Sulfide Inhibition of Nitrate Removal in Coastal Sediments

Microbial nitrate (NO3-) removal via denitrification (DNF) at high sulfide (H2S) concentrations was compared in sediment from a coastal freshwater pond in a developed area that receives salt-water influx during storm events, and a saline pond proximal to an undeveloped estuary. Sediments were incubated with added SO42- (1,000 mu g per gram dry weight basis (gdw)) to determine whether acid volatile sulfides (AVS) were formed. DNF in the sediments was measured with NO3-N (300 mu g gdw(-1)) alone, and with NO3-N and H2S (1,000 mu g S2- gdw(-1)). SO42- addition to the freshwater sediments resulted in AVS formation (970 +/- 307 mu g S gdw(-1)) similar to the wetland with no added SO42- (986 +/- 156 mu g S gdw(-1)). DNF rates measured with no added H2S were greater in the freshwater than the wetland site (10.6 +/- 0.6 vs. 6.4 +/- 0.1 mu g N2O-N gdw(-1) h(-1), respectively). High H2S concentrations retained NH4-N in the undeveloped wetland and retained NO3-N in the developed freshwater site, suggesting that potential salt-water influx may reduce the ability of the freshwater sediments to remove NO3-N.