 gC m−2 yr−1 in low condition and
65 ± 27 gC m−2 yr−1 in high condition sites. Low condition sites had lower mean soil carbon concentrations in
the upper 10 cm of the soil profile, suggesting that the higher carbon burial in these sites was related to allochthonous
carbon inputs in incoming sediment, rather than autochthonous carbon inputs. There were also
striking rate differences between ecoregions. Erie Drift Plain wetlands had significantly higher mean soil accretion
rates, compared to Ridge and Valley wetlands. These data indicate that freshwater wetlands play a role in
regulating climate by acting as carbon sinks and that anthropogenic disturbance can impact rates of carbon
burial.
In October 1993 and January 1994, two large floods with peak discharge of 9800 and 10,980 m³/s and total suspended solid transport of 10.7 × 10⁶ and 9.7 × 10⁶ tons, respectively, occurred on the Rhône River. Both floods led to multiple levee breeches in the Northern part of the delta resulting in the introduction of 131 × 10⁶ and 54.9 × 10⁶ m³ of river water, respectively. In both cases, the flood water drained to the southern lagoons and was partly pumped directly back to the Rhône or to the sea. Most of the 390,000 tons of sediment introduced remained in the Northern inundated area with accretion ranging from 70 mm near the breaches to 4 mm 6–8 km away. This last value is close to the mean accretion value (3.7 mm) inferred from the water budget and the estimation of the total quantity of sediment introduced in the flooded area. In a small area near the mouth of the Rhône river still receiving natural overflow from the river, total deposition during both floods was as high as 10 cm. The Rhône delta is facing an uncertain future with projected sea-level rise. The results of this study show that large introductions of river water can help sustain the delta in the face of climate change. Controlled introductions of river water using riverside closable structures, as in being done in other deltas, could be done in a way that delivers water and sediments to the places where it is needed most and at the same time protect important infrastructure.
Secondarily treated municipal effluent has been discharged since 2006 into a 1439 ha cypress-tupelo forested wetland in coastal Louisiana. Changes in carbon stocks of trees and soils as well as emissions of methane and nitrous oxide were measured over a one-year period and compared to baseline conditions derived from the scientific literature. Methods and equations were applied from the American Carbon Registry (ACR) wetland carbon offset methodology ‘Restoration of Degraded Deltaic Wetlands of the Mississippi Delta’. The cumulative carbon sequestered in the Project scenario was 4090 mt CO2e/y by trees and 13,752 mt CO2e/y by soils, while 32,982 mt CO2e/y of greenhouse gasses were emitted. The Baseline scenario sequestered 3790 mt CO2e/y by trees and 2435 mt CO2e/y by soils while emitting 70,870 mt CO2e/y in greenhouse gasses. The net difference between the Project and Baseline emissions was 11,617 mt CO2e/y if greenhouse gasses were omitted and 49,505 mt CO2e/y if greenhouse gasses were included. This study demonstrates the potential of using forested wetlands receiving treated municipal effluent for the net sequestration of carbon.
We carried out a 1.5-year study of the fate of organic carbon during experimental wetland loss using an herbicide at freshwater, brackish and saltwater emergent wetlands. Total carbon stocks in the upper 50 cm of the soil horizon were 15.0 ± 0.5 kg C/m2 (222.8 mt CO2e/ac) at the freshwater site, 11.1 ± 0.9 kg C/m2 (164.7 mt CO2e/ac) at the brackish site, and 8.5 ± 1.4 kg C/m2 (125.7 mt CO2e/ac) at the saltwater site. There were no significant differences detected in decomposition between the treatment and reference plots, which had 39.4 to 41.5 % material remaining by the end of the study at the three sites. The plots treated with herbicide had decreased elevation of −4.24 cm, −1.56 cm and −1.48 cm at the freshwater, brackish and saltwater sites, respectively, which equate to a mass loss of soil organic carbon of 1273 g C/m2, 389 g C/m2 and 207 g C/m2, respectively. Results indicate statistically greater greenhouse gasses were emitted at the brackish and saltwater plots treated with herbicide compared to the reference plots, with up to 4.2 mt CO2e/ac emitted at the brackish site and 3.1 mt CO2e/ac emitted at the saltwater site during the first 1.5 years of the study.
