[Spatial phosphorus retention in an agricultural headwater stream].

The spatial dynamics of phosphorus and suspended solids were investigated for two years in a 1.8 km agricultural headwater stream, located by Chaohu Lake, southeastern China. The stream form was greatly modified by human activities. The stream could be divided into 4 channelized reaches (1.3 km), a pond reach (0.15 km) and 3 estuary reaches (0.36 km). It was found that the retention of total phosphorus (TP), phosphate and total suspended solids (TSS) predominantly occurred in the pond reach and estuary reaches. TP, phosphate and TSS retained in the pond and estuary reaches accounted for more than 50% of those retained in whole stream. The retention mostly happened in the precipitation-runoff events and it was 10 to 27 times than that in baseflow. The results showed that channelized reaches were the most important source for pollutant release under either runoff or baseflow conditions, and it accounted for more than 90% of whole stream release. There was a high spatial variation of nutrient dynamics in different channelized reaches. The channelized reach directly discharging into the pond did always retain nutrients and TSS under base flow and runoff, whereas the other channelized reaches performed differently in different hydrological conditions. Stream forms, hydrological conditions, and nutrients characteristics controlled the high spatial variation of the nutrients and TSS in the stream, while the human practices would accelerate these spatial patterns.