Chemical characteristics and eco-environmental effect of groundwater in Ningbo Plain, Zhejiang Province

This paper is the result of groundwater geological survey engineering.

Objective In order to find out the characteristics of groundwater and its reason for evolution in Ningbo plain, and help to optimize the groundwater environment of Ningbo area.

Methods Groundwater in Ningbo plain was analyzed comprehensively and systemically based on field survey and samples analysis, making full use of the previous data, then multiple methods including the mathematical statistics, the correlation matrices, Piper diagram, the ratio coefficient of main ions and environmental isotope were used for this study.

Results The main of surface water and phreatic water were fresh water, however, confined water were mainly brackish water or salt water. HCO₃^- of phreatic water was the predominant anion and Cl^-, Ca²⁺, Na⁺ were all secondary. Contrastly, the dominant ions of surface water and confined water were Cl^- and Na⁺, HCO₃^- was the second. The four water were divided into twenty-three hydrochemical types, and surfer water and phreatic water were both influenced by precipitation evidently, whereas confined water deeply was closed in the aquifer during previous transgression, so there was little relationship with shallow water.

Conclusions Compared with that in the 1970s, the distribution of fresh water body in confined aquifer Ⅰ of Ningbo urban area had no significant change, but that in confined aquifer Ⅱ was changing obviously by the influence of both human activities and natural water recycle. Salt water appeared in the scope of fresh water by hydrochemical evolution, and the scope of fresh water body expanded outside, overall, the distribution area increased by twelve square kilometer approximately, and the environmental effect was being towards positive tendency.