| Summary: | The hydrogeochemical characteristics of groundwater, in an area where widespread contamination by nitrate ( NO 3 − ) was anticipated, were studied using traditional geochemical investigation and multivariate statistical analysis. Widespread NO 3 − contamination as high as 67.2 mg/L as NO3–N was observed, and positively correlated with that for chemicals ( Cl − , major cations) with surface origin. Principal component analysis (PCA) revealed that three processes affected groundwater chemistry of the area: (1) leaching of pollutants from the ground surface; (2) reduction of NO 3 − in areas with low dissolved oxygen (DO); and (3) ingress of low NO 3 − deep groundwater. Five sample groups were identified from cluster analysis, and analysis of land use patterns around each group showed that fate and distribution of NO 3 − contamination were mainly controlled by surface topography and predominant land use type. The highest NO 3 − concentrations were associated with confined livestock feeding operations in hilly terrain areas, where infiltrating water also had high DO. Lower NO 3 − concentrations found in the lowland flat areas were thought to be due to either reducing conditions in rice paddies leading to N attenuation or drawing in of deep groundwater by pumping to meet agricultural needs during periods of low rainfall.
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