Kashane Chalermwat

Water quality and uses of the Bangpakong River (eastern Thailand).

The Bangpakong River is the most important watershed in the Eastern part of Thailand. Water quality parameters were sampled from June 1998 through May 1999 at 11 sites along a 227 km gradient, covering the wet season (June-November) and the dry season (December-May). Surface water was collected at three different stations per site (close to the banks and in the middle of the river), and analyzed for temperature, dissolved oxygen, turbidity, suspended solids, pH. ammonia, fecal coliforms, biochemical oxygen demand and chemical oxygen demand as well as conductivity, phosphate, and heavy metals. The Scottish water quality index (WQI) was adaptated to the tropical environment. The averaged WQI was low (41%) and quality declined significantly during the dry season (ANOVA, p<0.001). Although the quality rose somewhat at middle sites, only 27% of the WQI values during wet season and 2.5% during dry season were higher than 50%, denoting poor environmental quality. Within each season, the main sources of variability were the differences between sites along the gradient (48% during the wet season, 63% during the dry season), whereas monthly variability represented less than 20% of the variability. The seasonal results show that the river is suitable only for tolerant fish and wildlife species and is of doubtful use for potable water supply during the dry season. As quality improves during the wet period, water can be used for the production of potable water, but only with advanced treatment, and for indirect and noncontact recreational activities. In the middle stretches of the river, higher water quality permits multiple uses at moderate cost.

Shellfish aquaculture in Thailand

Abstract Shellfish have been farmed in Thailand for over 100 years, and during this time, traditional culture techniques have gradually given way to more sophisticated and capital intensive methods. Farmed shellfish production increased from 73,976 to 138,202 metric tonnes between 1988 and 2000. Major species currently under cultivation include the green mussel Perna viridis, the blood cockle Anadara granosa, and three species of oyster (Saccostrea cucullata, Crassostrea belcheri, and Crassostrea iredalei). The horse mussel Arcuatula arcuatula is also produced in limited amounts for animal feed, and gastropods such as the abalone Haliotis asinina and the spotted babylon Babylonia areolata are in the initial phases of commercialization. With the globalization of fisheries commodity markets, the Thai shellfish sector is slowly implementing more rigorous management and certification processes. These procedures are required to access European, American and Japanese markets, and would also serve to decrease the risk of gastrointestinal disease for local consumers.

PERI-URBAN OYSTER FARMING IN THE UPPER GULF OF THAILAND

Oyster farming is an important source of income in many coastal communities throughout Asia. Little is known, however, about the productivity of the farming systems used and the challenges faced by growers. This paper presents the results of a study undertaken in the small peri-urban coastal community of Ang Sila on Thailands eastern seaboard. The community is located in one of Thailands most important oyster production areas, and is dominated by small farms that use simple semi-traditional culture techniques. Farm attributes together with the personal characteristics and opinions of farmers were obtained from a survey of 30 oyster farm owners. A typical farm of 100,000 strings was found to produce a net profit of approximately 90,000 baht (

Nutrient variability and its influence on nitrogen processes in a highly turbid tropical estuary (Bangpakong, Gulf of Thailand).

2250 USD). A high level of female participation in farm ownership was also identified that benefits women with relatively low levels of education and limited economic opportunities. Peri-urban coastal areas in Thailand cannot currently produce export quality shellfish owing to water quality concerns. Improved growing water management techniques and the introduction of seafood safety protocols could, however, improve the quality of oysters sold to domestic consumers and provide a basis for developing export opportunities in the future.

Ultrastructural alterations in the liver and kidney of white sea bass, Lates calcarifer, in acute and subchronic cadmium exposure

Estuarine ecosystems in SE Asia have been poorly studied when compared to other tropical environments. Important gaps exist particularly in the understanding of their biogeochemical function and contribution to global change. In this work we looked into N-turnover in the water column and sediments of the Bangpakong estuary (13°N). A seasonal sampling program was performed along the salinity gradient covering different stretches of the estuary (68km). Key physical and chemical characteristics were also monitored in order to unravel possible environmental controls. Results showed the occurrence of active denitrification in sediments (5.7-50.9nmol N-N2/(cm(3)·hr)), and water column (3.5-1044pmol N-N2/(cm(3)·hr)). No seasonal or spatial variability was detected for denitrification potential in sediment samples. However, in the water column, the denitrification activity peaked during the transition season in the downstream sites coinciding with high turbidity levels. Therefore, in that period of the year, the water column compartment may be an important contributor to nitrate reduction within the estuary. The rather low nitrification rates detected were not always measurable, probably due to the reduced oxygen content and high siltation. This study is one of the few dealing simultaneously with sediments and water column processes in a highly turbid tropical estuary. Therefore, it emerges as a valuable contribution for the understanding of the dynamics of the nitrogen cycle in tropical environments by exploring the role of estuarine N microbial activity in reducing the effects of increased nitrogen loads.