The major objective of this study was to develop appropriate water quality control policies for a sustainable fishery in Southern Songkhla Lake (Southern Lake) so the impact of water pollution on fishery production in the lake was the first consideration.

The three major components of this study were: (i) the identification of the situation and trends in fishery production associated with water quality in the lake, using secondary data and statistical analysis, (ii) the evaluation of technological options to improve water quality using secondary data and cost-effectiveness analysis, and (iii) the analysis of proposed policy alternatives for better water quality. In order to identify the current situation and trends in fishery production associated with water quality in Southern Lake, the natural shrimp catch was used as an indicator of water quality deterioration while the water quality composite index (WQCI) was used as the indicator of the relationship between water quality and pollution from various sources.

Our statistical analysis indicated that the water quality changes in the lake had a significant impact on shrimp production, i.e., one unit increase in the WQCI at UTapao would lead to a shrimp productivity increase of 3.4% (significant at the 0.05 level), and one unit increase in the WQCI at Pag-ro would lead to a shrimp productivity increase of 10% (significant at the 0.01 level). Also, an analysis of 12 years of water quality data (1992-2004) found that the amount of nitrogen and phosphate discharged into Southern Lake had increased over time at every river mouth. In particular, the total amount of nitrogen at the U-Tapao river mouth had increased significantly. Nitrogen was found in farm effluents and in both domestic and industrial waste and in large amounts, which was very harmful to aquatic animals. Therefore, in order to control and improve the water quality of Southern Lake, the wastewater from the various sources needs to be well managed in order to increase the fishery value of the lake.

There were two types of methodologies identified which affected treatment costs for basic technology options. First, land use applications had a higher fixed cost due to land use but lower operating costs, while technology-based applications, such as the Up-flow Anaerobic Sludge Blanket (UASB) or Activated Sludge (AS), had lower land use costs but higher operating costs. With high technology options, however, there was no particular cost pattern.

The results of the cost-effectiveness analysis (CEA) showed that the effectiveness of a treatment technology was sensitive to the size of the plant and the influent load. It was less effective for businesses with a lower influent load or a smaller size to invest in individual treatment plants while it was more cost-effective for smallscale polluters to share a common treatment plant.

For domestic treatment facilities at the municipal level, the CEA showed that the cost of treating the biological oxygen demand (BOD) per kilogram was very high even at full capacity. Large-scale domestic treatment facilities tended to be ineffective due to under-utilization and such operations required effective administrative management. Smaller-scale domestic treatment facilities are recommended because these are easier to operate effectively and also offer more flexibility for future development.

The command and control (CAC) policy is the current water pollution management system in Southern Lake. Overall, this study found that the CAC policy was deficient in encouraging the participation of all stakeholders and that they were not sufficiently aware of their responsibilities in environmental protection Based on our literature review and survey, it became evident that firms and farms had the potential to improve their wastewater treatment technologies but there were no incentives for them to do so. Market-based instruments have many advantages over CAC regulations. However, each instrument has different advantages and disadvantages. Therefore, three policy alternatives were carefully compared: the command and control (CAC) system, emission charge system (ECS) and tradable discharge permit (TDP) system. There were ten criteria selected to compare the different policies, namely, public acceptability, legal feasibility, implementation complexity, effectiveness, capital costs, operating costs, transaction costs, impacts, equity, and decentralization.

In order to select the best alternative, the study suggests that policy-makers apply different weights to the different criteria depending on their desired goals. Moreover, some congruence among the advantages of each policy option can also be considered. For example, due to the high outcome effectiveness of the TDP and high capital costs, it could best be applied to large-sized firms and farms, while the ECS would better suit small and medium-scale firms and farms because it involves lower capital costs. Whichever combination of policy options is ultimately selected, further studies will be needed to determine the effectiveness of such combinations.

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Pollution Control and Sustainable Fisheries Management in Southern Songkhla Lake, Thailand