Chlorophyll-A Content and Phytoplankton Population Downstream of Tuntang River, Demak, Central Java

The downstream of the Tuntang River accumulates pollutants from the upstream and human activities in the Demak Regency that are influenced by industries, agriculture, fisheries, and settlement. Various environmental monitoring methods can be used to determine the pollution level in a water area, including chlorophyll-a content and phytoplankton populations. This research analyses the productivity of the downstream of Tuntang River Demak in terms of chlorophyll-a content and phytoplankton population. The size of the dominant species influences the chlorophyll-a concentration and can indicate the environmental condition. Water samples were collected from four sites in September 2022 (dry season) and were analyzed for chlorophyll-a and phytoplankton populations. Chlorophyll-a concentration (0-022-21.27 mg/L) indicated that Tuntang Estuary was in eutrophic condition. This was supported by the dominance of Aulacoseira granulata in all sites. However, the chlorophyll-a concentration does not always follow the phytoplankton abundance due to the biovolume of phytoplankton. Biomonitoring water quality using chlorophyll-a and phytoplankton may express the trophic state condition.