Climate change and sea level rise (SLR) are global impacts threatening the sustainability of coastal territories and valuable ecosystems such as deltas. The Ebro Delta is representative of the vulnerability of coastal areas to SLR. Rice cultivation is the main economic activity in the region. Rice fields occupy most of the delta (ca. 65%) and are vulnerable to accelerated SLR and consequent increase in soil salinity, the most important physical factor affecting rice production. We developed a model to predict the impacts of SLR on soil salinity and rice production under different scenarios predicted by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change by coupling data from Geographic Information Systems with Generalized Linear Models. Soil salinity data were measured in agricultural parcels and rice production from surveys among farmers. The correlation between observed and soil salinity predicted values was high and significant (Pearson's r=0.72, P<0.0001), thus supporting the predictive ability of the model. Soil salinity was directly related to distances to the river, to the delta inner border, and to the river old mouth, while clay presence, winter river flow and surface elevation were inversely related to it. Surface elevation was the most important variable in explaining soil salinity. Rice production was negatively influenced by soil salinity, thus the models predict a decrease from higher elevation zones close to the river to the shoreline. The model predicts a maximum reduction in normalized rice production index from 61.2% in 2010 to 33.8% by 2100 in the worst considered scenario (SLR=1.8m), with a decrease of profit up to 300 € per hectare. The model can be applied to other deltaic areas worldwide, and help rice farmers and stakeholders to identify the most vulnerable areas to SLR impacts.
Accretion and surface elevation change were measured in riverine, marine and impounded wetland habitats of the Rhone Delta from 1992 to 1996 using a sedimentation-erosion table (SET) and marker horizons. Riverine habitat accreted at a significantly greater rate than the other habitats throughout the period of study, averaging 13.4 +/- 7.0 mm yr(-1) compared to 1.1 +/- 0.1 and 1.2 +/- 0.5 mm yr(-1) for impounded and marine habitats, respectively. Elevation change was similar to accretion in the riverine habitat (11.3 +/- 6.1 mm yr(-1)), reflecting an average 16% compaction and consolidation of recent, primarily mineral deposits. Over time, elevation change and accretion became more linearly correlated, showing that variation between these two processes decreases with time. Accretion and elevation change in impounded and marine habitats were less than current rates of relative sea-level rise, a result of isolation from riverine flooding and the lack of marine storms during the study period. There was more than 30 mm of accretion in the riverine habitat deposited during the 50 and 90-year floods in the Rhone in 1993 and 1994. Impounded and marine habitats gave no record of these events. Wetlands connected to the Rhone River can therefore accrete rapidly from sediments deposited during floods. Impoundments, the most common "natural areas" left in the delta, are not keeping pace with relative sea-level rise and may become vulnerable to increased sea-level rise if current management practices are continued.
Several attempts to estimate the suspended load and the sediment deficit caused by the reservoirs have been carried out in the lower Ebro River. However, existing data are scarce, scattered along time and space, and obtained under different hydrological conditions and methods. This study estimate the presently suspended sediment load of the lowermost Ebro River, using field data collected during three consecutive years at different verticals of a cross-section and covering a large range of discharges. In addition, the daily suspended load for the last 30 years has been reconstructed and validated. The suspended load for the period 2007–2010 has been estimated at 84,000 t/y (±9800 t) while 99,500 t/y (±18,000 t) accounted for 1981–2010 period. Approximately, 80% of the total suspended load (period 2007–2010) has been transferred as inorganic load. A significant seasonal variability in the total (organic and inorganic) suspended load is observed. Therefore, two distinct cycling phases in the suspended load production and transfer has been inferred: an initial phase in which the sediment was prepared into the basin followed by a second phase in which most of the load was transferred downstream. These two phases are governed by the relative temporal location of the natural floods and the river regulation from the reservoirs. Nowadays, less than 1% of suspended load is transferred compared to pre-dams construction. The current levels of suspended load are very low and not enough to supply the material needed to maintain the delta elevation and avoid coastal retreat. The sustainability of the lower Ebro River and its delta could only be guaranteed by the implementation of a new reservoir management concept with the allocation of an appropriate liquid and solid flow regime.
