Environmental impact of aquaculture-sedimentation and nutrient loadings from shrimp culture of the southeast coastal region of the Bay of Bengal

摘要

Nutrient loadings were measured for surface seawater and bottom sediments of semi intensive and improved extensive shrimp culture pond, adjacent estuary, and fallow land in the south east coastal region of Bangladesh during August, 2000—January, 2001 to evaluate the impact of shrimp culture. The mean levels of nutrients found in the pond surface water were 108 780 mg/L for CaCO 3, 0 526 mg/L for NH + 4 N, 3 075 wt% for organic carbon, 7 00 mg/L for PO 4 P, 5 57 mg/L for NO 3 N, and 7 33 mg/L for chlorophyll a. The maximum mean value of H 2S(0 232 mg/L) was found in estuarine water. Nutrients loading were found to be decreased with distance from the shrimp farm discharge unit in estuarine water. The mean level of organic matter, total nitrogen, and organic carbon were found in higher concentrations in sediments of cultured pond compared to bottom soil of adjacent fallow land at the same elevation. Extractable Ca values were found in higher concentration(550 33 ppt) in adjacent fallow land, as the shrimps for molting in shrimp ponds use extractable Ca. The relation between seawater H 2S value and sediment pH ( r= -0 94); sediment organic carbon and sediment pH values ( r= -0 76), sediment total nitrogen and sediment pH ( r= - 0 74) were found to be highly negatively correlated. Whereas the relation between seawater H 2S value and sediment total nitrogen ( r= 0 92), water NH + 4 N and sediment pH ( r= 0 66) were found to be positively correlated. The results revealed that load of nutrients at eutrophic level in estuarine water, and decrease of soil pH; leading to acid sulphate soil formation indicates a negative impact of shrimp culture.