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Wetland Biogeochemistry Lab., Soil and Water Science Dep., 106 Newell Hall, Univ. of Florida, Gainesville, FL 32611
Corresponding author (jrwh{at}gnv.ifas.ufl.edu)
Organic N mineralization can regulate the bioavailability of N in wetland soils and be controlled by the availability of inorganic electron acceptors. During the past 40 yr, the northern Everglades has been affected by nutrient loading as a consequence of the diversion of surface water runoff from agricultural lands. The greatest hydraulic loading occurs in the summer season when precipitation is highest. Fluctuations in water levels and loading of alternate electron acceptors (NO-3 and SO2-4) could result in variable N turnover rates. The effect of aerobic, NO-3 reducing, SO2-4 reducing, and methanogenic conditions on potential organic N mineralization rate was investigated. Soil at 0- to 10- and 10- to 30-cm depths and overlying plant detritus were collected from eight stations along a 10-km eutrophic gradient in the northern Everglades, Florida. Selected soil characteristics including microbial biomass C and N (MBC and MBN), total P, and extractable NH+4 were measured. Significantly (P < 0.05) higher rates of N mineralization were observed in the detritus, lower rates in the 0- to 10-cm depth, and lowest rates in the 10- to 30-cm depth under each of aerobic, NO-3 reducing, SO2-4 reducing, and methanogenic conditions. Organic N mineralization rates decreased sequentially from aerobic to NO-3 and SO2-4 reducing conditions to methanogenic conditions. Total P, MBC, and MBN were all significantly correlated (P < 0.05) to the N mineralization rates under dominance of each electron acceptor. Of all the measured soil characteristics, extractable NH+4 was the most strongly correlated (P < 0.01; r = 0.62–0.92) indicator of potential N mineralization rates. Results of this research have important implications for the biogeochemical cycling of N and ecosystem productivity in wetland systems.
Abbreviations: ANOVA, analysis of variance • MBC, microbial biomass C • MBN, microbial biomass N • SOD, soil oxygen demand • WCA, Water Conservation Area
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