Benthic Biofilm Potential for Organic Carbon Accumulation in Salt Marsh Sediments

Coastal salt marshes are productive environments with high potential for carbon accumulation and storage. Even though organic carbon in salt marsh sediment is typically attributed to plant biomass, it can also be produced by benthic photosynthetic biofilms. These biofilms, generally composed of diatoms and their secretions, are known for their high primary productivity and contribution to the basal food web. The growth of biofilms and the preservation of carbon produced by biofilms depends on the amount of sedimentation; low sedimentation rates will favor decomposition, while high sedimentation rates could decrease biofilm productivity. In this study, we conducted laboratory experiments to test (1) if biofilms can potentially accumulate carbon in marsh soil and (2) how different sedimentation rates affect the amount of carbon accumulation. Containers filled with a settled mud bed were inoculated with natural biofilms collected from a marsh surface and allowed to grow with favorable light exposure, nutrient supply, and absence of grazing. Mud was added weekly in different amounts, resulting in an equivalent sedimentation rate from 12 to 189 mm/yr. After 11 weeks, the sediment columns were sampled and analyzed for chl a, organic matter via loss on ignition (LOI), and total organic carbon (TOC). Chl a accumulation rates ranged from 123 to 534 mg/cm2/yr, organic matter accumulation ranged from 86 to 456 g/m2/yr, and TOC accumulation rates ranged from 31 to 211 g/m2/yr. These values are on the same order of magnitude of marsh carbon accumulation rates measured in the field. All three metrics (chl a, organic matter, and TOC) increased with increased sedimentation rate. These results show that biofilms can potentially contribute to carbon accumulation in salt marsh soils. Furthermore, areas with high sedimentation rates have the potential for higher amounts of organic matter from biofilms in the sediment

Role of tidal wetland stability in lateral fluxes of particulate organic matter and carbon

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Biogeosciences 124(5), (2019): 1265-1277, doi:10.1029/2018JG004920.Tidal wetland fluxes of particulate organic matter and carbon (POM, POC) are important terms in global budgets but remain poorly constrained. Given the link between sediment fluxes and wetland stability, POM and POC fluxes should also be related to stability. We measured POM and POC fluxes in eight microtidal salt marsh channels, with net POM fluxes ranging between −121 ± 33 (export) and 102 ± 28 (import) g OM·m−2·year−1 and net POC fluxes ranging between −52 ± 14 and 43 ± 12 g C·m−2·year−1. A regression employing two measures of stability, the unvegetated‐vegetated marsh ratio (UVVR) and elevation, explained >95% of the variation in net fluxes. The regression indicates that marshes with lower elevation and UVVR import POM and POC while higher elevation marshes with high UVVR export POM and POC. We applied these relationships to marsh units within Barnegat Bay, New Jersey, USA, finding a net POM import of 2,355 ± 1,570 Mg OM/year (15 ± 10 g OM·m−2·year−1) and a net POC import of 1,263 ± 632 Mg C/year (8 ± 4 g C·m−2·year−1). The magnitude of this import was similar to an estimate of POM and POC export due to edge erosion (−2,535 Mg OM/year and − 1,291 Mg C/year), suggesting that this system may be neutral from a POM and POC perspective. In terms of a net budget, a disintegrating wetland should release organic material, while a stable wetland should trap material. This study quantifies that concept and demonstrates a linkage between POM/POC flux and geomorphic stability.Use of brand names is for identification purposes only and does not constitute endorsement by the U.S. Government. This study was supported by the USGS Coastal and Marine Geology Program, the Department of the Interior Hurricane Sandy Recovery program (GS2‐2D), and the USGS Mendenhall Post‐doctoral Research Program. Viktoria Unger and Paula Zelanko are acknowledged for field and lab assistance. Core collection was funded under NJ SeaGrant/NOAA Grant 6210‐0011. Gil Pontius provided helpful feedback on statistical measures. Kevin Kroeger and two anonymous reviewers provided constructive reviews of the manuscript. All time series and water sample data are available at the U.S. Geological Survey's Oceanographic Time‐Series Data Collection (at https://stellwagen.er.usgs.gov/).2019-10-2

Elevated temperature and nutrients lead to increased N2O emissions from salt marsh soils from cold and warm climates

