Cadmium distribution in water, microalgae biomass, and sediment of River Bonan Dolok, Samosir-North Sumatra, Indonesia

River Bonan Dolok in Samosir is located on the watershed of Lake Toba, an ancient volcanic lake in North Sumatra. Some parts of this river bordered with paddy fields, a common source of cadmium through the leaching process, which then released into the water body. Meanwhile, this river has been proposed as endemic fish (called in the local name as Ihan) conservation area and eco-tourism area. Therefore a scientific reference base management concept is needed. Spatial distribution of cadmium (Cd) must be revealed since this metal is very toxic and can be easily transferred and accumulated in the aquatic food chain. This study aims to inform the distribution of Cd in water, microalgae biomass and sediment. All samples were taken compositely from the upper stream (Station 1), Station 2, Station 3, and lower stream (Station 4) in April 2019. The structure of microalgae community is also identified. The results show that Chlorophyte (mostly consisted of Microspora sp) biomass at Station 2, has the highest Cd concentration (0.57 µgCd/g dry weight). While Cyanophyte (dominated by Microcyctis aeruginosa) even observed bloomed at station 4, shows a lower Cd concentration (0.12µgCd/g dry weight). The distribution of Cd in water and sediment (particle size of ≤63 µm) at those sampling stations as well as some water quality also discussed. The range of Cd concentration in water was 0.02 to 0.64 µg Cd/L, while that in sediment was 0.10 to 0.39 µgCd/g dry weight. These data are expected to be used as essential references for developing the management concept of Bonan Dolok ecotourism area in the future.