IMPACTS OF LAND USE AND RAINFALL ON THE WATER QUALITY OF TRIBUTARIES OF SERIN RIVER, SARAWAK

Abstract

Water quality of the tributaries could be affected by land use such as agricultural activities. Thus, a study was conducted to determine the water quality at the mouth of six tributaries of the Serin River from September 2009 to September 2010. The study shows that in February 2010, when there was no rain two days before sampling and when the water level was low, higher concentrations of ammoniacal-nitrogen, nitrite-nitrogen, nitrate-nitrogen and soluble reactive phosphorus than other months were observed. Furthermore, 92.7% and 93.6% of the inorganic nitrogen in Pam River and Bukah River were in the form of ammoniacal-nitrogen. Nitrate was signifcantly higher and occasionally dissolved oxygen was below 5 mg/L at Bujang River. TSS ranged from 2.0-84.4 mg/L with the highest value observed during rainfall event. At Pam River, reactive phosphorus and ammoniacal-nitrogen exceeded 0.2 mg/L and 0.3 mg/L respectively throughout the sampling period and 50% of the dissolved oxygen values were less than 3 mg/L. For Bukah River 50% of the measured dissolved oxygen were less than 5 mg/L and occasionally reactive phosphorus was more than 0.2 mg/L. BOD5 at all tributaries exceeded 3 mg/L and 60%, 50%, 44% and 40% of the readings at Bukah, Pam, Bukar and Penat exceeded 12 mg/L respectively. Both Pam and Bukah watershed have animal farming actvities. This study shows that land use affected the water quality and over the sampling period rainfall events and water level played an important role in the nutrient concentrations as some of the highest concentrations were observed during low water level when less dilution occurred though concentrations were also influenced by the timing of effluent outflow.