AACL Bioflux, 2015, Volume 8, Issue 3. http://www.bioflux.com.ro/aacl 404 AACL BI OFLUX Aquaculture, Aquarium, Conservation & Legislation International Journal of the Bioflux Society Sediment grain-size distribution in the Lake Laut Tawar, Aceh Province, Indonesia 1 Syahrul Purnawan, 1 Ichsan Setiawan, 2 Zainal A. Muchlisin 1 Department of Marine Science, Faculty of Marine and Fishery Sciences, Syiah Kuala University, Banda Aceh 23111, Indonesia; 2 Department of Aquaculture, Faculty of Marine and Fisheries, Syiah Kuala University, Banda Aceh 23111, Indonesia. Corresponding author: S. Purnawan, syahrulpurnawan@unsyiah.ac.id Abstract . The objective of the present study was to evaluate the grain size distribution in Lake Laut Tawar. The study was done in May and June of 2012 at 5 locations: Boom, Klitu, Ujung Mumpar, Bintang and Toweran. The samples were collected using a grab sampler. The collected samples from the respective locations were sun dried and then sieved to examine the grain-size distribution. The result showed that the sediment types were divided into three categories: gravel, sandy gravel and gravelly mud. The Boom location had gravelly mud (predominantly mud) that was well sorted, while gravel was a major portion of the sediment in Ujung Mumpar and it was moderately well sorted. In addition, all of the locations had negatively skewed values, which indicates a coarse-skew particle distribution. Key Words: granulometric analysis, geostatistics, lake sediment, sorting, skewness. Introduction . Grain size is one of the most important sediment parameters and it is necessary to interpret the depositional environments (Friedman & Sanders 1978). Variations in grain size distribution of lake sediments may reflect the earth’s surface processes such as the developmental processes of landforms through changes in precipitation (Sivasamandy & Ramesh 2014). The grain size distributions are affected by various factors including transportation by rolling, suspension and saltation (Inman 1952; Dyer 1986; Folk 1974). Critical studies of the sediment grain size have been carried out by Udden (1914) and Wentworth (1922), who introduced the Udden-Wentworth scale. Furthermore, Friedman (1961) developed sediment statistical reviews based on arithmetic and moment methods, while Folk & Ward (1957) approached grain size distribution through a graphical method. Frequency distributions of sediment grain size (namely mean, sorting, skewness, and kurtosis) were used frequently to interpret the precipitation of sediment when they re-enter the natural environment (Folk & Robles 1964; Dyer 1986; Wachecka-Kotkowska & Kotkowski 2011; Weltje & von Eynatten 2004). Lake Laut Tawar is one of the oldest volcanic caldera in Indonesia and it has an important ecological role as the habitat for some endemic species of fishes i.e. Rasbora tawarensis and Poropuntius tawarensis (Muchlisin & Siti-Azizah 2009; Muchlisin et al 2012; Muchlisin et al 2015). This lake is situated about 1200 m above sea level. It is 16 km long and 4 km wide and surrounded by mountains reaching above 2000 m. The watershed is covered by rain forests which are extremely affected by deforestation and agricultural activities (Muchlisin et al 2010). Adhar (2008) stated that the erosion condition of Lake Laut Tawar was in a poor state and this has led to silting the bottom of this lake. In addition, Setiawan (2013) carried out a study of grain size in Laut Tawar Lake, but did not compromise the grain distribution analysis based on the statistical approach. Hence, this paper examines statistical analysis of the sediment grain size based on a previous study reported by Setiawan (2013). The grain size affects the water turbidity then influences the primary production of the lake and foraging behaviour of aquatic organisms (Jones et al 2015; Tirok & Scharler