The Environmental Impact of Urban Development on Nitrate Contamination of Groundwater Resources in Gorgan District, NE Iran

More than 80% of drinking water of highly populated and expanding city of Gorgan, as one of agricultural centers of Iran, is supplied by local groundwater resources (Ziarat, Garmabdasht, and Shast-kola aquifers). Chemical analysis of groundwater samples of Gorgan district indicates two regions of anomalously high concentration of nitrate (Ziarat aquifer) in the urban area. High chloride concentration in water from dug wells corresponds with the anomalous high values of nitrate. Low concentration of nitrate in Shast-kola as well as Garmabdasht aquifers, where main land use is agricultural activities respect to Ziarat aquifer, demonstrates low/no effects of fertilizers on the contamination of groundwater. Determination of NO3/Cl and K/Cl ratios depicts sewage effluents and urban runoff as the main sources of nitrate contamination of the groundwater. Moreover, rapid urbanization and the encroachment of residential development into surrounding forests release considerable nitrate to the underlying shallow aquifers.