Deep wastewater reservoirs in Israel - I: Limnological changes following selfpurification

Ma'ale Kishon, one of the largest reservoirs storing wastewater for irrigation in Israel, has a surface area of 1. 3 km**2, depth of 9 m and volume of 12 million m**3. Secondary effluent enters the northern basin and after a mean retention period of 6 weeks, flows into the southern one. Due to this two-basin structure, changes taking place during the water storage can be detected. The differences between the two basins were quantitatively studied by an interdisciplinary team. The sanitary, physico-chemical and biological variables indicated an improvement in water quality, leading to an increased ecosystem stability and a safer environmental performance. These results suggest that deep reservoirs of the type here described serving for wastewater disposal and reuse may have a wide application also in other countries having warm, subtropical climates.