| Coastal wetlands depend on vertical accretion maintaining surface elevation above water levels. Marsh loss in Louisiana is attributed to insufficient accretion resulting from inadequate mineral sedimentation or in situ produced organic material. The role of organic production in accretion suggests that soil fertility may influence coastal wetland sustainability. I determined how nutrient and hydraulic conditions affect organic matter accumulation and the influence of these factors on marsh elevation. Manipulations of hydroperiod, and fertilizer additions at Rockefeller Wildlife Refuge, in southwestern Louisiana, were used to evaluate the response of organic matter production to variation in hydroperiod and nutrient loadings. Total vertical accretion; bulk, mineral, and organic densities; percent nitrogen, carbon, and total phosphorus; pore water nutrients and sulfides were measured. These data suggest that above-ground and below-ground production of Spartina patens in tidally influenced marshes on the Chenier Plain is not limited by nutrient availability when marine influence (pore water salinity and hydrogen sulfide concentration) is high. However, production increases and nitrogen become limiting when marine influence is low. Management to restrict marine influence also oxidized soil, which limited accretion. In the long-term, accretion may be limited by hurricanes, which deliver most of the mineral sediments available to plants. |
