Contamination Characteristics And Release Mechanism Of Sediments In Shiwuli River Into Chaohu Lake

In this paper, Shiwuli River, flowing into Chaohu Lake, was taken too be an object to investigate the contamination characteristics of heavy metal contamination and nutrient content of nitrogen and phosphorus, and the release mechanism of nitrogen and phosphorus in the bottom sediments. The main contents and results were summarized as follows:(1) Heavy metal concentrations and spatial variation characteristics of Cu, Zn, Pb, Cd and Cr were obtained and analyzed. Study results showed that the concentrations of Cu, Zn, Pb, Cd and Cr parked at the depth interval of 0 ~ 10cm in the sediments, and at the depth interval of 0 ~ 60cm, in general, metal concentrations declined with the increase of buried depth. Meanwhile, the metal concentrations of Cu, Zn, Pb, Cd and Cr at the depth interval of 30 ~ 60cm declined more rapidly than that at the depth interval of 0 ~ 30cm. The results of enrichment factor (EF) indicated the order of pollution level Cd>Cu>Zn≈Pb>Cr. Combined with convergence of regional pollution sources, preliminary determination was made that the nutrient and heavy metal pollution in Shiwuli River sediments mainly derived from fertilizer production enterprises, agricultural soil erosion and sewage emissions by means of principal component analysis and correlation analysis. Generally, sediment heavy metal pollution was not serious and bio-toxicity was low, and the five metals toxic units were in the order of Cu>Pb>Cr>Cd≈Zn. The potential risk indexes of the five metals were in the order of Cd>Pb>Cu>Cr>Zn. The comprehensive risk index in midstream was higher than that in upstream and downstream.(2) The spatial variation of nutrient contents showed the richment of nutrients in the bed sediments of Shiwuli River. TN, TP and TOC presented the same trends, and declined along with the increase of buried depth. The ratio of carbon to nitrogen w (C) / w (N) showed that the sediments pollution of Shiwuli River mainly originated from outer sources. The significant positive correlation between TN, TP and TOC indicated the homology of the three obvious.(3) According to the soil quality standards of heavy metals, environmental quality of sediments was evaluated by using principal component analysis and fuzzy comprehensive evaluation techniques. The results showed that the sediments of Shiwuli River meet class I of soil quality standards on the heavy metals, and will not adversely affect crop growth. Furthermore, the disposal of dredged sediments including dredged area, dredging depth and ammount, was discussed quantitatively for Shiwuli River.(4) Through the experimental study on nitrogen and phosphorous release of sediments in Shiwuli River, the impacts of temperature, dissolved oxygen, pH, and other environmental factors on the release of sediment were revealed in the end.