Do NH3 and chemical oxygen demand induce continuous release of phosphorus from sediment in heavily polluted rivers?

•NH3 and CODcr may cause DO levels in surface water to fluctuate.•Hypoxia in river water induces NaOH-Pi and L-Po adsorption and hydrolysis.•Pore and surface water SRP increases because of processes triggered by the hypoxia.•NH3 and CODcr may be important for adsorption and desorption of P.

While phosphorus (P) is a vital element in freshwater systems, excessive P loads will induce eutrophication. Large inputs of various pollutants, including P, to rivers in semi-arid regions result in complex environmental problems. In this study, we investigate dissolved oxygen (DO), ammoniacal nitrogen (NH3), chemical oxygen demand (CODcr), soluble reactive P (SRP) in surface water and pore water, and sediment P in the Niuwei River, within the Hai River Basin. From our results we developed and tested a theory for P release in semi-arid regions driven by DO. The results show that NH3 and CODcr can cause variations in DO in surface water. The presence of pollutants at high concentrations caused seasonal hypoxia. Hypoxic river water induced adsorption and hydrolysis of NaOH-Pi and labile organic P (L-Po), which then resulted in increased SRP concentrations in pore water and surface water. Overall, our results illustrate that NH3 and CODcr may be important for P adsorption and desorption and for management of water quality problems in rivers in semi-arid regions.

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