Groundwater quality as affected by managerial decisions in agricultural areas. Effect of land development and irrigation with sewage effluents

This work presents two cases of groundwater contamination by agricultural related sources in the Coastal Plain aquifer of Israel. Nitrate contamination is considered to be an inevitable result of anthropogenic activity. Dissolved organic carbon contamination is the utilization of sewage effluents. Most of the nitrate found in groundwater reached the water table in the period 1930 to 1960 and is related to mineralization of organic matter from cultivated virgin soils. This inevitable source released about 1.1 10⁶ t of N. Field evidence indicates that high concentration of DOC (> 20 mg 1^-1) are found throughout a 30 m thick unsaturated zone under land irrigation with sewage effluents. The DOC is mobile through the unsaturated zone and is oxidized when it reaches the water table creating an anoxic groundwater system. These findings question the suitability of irrigation with water containing a high DOC on the replenishment area of phreatic aquifers. (Contribution No. 1, Department of Environmental Science and Energy Research, The Weizmann Institute of Science).