Structure community of macrozoobenthos in relation to water quality of Siak River, Riau Province, Indonesia

Benthic organisms such as macrozoobenthos are one of aquatic animals widely used in biological assessment of aquatic environment since this animals are food sources of fish, bird and mamalian, and mainatan the stability of geochemistery of the sediment. Study in order to know the structure community of macrozoobenthos in relation to water quality of the lower part of Siak River was carried out on June to October 2008. Twenty (20) sampling station were set up with purposive sampling method based on the differences condition of the micro habitat. Macrozoobenthos samples were collected compositely from 10 sampling stations in each station by using Ekman dredge with the area of 400 square meter, and analyzed further for abundance and diversity. Water sample with volume of 3-L were collected at 1 m depth from the water surface at each of the sampling stations. The water sample was distributed into three of 500 mL-plastic bottle and one dissolved oxygen and BOD bottle. Two bottle of 500-mL plastic bottle was preserved at temperature of 4 C for laboratory measurement. Parameters measured in the field were temperature, conductivity, pH, total alkalinity, and total hardness, while in the laboratory, they were total suspended solids (TSS), total dissolved solids (TDS), organic carbon, total phosphor and total nitrogen. Macrozoobenthos in the lower part of Siak River consisted of 18 genus deriving from 4 classes; Oligochaeta (7 genus from family of Tubificidae), Polychaeta (1 genus from family Neridae), Insect (8 genus from family of Chironomidae, and 1 genus from family of Elmidae), and Mollusc (1 genus of Pomacea). The presence of medium to very tolerance macrozoobenthos in almost sampling sites indicated that the lower part of Siak River suffered from moderate to high organic pollution and disolved solids deriving either from human settlement and chemical industries. Alteration of macrozoobenthos community structure was significantly recorded in Pelita Pantai, Indah Kiat, and Pelabuhan Tissue which in accordance with an increasing in TDS and conductivity and decreasing TSS.