Expansion of inland shrimp farming and its environmental impacts in Songkla lake basin

Amidst the heightened awareness of environmental issues in the Songkla Lake Basin, widespread concern has also emerged over potential environmental impacts of inland shrimp farming. Outbreaks of disease in the coastal areas and the development of low salinity culture techniques have been major factors behind the migration of shrimp farming into the basin freshwater areas well inland from the coast. Over a period of 18 years, from 1982 to 2000, shrimp cultivation areas rose dramatically from 3,491 ha to 7,799 ha, equivalent to an increase of 123.4 percent. Further analysis has revealed that 3,347 ha, or 77.7 percent of the increase in culture areas came from rice fields. The graphic consequence has been well-demonstrated problems of soil and water degradation resulting from the culture operations. Farmed soils possessed several chemical and physical limitations to the establishment of vegetation. The major chemical factors were largely associated with high salinity level and low organic carbon content whereas high bulk density and low saturated hydraulic conductivity were the major physical limitations. Analysis also revealed that salinity levels in soils located within 0, 20, 40, 60 and 100 meters distance from the culture pond were high and well above the suggested critical value of 1.6 mS/cm, indicating that soluble salt could be a limitation to the establishment of plants on these soils. Besides the salinization of soils, the discharge of untreated pond effluents caused deterioration of the quality of waterbodies in close proximity to the pond through the elevation of salinity level, BOD concentration and suspended solid level. The degradation of soil and water quality that occurs could render large areas of productive land unsuitable for arable crop husbandry. Moreover, poor water quality could contribute to outbreaks of disease which, in turn, resulting in a catastrophic collapse of the industry. Management strategy for the reversal of such degradation is discussed.