Carbon Sources in the Sediments of a Restoring vs. Historically Unaltered Salt Marsh (original) (raw)
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Organic Carbon Isotope Systematics of Coastal Marshes
Estuarine Coastal and Shelf Science, 1997
Measurements of nitrogen, organic carbon and δ13C are presented forSpartina-dominated marsh sediments from a mineral marsh in SW Netherlands and from a peaty marsh in Massachusetts, U.S.A. δ13C of organic carbon in the peaty marsh sediments is similar to that ofSpartinamaterial, whereas that in mineral marshes is depleted by 9-12‰. It is argued that this depletion in δ13C of organic matter in marsh sediments is due to trapping of allochthonous organic matter which is depleted in13C. The isotopic composition and concentration of organic carbon are used in a simple mass balance to constrain the amount of plant material accumulating in marsh sediments, i.e. in terms of the so-called net ecosystem production. Net ecosystem production (∼2-100 g C m-2year-1) is a small fraction (1-5%) of plant production (∼2000 g C m-2year-1). This small amount of plant material being preserved is nevertheless sufficient to support marsh-accretion rates similar to the rate of sea-level rise.
Refractory organic matter in coastal salt marshes-effect on C sequestration calculations
• We studied how refractory carbon inputs affect marsh age and C sequestra-tion budgets. • We measured Δ 14 C and δ 13 C of total organic carbon (TOC) and refractory carbon (C RF). • TOC was dominated by autochthonous inputs, C RF was dominated by allochtho-nous C. • Allochthonous C delivery was controlled by the size and slope of each watershed. • Steep-gradient rivers delivered Δ 14 C-depleted C RF to their estuarine marshes. Editor: Mae Sexauer Gustin The age and ability of salt marshes to accumulate and sequester carbon is often assessed using the carbon isotopic signatures (Δ 14 C and δ 13 C) of sedimentary organic matter. However, transfers of allochthonous refractory carbon (C RF) from the watershed to marshes would not represent new C sequestration. To better understand how refrac-tory carbon (C RF) inputs affect assessments of marsh age and C sequestration, Δ 14 C and δ 13 C of both total organic carbon (TOC), C RF , and non-C RF organic matter fractions were measured in salt marshes from four contrasting systems on the North Atlantic coast. To our knowledge, no salt marsh sediment study has considered refractory or allochthonous carbon in carbon budget calculations or the impact on chronologies. Stable and radiogenic isotope data suggest that while TOC was dominated by autochthonous plant inputs, C RF was dominated by locally recycled or allochthonous C, the delivery of which was controlled by the size and slope of each watershed. Steep-gradient rivers analyzed delivered Δ 14 C-depleted C RF to their estuarine marshes, while the site located in the low-gradient river was associated with larger C RF content. Finally, the marsh isolated from riverine input contained the least fraction of TOC as C RF. Laterally transported C RF caused only a small offset in Δ 14 C in relation to TOC in low-gradient systems (average Δ 14 C offset was −44.4 and −24.2‰ at each location). However, the presence of allochthonous Δ 14 C-depleted C RF in sediments of steep-gradient rivers led to large overestimates of the time of organic matter deposition (i.e. apparent age was older than the 'true' time of deposition) (Δ 14 C offset ranged from −170.6 to −528.9‰). Further, reliance on TOC or loss on ignition analyses to calculate C
Carbon Stocks and Accumulation Rates in Salt Marshes of the Pacific Coast of Canada
2018
Tidal salt marshes are known to accumulate "blue carbon" at high rates relative to their surface area and have been put forth as a potential means for enhanced CO2 sequestration. However, estimates of salt marsh carbon accumulation rates are based on a limited number of marshes globally and the estimation of carbon accumulation rates require detailed dating to provide accurate estimates. We address one data gap along the Pacific Coast of Canada by estimating carbon stocks in 34 sediment cores and estimating carbon accumulation rates using 210 Pb dating on four cores from seven salt marshes within the Clayoquot Sound UNESCO Biosphere Reserve and Pacific Rim National Park Reserve of Canada (49.2° N, 125.80° W). Carbon stocks averaged 80.6 ± 43.8 megagrams of carbon per hectare (Mg C ha-1) between the seven salt marshes, and carbon accumulation rates averaged 146 ± 102 grams carbon per square meter per year (g C m-2 yr-1). These rates are comparable to those found in salt marshes further south along the Pacific coast of North America (32.5-38.2° N) and at similar latitudes in Eastern Canada and Northern Europe (43.6-55.5° N). The seven Clayoquot Sound salt marshes currently accumulate carbon at a rate of 54.28 Mg C yr-1 over an area of 46.94 ha, 87 % of which occurs in the high marsh zone. On a per-hectare basis, Clayoquot Sound salt marsh soils accumulate carbon at least one order of magnitude more quickly than the average of global boreal forest soils, and approximately two times larger than rates for forests in British Columbia. However, because of their relatively small area, we suggest that their carbon accumulation rate capacity could best be considered as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services.
