Evaluation of nutrients and heavy metals in the sediments of the Heer River, Shenzhen, China

The parameters of water contents, oxidation-reduction potential, organic matter, total phosphorus, total nitrogen and heavy metals concentrations of mercury (Hg), cadmium (Cd), lead (Pb), arsenic (As), chromium (Cr), copper (Cu) and zinc (Zn) in surface sediment and their vertical distribution incore sediments of the Heer river were investigated. Evaluation of nutrients and heavy metals in the Heer River sediments was done by pollution index and potential ecological risk index (PERI) method, respectively. Environmental dredging depth was calculated. The parameters pH, water content, total nitrogen (TN), and organic matter (OM) as well as heavy metals decline with the increased depth. Nutrients of TN, total phosphorus (TP), OM, and heavy metals Cd, Cu, and Pb were classified into the same group and there were significant positive correlations according to the principal component analysis and Pearson correlation, implying that they have a common origin. The results of high pollution index value of OM, TP, and TN of surface sediment obtained from this research showed that the Heer River was in serious nutrient pollution. The contributions of individual metals to the potential ecological risk were in the following order: Cd > Cu > Ni > Cr > Zn > As > Pb. Cd presented serious ecological risk and contributed most to the sediments of the Heer River. The ecological risk (RI) was at a considerable high risk level, and therefore, the environmental dredging depth of the Heer River is 94 cm for the purpose of reducing heavy metal contamination of the Heer River.