The effect of farming practices on phosphorus transfer to a headwater stream in England

Characterization of phosphorus (P) sources in catchments is critical to the restoration of stream integrity following eutrophication. To better understand the effects of farming practices on P transfer in a small rural mixed farming catchment (Rosemaund), spatial and temporal patterns in P delivered from a field-drain (Foxbridge, 6 ha), and to two downstream stations (Jubilee, 31 ha and Belmont, 150 ha) were investigated in relation to detailed records on cultivation practices and fertilizer/manure P inputs over a 3-year period (1997–2000) with above-average rainfall. The Belmont catchment also included a farmstead and a small sewage treatment works (STW). The main source of P in drainflow (December–April) was the soil with flow-weighted concentrations of particulate P (PP) up to 2 mg L−1 and concentrations of dissolved-reactive P (DRP) (0.1–0.4 mg DRP L−1) above current riverine targets to limit eutrophication. Agricultural operations carried out in autumn/early winter sporadically increased concentrations of DRP (fertilizer/manure applications) and PP (cultivations) in drain/stream discharge, but only during events that produced small amounts of stormflow. Occasionally large DRP and PP concentrations in drainflow were also recorded during the ecologically sensitive summer months, but this was unrelated to any farming practice. Stream P concentrations were further influenced by processes of baseflow dilution, in-stream retention/release and discharges from the STW and farmstead. The results highlight the disparity between the timing of farming operations at this site (autumn/early winter), the main period of land drainage (winter/spring) and the main period of biological activity (spring and summer). A greater understanding of the ecological significance of variably timed P inputs to headwater streams is needed to develop effective catchment management.