Updated estimates of carbon accumulation rates in coastal marsh sediments
Biogeosciences, 2014
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 storage in these vulnerable coastal habitats, thus hindering the assessment of their importance. Combining direct data and indirect estimation, this study compiled studies involving 143 sites across the Southern and Northern hemispheres, and provides an updated estimate of the global average carbon accumulation rate (CAR) at 244.7 g Cm−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 estimated at 10.2 TgC yr−1. Latitude, tidal range and elevation appear to be important drivers for CAR of salt marsh sediments, with considerable variation among different biogeographic 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 availability.
Origin of organic carbon in the topsoil of Wadden Sea salt marshes
Marine Ecology Progress Series, 2019
Blue carbon ecosystems, including salt marshes, play an important role in the global carbon cycle because of their high efficiency to store soil organic carbon (OC). Few studies focus on the origin of OC stored in salt-marsh soils, which comes from either allochthonous or autochthonous sources. The origin, however, has important implications for carbon crediting approaches because the alternative fate of allochthonous OC (AllOC), i.e. if it had not accumulated in the Blue C ecosystem, is unclear. Here, we assessed the origin of OC in two mainland salt-marsh sites of the European Wadden Sea, analyzing δ 13 C of topsoil (0-5 cm) samples, freshly deposited sediment (allochthonous source), and of above-and belowground biomass of vegetation (autochthonous sources). We tested for effects of geomorphological factors, including elevation and the distance to sediment sources, and of livestock grazing, as the most important land-use form, on the relative contributions of allochthonous versus autochthonous sources to the topsoil OC stock. A negative effect of distance to the creek on the relative contribution of AllOC was found at only one of the two salt marshes, probably 2 due to differences in micro-topography between the two salt marshes. Additionally, the relative contribution of AllOC increased with increasing distance to the marsh edge in areas without livestock-grazing, while it decreased in grazed areas. Our findings demonstrate that spatial factors such as surface elevation and distance to a sediment source, which have been found to determine the spatial patterns of sediment deposition, also are important factors determining the relative contribution of AllOC to topsoil OC stocks of salt marshes. Furthermore, we provide first evidence that livestock-grazing can reduce the relative contribution of AllOC to the soil OC stock. These findings thereby yield important implications for C crediting and land-use management.
Assessing coastal carbon variability in two Delaware tidal marshes
Journal of Coastal Conservation, 2020
Coastal wetlands provide numerous ecosystem services, including the ability to sequester and store carbon. Recent initiatives, such as the U.S. Climate Alliance’s National Working Lands Challenge, have sought to better understand and quantify this ‘blue carbon’ storage as a land management approach to maintain, or potentially offset, atmospheric carbon emissions. To build on this effort locally, loss on ignition and elemental analyses were used to assess sediment organic matter, dry bulk density, and carbon density variability within the root zone of a mesohaline and oligohaline tidal marsh in Delaware. Additionally, we assessed sediment carbon variability at depth greater than one meter and quantified the black carbon fraction in the mesohaline tidal marsh. Organic matter concentrations ranged between 11.85 ± 1.19% and 23.12 ± 6.15% and sediment carbon density ranged from 0.03 ± 0.01 g cm−3 to 0.06 ± 0.02 g cm−3 with both found to significantly differ between the mesohaline and oli...
