Assessing Spatial and Temporal Variations of Coastal Groundwater Quality with Regard to Different uses

The quality of coastal water resources at the downstream of watersheds is decreasing mainly due to different anthropogenic activities. In this research, temporal variations of groundwater quality were investigated in a 25000 ha coastal area in Mazandaran province. Groundwater samples were taken from 37 observation wells in the region before (winter 2009), during (spring 2010) and after (Summer 2010) a rice growing season. The samples were analyzed to determine electrical conductivity, acidity and the concentration of calcium, sodium, magnesium, potassium, bicarbonate, chloride and sulphate. Groundwater quality was assessed for agriculture, industry and drinking uses based on various criteria and standards. The average electrical conductivity of groundwater in winter, spring and summer was 5806, 3524 and 8656 μs cm-1, respectively, indicating increase in salinization risk of groundwater at the end of rice growing season. From alkalinity viewpoint, approximately 60% of the groundwater samples were in C4-S1, C4-S2, C4-S3 and C4-S4. Chloride concentration in groundwater was more than its permitted limit for industrial use. The groundwater quality of the 2010 summer season was the worst from drinking viewpoint compared with the samples collected in the 2009 winter and 2010 spring. Results showed that rice cultivation had considerable effect on groundwater quality of the study coastal area. Therefore, the proper management of water and nutrient during rice growing season can be effective to protect groundwater quality in the study area.