SEDIMENT INDUCED ACIDIFICATION OF SHRIMP CULTURE PONDS: CONSEQUENCES AND IMPACTS

Due to continued pressure on land resources, highly pyritic soils have been converted to coastal aquaculture activities. Sediment induced acidification is considered as a major technical and environmental problem in coastal shrimp culture in ponds constructed in acid sulphate soils.

Technical constraints of utilization of pyritic sediments include acidification of pond soil and pond water, poor natural productivity in ponds, slow growth of culture organisms, low production, higher water temperatures, low turbidity and poor fertilizer response.

Health related problems of cultured shrimps identified in these ponds are deposition of hydrated iron oxides on exoskeleton and clogging of gill lamellae, deposition of higher incidences of soft shell syndrome and black/brown gill syndrome and high mortality during heavy rains after prolonged dry spells. Shrimps cultured are more vulnerable to infections.

In addition higher concentrations of nutrients, metabolic toxic end products, and suspended solids of normal farm effluents, shrimp ponds on pyritic sediments release highly acidic effluents with higher concentrations of soluble iron, manganese and aluminum.  Discharges during pond conditioning are heavily loaded with iron oxides and are with very low pH. Several short term and long term environmental consequences have been identified in coastal areas due to reclamation of pyritic soils for shrimp farming. However, specific impacts on biodiversity and fishery resources are yet to be assessed.

Key words: shrimp culture, pyritic sediments, shrimp health, environment.