Integration of aquatic ecology and biological oceanographic knowledge for development of area-based eutrophication assessment criteria leading to water resource remediation and utilization management: a case study in Tha Chin, the most eutrophic river of Thailand

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 NH₄⁺ and PO₄³⁻ 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.