Nitrate Contamination of Groundwater in Minqin Oasis in Northwestern Arid Region, China

Groundwater constitutes the largest single source of fresh water in many parts of the world and provides a risk buffer to sustain critical water demands during cyclic and prolonged dry periods, especially in semi-arid and arid regions. Intensification of agriculture, increases in land area devoted to arable crops, intensification of animal husbandry, and a move away from arable rotations toward monoculture have caused groundwater fast depletion of already critically low stocks accompanied by persistent degradation of water quality due to salinization, and contamination by pesticides and fertilizers. An assessment study of groundwater nitrate contamination conditions in the Minqin Basin was conducted in support of efforts to manage water quality in the basin. There were 65 observation well water samples collected and analyzed for nitrate. The results of analysis include distribution of nitrate contamination and probability of exceedance of drinking-water nitrate regulatory limit. The concentration of the nitrate is ranges between 0.03 and 59.75 mg L^-1. There are NO₃ ^--N levels of the 1.54% samples in groundwater exceeded standard limits (10 mg L^-1) for drinking water in the basin. Results thus indicated that most of the groundwater of the study area is presently safe for drinking purpose but some anthropogenic activities associated with intensive cultivation had a positive influence on its loading with NO₃ ^-. The distribution of nitrate contamination conditions was clarified in this study by using GIS, which will be applicable to the effective management of groundwater quality.