Geostatistical analysis of the integration of spatial information on nitrate-N observations and agricultural land uses for establishing groundwater pollution zones

Groundwater nitrate-N pollution is common in agricultural regions, mainly originating from surface agricultural activities. Integrating spatial information on nitrate-N observations and agricultural land uses is crucial for establishing groundwater pollution zones. To combine agricultural land uses into groundwater nitrate-N pollution, this study used regression kriging (RK) to determine groundwater pollution zones in the Choushui River alluvial fan in Taiwan. First, a multivariate linear regression (MLR) model was employed to explore the relationship between groundwater nitrate-N pollution and agricultural land-use types. Then, simple kriging (SK) was adopted to analyze residuals obtained from gaps between nitrate-N observations and MLR predictions; the SK estimates of the residuals with the addition of the MLR predictions served as the RK estimates for groundwater nitrate-N pollution. Finally, groundwater pollution zones were determined according to a specific anthropogenic nitrate-N pollution level. The study results revealed that the orchard land-use type positively contributed to groundwater nitrate-N in contract to the livestock house and agricultural facility land-use types, which were negatively related to groundwater nitrate-N. Moreover, the RK estimates, which had the ability to characterize the potential pollution source of the orchard land-use type and enhanced the accuracy of the classification of polluted and unpolluted areas through modification of the residuals, were suitable for establishing groundwater pollution zones. In addition, feasible management strategies of orchards located in the groundwater pollution zones must be implemented to reduce nitrate-N leaching.

Automated summary

This study used regression kriging (RK) to determine groundwater pollution zones in the Choushui River alluvial fan in Taiwan by integrating agricultural land uses with groundwater nitrate-N pollution. The results showed that orchard land-use type positively contributed to groundwater nitrate-N, while livestock house and agricultural facility land-use types were negatively related to groundwater nitrate-N. RK estimates characterized the potential pollution source of orchard land-use type and enhanced the accuracy of polluted and unpolluted areas classification by modifying the residuals, making it suitable for establishing groundwater pollution zones.