Denitrification in South Carolina (USA) Coastal Plain Aquatic Sediments

Abstract

AbstractDenitrification rates in aquatic sediments from three sites upland of high salinity estuaries were measured to compare nitrate (NO−3) removal by sediment bacteria. The study sites included two blackwater creeks that drain to coastal inlets (one in an undeveloped coastal forest and the second in a suburban residential development) and drainage pond on a golf course. Two to 20 mmol NO−3 kg−1 soil was added to microcosms and the acetylene block technique was used to estimate denitrification. Nitrate, nitrous oxide (N2O) and ammonium (NH+4) concentrations were monitored over time. The rate and efficiency of denitrification was low at the 2 mmol NO−3 kg−1 addition and increased proportionally with NO−3 added. Across all treatments, the golf course sediment that received consistent N inputs in situ had the most rapid and greatest N2O production, while the salt marsh in the undeveloped area had the least. The NH+4 concentrations remained constant and low (2 mmol N kg−1) except at the undeveloped, forested Oyster Creek (8 mmol NH+4‐N kg−1). In most cases, the majority of NO−3 removal did not occur until 24 to 48 h of incubation, regardless of N2O production. During typical low‐ and no‐flow periods, this time frame may be adequate for slow diffusion of nutrients and removal of NO−3 prior to transport to coastal estuaries or ground water, particularly at the golf course site. However, this time frame may not be adequate during rapid water and nutrient transport due to severe storm events typical of this region.