Environmental and human facets of the waterweed proliferation in a vast tropical Ramsar wetland - Vembanad lake system

Abstract

The Vembanad Lake and its associated low-lying areas and network of canals (hereafter VBL) form the major part of India’s second-largest Ramsar wetland (1512 km2) located in Kerala State along India’s southwest coast. The extensive VBL has a large fishery, inland waterways, and popular tourist attractions that support the livelihoods of thousands of people. Over the last several decades, the proliferation of water weeds in the VBL has alarmingly increased, causing many adverse ecological and socioeconomic effects. This study based on a review and synthesis of long-term data introduced the environmental and human dimensions of water weed proliferation in the VBL. Eichhornia (= Pontederia) crassipes, Monochoria vaginalis, Salvinia molesta, Limnocharis flava, Pistia stratiotes, and Hydrilla verticillata are the most troublesome water weeds in the VBL, with the first three being the most widespread. They were mostly imported to India long ago before becoming a part of the VBL. These weeds harmed water quality, waterways, agriculture, fisheries, disease vector management, as well as the vertical and horizontal shrinkage of the VBL through increased siltation and faster ecological succession. The inherently fragile VBL was harmed by extensive and long-term reclamation, the construction of saltwater barrages, and many landfill roads that crisscross water bodies serving as coastal dams, creating water stagnation by blocking natural flushing/ventilation by periodic tides from the adjacent southeastern Arabian Sea. These ecological imbalances were exacerbated by excessive fertiliser use in agricultural areas, as well as the addition of nutrient-rich domestic and municipal sewage, which provided an adequate supply of nutrients and a favourable habitat for the expansion of water weeds. Furthermore, because of recurrent floods and a changing ecology in the VBL, the water weed proliferation has become a more significant problem, with the potential to disrupt their current distribution pattern and spread in the future