| In recent years, some urban rivers of Hangzhou have received mixed pollutants, including industrial wastewater, municipal sewage, etc. Consequently, a great quantity of oxygen-consuming contaminants, inorganic nutrients (N and P), heavy metals and other pollutants have accumulated in the sediment. And in certain conditions, the different kinds of pollutants would be realeased from the sediment, polluting overlying waterbody and leading to further deterioration in water quality, which has attracted a lot of attention from river management departments in Hangzhou as well as environmental organizations.Firstly, we investigated the five river areas in the survey region, and selected six rivers of the Canal and the Shangtang River system as research targets. Then, the appropriate sampling sections for these rivers were determined, and water and sediment samples were taken respectively in April, July and October in 2011. First of all, the water quality indexes of selected rivers, including pH, inorganic nutrients, DO, CODMn, BOD5 and heavy metal Cu, Zn, Pb, Cd were analyzed. Using single gene index method (choosing the worst individual index of the water to determine the water quality), the results of water quality evaluation in different periods were analyzed as follows:the water quality of studied rivers was five-class, however, the concentrations of Cu, Zn, Pb and Cd in the water were below national standards, according to<<Environmental Quality Standard for Surface Water>> (GB3838-2002). Then, it was determined that ammonia nitrogen and total phosphorus were the main pollutants in the rivers.Secondly, in part of the river sediments, we have monitored the concentration of the inorganic nutrients, organic matter and heavy metals. The main source of organic matter in the surface sediments were decided using the ratio of sediment inorganic nutrients. The contents of Cu, Zn, Pb and Cd in the substrate have all exceeded those in overlying water. Except Cd and Zn, the contents of heavy metals were three-class according to <<Standard of Soil Environment>> (GB15618-1995) and satisfied <<Contamination Control Standards in Agricultural Sludge>> (GB4284-84). Heavy metal pollution in bottom sediments of the studied rivers was assessed by the potential ecological harm index method. The results showed that Cu, Zn and Pb experienced a slight degree of hazard, and Cd belonged to severe pollution level. There were middle risks of heavy metal pollution in the six rivers. And the evaluation based on geo-accumulation index method indicated that the order of heavy metal pollution was Cd>Zn>Pb>Cu.The correlations among the contaminants of the river waterbodies were analyzed, which showed that there were significant correlations among TN, TP and NH3-N. And CODMn in the waterbody was significantly correlated with BOD5. Besides, the correlation analysis was conducted among sediment indexes, which indicated that there was significant correlation between TN and organic matter, overall, the correlations were remarkable among TP and TN, organic matter. There were conspicuous correlations between the heavy metals Pb and Cd, Zn. The contents of heavy metals and the organic matter in the sediment had good correlations, and the accumulating order for these heavy metals by the organic matter was Cd>Pb>Zn>Cu.At last, the situation of comprehensive control on researched rivers was elaborated in this paper. And according to the pollution characteristics mentioned in this paper, the pollution sources of the urban rivers in Hangzhou were analyzed, including domestic sewage, pollutants from the upper river, city garbage and industrial waste, as well as the waste pollution resulting from ship navigation. Furthermore, several countermeasures and suggestions were provided according to present situation of the pollution characteristics. |
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