Using cluster analysis for understanding spatial and temporal patterns and controlling factors of groundwater geochemistry in a regional aquifer

摘要

Understanding spatial and temporal patterns of groundwater geochemistry at the regional scale over a long time period is challenging, due to the lack of data and effective statistical approaches to characterize complex natural processes and anthropogenic activities. We applied a recently developed cluster analysis method to investigate spatial and temporal patterns and controlling factors of groundwater geochemistry in the confined aquifer of the Jianghan Plain, China. The cluster analysis is applied to a dataset of 13,024 groundwater geochemical measurements for 11 geochemical parameters of 1,184 groundwater samples collected over 23 years from 29 monitoring wells distributed over the Jianghan Plain. The cluster analysis yielded a classification of seven clusters, and the classification was confirmed by using principal component analysis and Stiff and Piper diagrams. Based on the spatial distribution of the seven clusters, the Jianghan Plain is separated into four geochemical zones (i.e., recharge zone, transition zone, flow-through zone, and discharge-mixing zone) along the regional groundwater flow path, which has not been attempted in the past. The temporal changes of groundwater geochemistry are controlled by short- and long-term factors of water-rock interactions and anthropogenic activities. A particular finding of this study is that the Three Gorges Reservoir has a long-term impact on groundwater geochemistry, because the reservoir increased river discharge to groundwater after 2009. This study demonstrates that using the cluster analysis method together with hydrogeochemical analysis can identify spatiotemporal patterns and controlling factors of groundwater geochemistry at the regional scale over a long monitoring period.