Radioactive fallout 137Cs (cesium-137) deposited across the landscape from atmospheric nuclear tests is strongly absorbed on soil particles limiting its movement by chemical and biological processes. Most 137Cs movement in the environment is by physical processes; therefor, 137Cs is a unique tracer for studying erosion and sedimentation. Cesium-137 loss from a watershed has been shown to correlate strongly with soil loss calcualted by the Universal Soil Loss Equation (USLE) or measured from small runoff plates. By measuring spatial patterns of 137Cs in vertical and horizontal planes across the landscape, rates of soil loss or deposition can be measured for different parts of a watershed. Even within landscape units, redistribution of soil can be mapped and erosion or deposition rates for different parts of individual fields measured and mapped. Sediment accumulation rates can be measured by comparing the vertical distribution of 137Cs in sediments with the temporal deposition of fallout 137Cs from the atmosphere to locate sediment horizons. Using these dated sediment horizons, sediment accumultion rates can be measured. Interpretations about the location of these dated horizons must consider particle size of the sediments, reworking of deposited sediments, diffusional movement of 137Cs, and time rates of physical process in the sedimentation process. The 137Cs technique can be used to determine sediment accumulation rates in a wide variety of depositional environments including reservoirs, lakes, wetlands, coastal areas, and floodplains. The bibliography shows that 137Cs has been used widely for studying erosion and sedimentation in many different environments around the world.
The response of deltas to sea level rise (SLR) has mostly been studied from a perspective of human impacts like global warming and impoundment, or from a perspective of natural changes associated with glacial cycles. Here we synthesize the response of deltas to SLR by integrating research looking at past and future evolution to improve the potential to manage deltas to adapt to high rates of SLR. We hypothesize that fluvial-dominated deltas can be managed to survive high rates of SLR (>1 cm year−1) that characterized the post-glacial period and will likely characterize coming centuries due to global warming. There are three known mechanisms for deltas to cope with SLR that are self-reinforcing as the rates increase, tending to enhance the efficiency of the deltaic sedimentary trap:
Eutrophication is now a serious environmental problem worldwide because it disrupts the metabolism of aquatic ecosystems. In the Ebro Delta, intensive rice farming during the 20th century has increased coastal eutrophication and caused ecological and economic impacts. Marsh restoration is as an effective economic and ecological tool to remove nutrients from agricultural runoff, thereby limiting coastal eutrophication impacts and also providing other ecosystem services. The objective of this experimental study was to assess overall N and P concentration reduction, C accumulation and Si buffering in an oligohaline restored marsh receiving nutrient and sediment inputs from river irrigation and rice field drainage waters under different water levels. We established the experimental restored marsh in abandoned deltaic rice fields from August 2009 to June 2012. The study of changes in nutrient concentration was performed in 2010 from June to November. The study of nutrient and carbon accumulation was performed from August 2009 to May 2011. We used two freshwater input type treatments (riverine irrigation and rice field drainage water) and three water level treatments (10, 20 and 30 cm). Our results showed that higher water nutrient concentrations from rice fields caused significantly higher N- NH4+ and P- PO43− concentration reduction (80.76 ± 1.8% and 17.99 ± 3.92% respectively). There was also an export in TP and P- PO43− (−45.08 ± 13.12 and −23.85 ± 8.15%, respectively) in experimental marsh units receiving river irrigation waters. Significantly lower soil redox conditions and higher total maximum aboveground biomass in the IW treatment were associated with lower N- NO3− concentration reduction and higher Si-SiO2 concentration reduction (94.14 ± 0.72% and 58.54 ± 1.08% respectively) than the DW treatment. Higher sediment concentrations from rice fields were associated with higher C accumulation rates (126.10 ± 6.25 g m−2 y−1) compared with experimental marsh units receiving river irrigation waters (99.44 ± 8.23 g m−2 y−1). Higher water levels also increased significantly P- PO43− and Si-SiO2 concentration reduction and C accumulation rates within both water type treatments. Our experimental study showed how multiple mechanisms control N and P concentration reduction, Si buffering and C accumulation. Plant growth may decrease the ability to reduce the input concentration of N- NO3− possibly due to denitrification inhibition via plant oxygenation of marsh soils. Plant uptake may favor Si buffering in the restored marsh, although high water levels may also control Si buffering through higher residence time for diatom uptake. This study indicates that Mediterranean oligohaline restored marshes removed N and P using both river irrigation and rice field drainage waters and also provide C accumulation and Si buffering services. The use of agriculture runoff as a primary source of nutrient and sediment is beneficial for marsh restoration projects focused on C accumulation. In general, higher water levels (20–30 cm) were better for nutrient concentration reduction and C accumulation, but higher water levels were also associated with lower plant biomass.
