| Summary |
The purpose of this thesis is to determine what factors affect the spatial and temporal variability of nitrogen, phosphorus, and sediment flux in a coastal plain watershed. Water samples were collected at 13 sites across the basin during baseflow and stormflow over a six-month period. Autosamples were collected at the basin outlet during four major storms, while runoff samples were collected from field slopes during a fifth storm. The samples were analyzed for dissolved kjeldahl nitrogen (DKN), total dissolved phosphorus (TDP), nitrate-plus-nitrite, particulate phosphorus (PP), particulate nitrogen (PN), and total suspended solids (TSS). Methods of data analysis include statistical analysis, hydrograph analysis, production of chemographs and hysteresis plots, and calculation of pollutant exports. Results show that the croplands contributed to pollution through the leaching of nitrate and erosion of sediment and particulates. The upper basin contributed a large amount of sediment and particulates due to erosion of nearby ditch banks. Runoff of livestock waste from the pasture increased phosphorus concentrations in the adjacent stream. Hydrological analysis revealed that storm runoff was highest in the fall due to increased basin moisture. Pollutant exports generally increased with storm runoff, with the exception of nitrate-plus-nitrite, which was likely transported by subsurface flow. High nutrient concentrations during a low flow period in late summer were possibly due to absence of a dilution effect. Fertilizer application and crop harvesting increased pollutant concentrations after rainfall. The phosphorus concentrations were significantly higher during stormflow than baseflow, while the nitrogen concentrations showed no significant difference. Analysis of specific storms indicated that nitrate-plus-nitrite was transported quickly in saturated overland flow during intense rainfall, and transported slowly in subsurface flow during a lengthy storm. PP, PN, and TSS were flushed out of the basin in storm runoff from various sources during different storms. The field runoff data indicated that concentrations of PP, PN, TSS, DKN and TDP in runoff were higher than at the outlet due to deposition, dilution, and nutrient uptake by plants. Finally, concentrations of nitrate-plus-nitrite at the outlet were greater than runoff concentrations due to nutrient enrichment or transportation by subsurface flow. |
