Phosphorus contamination of the surface sediment at a river confluence

Abstract

River confluences are key features of a river network, and their effects on contaminant transport and transformation need to be understood to control the contamination of a river network. This paper investigates the dynamic characteristics of phosphorus (P) contamination on the surface sediment at a river confluence of the Huai River, China, where water and sediment contamination is severe. The results highlight that P contamination of the surface sediment at a river confluence is more severe than that of the main stream of the river network to which the river confluence belongs. Floods have critical impact on the transport of sediment and its surface texture. In the annual water cycle the initial small flood can convey much more contaminated sediment and pollute the downstream river, whereas the subsequent large flood leads to the coarsening of the surface sediment and decrease of the total P (TP) content on the surface sediment (TPS). Water temperature is one of the most important factors affecting the temporal variability of the TPS at the river confluence. Higher P amounts are adsorbed on the surface sediment during lower water temperatures in winter and spring. Calcium bound P (Ca-P) is a relatively stable fraction of the sedimentary P during the dynamic processes of contamination of the surface sediment, and the nonapatite P gets released from the surface sediment during the summer. Effects of P concentration of the surface water and that of pH on TPS variability are not discernable in the current study. These results will be useful for controlling phosphorus contamination at river confluences and in river networks.