evaluation of nitrate concentration and vulnerability of the groundwater by gods and avi methods (case study: kordkandi-duzduzan plain, east azarbaijan province)

the aim of this study is to assess the concentration of nitrate in groundwater resources of the kordkandi-duzduzan plain and to evaluate the vulnerability of the groundwater using avi and gods methods. kordkandi-duzduzan plain is located in east azarbaijan province in the northwest of iran, which groundwater is important for drinking and agriculture in the region due to scarcity of suitable surface waters. as well as, intensive agricultural activities and excessive use of agricultural fertilizers have caused groundwater nitrate contamination. therefore, it is required to assess the quality of the groundwater regarding nitrate and to determine the vulnerability of the aquifer. for this purpose, 22 water samples were collected from shallow and deep water wells in july 2015 and analyzed. the lowest concentration of nitrate with 3.31 mg/l was from the northof the plain and adjacent of the central ranges which was due to high depth of groundwater level and fine grain of the sediments. the highest nitrate concentration with 37.23 mg/l was from the southeast of the area which can be attributed to the course sediments of this area. the results showed that anthropogenic activities are the main reason for the presence of nitrate in the groundwater. these activities can be caused by overuse of fertilizers by farmers or leakage from domestic sewage systems in the area. the moderate correlation (r = 0.497) between nitrate concentration of bicarbonate also support the use of nitrogen fertilizers in agricultural lands. in order to initial estimation of the vulnerability, simple avi and gods methods were used. according to the avi method, northwest and east of the plain and based on gods method, northwest and southeast of the plain were determined as the highest contamination potential in comparison with other parts of the plain.