Watershed-scale simulation of sediment and nutrient loads in Georgia Coastal Plain streams using the annualized AGNPS model

摘要: Sediment and nutrient loadings in the Little River Research Watershed south central Georgia were modeled using continuous simulation Annualized Agricultural Nonpoint–Source Pollution (AnnAGNPS) model, part of AGNPS suite modeling components. Specifically, nitrogen, phosphorus, sediment, runoff predicted over a seven–year period. Land under cultivation makes up approximately 25% 333 km2 watershed. Livestock facilities include swine, poultry, dairy cows, beef cattle. Results from compared to seven years monitoring data at outlet of five nested subwatersheds outlet (LRRW). The average annual predicted runoff upper watershed was one–third half observed runoff. In contrast, lower part close observed, 100% Runoff underprediction was attributed method landcover discretization. extent forest land (55% 63%) and the fragmented landscape that has relatively small fields surrounded by riparian forests tracts resulted in overestimation forested area addition runoff, sediment loads also underpredicted in LRRW. Two factors are most likely responsible for underprediction. is underpredicted these sites, which reduces carrying capacity loads. addition, overestimation areas these sites coincides with underestimation sediment–producing areas, such as cropland. contrast watershed, sediment overpredicted lower This may have inadequately simulating nonpoint–source pollution attenuation extensive in–stream wetland areas found watersheds. Prediction results can be improved through better input into well modification of processes within model account conditions.