Characterizing land use effect on shallow groundwater contamination by using self-organizing map and buffer zone

Nitrate–nitrogen (NO3–N) contamination in groundwater is a major problem of drinking and domestic waters in rural areas. This study revealed the influence of land use type on shallow alluvial groundwaters in a typical rural area in South Korea by applying a self-organizing map (SOM), principal component analysis (PCA), and hierarchical cluster analysis (HCA). The uncertainty of spatial information on land use was improved by using a buffer zone of the average influence radius of 32.65 m surrounding wells. Two major land-use types, forests (44.9%) and rice fields (28.8%), occupied a total of 73.7% of the rural area. The higher concentrations of NO3–N in public facilities and livestock areas were demonstrated to directly recharge groundwater pollutants. NO3–N contamination in rice paddies, which also contained chlorine (Cl) and sulfate (SO4), was assessed according to the nutrients and residual salt in the soil. In addition, different NO3–N concentrations for the same land use indicate various biochemical reactions and NO3–N recharge types into the groundwater system. The shallow groundwaters in the study area were classified into three clusters according to their chemical constituents and land–use properties, especially NO3–N concentration, including pH, Cl, and SO4, using a SOM, PCA, and HCA. Unlike existing studies, we applied a buffer zone based on the Cooper–Jacob equation to obtain an improved SOM model prediction accuracy approximately 10% greater than that using the original dataset. [Display omitted] •PCA, HCA, and SOM models characterized shallow groundwater contamination.•We applied a buffer zone based on the Cooper–Jacob equation.•The proposed method improved land-use property prediction by ~10%.•NO3–N and pH relationship accelerates groundwater pollution in agricultural areas.