Water quality assessment and isotope studies of Vembanad Wetland System

Abstract

The indiscriminate exploitation of wetlands beyond its supportive capacity, and input of residues exceeding its assimilative capacity, pollutes the wetland system of Kerala state of India, the magnitude of which is very alarming. The Vembanad wetland system is a complex aquatic system of coastal backwaters, lagoons, marshes, mangroves and reclaimed lands with an intricate network of natural and man made channels and its associated drainage basins are situated in the humid tropical region on the south west coast of the Indian peninsula. Numerous studies have demonstrated that wetlands in general are sinks for various pollutants. Pollution in the wetland is attributed to industrial, urban and agricultural effluents from the city of Kochi and adjoining areas. The environmental status of this wetland including the water and sediment quality had been carried out in the present study. The wetland is an important water body formed by backwaters, estuaries, lagoons and canals, spreading over 196Km in the north-south direction and 29Km in the east-west direction, play an important role in hydrologic functions. Hence the study also focuses on the distribution of various natural isotopes in the wetland system and its use in identifying the source of pollution. The study on the spatial and temporal variation in water quality of Vembanad Lake indicated that the physico-chemical and microbiological status of the wetland system had been worsened by pollutants. The source of major cations and anions in the system is mainly from the saline contribution of Cochin estuary. Nutrient level in water is as high to cause eutrophication in the system, which is reflected by hypereutrophic stage in many parts of the water body. The sewage running through the open canals of Alappuzha contributed high amount of inorganic and organic components to the water body. The dewatering from the agricultural areas also causes damage to physical and chemical quality of water. The improper management of Thanneermukkom bund flushes high concentrations of ions to the fresh water region which poses threat to the paddy fields. Absence of dissolved oxygen in some sites in the southern part of Thanneermukkom bund is a major threat to the aquatic organisms. The microbiological contamination of the lake is caused by domestic sewage, tourist boats and other anthropogenic activities. In monsoon no stations were free of Escherichia coli. The uncontrolled playing of house boats discharges organic wastes, which is threatening the system with very high amount of oil and grease. With respect to the drinking water guidelines, most of the groundwater samples in the basins of Vembanad Lake were not found to be good for drinking. Chemical classification of wetland system based on Wilcox and USSL diagrams were carried out. The different chemical characteristics such as sodium absorption ratio, sodium percentage, soluble sodium percentage, Kelly’s ratio, magnesium hazard ratio, residual sodium carbonate, chloro-alkaline index and permeability index of the surface and groundwater samples were calculated.