Changes of water exchange cycle in Lake Taihu (1986-2018) and its effect on the spatial pattern of water quality

Abstract

针对太湖水体交换周期近十余年发生的变化，本文收集整理了1986—2018年太湖水文巡测、汛期水文巡测数据以及太湖流域沿江城市引水量、流域降雨量变化数据，基于太湖出入湖水量的变化研究了太湖水体交换周期的变化及原因，并对交换周期变化对水质空间格局的影响进行分析.结果表明：太湖入湖水量有显著上升，2007年以来平均每年入湖水量增长30.8亿m³/a.水体交换周期显著下降，2007年以后约为184 d，相比2007年前下降了26 d.太湖流域及各水利分区近70年来，除去2015和2016年，降雨量无显著变化，主要入湖区下垫面变化造成的入湖水量增加估算在每年2.0 m³左右.太湖入湖水量增加主要集中在湖西区，与沿江口门引水量明显相关.相比2007年前，沿江口门引水量年均增长28.9亿m³/a，而这期间太湖入湖水量增量与这一引水有关.入湖水量的增加开始影响太湖存在的“西浊东清”水质结构，水体交换周期缩短会使东西太湖水质出现均化的现象，东部太湖水质会出现下降的趋势.;In view of the changes of Lake Taihu water exchange cycle in recent ten years, this paper collected and sorted out the hydrological survey data of Lake Taihu from 1986 to 2018, the water diversion quantity change of cities along the Yangtze River in Taihu Basin, rainfall change data of the basin, studied the changes and reasons of Lake Taihu water exchange cycle based on the changes of water inflow and outflow in Lake Taihu, and analyzed the effect of the change of water exchange cycle on water quality spatial pattern. The results show that the inflow of Lake Taihu has increased significantly, with an average annual inflow of 3.08 billion m³/a from 2007. The water exchange cycle has dropped significantly. It is about 184 days after 2007, which is 26 days lower than that before 2007. Over the past 70 years in the Taihu Basin and various water conservancy divisions, except for 2015 and 2016, there has been no significant change in rainfall. The increase in the amount of water inflow into Lake Taihu caused by changes in the underlying surface of the main lake inflow area is estimated to be about 2.0 m³/a. The increase of water inflow into Lake Taihu is mainly concentrated in the west of Lake Taihu, which is obviously related to the water diversion along the Yangtze River. Compared with that before 2007, the water diversion volume along the Yangtze River has increased by 2.89 billion m³ on annual average, and the increase in the amount of water inflow into Lake Taihu during this period is related to this diversion. The increase of water inflow into Lake Taihu began to affect the water quality structure of “Turbid in the West and Clear in the East”. The shortening of the water exchange cycle will homogenize the water quality of east and west Lake Taihu, and the water quality of the east Lake Taihu will show a downward trend.