Plankton Assemblage and Potential Indicator Species for Water Quality Assessment in Selected Wetlands in Colombo

Wetlands are considered one of the most productive ecosystems on Earth. Plankton is an essential part of wetland biodiversity and vital to wetland functioning. Plankton is an ideal bioindicator for assessing wetlands' water quality and environmental status. This study was carried out to determine plankton assemblage and to identify potential indicator species for water quality assessment in selected wetlands in Colombo Ramsar Wetland City, including Nawala Wetland Park, Diyatha Uyana, Diayasaru Park, and Beddagana Wetland Park. Water and plankton samples were collected for four months (October 2022- February 2023). Both phytoplankton and zooplankton were studied. During the study period, 39 phytoplankton and 24 zooplankton species were reported. The identified phytoplankton species were categorised into three prominent families: Bacillariophyceae, Chlorophyceae, and Cyanophyceae. Genus Melosira was recorded as the Most abundant species in all wetlands (more than 50%). Identified zooplankton were categorized into three main groups: Rotifera, Copepoda, and Ichthyoplankton. Rotifers were the dominant zooplankton group, and Keratella spp.; Brachionus spp. were dominant in all wetlands. Pediastrum spp., Chlorella sp., Closterium sp., Phacus sp., Euglena sp., Melosira spp., Microcystis spp., Navicula sp., Oscillatoria sp., Scenedesmus sp., and Synedra sp., Keratella spp., Brachionus spp., and Lecane spp. were identified as potential bioindicators for pollution. According to the Shannon-Wiener diversity index, phytoplankton diversity is higher than zooplankton diversity. Fourteen indicator species were observed, exhibiting varying levels of abundance. Most of them are indicators of pollution. Hence, it may be inferred that the population density of these species was relatively high, and the degree of contamination in the wetland was also found to be high.