Investigation of temporal variation of drought and its impacts on groundwater nitrate concentrations in drinking water wells (Case Study: Gorgan city and vicinity)

Effects of drought is not limited only to arid and semiarid regions and can have a harmful effect on groundwater resources. Occurrence of severe drought is resulted in reduction of surface water resources in the country and use of groundwater increased. In addition to this severe drop in water levels in groundwater aquifers, changing in groundwater quality and increasing use of these resources for consuming a drinking water are other problems. Nitrate is a common contaminant of drinking groundwater. In this study, temporal variation of the concentration of nitrate in drinking water wells were reviewed in the region in the period of 1383 to 1389. In addition, based on the monthly rainfall amounts, standardized precipitation index (SPI) has been analyzed by software DIP to determine seasonally and drought effects on groundwater nitrate concentrations. Also the water table changes were drawn and the effect of changes in water table was determined based on the fluctuations of nitrate concentrations. The results showed that the drought and water table changes did not have clear relationship with the nitrate concentration in this region. Therefore, domestic sewage could be a major source of groundwater nitrate in the study area.