Distribution of sediment nutrients of Vellar estuary in relation to shrimp farming

Abstract

Shrimp farming picked up fast in India particularly in the southern states, due to promotion on the part of Government agencies and high return on investment (ROI). The discharge of used water from the shrimp farms into the estuaries, backwaters and mangroves became a matter of great concern of the environmentalists. In the absence of reliable data collected over a period of time, no definite conclusions could be drawn about the negative impact of shrimp farming. This emphasized the imperative need for monitoring different physico-chemical and biological parameters of the estuaries, backwaters and mangroves where shrimp farming has a strong presence. In the Vellar estuary (lat.11°29′N; long. 79°46′E) shrimp farms were started in the year 1992 and by 1995, there were as many as 42 shrimp farms with a water spread area of 150 ha. The formulated pellet feed given to the shrimp is rich in protein, fat, fibre and minerals etc. These nutrients get dissolved in water, settle in the sediment of the shrimp farms and discharged into the Vellar estuary during periodic draining. Estimation of the levels of nutrients can serve as indicator of enrichment and eutrophication in the estuary arising out of shrimp farming. Therefore in the present study, data on levels of carbon, nitrogen and phosphorus in sediments were collected for a period of two years with the view of ascertaining changes in their levels arising out of discharge of used water from shrimp farms into the estuary.