Abstract
Assessment of river water quality is essential as it provides the knowledge required to make informed decisions. Therefore, water quality was determined at 15 tributary stations located along the Batang Baleh, Sarawak. Results of the study indicate that all tributaries were well-aerated (≈ 7.7 mg/L) with pH (≈ 7.3) and conductivity (≈ 37.3 μS/cm) values falling within acceptable ranges. However, there were tributaries that showed very high turbidity (> 1000 NTU) and suspended solids (> 800 mg/L) which were contributed by the soil erosion from logging activities in the watershed. Tributary stations associated with logging activities also showed significantly higher total phosphorus and organic nitrogen. Cluster analysis demonstrated that water quality at tributary stations along the Batang Baleh exhibited a longitudinal variation from upstream to downstream regions, particularly, dissolved oxygen, five-day biochemical oxygen demand, and nitrite-nitrate nitrogen, which were found higher in upstream region and steadily decreased towards the downstream region. Two stations located at Sg. Serani and Sg. Melatai were distinct from the other stations with the highest concentrations of turbidity, total suspended solids, organic nitrogen, and total phosphorus. Thus, there is an urgent need to reduce the pollutants in the tributaries of Batang Baleh for the health of the sensitive aquatic organisms.
Highlights
Batang Baleh is one of the main tributaries of the Rajang River (551 km) which is the longest river in Malaysia
Tributary stations were relatively shallow in the study area, ranging from 0.15 ± 0.09 m to 3.10 ± 0.00 m (Table 2)
The tributary water quality of the Batang Baleh was determined and the results show that pH, dissolved oxygen (DO), and conductivity were classified as Class I and/or II according to the National Water Quality Standard (NWQS) for Malaysia
Summary
Batang Baleh is one of the main tributaries of the Rajang River (551 km) which is the longest river in Malaysia. These rivers flow through the Kapit Division which is a forested mountainous region. Logging activities have been known to increase suspended solids and nutrients [1,2,3,4,5,6]. As annual rainfall measured at Kapit is among the highest in Sarawak which exceeds 5000 mm in most years, the impact of logging activities could be more severe in the area due to the surface runoff which contains high suspended solids and nutrients from logging sites [7, 8]. The baseline data is useful in management decision for improving and protecting the environment
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