Present-day altered distribution of the natural habitats in the Ebro Delta is consequence of intensive human settlement in the last two centuries. We developed spatial predictive models of potential natural wetland habitats of the Ebro Delta based on ecogeographical predictors and presence/ pseudo-absence data for each habitat. The independent variables (i.e elevation, distance from the coast, distance from the river and distance from the inner border) were analysed using Generalized Additive Models (GAMs). Elevation and the distance from the coast appeared as key predictors in most of the coastal habitats (coastal lagoons, sandy environments, Salicornia-type marshes and reed beds), whereas distances from the river and from the inner border were relevant in the most terrestrial or inland habitats (salt meadows, Cladium-type marshes and riparian vegetation). Our findings suggest that the most inland habitats (i.e. Cladium-type marshes, salt meadows and riparian vegetation) would have undergone a severe reduction (higher than 90%), whereas in the most coastal habitats (coastal lagoons, sandy environments, Salicornia-type marshes) the reduction in relation to their potential distribution would be around 70%. This modelling approach can be applied to other deltaic areas, since all them share a similar topographic.
Maintaining the ecological diversity and hydrologic connectivity of freshwater delta systems depends on regular recharge of floodplains with river water, which can be difficult to observe on the ground. Rivers that form deltas often carry large amounts of suspended sediment, but floodplain lakes and wetlands usually have little sediment in suspension. Remote observation of high sediment water in lakes and wetlands therefore often indicates connectivity with the river network. In this study, we use daily 250-m MODIS imagery in band 1 (620–670 nm) and band 2 (841–876 nm) to monitor suspended sediment transport and, by proxy, hydrologic recharge in the Peace–Athabasca Delta, Canada. To identify an appropriate suspended sediment concentration (SSC)-reflectance model, we compare 31 published empirical equations using a field dataset containing 147 observations of SSC and in situ spectral reflectance. Results suggest potential for spatial transferability of such models, but success is contingent on the equation meeting certain criteria: 1) use of a near infrared band in combination with at least one visible band, 2) development based on SSCs similar to those in the observed region, and 3) a nonlinear form. Using a highly predictive SSC-reflectance model (Spearman's ρ = 0.95), we develop a twelve-year time series of SSC in the westernmost end of Lake Athabasca, observe the timing and sources of major sediment flux events, and identify a threshold river discharge of ~ 1700 m3/s above which SSC in Lake Athabasca is clearly associated with flow in the Athabasca River. We also track the influx of Athabasca River water to floodplain lakes, and in three of the lakes identify distinct discharge thresholds (1040 m3/s, 1150 m3/s, and 1850 m3/s) which result in lake recharge. For each of these lakes, we find a statistically significant decline in the threshold exceedence frequency since 1970, suggesting less frequent recharge during the summer.
Suspended sediment concentrations and fluxes between Fourleague Bay, Louisiana and the northern Gulf of Mexico were sampled every 3h for 3 months to examine the importance of atmospheric cold fronts and riverine forcing on the functioning of this estuarine system. A cold front index was developed and used to identify major winter frontal passages likely to have the largest effects on material concentrations and transport. Suspended sediment concentrations ranged from 11 to 1527mg l−1; the highest values occurred during winter frontal passages and the lowest during calm periods. High concentrations are generated by a continuous source of sediment from the Atchafalaya River and resuspension of benthic sediment via high intensity winds associated with cold fronts along with sufficient duration to keep the sediment in suspension. Spring peak discharge of the Atchafalaya River increased water levels and sediment concentrations in the bay leading to strong seasonal net exports of water (1·02×109m3) and sediment (1·72×108kg) into the Gulf of Mexico through Oyster Bayou over the 89-day study. Net fluxes associated with tidal forcing were nearly balanced with a small net export due to freshwater input. The combination of high volumes of water originating from the northern bay and the restricted outlet to the Gulf often cause increased water levels and inundation of the surrounding marshes and potential advection of sediments onto the marsh surface. The results suggest that marsh drainage often increases the particulate organic carbon export as a result of marsh flushing.
