Seasonal variation in water quality parameters for the lower Tapee river of southern Thailand
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- The purposes of this study are for the Lower Tapee River of Southern Thailand: (i) to identify significant pollutants and their sources; (ii) to compare the concentrations of water pollutants and some water quality parameters between the rainy season and the dry season; (iii) to study tidally-induced variation in water quality parameters in both tidal and upstream parts of the river; (iv) to study the correlation between water quality parameters of the river and their correlation with rainfall; (v) to compare the water quality parameters with the Thai and some international water quality standards. Water quality parameters were investigated for two years. The results indicated that the most polluted site was within the city of Surat Thani which received municipal effluent continuously with the concentration of major pollutants becoming higher at low tide. Phunpin District was also another municipal pollutant source. Pollution was also detected at a sampling site located downstream of rubber latex and the rubber sheet factories. In the tidal zone, water pH, conductivity, salinity, total dissolved solids, chemical oxygen demand, chloride, sulfate, calcium, magnesium and sodium concentrations in the dry season were significantly higher than those of the rainy season while their concentrations in the upstream part were not significantly different between seasons. For dissolved oxygen, turbidity, suspended solids and iron, their concentrations in the rainy season were higher than their dry season concentrations. Average ammonia concentrations in the two seasons are not different both in the tidal zone and in the upstream zone. It was found that pH in the rainy season and at high tide was significantly higher than at low tide in this season, but in the dry season the difference of the means was not significant. Conductivity, salinity, total dissolved solids, chloride, sulfate, calcium, magnesium and sodium means at high tide were higher than at low tide in the tidal zone of the river. Dissolved oxygen means for high tide were higher than the means at low tide both in the tidal zone and upstream zone of the river. Chemical oxygen demand changed with the tide and in the opposite way to dissolved oxygen. Turbidity, suspended solids and iron revealed their characteristics as seasonally dependent and non-tidally dependent parameters. Correlation between rainfall and dissolved oxygen, turbidity, suspended solids and iron were highly positive while correlation between rainfall and pH, conductivity, salinity, total dissolved solids, chloride, sulfate, calcium, magnesium, sodium, chemical oxygen demand and ammonia were strongly negative. Chemical oxygen demand and ammonia had weakly negative correlation to rainfall. The overall water quality of the Lower Tapee River was evaluated to conform with Class 3 of the Thai Surface Water Quality Standards. Low dissolved oxygen and high ammonia concentrations were the major problems at some sites. Suspended solids concentrations were higher than the maximum acceptable concentration of the Thai Industrial Effluent Standards in the rainy season while iron and ammonia concentration exceeded the limits of fishery water standards for the European Union and Russia.
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