Publications

Abstract: Marsh edge erosion results in soil organic matter (SOM) loss from coastal wetlands and is differentially affected by wind waves, soil properties, and vegetation cover. The degradation of SOM may make the marsh edge susceptible to erosion. The objective of this study was to investigate the effect of in situ biogeochemical degradations of SOM on marsh edge erosion using porewater spectroscopic analyses. Edge erosion was monitored at 12 transects in one of the highly eroding coastal basins of Louisiana. A total of 36 cores were collected at different distances from the edge of the marsh. Porewater was extracted and analyzed for dissolved organic carbon (DOC) and spectroscopic indicators. The north and west side had greater erosion rates (102.38 ± 5.2 cm yr−1) than east and south side (78.47 ± 3.3 cm yr−1). However, the north and east side had greater DOC and refractory carbon but less microbial activity indicating SOM degradation alone did not correlate to edge erosion. The intersecting trend between erosion rate and SOM degradation among four sides of the island indicates the complex nature of edge erosion drivers. The estuarine bottom indicators suggest the eroded SOM is not reburied but rather degraded and emitted back into the atmosphere as CO2, potentially contributing to global change. The coastlines projected to experience high sea-level rise in the coming century are vulnerable to losing a large amount of stored carbon in the absence of efficient mitigation measures. 

 

Citation: Hayes, M, Sapkota, Y, White, J., Cook, R, Investigating the impact of in situ soil carbon degradation through porewater spectroscopic analysis on marsh edge erosion. Chemosphere 2021; 268 (129266)

Abstract: The fate of soil carbon in eroding coastal wetlands is of great concern, given the potential for a feedback loop from coastal wetland soil that would dramatically increase atmospheric CO2 concentrations. The biogeochemical transformations and overall fate of this soil carbon upon coastal erosion were investigated through geophysical and spectroscopic analysis of soil and associated dissolved organic matter. Bay water and core sections were collected across transects encompassing both intact and eroded, submerged, sections of a coastal marsh in Barataria Bay, Louisiana. We noted: i) a vertical increase in carbon content, humification of organic matter, and decrease in biotic degradation with depth at all sites; ii) an erosion and ultimate collapse of the top ~ 0–20 cm of the intact marsh’s edge into the bay water due to the undercutting caused by tidal/wave forces; iii) the loss of the stored carbon from the submerged site’s top 10 cm layer; and iv) leaching, dilution, abiotic, and biotic degradation of the marsh carbon due to the exposure to the bay water. This erosion and degradation of wetland soil carbon stores demonstrates the potential impact of rising sea levels on the future fate of coastal wetland carbon and atmospheric CO2 levels.

 

Citation: Haywood, B., Hayes, M., White, J., Cook R., Potential fate of wetland soil carbon in a deltaic coastal wetland subjected to high relative sea level rise. Science of The Total Environment 2020; 711 (135185)

Abstract: Coastal wetlands in Louisiana experience high rates of edge erosion due to combined eustatic sea level rise and coastal subsidence. This study sought to (1) evaluate site-specific spatial and temporal patterns in marsh edge erosion rates within Barataria Bay, LA, (2) develop an understanding of the physical and chemical properties of eroding soils through biogeochemical and spectroscopic characterization, and (3) evaluate interactions between erosion, saltwater incursion, and soil properties through a comparison of sites with different erosion rates and varying distances from the eroding edge. Replicate soil cores were collected at three distances inland (1 m, 3 m, 5 m) at three different sites (west, south, and north) to a depth of 1 m. Erosion rates were measured at each site, and soils were sectioned into 10 cm intervals for a total of 270 soil and porewater samples. Each soil sample was subjected to soil physicochemical analysis (bulk density, moisture content, organic matter content, and total carbon (C), nitrogen (N), and phosphorus (P)) as well as assessments of biogeochemical cycling (production of CO2, mineralization of N and P, and extractable nutrient concentrations). Porewater samples were analyzed to elucidate spectroscopic and fluorometric indicators of carbon quality (aromaticity, humification, lignin proportion, and C source). Erosion rates at the west, north, and south sites were 3.36 ± 0.4, 1.34 ± 0.2, and 0.58 ± 0.03 m yr−1, respectively. Neither erosional magnitude nor saltwater incursion was found to be significant predictors of any measured spectroscopic or biogeochemical parameters, though depth was a significant control on 18 of the measured 20 parameters. The top 30 cm were more biologically active (as indicated by greater mineralization of C, N and P) and were characterized by lower molecular weight porewater DOM with less aromaticity. Degree of humification and aromaticity of porewater DOM increased with both depth and distance inland. Concentrations of bioavailable N and P at 1 m depth were at least 5 times greater than surface concentrations, representing a pool of nutrients that could be exported into the coastal ocean with ongoing erosion. This study is the first to couple spectroscopic and biogeochemical measurements for the purpose of assessing soil and porewater physicochemistry within wetland soils and illustrates an as-yet unaccounted for potential for the export of labile C, N, and P into the coastal ocean.

 

Citation: Steinmuller, H., Hayes, M., Hurst, N., Sapkota, Y., White, J., Cook, R., Xue, Z., Chambers, L., Coupled biogeochemical and spectroscopic assessment of carbon dynamics within an eroding brackish marsh. Catena 2020; 187 (104373)