Spatial distribution characteristics and source analysis of shallow groundwater pollution in typical areas of Yangtze River Delta.

With the accelerated industrialisation and urbanisation in the Yangtze River Delta region, shallow groundwater has also suffered some pollution. In order to clarify the current state of pollution and its causes, principal component analysis (PCA) was used to classify the main factors. An absolute principal component-multiple linear regression model (APCS-MLR) was also used to determine the contribution of the main pollution sources to the shallow groundwater quality. The analysis results showed that the exceedance of water quality indicators such as iron, manganese, aluminium and COD in shallow groundwater in the study area was more serious. With the exception of Mg, the other indicators are highly variable and are more likely to be influenced by human factors. The main pollution factor affecting the quality of shallow groundwater is the dissolution filtration - migration enrichment factor, followed by agricultural and urban sewage factors, industrial pollution factors, and geological environmental background factors. And the main sources of pollution in shallow groundwater are mainly located in the western, northwestern and northern parts of the study area. The use of fertilizers and pesticides in urban life and urban runoff, industrial production and agricultural production are the main causes of pollution. The effects of leaching and transport enrichment, agricultural and urban runoff, and industrial pollution on groundwater quality are significant. The predicted concentrations calculated by the model are generally consistent with the measured concentrations, indicating the accuracy of the calculation of the contribution of each pollution source. This study is applicable to the analysis of shallow groundwater pollution sources in the study area, and also provides a scientific basis for the evaluation of regional groundwater resources and pollution prevention.