Nitrate Additions to Wetland Sediments to Test for Evidence of N-S Coupled Dissimilatory Nitrate Reduction to Ammonium

Abstract

Nitrogen (N) levels in aquatic ecosystems have been increasing for the past two centuries, with a significant surge in levels following widespread use of synthetic fertilizers. Excessive synthetic fertilizer application has resulted in runoff; as a result nitrate concentrations in ground water have increased. The purpose of this investigation is to examine the effects of a gradient of nitrate additions to sediment porewater in wetlands, and possible linkages to N-sulfur (S) coupled dissimilatory nitrate reduction to ammonium (DNRA). Research was conducted in two wetlands, Turkey Marsh and Loosestrife Pond, near the W.K. Kellogg Biological Station, in Southwest Michigan. Porewater equilibrators were used to add nitrate amendments to the porewater. Longpath length spectrophotometry and ion chromatography were used to analyze samples for hydrogen sulfide, ammonium, sulfate, and nitrate. It was anticipated that the nitrate additions would lead to a decrease in sulfide concentrations with a simultaneous increase in concentrations of ammonium and sulfate. Results indicated that nitrate additions of 50 and 100 mg/L led to significant increases in ammonium and sulfate and decreases in sulfide in both sites. Additions of 10 and 25 mg/L of nitrate had less significant results. These findings show that N-S coupled DNRA increases the ammonium production in wetlands. Promoting this process could help reduce the toxic levels of nitrate accumulating in marine ecosystems, resulting in eutrophication, hypoxic zones, and harmful algal blooms.