Denitrification in South Carolina (USA) Coastal Plain Aquatic Sediments

Abstract

Denitrification 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.

Denitrification Potential in Relation to Lithology in Five Headwater Riparian Zones

“…Some of the deeper sediment samples showed a lag phase of 24 or 48 h before rapid N 2 O accumulation was measured. Similar time lags in N 2 O production have been previously reported, particularly for sites where ambient nitrate levels were low (Aelion and Shaw, 2000). These data suggest that short‐term incubations may seriously underestimate the DNP of deeper riparian sediments that require longer time periods of nitrate amendment to provide an opportunity for the microbial community to respond.…”

Influence of base flow stream bank seepage on riparian zone nitrogen biogeochemistry

“…A lag in potential denitrification measured as N 2 O production also occurred in some lab incubations of riparian sediments from Vivian Creek (Hill et al 2004). Similar time lags have been previously reported for sites where ambient nitrate levels were low and denitrifiers must build up in numbers (Aelion and Shaw 2000). The low rate of nitrate depletion observed in some piezometers was probably the result of temporary saturation of the removal process due to the large concentration of nitrate transported to these sites.…”

Photosynthetic and Heterotrophic Impacts of Nutrient Loading to Blackwater Streams

“…However, during research on two blackwater rivers in this region, it was determined that chlorophytes, diatoms, and cryptomonads responded positively to ammonium and urea inputs, whereas dinoflagellates and euglenoids were minor parts of the community and displayed little response to the treatments (Mallin et al 2001a). Additionally, denitrification likely removes some biologically available nitrogen in the extensive wetlands in the Colly Creek watershed (Aelion and Shaw 2000). Thus, nitrogen fixation is probably not a significant nutrient source to these waters.…”