Phosphorus fractionation in sediments of the Pichavaram mangrove ecosystem, south-eastern coast of India

Present study examined phosphorus dynamics through delineation of source as well as availability of phosphorus and its fractionation within the intertidal sediments of Pichavaram mangrove ecosystem. Twelve sediment samples and two cores were collected from the mangrove forest along with estuarine area (Vellar-Coleroon) during January 2005. Sediments were analyzed for total phosphorus and its fractionation using operationally defined chemical sequential extraction scheme (SEDEX). Dissolved phosphorus (in water) and total phosphorus (in sediments) concentrations were high in the Vellar region of Pichavaram mangrove area due to pollution load from nearby villages and agricultural fields. However, the spatial variation in dissolved phosphorus were insignificant (at significance level = 0.05). The results for the phosphorus fractionation (post-tsunami) were compared with earlier studies (pre-tsunami). It was observed that all phosphorus fractions (except adsorbed-phosphorus) showed a highly significant (at significance level = 0.05) increase in concentration after the tsunami event. There was significant decrease in the adsorbed phosphorus concentration as a result of tsunami. The changes were more pronounced for organic phosphorus which increased by almost twofold following the event. These variations were attributed to change in salinity, increase in dissolved oxygen as well as the retreat of tsunami water carrying the waste load. The vertical distribution of phosphorus through core sediments showed that mixing after tsunami had altered the different phosphorus fraction and its availability. Overall, the study indicated that the fluvial weathering along with litter degradation and anthropogenic sources controlled the biogeochemistry of phosphorus in this mangrove ecosystem. Observed changes in the concentrations are a result of altered physico-chemical characteristics caused by tsunami.