Distribution of phosphorus species and their release risks in the surface sediments from different reaches along Yellow River.

In order to further explore the relationship between water body eutrophication of some reaches of Yellow River and phosphorus species in sediments, and evaluate phosphorus release potential from sediments to overlying water, we investigated the distribution of P species and their release risk in the surface sediments from different reaches along Yellow River, as well as the influence of artificial dam on phosphorus cycle in Yellow River. The results show that the content of calcium phosphorus (PCa) is higher than the content of bioavailable phosphorus (BP) (BP = Pex + PFe; in the formula, Pex means exchangeable phosphorus and PFe means iron phosphorus) in the surface sediments from Yellow River. Among all the surface sediment samples from 21 stations, only Dayudu section (H15) has a ratio of W (BP)/W (PCa) higher than 0.5; the results show that the intensity of phosphorus release from H15 is high, and there is a potential risk of eutrophication in water, while the phosphorus release level of water sediment in other reaches of Yellow River is low. The content of BP and total phosphorus (∑P) in surface sediments along the Yellow River is in descending order: middle reaches of Yellow River > upper reaches of Yellow River > Yellow River downstream, while the content order of total phosphorus (TP) in the overlying water is as follows: Yellow river downstream > middle reaches of Yellow River > upper reaches of Yellow River (except the H7 station), indicating that extensive artificial corresponding damming in Yellow River basin makes the concentration of TP increasing significantly in overlying from upstream to downstream. The establishment of Haibowan water conservancy project in Yellow River makes the total particulate matter (TPM) concentration in the water to reduce to very low lever in Wuhai H7 section, and the phosphorus concentration in the overlying water reaches 0.136 mg L-1.