Water Quality Assessment And Water Environment Analysis Of The West Lake Longhongjian Multi-stage Ecological Purification Pond

Longhongjian stream is one of the important upstreams into the West Lake in Hangzhou city, as one important source of nutrients, which has a great impact on water quality of the West lake, and it is divided into mainstream and tributary. There are multi-stage ecological purification ponds respectively in the two streams, with researching and exploring on Longhongjian stream and monitoring of water quality. Through analyzing the characteristics and changes of its water body, the results showed that the water quality of the mainstream and tributary was in a “low-carbon, low-phosphorus, high-nitrogen” status.The multi-stage ecological pond removed the contaminants of the water body by phytoremediation technology, which includes physical, chemical, biological and other effects. The cumulative removal rates of TN, TP, NO3-N and COD in the mainstream were 42.5%, 42.8%, 52.9% and 52.6% respectively, and those in the tributary were 62.1%, 77.3%, 69.3% and 59.6% respectively. The effluent quality of the mainstream and tributary could meet the class Ⅴ and Ⅳ criteria specified in the Environmental Quality Standards for Surface Water(GB3838-2002). Besides, after assessing and analyzing the level of water body eutrophication on the ecological ponds, the results showed that the mainstream was at medium level of eutrophication, and the tributary was in a mild degree of eutrophication.On the basis of the water balance analysis, through the establishment of the Net Pollutants Accumulation(NPA) mathematical model, the results of the annual total contaminants for the mainstream and tributary showed that the net accumulation of COD, TN and TP for the mainstream were 11696 kg, 3759 kg and 35.7kg respectively, and those for the tributary were 12360 kg, 3340 kg and 91.3kg. According to the NPA values, it indicated that the ecological ponds had a powerful interception capacity to water pollutants. Taking TN as one factor to establish one-dimensional water quality model and analyze the water environmental capacity of the ecological ponds and their current environmental capacity, the results showed the current environmental capacity of the mainstream ecological ponds had far exceeded the capacity of the water body, on the contrary, those of the tributary meet the environmental capacity allows.Through assessing the water body eutrophication level and current water quality status, and analyzing the environmental capacity, based on the analysis results, we could grasp the water quality’s status of ecological ponds and obtain the major pollutants, and provide a scientific basis on the effective control and management for water quality.