Impact of land use and cover on shallow groundwater quality in Songyuan city, China: A multivariate statistical analysis.

The utilization and development of land resources is an important process in which human activities affect groundwater quality. However, the impact of land use on groundwater chemical composition has complex multiple relationships, and is affected by the scale of the buffer zone. Based on these problems, this study used correlation analysis (CA) and principal component analysis (PCA) to discuss the mechanism of the effect of land use/land cover (LULC) on the hydrochemical composition of groundwater in Songyuan City. Samples were divided into two groups, i.e., quaternary unconfined aquifer (0-30 m) and quaternary confined aquifer (30-100 m). By comparing the variation trends of the correlation coefficient and cumulative variance interpretation rate of PCA in different buffer ranges, it was found that the optimal buffer range was 3000 m. Cropland had the greatest impact on groundwater hydrochemistry in the city. The transformation of natural landscapes (such as saline‒alkaline alkali land and grassland) to cropland inhibited salt accumulation in groundwater. This finding is noteworthy since few studies have involved areas where saline‒alkaline land is widely distributed. Compared with CA results, PCA results emphasized the deterioration of groundwater quality by agricultural pollution. Moreover, agricultural pollutants such as NO and K were accumulated in areas where cropland transitioned to natural landscapes such as grassland and water bodies. Considering that wide lakes and rivers provide the drainage area for irrigation water in the study area, the groundwater quality in the surrounding area was affected by the contaminated surface water. The multiple interaction relationship between LULC and hydrochemistry was further confirmed by the combination of principal component scores.