Spatial Dynamics of Pollution in a Tropical Lagoon Ecosystem and Its Social-Ecological Impacts

Tropical lagoon ecosystems constituting lagoons with fringe mangroves are continually polluted with effluents from different sources. This study assessed the spatial variation of selected physicochemical parameters (pH, nitrates, phosphates, and conductivity) in water and sediments from the Chilaw lagoon and its fringe mangroves located on the North-Western coast of Sri Lanka. Interviews were also conducted with local communities (including fishermen) on the social-ecological impacts of pollution in the lagoon ecosystem. Physicochemical analysis was conducted following the APHA standard methods. Statistically significant differences at 95% confidence interval were observed for levels of physicochemical parameters in water and sediment samples, with a horizontal (i.e. length-wise) and vertical (i.e. depth-wise) pollution stratification in the lagoon. Latitude had significant effects on the levels of physicochemical parameters recorded in surface water samples. High levels of pH (pH> 9) recorded in water samples were evidenced by the observation of algal blooms and limited fish catch in the lagoon over the years. Local people report a novel impact of effluent pollution on mangroves, where redworms feed on mangrove leaves. The study, therefore, calls for immediate control of effluent pollution from shrimp farming and other point sources.