Ecosystem health of Sasthamkotta Lake, a Ramsar site from India based on food web analysis and ecological indicators

Abstract

Water abstraction and subsequent lowering of water table in Sasthamkotta, the largest freshwater lake in South West coast of India raised serious concerns on its management and future implications to terrestrial and aquatic associated fauna. Though a designated Ramsar site, Sasthamkotta Lake has been exposed to various anthropogenic stressors, which in recent years have caused a sudden decrease in its productivity. The study therefore aimed to delineate the present ecological health of the lake in terms of its trophic dynamics and ecosystem efficiency using ecosystem modeling approach. The estimated trophic level (TL) of the lake ranged between 1 (detritus) to 3.76 (fish-eating birds), indicating a skewed structure towards lower carnivorous groups. The ecosystem maturity indices (connectance index, and system omnivory index) revealed the lake to be immature and in the developing stage, though the origin of the lake has been traced back to the quaternary era. The higher value of system overhead (66%) denotes that this ecosystem has been resisting ecological perturbations, in spite of its age is noteworthy. Though the study indicates that the lake’s trophic structure is well-established, a variety of anthropogenic stressors reduce ground water levels and diminish aquifer recharge into the lake. This would significantly reduce the lake’s catchment area, affecting the entire biota. The results presented here is a pioneering attempt to understand the current ecological condition and impact of future possible stressors that need to be monitored for ensuring ecosystem integrity of the lake.