Sulfide Inhibition of Nitrate Removal in Coastal Sediments

Abstract

Microbial nitrate (NO ⁻₃ ) 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 SO ²⁻₄ (1,000 µg 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 µg gdw⁻¹) alone, and with NO₃–N and H₂S (1,000 µg S²⁻ gdw⁻¹). SO ²⁻₄ addition to the freshwater sediments resulted in AVS formation (970 ± 307 µg S gdw⁻¹) similar to the wetland with no added SO ²⁻₄ (986 ± 156 µg 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 µg 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.