Farzana Rahman

B.S. Candidate, Drexel University

Conference Travel Grant Type 2 (Society of Wetland Scientists)

High nutrient loads amplify carbon cycling across California and New York coastal wetlands

“This project was catalyzed by observations of pervasive marsh subsidence at a eutrophic California estuary with high nutrient inputs in spite of robust sediment accretion patterns. We hypothesized that the high nutrient loads might be negatively impacting marsh survival through reduced belowground biomass production and enhanced carbon mineralization.  We tested this hypothesis by characterizing belowground productivity and decomposition, carbon mineralization rates, soil respiration rates, microbial biomass, humification, soil C, N, and P inventories, N isotopic ratios, and reactive porewater profiles at high and low marsh elevations across eight marshes in four estuaries California and New York that have strong contrasts in nutrient inputs. Porewater DIN levels were not consistently higher under more N enriched conditions, although soil del 15N ratios were much higher, suggesting that denitrification rapidly removed N inputs. Overall the higher nutrient load marshes were characterized by faster carbon turnover, with higher belowground production and decomposition and greater carbon dioxide efflux than lower nutrient load marshes.  More rapid C cycling has a number of implications for wetland ecosystem functions, and may predispose wetlands to vegetation die-back where low elevations are combined with poor water quality, as more rapid heterotrophic decomposition can result in elevated porewater sulfide concentrations.”