Analyzing Temporal and Spatial Variations of Nitrate Concentration and its Health Risks in Groundwater in Mazandaran Province

Intensive agriculture along with increasing urban and industrial wastewater, intensify health risks from nitrate contamination in groundwater resources. In this study, spatial and temporal changes in groundwater nitrate concentration and its health hazards were investigated in Mazandaran Province as one of the major agricultural poles with high population density in the country. For this purpose, nitrate concentration data of 1333 drinking and agriculture wells were collected from 2011 to 2016.Using these data, annual and seasonal changes in nitrate concentration were analyzed using GIS software. Human health hazard (HQ) due to exposure to this pollutant were calculated by the methods proposed by the United States Environmental Protection Agency. In addition, the relationship between groundwater depth and nitrate concentration was investigated in different season. During the study period, nitrate concentration in groundwater ranged from 0.1 to 218 mg L-1. The annual average concentration of groundwater nitrate in the province increased steadily, mainly due to agricultural activities and the use of chemical fertilizers. The average nitrate concentration in the autumn was 15.1 mg L-1 and in the spring was 14.5 mg L-1.In addition, the shallow water table depth was effective in increasing groundwater nitrate in rice paddies. The lowest and highest HQs were 0.002 (in 2011) and 3.88 (in 2016), respectively. During 2011 to 2016, the average of nitrate concentration in agricultural lands, rice fields, residential lands and gardens increased by 78.9, 84.5, 85.6 and 87 percent, respectively. Based on the results, improving the level of health of residents in the study area requires control of groundwater pollution, especially through improving management of water and agricultural inputs.