Nutrient Exports from Two Agriculture-Dominated Watersheds in Southern Sweden

Nutrient concentrations and exports were monitored for eight years in two agriculture-dominated watersheds in the central part of the Västgöta Plain in Sweden. The hydrology and the nutrient concentrations in the streams were very similar. Concentrations (monthly flow-weighted) of dissolved phosphate-phosphorus (PO₄P) varied substantially during the year (from 0.03 to 0.27 mg 1⁻¹) whereas concentrations of particulate phosphorus (PartP) varied less (from 0.03 to 0.16 mg ⁻¹). No trends in nutrient export during the eight years were found after flow-normalization of export data. Three wet periods dominated the long-term loads of the streams. Although a few events dominated annual yields of suspended solids (SS) from drainage pipes, standard deviation of annual mean SS concentration was reasonably constant between different years. However, when further developing phosphorus load models the variation in SS concentration should probably be considered. In-stream processes may contribute nearly as much to the phosphorus export as those occurring on and in arable soils in terms of their impact on the magnitude of phosphorus export. Total nitrogen (TotN) mean concentration was 5 mg 1⁻¹ and was similar in drainage pipes and in the streams.