Soil organic matter in created and natural estuarine wetlands: Importance to benthic macrofaunal communities and elemental cycling (carbon, nitrogen, phosphorus, sulfur and iron)

I investigated the importance of organic matter to estuarine ecosystem functioning by investigating (1) how variations in vegetation and consequently soil organic matter, resulting from bridge shading, impacted the benthic invertebrate community in estuarine wetlands of North Carolina, (2) how soil organic matter and the invertebrate communities vary among three vegetation types representative of the gradient from oligohaline to polyhaline marshes found in estuarine systems, and (3) how stable isotopes (C, N, and S) can be used to evaluate the development of reducing conditions and organic matter sequestration following brackish marsh creation.; I found low bridges (HW ratio < 0.7) that attenuate light below 260 μmol s−1 m−2, adversely affect estuarine marsh food webs by reducing macrophyte growth and soil organic carbon. Marshes under low bridges had lower overall invertebrate density, taxa richness, density of dominant taxa (oligochaetes, nematodes, and Capitella sp.), and trophic feeding groups (surface and subsurface deposit feeders) compared to natural marshes.; Along the estuarine gradient, invertebrate densities were three to four times greater and taxa richness 40–60% greater in oligohaline Spartina cynosuroides and polyhaline Spartina alterniflora marshes compared to mesohaline Juncus roemerianus marshes. Spartina marshes also had two to three times the density of subsurface feeders and 28%–75% more surface feeders compared to the mesohaline marshes.; Based on isotopic analyses of marsh soils, I found an irregularly flooded, 21 year old, created tidal marsh developed reducing conditions and accumulated carbon, nitrogen, phosphorus, iron, and sulfur at rates similar to a natural wetland. I conclude the development of macrophytic vegetation and its contribution to the organic matter pool in soils is a key factor for invertebrate community development, nutrient cycling and storage, and development of anaerobic biogeochemical processes (e.g. sulfate reduction) in estuarine ecosystems and is necessary for created or impaired marshes to reach functional equivalency with natural coastal marshes.