Salt marshes can attenuate nutrient pollution and store large amounts of ‘blue carbon’ in their soils, however, the value of sequestered carbon may be partially offset by nitrous oxide (N2O) emissions. Global climate and land use changes result in higher temperatures and inputs of reactive nitrogen (Nr) into coastal zones. Here, we investigated the combined effects of elevated temperature (ambient + 5℃) and Nr (double ambient concentrations) on nitrogen processing in marsh soils from two climatic regions (Quebec, Canada and Louisiana, U.S.) with two vegetation types, Sporobolus alterniflorus (= Spartina alterniflora) and Sporobolus pumilus (= Spartina patens), using 24-h laboratory incubation experiments. Potential N2O fluxes increased from minor sinks to major sources following elevated treatments across all four marsh sites. One day of potential N2O emissions under elevated treatments (representing either long-term sea surface warming or short-term ocean heatwaves effects on coastal marsh soil temperatures alongside pulses of N loading) offset 15–60% of the potential annual ambient N2O sink, depending on marsh site and vegetation type. Rates of potential denitrification were generally higher in high latitude than in low latitude marsh soils under ambient treatments, with low ratios of N2O:N2 indicating complete denitrification in high latitude marsh soils. Under elevated temperature and Nr treatments, potential denitrification was lower in high latitude soil but higher in low latitude soil as compared to ambient conditions, with incomplete denitrification observed except in Louisiana S. pumilus. Overall, our findings suggest that a combined increase in temperature and Nr has the potential to reduce salt marsh greenhouse gas (GHG) sinks under future global change scenarios

Organic Matter and Nutrient Cycling in Coastal Wetlands and Submerged Aquatic Ecosystems in an Age of Rapid Environmental Change—The Anthropocene

Coastal ecosystems, such as marshes, mangroves, seagrasses and estuaries, are biogeochemical hotspots, receiving and transforming organic matter and nutrients from terrestrial watersheds and the coastal ocean [...

Salt Water Exposure Exacerbates the Negative Response of <i>Phragmites australis</i> Haplotypes to Sea-Level Rise

The response of coastal wetlands to sea-level rise (SLR) largely depends on the tolerance of individual plant species to inundation stress and, in brackish and freshwater wetlands, exposure to higher salinities. Phragmites australis is a cosmopolitan wetland reed that grows in saline to freshwater marshes. P. australis has many genetically distinct haplotypes, some of which are invasive and the focus of considerable research and management. However, the relative response of P. australis haplotypes to SLR is not well known, despite the importance of predicting future distribution changes and understanding its role in marsh response and resilience to SLR. Here, we use a marsh organ experiment to test how factors associated with sea level rise—inundation and seawater exposure—affect the porewater chemistry and growth response of three P. australis haplotypes along the northern Gulf of Mexico coast. We planted three P. australis lineages (Delta, European, and Gulf) into marsh organs at five different elevations in channels at two locations, representing a low (Mississippi River Birdsfoot delta; 0–13 ppt) and high exposure to salinity (Mermentau basin; 6–18 ppt) for two growing seasons. Haplotypes responded differently to flooding and site conditions; the Delta haplotype was more resilient to high salinity, while the Gulf type was less susceptible to flood stress in the freshwater site. Survivorship across haplotypes after two growing seasons was 42% lower at the brackish site than at the freshwater site, associated with high salinity and sulfide concentrations. Flooding greater than 19% of the time led to lower survival across both sites linked to high concentrations of acetic acid in the porewater. Increased flood duration was negatively correlated with live aboveground biomass in the high-salinity site (χ2 = 10.37, p = 0.001), while no such relationship was detected in the low-salinity site, indicating that flood tolerance is greater under freshwater conditions. These results show that the vulnerability of all haplotypes of P. australis to rising sea levels depends on exposure to saline water and that a combination of flooding and salinity may help control invasive haplotypes

Muench_Quirk_Data_2019

This data was used for Muench & Elsey-Quirk 2019. the data was collected in the field and lab

Organic Matter and Nutrient Cycling in Coastal Wetlands and Submerged Aquatic Ecosystems in an Age of Rapid Environmental Change—The Anthropocene

Coastal ecosystems, such as marshes, mangroves, seagrasses and estuaries, are biogeochemical hotspots, receiving and transforming organic matter and nutrients from terrestrial watersheds and the coastal ocean [...