Phytoplankton abundance and trophic status of Belawan Waters, North Sumatra

Abstract

Belawan is a district of Medan City and one of estuary areas in North Sumatra that is currently facing pollution due to anthropogenic activities. The study analysed the abundance of phytoplankton and assessed the marine trophic status of Belawan waters to determine the possibility of eutrophication caused by human activities. Water samples were collected from four sampling stations in October 2020: a ship dock (Station-1), a fishery (Station-2), a mangrove area (Station-3), and an estuarine region (Station-4). The abundance of phytoplankton was analysed under a light microscope, and the trophic status of Belawan waters was determined using the Tropical Index for Marine Systems (TRIX), which considers factors such as chlorophyll a content, oxygen saturation, nitrogen, and phosphorus content. The phytoplankton abundance was found to range from 160 ind/L at the ship dock (Station-1) to 241 ind/L at the fishery (Station-2) site. The results indicated a high fertility (hypereutrophic) with a TRIX value greater than 6.0 at both the ship dock (Station-1) and the fishery site (Station-2) in Belawan waters.