Assessment of groundwater contamination by NO3 - using geographical information system in the Zhangye Basin, Northwest China

Geographical information system (GIS) technology was used to investigate NO3 (-) concentration of groundwater in the Zhangye Basin, Northwest China. Thematic information and NO3 (-) data of groundwater from the Zhangye Basin were analyzed in a GIS environment to study the extent and variation of NO3 (-) concentration and to establish spatial relationships with corresponding land use types. About 38.8% of groundwater samples showed NO3 (-) concentration above the human affected value (13 mg/l NO3 (-)), while more than 10.2% exceeded the maximum acceptable level (50 mg/l NO3 (-)) according to WHO regulations. The spatial distribution of NO3 (-) of groundwater in the Zhangye Basin showed an obvious character of zonation; the high NO3 (-) concentration was mainly located in the city seat areas, and Zhangye City was the high-value center. The probability of over 90% for NO3 (-) concentration exceeding 13 mg/l was found in urban seat areas. The spatial analyses indicated that groundwater contamination by NO3 (-) was closely related to one specific land use class, the urban. The NO3 (-) concentration of groundwater under urban was significantly higher than that under irrigation land or sand dune. Most of the unacceptable NO3 (-) levels were found in groundwater samples assigned to urban area, but a few were also found allotted to irrigation land class. Therefore, urban source was considered the principal source of NO3 (-) contamination of groundwater in the Zhangye Basin, while irrigation land source was still a possible source of NO3 (-) contamination.