Gregory P. Lewis

Low stream nitrate concentrations associated with oak forests on the Allegheny high plateau of Pennsylvania.

Stream nitrate (NO3−) concentrations were 2.6–7.0 times lower in watersheds in which red oak (Quercus rubra) stands were present than in other forested watersheds in northwestern Pennsylvania. Also, seasonal variations in NO3− concentrations were smaller in watersheds with oak stands than in watersheds without oak stands. Stream water concentrations of calcium, magnesium, potassium, sodium, chloride, and sulfate did not differ significantly between the two groups of watersheds. The variability in NO3− concentrations among streams did not appear to be due to differences in atmospheric nitrogen deposition among watersheds. Low stream NO3− concentrations occurred even if only 10–20% of a watershed was covered by oak stands. We suggest that oaks, rather than directly controlling NO3− losses, instead merely occur on soils which have low NO3− losses.

Chapter 24 Relations among land cover, vegetation index, and nitrate concentrations in streams of the Enoree River Basin, piedmont region of South Carolina, USA

Abstract Globally, high nitrate concentrations and fluxes in rivers are correlated with human population density and can lead to eutrophication of estuaries and coastal oceans. Although elevated nitrate concentrations often are associated with agricultural land cover, urban land cover also can contribute substantially to elevated nitrate concentrations in streams and rivers. In the piedmont region of the southeastern United States, urban areas typically are located in the headwater areas of watersheds. Because headwaters account for the majority of stream channel length in a watershed, the effect of urbanization on the biogeochemical cycling of nitrogen is magnified. We examined the relations between stream nitrate concentrations, land cover, and vegetation density in watersheds of nineteen tributaries of the Enoree River in northwestern South Carolina, USA. Based on data from 134 sample localities, stream nitrate concentrations generally increased with increasing urban land cover and decreased with increasing forest cover and vegetation density (normalized density vegetation index). Although watersheds with the highest percent urban land cover typically had the highest nitrate concentrations, nitrate concentrations were most variable spatially in drainage basins with 5 to 20% urban land cover. The relations between land cover, vegetation density, and nitrate concentrations are complicated by variation in the intensity of urbanization and spatial location of urban and forested land within the drainage basin of each sample locality. Artificial ponds in urban areas appear to play an important role in lowering stream nitrate concentrations and contribute to the spatial variability of nitrate concentrations.

Impacts of a Poultry Processing Plant on the Diversity of Escherichia coli Populations and Transferability of Tetracycline Resistance Genes in an Urban Stream in South Carolina

Poultry feed is often supplemented with low dosages of antibiotic to promote growth, making farms and animal processing facilities potential point sources of antibiotic-resistant fecal bacteria to aquatic ecosystems. In 2010 and 2011, we detected high concentrations of fecal indicator bacteria (FIB) in effluent released from a poultry processing plant into a headwater stream in Greenville, South Carolina. The FIB pollution became undetectable in 2012 with the plant under new management. To determine the plant’s impacts on the stream, we compared the genetic variations of Escherichia coli populations from upstream and downstream of the plant and from reference streams in the same watershed by classifying each isolate into an E. coli reference collection (ECOR) phylogenetic group. For tetracycline-resistant E. coli isolates, we analyzed the resistance genes, minimum inhibitory concentrations (MICs), gene transferability, and plasmid incompatibility groups (Inc). Distributions of ECOR groups upstream and downstream of the plant differed significantly in 2011 but not in 2012. The resistance genes tet(A) and tet(B) were prevalent, with tet(A) more likely to be found on the promiscuous IncP plasmid. A higher percentage of isolates having both tet(A) and tet(B) was found downstream in 2011 than in 2012. Dual-gene isolates did not have higher MICs than single-gene isolates but were more likely to transfer tet(A) on IncP. We propose that the processing plant acted not only as a point source of FIB but also as a factor influencing gene transferability. Additionally, given the results from 2012, the FIB impacts of the processing plant appeared to be reversible.

Relationships between Dry Deposition of Ions and Urban Land Cover in the South Carolina Piedmont

Atmospheric deposition can be an important source of ions to terrestrial and aquatic ecosystems. Previous studies have indicated that dry deposition of ions in and near large cities is greater than in nearby rural areas. However, few studies have compared dry deposition in and near smaller cities. We measured dry deposition of ions at various distances from Greenville, a smaller city in the piedmont of northwestern South Carolina. Dry deposition was estimated by exposure of artificial surfaces (glass Petri plates and paper filters) to the atmosphere at 13 locations during June–July 2008. Petri plates were expected to collect dust particles primarily, whereas filters were expected to collect both dust and gases. Fluxes measured by filters were significantly greater than those measured by Petri plates for nitrate and ammonium, suggesting that dry deposition of nitrogen in gases exceeded dry deposition in dust. Dry deposition of ammonium and nitrate declined significantly with distance from Greenville, and rates were significantly higher at urban than at rural locations. Also, dry deposition rates of ammonium correlated positively with road densities and traffic volumes around sampling locations, suggesting that automobiles were important sources of ammonia gas. Relationships between ammonium deposition and urban land cover and roads were stronger than for nitrate deposition, perhaps reflecting the influence of automobiles using catalytic converters. Base cation concentrations in dry deposition typically were below detection, precluding flux calculations. Overall, our results provide evidence that smaller cities influence atmospheric deposition of nitrogen, though perhaps not as strongly as larger cities.

Hydrogeochemical Characterization of Headwater Seepages Inhabited by the Endangered Bunched Arrowhead (Sagittaria fasciculata) in the Upper Piedmont of South Carolina

Abstract Sagittaria fasciculata (Bunched Arrowhead) is an endangered plant known to grow only in Greenville County, SC, and Henderson and Buncombe counties, NC. This study compared the hydrogeochemical characteristics (hydrologic setting, water chemistry, substrate grain size, and organic matter content) of fourteen Bunched Arrowhead sites across Greenville County. All Bunched Arrowhead were found in partially to fully shaded and saturated discharge areas in close proximity to and fed by continuous and consistent groundwater seeps. The plants grew in sandy substrata with highly variable organic matter contents. Surface waters at these sites were shallow, dilute, and acidic (pH 4.5–5.7). However, the degree to which water chemistry influences the plants growth and survival remains to be determined.