An official website of the United States government
Blue carbon habitats, such as mangroves and salt marshes, have been recognized as carbon burial hotspots; however, methods on measuring blue carbon stocks have varied and thus leave uncertainty in global blue carbon stock estimates. This study analyzes blue carbon stocks in northern Florida wetlands along the Atlantic and Gulf coasts. Carbon measurements within 1–3m length vibracores yield total core stocks of 9.9–21.5 kgC·m −2 and 7.7–10.9 kgC·m −2 for the Atlantic and Gulf coast cores, respectively. Following recent IPCC guidelines, blue carbon stock estimates in the top meter are 7.0 kgC·m −2 –8.0 kgC·m −2 and 6.1 kgC·m −2 –8.6 kgC·m −2 for the Atlantic and Gulf cores, respectively. Changes in stable isotopic (δ 13 C, C/N) and lignin biomarker (C/V) indices suggest both coastlines experienced salt marsh and mangrove transgressions into non-blue carbon habitats during the mid- to late-Holocene following relative sea-level rise. These transgressions impact carbon storage within the cores as the presence of carbon-poor soils, characteristic of non-blue carbon habitats, result in lower 1m carbon stocks in north Florida Gulf wetlands, and a deeper extent of carbon-rich soils, characteristic of blue carbon habitats, drive higher 1m and total carbon stocks in north Florida Atlantic wetlands. Future blue carbon research should assess carbon stocks down to bedrock when possible, as land-cover and/or climate change can impact different depths across localities. Ignoring carbon-rich soil below the top meter of soil may underestimate potential carbon emissions based on these changes.
more »
« less
Minerogenic salt marshes can function as important inorganic carbon stores
Abstract Stocks and fluxes of soil inorganic carbon have long been ignored in the context of coastal carbon sequestration, and their implications for the climate cooling effect of blue carbon ecosystems are complex. Here, we investigate the role of soil inorganic carbon in five salt marshes along the northern coast of the European Wadden Sea, one of the world's largest intertidal areas, harboring ~ 20% of European salt‐marsh area. We demonstrate a substantial contribution of inorganic carbon (average: 29%; range: 7–57%) to the total soil carbon stock of the top 1 m. Notably, inorganic exceeded organic carbon stocks in one of the studied sites; a finding that we ascribe to site geomorphic features, such as proximity to marine calcium carbonate sources and hydrodynamic exposure. Contrary to our hypothesis that inorganic carbon stocks would decline along the successional gradient from tidal flat to high marsh, as carbonate deposits would progressively dissolve in increasingly organic‐rich rooted sediments, our findings demonstrate the opposite pattern—an increase in inorganic carbon stocks along the successional gradient. This suggests that the dissolution of calcium carbonates in the root zone is counterbalanced by other processes, such as trapping of sedimentary carbonates by marsh vegetation and calcium carbonate precipitation in anaerobic subsoils. In the context of blue carbon, it will be critical to develop an improved understanding of these plant‐ and microbiota‐mediated processes in calcium carbonate cycling.
