Nitrogen And Heavy Metals In Sediments Of Typical Reservoirs For Drinking Water Supply In Guangdong Province

Twenty-two reservoirs for drinking water supply in six watersheds of Guangdong Province were investigated to know the contamination and distribution of nitrogen and heavy metals, and the Lars Hakanson's potential ecological risk assessment method was used to analyze the pollution of heavy metals in surface sediments.The results showed that:the average contents of TN(total nitrogen)and NH4+ ammonium)in surface sediments of six watersheds were 0.96-2.75 mg g-1 and 50.66-368.64μg g-1,and the highest content of TN and NH4+ were all appeared at the Pearl River Delta. The contents of TN and NH4+ in the all reservoirs'surface sediments ranged from 0.96 to 2.75mg g-1 and from 35.12to 2154.18μg g-1 respectively, and they were highest in Tongsha Reservoir located in Dongguan City. Trophic state, external pollution, reservoir volume, hydraulic retention time and land use were the key elements affecting the contents of nitrogen. The contents of nitrogen in the reservoirs located at the coastal zones which usually received more loading than those at other zone, especially in the Pearl River Delta, and the nitrogen content in the eutrophic reservoirs was higher than that in the oligotrophic reservoirs. The contents of nitrogen usually increased vertically from the bottom to surface of the sediment columns, indicating a historically increase of external loading. However, the reverse profiles were observed in some oligo or meso-trophic reservoirs. The content distribution of heavy metals had the similar pattern to the nitrogen. The result of potential ecological risk assessment indicated that the contamination of the surface sediments in Guangdong reservoirs were relatively heavy. By analyzing the accumulation coefficient and comprehensive contamination coefficient for heavy metals, the sediments were polluted with Cd, Zn, Pb seriously, the heavy order of pollution level over watersheds was:East part of Guangdong>Beijing river basin>Pearl River Delta>West part of Guangdong>Hanjiang river basin>Dongjiang river basin. From the toxic-response factor(Er1)and the potential ecological risk index (RI),we found that Cd was the major factor of potential ecological risk and it was also the main contributor to the RI, followed by Hg.