Water Quality Monitoring in Forested, Agricultural and Mixed Forested-Agricultural Areas using Small Watersheds in the Mae Thang Sub-Watershed, Phrae Province

Abstract

Water quality monitoring in forested, agricultural and mixed forested -agricultural areas using small watersheds was carried out in the Mae Thang sub-watershed, Phrae province. The study focused on the effects of land-use practices on some parameters of surface water quality. Samples were taken during May-November 2007 at the outlets of six smalls watersheds, namely: Huai Namkla (FW1); Huai Tub (FW2); Huai Namgor (AW1); Huai Manai (AW2); Huai Pathan (FAW1); and Huai Phaqhwan (FAW2). The results revealed that the average temperature and pH of water in all land uses ranged from 25.29 to 26.390C and from 8.17 to 8.51, respectively, with no differences among sites, indicating that all sites were categorized as within the standard range of values for surface water quality. Values for dissolved oxygen (DO) and biochemical oxygen demand (BOD) ranged from 3.35 to 4.02 and 0.51 to 1.04 mg/l, respectively. Turbidity of water taken from the mixed forested-agricultural area was the highest. Nitrate-nitrogen, ammonia-nitrogen and total phosphate in the agricultural area were the highest due to the use of fertilizer and chemical substances. Total hardness of water in the Huai Namkla forest area ranged within the standard values, while the others had higher values. It could be concluded that runoff from the forested watershed was identified as first class based on water quality standards, while that from either the agricultural area or the mixed forested-agricultural area was third class.

Keywords: water quality, land use, Mae Thang watershed