Assessing Aquifer Contamination by Nitrate and Salinity Using the Concepts of Thresholds and Carrying Capacity: A Case Study of Eshtehard Plain, Alborz Province, Iran

The objective of this research is to assess the contamination of Eshtehard aquifer using the concepts of carrying capacity and threshold. For this purpose, on the basis of continuous measurement of groundwater level of 16 wells in the study area, the isolevel map of groundwater was prepared, then 14 resources including 9 wells and 5 aqueducts were selected and two sampling were carried out in 2010- 2011. After chemical analysis of samples, the maps of EC and NO3 were drawn in GIS. The average annual drawdown of water table was calculated to be 0.69 meter using the annual hydrograph, which was indicative of the over exploitation of the aquifer. Moreover, the results showed that the EC and Nitrate concentration was high, for they passed the thresholds in most parts. Thus, it would be a serious threat to the aquifer. According to the concepts of threshold and carrying capacity, groundwater has been exploited over the carrying capacity of aquifer in most parts and since the exploitation and use of water in agriculture is the major consumption in the study area, the residual of chemical fertilizers has been kept in the soil and permeated to the aquifer by the agricultural water which leads to the increase in Nitrate.