Annual variation of water quality for the Hengtang River in the Taihu basin

HengTanghe River, which is a channel along the west coast of Taihu Lake, connects several inflow rivers into the lake. It has a certain distance away from the lake embankment. From June 2010 to May 2011, the water samples of Hengtanghe River were collected in Zhoutie town near the village of Yangxi, Yixing. The variation of river water quality was analyzed throughout the whole year. The results showed that: (1) the annual total nitrogen (TN) concentration was inferior to Class V water quality except August, while other indexes were superior to Class V water quality. (2) Dissolved total nitrogen (DTN) accounted for the main form in TN in the river, while TP was mainly in the form of particulate phosphorus (PP). Chemistry oxygen demand (CODMn) had a higher concentration during June and August compared to other months, and the maximum chlorophyll a (Chla) concentration was monitored in August. There were significantly higher CODMn and Chla concentrations in the hot season than that in the cold season, while the TN concentration exhibited the opposite tendency with CODMn and Chla. (3) There was a significant correlation among the water quality indexes except TP.