Hot Moments and Hot Spots of Nutrient Losses From a Mixed Land Use Watershed.

Non-point nitrogen (N) and phosphorus (P) pollution from agriculture has increasingly received more public attention. However, when, where and how N and P export occurs from a watershed is not completely understood. In this study, NO₃-N, dissolved P and particulate P concentrations and loads were investigated for four sub-basins (labeled 1 to 4 going up the watershed) within a mixed land use watershed (39.5 ha) in the Appalachian Valley and Ridge Physiographic Province. Greater NO₃-N concentration and load were observed in base flow than in storm flow and during the non-growing season. Dissolved P and particulate P concentrations and loads were low and temporally consistent in base flow, but high and temporally variable in storm flow. The dissolved P concentration and load were great from May to Dec. and from Sept. to Nov., respectively, while the particulate P concentration and load were great from Jan. to June. The NO₃-N, dissolved P, and particulate P loads were compared for all four sub-basins on a loss per length of stream reach basis). The greatest NO₃-N loads were observed in Sub-basins 1 and 4 during the non-growing season base flow period and in Sub-basin 2 during post-growing season base flow period (> 110 g m^-1 mo^-1). The greatest DP loads were also observed in Sub-basins 1 and 4, but during the growing and post-growing season storm flow period (>1.4 g m^-1 mo^-1). In contrast, the particulate P load was the greatest in Sub-basin 3 during the pre-growing and growing season storm flow, as much as 13.4 and 14.1 g m^-1 mo^-1, respectively. Controlling factors of nutrient export were discussed in this study, including season, hydrology (base flow, storm flow, surface and subsurface runoff) and land use. Although different hot moments and hot spots within the watershed were identified for NO₃-N, DP, and PP losses, the implementation of a couple of management practices (cover crops and no-till) might still be efficient to reduce nutrient losses from this and similar valley and ridge watersheds.