Soil organic C, N, and P were measured in salt, brackish, and tidal freshwater marshes in river-dominated estuaries (Ogeechee, Altamaha, and Sarilla) of the Georgia coast to evaluate the effects of salinity on C, N, and P storage and accumulation. Tidal freshwater marshes had greater concentrarions of organic C (10.81% w/w) and N (0.71% w/w) than brackish (7.71% C,0.50% N) or salt (5.95% C,035% N) marshes. Soil accretion rates of l37Cs were greater in tidal freshwater (4.78 mm yr-1) and brackish marshes (441 mm yr-1) than in salt marshes (1.91 mm yr-1). Consequently, organic C and N accumulation was greater in tidal freshwater (124 and 8.2 g m-2 yr-1) and brackish (93 and 6.5 g m -2 yr-1) marshes than salt marshes (40 and 2.4 g m -2 yr-1). Phosphorus accumulation was greater in the brackish marshes. Lower salinity tidal freshwater and brackish marshes remove more C, N, and P; however, salt marshes dominate the spatial extent of the study area (60%) vs. brackish (33%) and tidal freshwater marshes (7%). Combining measurements of C, N, and P accumulation with tidal marsh area, we estimated that tidal freshwater, brackish, and salt marshes stored or removed the equivalent of 2 to 20% of watershed N inputs entering the estuaries from the terrestrial landscape. After accounting for N2 fixation and denitrification, tidal marshes collectively removed the equivalent of 13 to 32% of the N entering estuaries. Tidal marshes, especially tidal freshwater and brackish marshes, are important for improving water quality and decreasing the impacts of N eutrophication of estuarinc ecosystems. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All rights reserved.
We used field and laboratory measurements, geographic information systems, and simulation modeling to investigate the potential effects of accelerated sea-level rise on tidal marsh area and delivery of ecosystem services along the Georgia coast. Model simulations using the Intergovernmental Panel on Climate Change (IPCC) mean and maximum estimates of sea-level rise for the year 2100 suggest that salt marshes will decline in area by 20% and 45%, respectively. The area of tidal freshwater marshes will increase by 2% under the IPCC mean scenario, but will decline by 39% under the maximum scenario. Delivery of ecosystem services associated with productivity (macrophyte biomass) and waste treatment ( nitrogen accumulation in soil, potential denitrification) will also decline. Our findings suggest that tidal marshes at the lower and upper salinity ranges, and their attendant delivery of ecosystem services, will be most affected by accelerated sea-level rise, unless geomorphic conditions (ie gradual increase in elevation) enable tidal freshwater marshes to migrate inland, or vertical accretion of salt marshes to increase, to compensate for accelerated sea-level rise.
To identify relationships between freshwater input and marsh soil properties, measurements of bulk density, nutrients (carbon [C], nitrogen [N], phosphorus [P]), accretion, and accumulation were compared in tidal marshes of three estuaries of Georgia that varied in delivery of freshwater. Soil organic C and N (0-30 cm) were two times greater in marshes of the freshwater-dominated Altamaha River than in the salt marshes of Doboy Sound and Sapelo River. 137Cs accretion and accumulation of organic C and N were three to five times greater in freshwater-dominated marshes than in salt marshes. The patterns observed in Georgia marshes were geographically general; data for tidal freshwater and brackish marsh soils compiled from 61 studies in the conterminous United States showed lower bulk density and higher percent organic C and N than salt marshes, regardless of geographic region. Salinity, a proxy for freshwater input, was inversely correlated with percent soil organic C and N and with vertical accretion in Georgia marshes and in marshes elsewhere in the conterminous United States. There was no relationship between above- or belowground emergent plant production and salinity of Georgia marshes but the rate of root decomposition was positively related to salinity, and decomposition rate was negatively related to percent soil organic C and C accumulation. In Georgia tidal marshes and elsewhere, soil organic matter content and accumulation are mediated by freshwater through its effects on decomposition. © 2007, by the American Society of Limnology and Oceanography, Inc.
This paper reviews the literature on structure and production of Mediterranean microtidal marshes. Literature on structure
and zonation is relatively abundant but there are relatively few studies of coastal wetland primary productivity in the Mediterranean.
