Abstract:

Drainage basin hydrological cycle is the core of watershed ecosystem processa, and basinscale passingby water is one of the most important factors. It includes two parts: natural and artificial. The Taihu Lake Basin is widely recognized as an area which is most severely affected by human activities in China. The evergrowing water demand  for modern industry and domestic life nearly dries up all the local natural runoff. Meanwhile, industrial, agricultural and domestic wastewater discharges cause severe deterioration in water quality. And the drainage basin hydrological cycle has been effectively modified by hydro projects, including the introduction of basinscale passingby water. Then the basinscale passingby water has been reducing crisis of water resources more or less.
In this paper, using the modified dualistic water cycle pattern, based on the data about the Taihu Lake Basin waterbalance, we analyzed the impacts of basinscale passingby water on drainage basin hydrological cycle. The results showed that Taihu Lake Basin was one of the basins where basinscale passingby water had the most important impacts on drainage basin hydrological cycle among all subbasins in the Yangtze River Basin.
In the Taihu Lake Basin, the introduction of basinscale passingby water that mainly came from the Yangtze River,expanded the flux of drainage basin hydrological cycle for 67%, changed the pathway of “precipitation → runoff (groundwater) → artificial water (pumping) → drainage (or evaporation) → discharge into the sea (or into the atmosphere)” by “artificial water”, decreased the cycles of “artificial water (pumping) → drainage (or evaporation) → artificial water (pumping) → drainage (or evaporation) →…” or water recycle form more than 3 times to 15 times, and modified the pattern of water resources configuration. 
Because of the characters of plain river network, the basinscale passingby water had their influence extended to every hydraulic regions. There was 560×108 m3 coming form the Yangtze River directly in Huxi Hydraulic Region, which most effectively impacted hydrological cycle of all the hydraulic regions in the Taihu Lake Basin because Huxi Hydraulic Region was located at the upstream of the Taihu Lake Basin. In Huxi Hydraulic Region, WuChengXiYu Hydraulic Region, YangChengDianMao Hydraulic Region, Zhexi Hydraulic Region, HangJiaHu Hydraulic Region, Pudong and Puxi Hydraulic Region and Taihu Hydraulic Region, the basinscale passingby water respectively occupied the flux of hydrological cycle for 62%, 48%, 36%, 13%, 13%, 37%, 27%.
At the same time, because that hydrological cycle was the supporter of solute translocation, basinscale passingby water also had important impacts on the translocation of solute in Taihu Lake Basin. The most important part was the impacts on the translocation of pollutant. In the Taihu Lake, the basinscale passingby water increased the pollutant flux accompanying the increase of the water flux. But the more serious problem was that the pollutant volume of importlake was 205~330 times more than that of exportlake taken by basinscale passingby water. It meanes that there was more and more pollutant deposited and detained in the Taihu Lake. Even the water which imported by the project of water diversion from the Yangtze River to the Taihu through the WangYu river directly  had the perfect water quality, sometimes leaved the pollutant in the Taihu Lake. It is concluded  that the basinscale passingby water not only has important impacts on drainage basin hydrological cycle, but also on pollutant translocation. This paper shows the importance of basinscale passingby water in watershed ecosystem process and the impacts on drainage basin hydrological cycle and on pollutant translocation, pave the way for a better understanding on drainage basin hydrological cycle