Siregar, Sofyan Husein2016-04-072016-04-072016-04-07978-602-17943-2-6wahyu sari yenihttp://repository.unri.ac.id/xmlui/handle/123456789/8180In recent years, Dumai River Estuary has become one of area indicated increasing of polution caused by human activities. Nipah Trees is abundant found in this location. In directly, epiphytic diatom composition attached with Nipah Trees will be affected by river environtment. The aim of this research is to describe the composition of epiphytic diatom on Nipah Trees from several area at Dumai River Estuary. Epiphytic diatom sampel was collected by scrapping 5 x 5 cm on Nipah Trees from 5 station (from river mouth to river body) on July 2011. Water quality parameter was also meseured in the same time when diatom collected. Thirteen species (Actinocyclus ehrenbergi, Bacillaria paradoxa, Biddulphia granulata, Biddulphia reticulata, Coscinodiscus sp, Licmophora abbreviate, Melosira sp, Navicula sp, Pleurosigma sp, Rhizosolenia alata, Skeletonema costatum, Thalassiothrix frauenfeldii, Triceratum reticulum) were found at Dumai River Estuary. Morever, The number of diatom species were 3 species at mouth river estuary and was only 1 species at river body. The abundance of epiphytic diatom on Nipah Trees along Dumai River Estuary ranged from 1634 to 6536 cells/cm2. The highest abundance of epiphytic diatom was found at the mouth river estuary and was gradually tended to decrease toward river body. Beside that values of water quality parameters were varied along the river estuary, with Salinity ranged was from 1 to 24 ppt, pH was 4,8 to 7,Total Solid Suspence was 30 to 143 ppm, Current was 0.02 to 0.72, BOD5 was 4.2 to 9.0 ppm and COD was 10.8 to 43.2 ppm . Based on number and abundance spesies, water quality parameters that affected the composition of epiphytic diatom was currentenepiphytic diatomcompositionnipahestuaryUR-Proceedings