Environmental Impacts of Nitrogen and Phosphorus Nutrient Diffusion Fluxes at a Sediment-Water Interface: The Case of the Yitong River, China

Under the premise of controlling the external input of nitrogen and phosphorus, endogenous release is the main cause of eutrophication in lakes. To investigate the characteristics of endogenous nitrogen and phosphorus release from urban rivers, the Yitong River, an urban river in northern China, was used as an experimental object. Eight sampling sites were set up in the upstream, urban, and downstream regions of an urban section. The nitrogen and phosphorus nutrient exchange fluxes at the sediment-water interface of the Yitong River were assessed by analyzing the sediment and overlying water, and the effects of environmental factors on nitrogen and phosphorus release were investigated using static release experiments. The results showed that the diffusive fluxes of endogenous total nitrogen (TN), ammonia nitrogen (NH4+-N), and total phosphorus (TP) in the urban section of the Yitong River ranged from −1.571 to 19.365 mg·(m2·d)−1, −0.171 to 9.227 mg·(m2·d)−1, and −0.052 to 0.595 mg·(m2·d)−1, respectively. The diffusive fluxes of nitrogen and phosphorus nutrients were all greater under anaerobic conditions than under aerobic conditions. The diffusive fluxes of nitrogen and phosphorus were influenced by changes in pH, DO, and temperature of the overlying water, and the release of phosphorus from the sediment was accelerated by high temperatures in the range of 5–25 °C. Acidic conditions favored the release of TN, whereas alkaline conditions favored the release of TP from the sediment. Furthermore, during the control of nitrogen and phosphorus pollution, it should be noted that fluxes are higher in spring and autumn. Thus, when appropriate techniques should be implemented to achieve better control. These findings are intended to provide a reference for the study of nitrogen and phosphorus diffusion fluxes at the sediment-water interface in urban rivers and other surface waters around the world.