PLOS ONE
Eutrophic conditions in estuaries are a globally important stressor to coastal ecosystems and have been suggested as a driver of coastal salt marsh loss. Potential mechanisms in marshes include disturbance caused by macroalgae accumulations, enhanced soil sulfide levels linked to high labile carbon inputs, accelerated decomposition, and declines in belowground biomass that contribute to edge instability, erosion, and slumping. However, results of fertilization studies have been mixed, and it is unclear the extent to which local environmental conditions, such as soil composition and nutrient profiles, help shape the response of salt marshes to nutrient exposure. In this study, we characterized belowground productivity and decomposition, organic matter mineralization rates, soil respiration, microbial biomass, soil humification, carbon and nitrogen inventories, nitrogen isotope ratios, and porewater profiles at high and low marsh elevations across eight marshes in four estuaries in Ca...
Estuaries and Coasts, 2020
Coastal wetlands can sequester large amounts of organic carbon (OC), providing an additional motivation for the preservation and restoration of these ecosystems. In Tampa Bay (Florida, USA), created coastal wetlands are initially planted with Spartina spp., but nearly all sites naturally transition into mangrove forests. It was hypothesized that carbon storage in the created wetlands would increase with site age due to the accumulation of soil organic carbon and replacement of salt marsh vegetation with mangrove forests. Mature, mangrove-dominated sites had higher total organic carbon stocks (138.7 ± 13.8 Mg C ha−1) than middle-aged transitional sites (85.6 ± 25.5 Mg C ha−1) or young salt marshes (34.5 ± 7.7 Mg C ha−1). Mature sites consisted of tall trees (> 130 cm tall) and scarce salt marsh vegetation. Transitional sites contained mangrove scrubs (30–130 cm tall) and seedlings (< 30 cm tall) while still supporting salt marsh vegetation; younger sites were dominated by salt marsh vegetation and had no trees. Belowground OC constituted the greatest carbon pool (59.4% of the total OC stock), but belowground OC stocks were not significantly different among the site age classes, suggesting that aboveground OC stocks drove the difference in total OC stocks. The total carbon accumulation rate, including both aboveground and belowground OC, was 4.7 Mg C ha−1 year−1 across the 26-year chronosequence. This study has demonstrated that carbon storage in created coastal wetlands is correlated to wetland age, indicating that these ecosystems have the potential to become significant sources of OC storage.
Carbon accumulation rates are highest at young and expanding salt marsh edges
Communications earth & environment, 2022
An objective of salt marsh conservation, restoration, and creation is to reduce global carbon dioxide levels and offset emissions. This strategy hinges on measurements of salt marsh carbon accumulation rates, which vary widely creating uncertainty in monetizing carbon credits. Here, we show the 14-323 g C m −2 yr −1 range of carbon accumulation rates, derived from cores collected at seven sites in North Carolina U.S.A., results from the landward or basinward trajectory of salt marsh colonization and the intertidal space available for accretion. Rates increase with accelerating sea-level rise and are highest at young and expanding marsh edges. The highest carbon densities are near the upland, highlighting the importance of this area for building a rich stock of carbon that would be prevented by upland development. Explaining variability in carbon accumulation rates clarifies appraisal of salt marsh restoration projects and landscape conversion, in terms of mitigating greenhouse gas emissions.
Soil Organic Carbon Storage in Restored Salt Marshes in Huntington Beach , California Cover
2019
for funding this project as the laboratory component of the Fall 2011 Ecosystems Ecology course. Kody Cabreros, Lauren Cruz, Jessica Jung, and Elizabeth Malcolm contributed to the field and laboratory aspects of this project. Dr. J. Patrick Megonigal at the Smithsonian Environmental Research Center generously provided the static chambers used to measure net ecosystem respiration. The Board of the Huntington Beach Wetlands Conservancy under the leadership of Dr. Gordon Smith provided access to field sites and valuable insights into the history and ecology of these ecosystems. Comments from 2 anonymous reviewers greatly improved this manuscript. Drs.