Isolating Non-Point Sources of Nitrogen in a Black Water River in Coastal Georgia

Presented at Geological Society of America Southeastern Section Meeting Water quality problems associated with nutrient loading from non-point sources were investigated along an eleven-mile reach of the Canoochee River, a black water stream in coastal Georgia. The river was monitored weekly and tributaries bimonthly over the course of 9 months to determine whether the entry point of specific non-point sources could be identified. Water samples were collected and analyzed in the field for temperature, pH, dissolved oxygen, and conductivity, with nitrate (NO3-) and ammonia/ammonium (NH3/NH4+) concentrations determined in the laboratory. Entry points of nitrogen from surface sources were identified by variations in NH3/NH4+ concentrations between sample sites. Sampling of adjacent tributaries then allowed specific surface sources to be identified within the drainage basin. Contributions of nitrogen from groundwater sources were detected when significant increases in NO3- occurred between sample sites and where adjacent tributaries did not provide any additional input of NO3- or NH3/NH4+. Analysis of temporal changes in nitrogen concentrations showed that both NH3/NH4+ and NO3- concentrations in the river were highest during summer months when discharge was low. During the period of low discharge, the concentration of NH3/NH4+ was found to correspond temporally with discrete precipitation events, but no spatial correspondence was found with respect to sample location. However, the concentration of NO3- was found to correspond spatially with sampling stations, but not temporally with precipitation events. These results indicate that nitrogen contamination within the basin occurs from multiple surface sources associated with specific precipitation events and from plumes of contaminated groundwater which provides a more steady supply of nitrogen. Finally, this research demonstrates the effectiveness of using NH3/NH4+ analysis, in conjunction with multiple sampling sites, as a means of isolating both surface and subsurface non-point sources of nitrogen