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Soil Respiration and Belowground Carbon Stores Among Salt Marshes Subjected to Increasing Watershed Nitrogen Loadings in Southern New England
Citation:
WIGAND, C., E. W. DAVEY, R. L. JOHNSON, M. Stolt, M. Holt, R. TIEN, AND L. Gamez. Soil Respiration and Belowground Carbon Stores Among Salt Marshes Subjected to Increasing Watershed Nitrogen Loadings in Southern New England. Presented at New England Estuarine Research Society Spring 2009 Meeting, Salem, MA, April 02 - 04, 2009.
Impact/Purpose:
Rising sea level and cultural eutrophication are stressors that will affect coastal salt marshes. We examined the belowground organic matter stores (i.e., roots, rhizomes, surface carbon, nitrogen, and percent organic matter) and soil respiration rates in a number of salt marshes along a gradient of increasing watershed nitrogen loadings. Rising sea levels will cause an increase in the frequency and duration of flooding which will likely exacerbate the effects of nitrogen enrichment in organic-rich salt marshes. Losses of belowground macroorganic matter may result in marsh soils more prone to subsidence and erosion.
Description:
Coastal salt marshes are ecosystems located between the uplands and sea, and because of their location are subject to increasing watershed nutrient loadings and rising sea levels. Residential development along the coast is intense, and there is a significant relationship between residential development and watershed nitrogen (N) loadings in Narragansett Bay, RI. We examined soil respiration and belowground carbon stores (roots, rhizomes, percent organic matter, carbon and nitrogen) among salt marshes along a gradient of increasing watershed N loadings. Soil respiration significantly increased in Narragansett Bay salt marshes with increasing watershed N loadings. There was also a significant increase of detritivores in the low marsh soils with high watershed N loadings and high soil respiration rates. Belowground root and rhizome stores in the high marsh, and surface layer percent carbon and nitrogen in the low marsh, decreased with increasing soil respiration, suggesting that nutrient enrichment contributes to increased turnover of belowground macro-organic matter. Similar responses of increased soil respiration rates and decreased macro-organic matter stores were found in marshes in Jamaica Bay, NY that are currently experiencing major areal losses as high as 45 acres per year. In general, the marshes receiving low watershed N loadings had lower soil respiration rates, greater belowground macro-organic matter, and less detritivores. Rising sea levels will cause an increase in the frequency and duration of flooding which will likely exacerbate the effects of N enrichment in organic-rich salt marshes. Losses of belowground macro-organic matter may result in marsh soils more prone to subsidence and erosion.