more »
« less
- Award ID(s):
- 2051602
- PAR ID:
- 10406643
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 68
- Issue:
- 4
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 942-952
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Environmental gradients can affect organic matter decay within and across wetlands and contribute to spatial heterogeneity in soil carbon stocks. We tested the sensitivity of decay rates to tidal flooding and soil depth in a minerogenic salt marsh using the tea bag index (TBI). Tea bags were buried at 10- and 50- cm along transects sited at lower, middle, and higher elevations that paralleled a headward eroding tidal creek. Plant and animal communities and soil properties were characterized once while replicate tea bags and porewaters were collected 3 and 4 times respectively over one year.more » « less
-
Coastal ecosystems rapidly transform as sea levels rise faster than ecosystems can build elevation through biological processes that accrete organic matter and inorganic sediment. Benthic microbial communities (periphyton) are a crucial driver of sediment accretion in coastal wetlands by forming, trapping, and stabilizing sediments. Inorganic sediments can be either generated in situ by mineral-accreting organisms (e.g., calcium carbonates by periphyton), or materials can be transported from a different origin when sediments become resuspended and displaced, such as during high-wind weather events. In situ-generated sedimentary materials may contribute significantly to elevation gains. This study examines the drivers of coastal periphyton mineral production and whether periphytic diatoms may be used to characterize gradients in these drivers. Periphyton mineral production rates and diatom assemblage composition were measured along three coastal gradients of surface water salinity, conductivity, pH, and periphyton nutrient content in the Biscayne Bay Coastal Wetlands of South Florida. Periphyton mineral production rates ranged from 0.20-0.53 g/m2/d and were greatest at sites with the highest periphyton total carbon and mineral content while lowest at sites with the highest periphyton organic content and total nitrogen and soil depth. Diatom assemblages that sorted consistently along the coastal salinity gradient were reliable indicators of periphyton mineral production, with seven taxa indicating high rates and seven indicating low rates. Diatoms can provide a helpful link between biotic and abiotic processes, indicating where periphyton-driven mineral production contributes most to inorganic carbon cycling and mineral-driven elevation recovery and, hence, to resiliency to sea level rise.more » « less
-
Abstract Drylands occupy nearly 40% of the land surface and comprise a globally significant carbon reservoir. Dryland‐atmosphere carbon exchange may regulate interannual variability in atmospheric CO2. Quantifying soil respiration rates in these environments is often complicated by the presence of calcium carbonates, which are a common feature of dryland soils. We show with high‐precision O2measurements in a laboratory potted soil experiment that respiration rates after watering were similar in control and carbonate treatment soils. However, CO2concentrations were up to 72% lower in the carbonate treatment soil because CO2was initially consumed during calcite dissolution. Subsequently, CO2concentrations were over 166% greater in the carbonate treatment soil as respiration slowed and calcite precipitated, releasing CO2. Elevated δ13C values of soil CO2(>6‰ higher in the treatment than control) confirm that observed differences were due to calcite dissolution. These findings demonstrate that calcite dissolution and precipitation can occur rapidly enough to affect soil gas compositions and that changes in soil CO2are not always directly related to changes in soil respiration rates. Studies of local soil respiration rates and carbon exchange are likely to be influenced by dissolution and precipitation of calcium carbonates in soils. We estimate that one fifth of global soil respiration occurs in soils that contain some amount of soil carbonate, underscoring the need to account for its obscuring effects when trying to quantify soil respiration and net ecosystem exchange on a regional or global scale.more » « less
-
Abstract Salt marshes sequester carbon at rates more than an order of magnitude greater than their terrestrial counterparts, helping to mitigate climate change. As nitrogen loading to coastal waters continues, primarily in the form of nitrate, it is unclear what effect it will have on carbon storage capacity of these highly productive systems. This uncertainty is largely driven by the dual role nitrate can play in biological processes, where it can serve as a nutrient‐stimulating primary production or a thermodynamically favorable electron acceptor fueling heterotrophic metabolism. Here, we used a controlled flow‐through reactor experiment to test the role of nitrate as an electron acceptor, and its effect on organic matter decomposition and the associated microbial community in salt marsh sediments. Organic matter decomposition significantly increased in response to nitrate, even at sediment depths typically considered resistant to decomposition. The use of isotope tracers suggests that this pattern was largely driven by stimulated denitrification. Nitrate addition also significantly altered the microbial community and decreased alpha diversity, selecting for taxa belonging to groups known to reduce nitrate and oxidize more complex forms of organic matter. Fourier Transform‐Infrared Spectroscopy further supported these results, suggesting that nitrate facilitated decomposition of complex organic matter compounds into more bioavailable forms. Taken together, these results suggest the existence of organic matter pools that only become accessible with nitrate and would otherwise remain stabilized in the sediment. The existence of such pools could have important implications for carbon storage, since greater decomposition rates as N loading increases may result in less overall burial of organic‐rich sediment. Given the extent of nitrogen loading along our coastlines, it is imperative that we better understand the resilience of salt marsh systems to nutrient enrichment, especially if we hope to rely on salt marshes, and other blue carbon systems, for long‐term carbon storage.more » « less
