Investigation of Water Quality Deterioration from Different Land Use Type by Using Water Quality Index in Kwae-Om and Wat-Pradu Sub-district, Samut Songkhram Province, Thailand

The objectives of this research are to assess water quality from different land use types; to evaluate surface water quality deterioration using Water Quality Index (WQI); and to compare between WQI from residential and agricultural land uses. The water samples were collected from two sub-districts, Kwae-Om sub-district and Wat-Pradu sub-district. Twenty sample sites were identified for each sub-district. Samples were taken between October 2018 to September 2019 to analyze for DO (Dissolved oxygen), BOD (Biochemical Oxygen Demand), TCB (Total Coliform Bacteria), FCB (Fecal Coliform Bacteria), and NH3-n (Ammonia). These parameters were used to calculate Water Quality Index (WQI), which is the water quality standard issued by the Pollution Control Department of Thailand. In Wat-Pradu sub-district, the results showed that average water quality from residential area including DO, BOD, TCB and FCB were all in class 4 (deteriorated) except for NH3-n that was below the standard. Water quality from agricultural area including DO, TCB and FCB were in class 4 (deteriorated) while BOD was in class 3 (fair) and 4 (deteriorated) and NH3-n was below the standard. In Kwae-Om sub-district, the results showed that all average water quality from both residential and agricultural area were in class 4 (deteriorated). After converting water quality parameters to WQI, it was found that water quality from residential and agricultural area of both sub-districts were all in deteriorated level (WQI = 31-60). The comparison of WQI between residential and agricultural land uses indicated WQI from both land use types in Wat-Pradu sub-district were not significantly different (Sig 0.086) as well as Kwae-Om sub-district (Sig 0.962) at a significance level of 0.05.