عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The atmospheric conditions and rainfall shortage have increased the utilization of groundwater resources in the northern regions of the country. Therefore, the evaluation of groundwater resources in the aquifer of the Nekarod plain is of a great importance due to the high use of groundwater resources and subsequent use of chemical agents such as fertilizers and pesticides in agricultural lands. In recent years, lack of appropriate management of groundwater in the East of Mazandran province, Iran, causes a critical situation in groundwater resources. Therefore, the purpose of this study is assessing the vulnerability of aquifer Nekarod area in with DRASTIC model. In the current study the potential of groundwater contamination was evaluated with the DRASTIC model. This model evaluates the groundwater potential vulnerability in aquifers with seven different parameters, including: Depth, Net nutrition, Aquifer media, Soil media, Topography, Non-saturated media, and Hydraulic conductivity. All data were provided by Mazandran Reginal Water Authority (2016-2017). According to the data, the most vulnerable situation was determined in September and October, due to the minimum level of groundwater. In order to gain the purposes, the weights for each of the parameters were first determined using the layer overlay method in GIS software, for each of the seven parameters and the desired range. Weight ranges in the DRASTIC method are from one to five, in ascending order of importance. Then, the columns of each of the ranges in the GIS were converted to the Raster layer. Thereafter, the total number of layers with the obtained weight was summed up, using the Raster calculator. In the next step, the risk maps were finalized in the region according to the model of the DRASTIC. Kriging statistical method was used to illustrate the variation of water quality elements. To determine the correlation coefficient of the results from the DRASTIC model and the aquifer data, Spearman method was applied. Also, SPSS 22 software was employed to determine the final stroke index with nitrate, pH and EC parameters. The results of the evaluation with the DRASTIC model in the area of Nekarod showed that the area with a high vulnerability only has 17.33 percent of the total area of the region and the area with low vulnerability potential covered 52.97 percent. Also, the most vulnerable depth was determined in range of 3 to 9 meters with 62.71%. The most extended area (87.28) with the highest contamination risk had the precipitation less than 500 mm and slope of 0-2%. Pearson statistical test was used to show the relationship between the results of the DRASTIC model and the values of nitrate, pH and EC, which was 0.610, 0.254 and 0.277, respectively.
The Nekarod plain is one of the major contaminated areas due to the use of pesticides and chemical fertilizers with the aim of increasing the yield of agricultural products. Therefore this plain is vulnerable and suffers from lack of groundwater management. According to the results of the DRASTIC model for assessing vulnerability, the southeastern part of the region has the highest vulnerability due to the different texture and physical conditions of the soil, and the north-east to a part of the center of the plain has a low vulnerability. Downstream areas (northern part) have the more coarse texture than the southeastern part, and this is due to the movement of materials to the Caspian Sea, so there is less pollution there. By verifying the model of the DRASTIC and determining the coefficient of correlation between the data (2016-2017) and observed values of the model, it was determined that the DRASTIC model had significant results in the level of 0.05. The correlation in nitrate results has the highest amount in compare with pH and EC, which could be due to the contamination in groundwater. The amounts of pH and EC had inverse correlation with the results of the model. So that with increasing pH, the value of contamination index decreased in the model; while for the parameter of nitrate, the effect is direct and positive. Consequently, applying DRASTIC model is an appropriate scientific strategy for studying and determining the sensitivity of the aquifer in the region of Nekarod. The results of this study corroborated two relevant researches which applied DRASTIC Model for other aquifers in Iran (Ghaen and Ansimeshk).