Human interventions and consequent environmental degradation of a protected freshwater lake in Kerala, SW India

Abstract

Sasthamkotta lake in the southwestern coast of India is the largest freshwater lake in the region. The lake has a water spread area of about 3.75 km2 and serves as a drinking water source for about seven lakh people in southern Kerala. Unfortunately, the lake is at the verge of severe degradation consequent to different kinds of human interferences. The Sasthamkotta lake receives water mainly from rainfall (2,350 mm/year) and surface run-off (3.33 million m3/ year). Apart from these, a significant quantity of water reaches the lake through underwater springs emerging from the Quaternary and Neogene aquifers as well. Rampant removal of construction grade sand using high power jet pumps from the Quaternary aquifers linking the lake with the adjoining river, over exploitation of lake water, unscientific engineering constructions, etc. are some of the externalities leading to degradation and ultimate drying up of the lake. The floodplain of the Kallada river, hosting the lake Sasthamkotta, was unaffected by sand extraction till early 1970’s. The results of the present study revealed that indiscriminate sand mining has turned floodplain area of about 3.57 km2 into fallow lands, during the past 3–4 decades. This together with the riverbed lowering due to instream sand mining has significantly reduced the groundwater replenishment of the lake system. The construction of embankment on the southern side of the lake has not only isolated the lake system from its natural settings, but has prevented the flood pulse contribution of monsoon waters to a considerable extent. The present paper examines in detail the pros and cons of the human induced environmental degradation of the Lake Sasthamkotta which is declared recently a Ramsar wetland of international importance. Based on the study, a set of recommendations are also drawn for improving the overall environmental quality of the Sasthamkotta lake in particular and the freshwater lakes in the coastal lands of densely populated tropics in general.