No abstract

Investigations on the water quality of the Mae Klong River and Estuary were conducted from April 2005 to February 2006 during periods of early-, mid-, and late-loading. Nutrient loads and transfer patterns were studied together with clarification of contaminated sites. The results indicated that NH4+, NO2- + NO3-, Si(OH)4 and PO4(3-) concentrations varied by season and were comparatively high in the mid-loading period. Analysis of DIN:P and Si:P molar ratios indicated that P04(3-) could possibly be a limiting nutrient. Highly contaminated sites were in the middle (Ratchaburi province) and lower (Samut Songkhram province) river zones in which anthropogenic wastewater discharges were significantly (p < 0.05) loaded. Analysis of the DIN and P transfer patterns showed that self-remediation efficiencies were rarely found. The highest DIN and P loads of 23.87 and 4.03 t/day, respectively, were found in Samut Songkhram province. Nutrients were found to contribute to the hypertrophic condition of the lower river and the estuary. The baseline level of chlorophyll a in the upper river was approximately 3.3 microg/L, while levels exceeded 10 microg/L in the estuarine zone. Such chlorophyll a levels were highly significant (p < 0.01) related to DIN and P (with correlation coefficients of 0.44 and 0.37, respectively). In order to maintain river conservation to an acceptable degree, levels of about 20 micromol/L DIN and 1 micromol/L P were suggested as the upper limits. To achieve such levels will require serious consideration with regard to the development of nutrient criteria for water resource conservation management and sustainable utilization purposes.

No abstract

The trophic dynamics of a newly-impounded south east Asian reservoir, Pasak Jolasid, Thailand, monitored from its creation, were constructed using ECOPATH, a mass-balanced model. The trophic levels (TLs) of 36 ecological groups varied between 1.0 and 3.2. The majority of fish biomass was at the second TL, where the fishery is concentrated. Some food resources (benthic organisms and zooplankton) were not fully used, whereas phytoplankton and benthic algae were important components of the food web, which is based on phytoplankton and detritus. The implications of these findings are discussed in terms of ecological maturity of the ecosystem and possible fishery management of this multi-purpose reservoir.

No abstract

This research was carried out in Tha Chin Watershed in the central part of Thailand with attempts to apply multidisciplinary knowledge for understanding ecosystem structure and response to anthropogenic pollution and natural impacts leading to a proposal for an appropriate zonation management approach for sustainable utilization of the area. Water quality status of the Tha Chin River and Estuary had been determined by analyzing ecological, hydrological, and coastal oceanographic information from recent field surveys (during March 2006 to November 2007) together with secondary data on irrigation, land utilization, and socio-economic status.Results indicated that the Tha Chin River and Estuary was eutrophic all year round. Almost 100% of the brackish to marine areas reflected strongly hypertrophic water condition during both dry and high-loading periods. High NH(4)(+) and PO(4)(3-) loads from surrounding agricultural land use, agro-industry, and community continuously flew into the aquatic environment. Deteriorated ecosystem was clearly observed by dramatically low DO levels (ca 1 mg/l) in riverine to coastal areas and Noctiluca and Ceratium red tide outbreaks occurred around tidal front closed to the estuary. Accordingly, fishery resources were significantly decreased. Some riverine benthic habitats became dominated by deposit-feeding worms e.g. Lumbriculus, Branchiura, and Tubifex, while estuarine benthic habitats reflected succession of polychaetes and small bivalves. Results on analysis on integrated ecosystem responses indicated that changing functions were significantly influenced by particulates and nutrients dynamics in the system.Based on the overall results, the Tha Chin River and Estuary should be divided into 4 zones (I: Upper freshwater zone; II: Middle freshwater zone; III Lower freshwater zone; and IV: Lowest brackish to marine zone) for further management schemes on water remediation. In this study, the importance of habitat morphology and water flow regimes was recognized. Moreover, nearshore extensive shrimp culture ponds, irrigation canals, and surrounding mangrove habitats belonging to local households seemed to act as effective natural water treatment system that can yet provide food resources in turns. These remediation-production integrated functions should be deserved depth considerations for water quality development of the Tha Chin areas.

No abstract

The Tha Chin River Basin located in the great central basin of Thailand is used for water supply, aquaculture, transportation, and recreation as well as a sink for wastewater discharges. Because of gradual deterioration of water quality and fishery resources, this study aimed to explain recent status of the river self-remediation efficiency that was influenced by nutrient inputs and outputs from the river system. Field surveys were carried out during May 2007 (early rainy season) and October 2007 (late rainy season) within the Tha Chin River located in 4 provinces; Chainat, Suphan Buri, Nakhon Pathom, and Samut Sakhon. The nutrient budgets in each province section were analyzed. Results indicated that the river was in eutrophic condition all year round. High nitrogen and phosphorus loads from surrounding agricultural land use, agro-industry, and community continuously flew into the river system. Those nutrient concentrations were higher in the early rainy season than the late rainy season. The lowest river zone (in Samut Sakhon province) indicated highest dissolved inorganic nitrogen (DIN) and orthophosphate phosphorus (P) discharges of 145.54 and 36.14 tons/day, respectively. The highest remediation efficiency of the river (ca 60% of the total input) was found in the uppermost area of Suphan Buri province. The lowest remediation efficiency (ca 12%) was found in Samut Sakhon province. From the overall view, long term monitoring of river and estuarine DIN and P should be conducted. To make better condition of aquatic environment and fishery resource in each province-based section, the controls of DIN and P remediation efficiencies (e.g. by effective management of flow speed) at 20 and 50%, respectively, were recommended.