These tidal marshes are poorly flushed because of the low tidal range and freshwater tidal marshes are rare. Most marshes
are found in deltas and fringing coastal lagoons. Recent studies carried out in the Ebre, Po and Rhone deltas show that net
primary production (NPP) of marshes is strongly influenced by soil salinity and flooding. The productivity of these marshes
is generally low, but there are significant exceptions. Minimum values of NPP of emergent vegetation (below-plus above-ground)
were obtained in salt marshes dominated by Arthrocnemum macrostachyum 237 g m−2 y−1), characterized by low flooding frequency and high salt stress. Maximum values (up to 9685 g m−2 y−1) were obtained in fresh marshes dominated by Cladium mariscus, with high flooding frequency. In general terms, Mediterranean microtidal marsheshave low production due to salt stress and
weak tidal flushing. This suggests that there is low export of marsh production to coastal lagoons, bays and open coastal
waters.
Despite the frequent citation of wetlands as effective regulators of water quality, few quantitative estimates exist for their
cumulative retention of the annual river loads of nutrients or sediments. Here we report measurements of sediment accretion
and associated carbon, nitrogen, and phosphorus accumulation as sedimentation over feldspar marker horizons placed on floodplains
of the non-tidal, freshwater Coastal Plain reaches of seven rivers in the Chesapeake Bay watershed, USA. We then scale these
accumulation rates to the entire extent of non-tidal floodplain in the Coastal Plain of each river, defined as riparian area
extending from the Fall Line to the upper limit of tidal influence, and compare them to annual river loads. Floodplains accumulated
a very large amount of material compared to their annual river loads of sediment (median among rivers=119%), nitrogen (24%),
and phosphorus (59%). Systems with larger floodplain areas and longer floodplain inundation retained greater proportions of
riverine loads of nitrogen and phosphorus, but systems with larger riverine loads retained a smaller proportion of that load
on floodplains. Although the source and long-term fate of deposited sediment and associated nutrients are uncertain, these
fluxes represent the interception of large amounts of material that otherwise could have been exported downstream. Coastal
Plain floodplain ecosystems are important regulators of sediment, carbon, and nutrient transport in watersheds of the Chesapeake
Bay.
Soil accretion, sediment deposition, and nutrient (N, P, organic C) accumulation were compared in floodplain and depressional
freshwater wetlands of southwestern Georgia, USA to evaluate the role of riverine (2600 km2 catchment) versus depressional (<10 km2 catchment) wetlands as sinks for sediment and nutrients. Soil cores were collected from three floodplain (cypress-gum) and
nine depressional (three each from cypress-gum forest, cypress-savannah, and herbaceous marsh) wetlands and analyzed for radionuclides
(137Cs, 210Pb), bulk density, N, P, and organic C to quantify recent (30-year) and long-term (100-year) rates of sediment and nutrient
accumulation. There was no significant difference in organic C, N, or sediment accumulation between depressional and floodplain
wetlands. However, P accumulation was 1.5 to three times higher in the floodplain (0.12–0.75 g/m2/yr) than in the depressional wetlands (0.08–0.25 g/m2/yr). Sediment and nutrient accumulations were highly variable among depressional wetland types, more so than between depressional
and floodplain wetlands. This variability likely is the result of differences in historical land use, hydrology, vegetation
type, NPP, and perhaps fire frequency. Mean (n=12) one-hundred-year rates of sediment deposition (1036 g/m2/yr), organic C (79 g/m2/yr), N (6.0 g/m2/yr), and P accumulation (0.38 g/m2/yr) were much higher than 30-year rates (sediment=118 g/m2/yr, C=20 g/m2/yr, N=1.5 g/m2/yr, P =0.09 g/m2/yr). Higher 100-year (210Pb) sediment and nutrient accumulations likely reflect the greater numbers of farms, greater grazing by livestock, and the
absence of environmentally sound agricultural practices in southwestern Georgia at the turn of the century. Our findings suggest
that the degree of anthropogenic disturbance within the surrounding watershed regulates wetland sediment, organic C, and N
accumulation. Phosphorus accumulation also is greater is floodplain wetlands that have large catchments containing fine textured
(clay) sediments that are co-deposited with P.