Sediment Dynamics for a Changing Future (Proceedings of the ICCE symposium held at Warsaw University of Life Sciences - SGGW, Poland, 14–18 June 2010). IAHS Publ. 337, 2010. 258 Sediment impacts on aquatic ecosystems of the Bukit Merah Reservoir, Perak, Malaysia WAN RUSLAN ISMAIL 1 , ZULLYADINI A. RAHAMAN 1 , SUMAYYAH AIMI MOHD NAJIB 1 & ZAINUDIN OTHMAN 2 1 HydroGeomorphology Research Group, Section of Geography, School of Humanities, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia wruslan@usm.my 2 Department of Geography, School of Humanities and Social Sciences, Universiti Pendidikan Sultan Idris, 35900 Tanjong Malim, Perak, Malaysia Abstract In recent decades interest in suspended sediment dynamics has increased. There are many issues related to high suspended sediment concentrations, such as reservoir sedimentation, channel and harbour silting, as well as the ecological and recreational impacts of sediment management. This paper describes a study of the input and output of sediment in the small Bukit Merah Reservoir (BMR) in Perak, Malaysia. The reservoir received inputs from four rivers totalling about 37 600 t year -1 . More than 90% of the sediment input (approx. 35 000 t) came from the Sg. Kurau River. The average lake sedimentation rates were 0.36 mm year -1 (1995–2000) and 0.48 mm year -1 (2000–2005). The average suspended sediment concentration in the lake was between 8.6 and 13.5 mg L -1 , while turbidity ranged between 5.8 and 64.1 NTU. The reservoir is slightly eutrophic, caused by the impact of sediment and nutrients on the receiving water body. Key words sediment inputs; Sg. Kurau; turbidity; secchi depth; eutrophication; Bukit Merah Reservoir (BMR) INTRODUCTION Human activities exacerbate soil erosion within catchments and this causes increased delivery of sediment to aquatic systems. Some examples of human activities affecting sediment delivery include mining, urban development, construction and the presence of roads (e.g. Gruszowski et al., 2003; Motha et al., 2004; Rijsdijk et al., 2007). Land-use change over the last half century has also altered the hydrological and geochemical regime of rivers, and lakes and reservoirs (Hatton et al., 2003). In many regions of the world, land clearing for agriculture is responsible for much of the sediment transported out of catchment areas and delivered to waterways and lakes (Dai et al., 2007). Sedimentation of reservoirs has become a serious problem due to the synergistic action of population growth, intensity of agricultural operations, poor soil conservation and deforestation (Bowonder et al., 1985). Although the delivery of sediment to lakes has reduced in some regions owing to the introduction of sediment control programmes and improved soil conservation practices, excessive sediment loading remains one of the primary forms of anthropogenic disturbance of aquatic ecosystems in both tropical and temperate regions (Donohue & Molinos, 2009). This paper describes a study on the fate of sediment inputs into the small Bukit Merah Reservoir (BMR), a shallow reservoir which was principally built for irrigation of paddy fields and for water supply in North Perak, Malaysia. MATERIALS AND METHODS Study area Bukit Merah Reservoir (4°59.3′–5°4.4′N; 100°39.2′–100°42.8′E; Fig. 1), in north Perak, is the oldest reservoir in Malaysia, built in 1902 during the British colonial period. Bukit Merah Reservoir (BMR) is categorized as a shallow human-made lake, with a maximum depth of 5 m located in the thalweg of the pre-existing, main river channel. The river inlets are the Sg. Merah, Sg. Jelutong, Sg. Selarong and Sg. Kurau. The main purpose of its construction in 1902 was to supply water to the rice fields in the Kerian District. It was created by damming the Sg. Kurau River, which is the main source of water to the dam. The capacity of the reservoir is 70 × 10 6 m 3 at a water depth of 8.63 m. The BMR is the main source of fish for the people in the surrounding Copyright © 2010 IAHS Press