Comprehensive Evaluation of Geological Environmental Quality and Water Ecological Function in Zipingpu Reservoir Area of Chengdu City

Abstract

Zipingpu Reservoir, located in the upper reaches of the Minjiang River Basin in the middle section of Longmen Mountain in western Sichuan, is a large-scale water control project mainly for irrigation and water supply, with comprehensive benefits such as power generation, flood control, environmental protection, tourism and so on. The area of the reservoir area is 18.16 square kilometers. In May 2021, the group has carried on the detailed survey sampling in the scope, including five parts, the surface water sediment sample 6, 3 pieces of rock samples, respectively, the water of heavy metal measurement and analysis of characteristics of phytoplankton community structure, sediment measurement of heavy metals, petrophysical parameters and microscopic thin section identification, etc. Through the qualitative and quantitative analysis of the geological structure, hydrogeological conditions, it is considered that the reservoir area has the conditions for the occurrence of structural earthquakes; And the lateral percolation of the water body in the reservoir area is not strong. The environmental quality of surface water in the reservoir area is good, which is much lower than the standard limits of surface water resources class I and centralized drinking water; the content of heavy metals in surface sediments is generally between the limit of grade I and grade II of soil environment (alkalinity); the element accumulation index of the sampling site is between −4.30–0.37, indicating that there is no pollution; In which the individual samples of Cu, Cd, Cr and Pb elements 0 < I_geo < 1, and the accumulation indexes of Fe, Mn, Ni and Zn are all less than zero; the dominance index of phytoplankton in the sampling area varies from 0.00 to 0.14, with more dominant species; the range of phytoplankton density at sampling sites is 4585.9 −321019.1 cells/L, and the Shannon-Wiener diversity index is between 3.6874–4.1508, indicating that the water quality in the sampling area is relatively good, showing micro-pollution or non-pollution. It will be a hot topic to apply the methods of structural geology, environmental geology, ecological geology and so on to water environmental quality assessment.