Modification of phosphorus export from an eastern USA catchment by fluvial sediment and phosphorus inputs

Phosphorus (P) export from agricultural catchments can accelerate freshwater eutrophication. Landscape-based remedial measures can reduce edge-of-field P losses. However, stream channel hydraulics and fluvial sediment properties can modify the forms and amounts of P exported by the time it reaches the catchment outlet. This study examines if land use, fluvial sediment properties, and storm flow dissolved and particulate P are interdependent within a mixed land use catchment in Pennsylvania, USA, so that remedial strategies can be most effectively targeted within the catchment to mitigate P export. Samples of the top 2–3 cm of stream-bed sediments (n = 40) were collected in April 2001, above and below tributary confluences and in areas of likely deposition. Stream water samples were collected at each of 23 sub-watershed outlets during base (n = 7) and storm flow (n = 3) events between 2000 and 2002. The P content and sorptive properties of deposited fluvial sediments varied among tributaries and flow regimes. Total P of sediments in tributaries (322 mg kg−1) was greater than below confluences (239 mg kg−1), whereas dissolved P release rate was lower (92 and 166 mg P kg−1 min−1, respectively). This was attributed to physical disturbance by turbulent mixing and presence of more sand-sized particles at confluences (747 g kg−1) than tributaries (707 g kg−1). The percent cropped (r = 0.51) and forest (r = −0.57) land was related to the Mehlich-3 extractable P concentration of outflow sediment for each sub-catchment. This in turn influenced sediment P release, which was related to base flow P when sediments establish a quasi-equilibrium with flowing water within the catchment. However, storm flow P was not related to any sediment P properties but to percent of each sub-catchment in cropland (r = 0.58), reflecting the importance of erosion in P transport. Storm flow suspended sediment was related to sub-catchment area in crop (r = 0.78). To gain a better understanding of processes controlling P transport within and from a catchment and, thus, mitigation of losses, measures such as conservation tillage, manure management, and buffer strips, fluvial sediment properties as well as landscape management must be considered. Published by Elsevier B.V.