Ecological risk related to fish ponds’ eutrophication in y yen, nam dinh using biovolume method

Abstract

The quality of water and phytoplankton in 15 fish ponds in Yen Dinh commune, Y Yen district, Nam Dinh province were assessed to classify and warn of toxic algae ecological risk by biovolume method. These ponds are semi-intensive (53.3%) and intensive. The parameters of COD, TSS, NH₄⁺, PO₄^3-, DO, and total coliform in some ponds, some times exceeded NRT 08-MT:2015/MONRE. In comparison to semi-intensive ponds, most intensive ponds had higher concentrations of COD, NH₄⁺, PO₄^3-, total nitrogen, phosphorus, and coliform. There were 45 algal genera belonging to 6 phyla were detected in 15 aquaculture ponds in 2019 – 2020 (4 sampling times). In which, toxic algal genera appeared in 60% of the studied ponds with an average density of 115 – 1,274 cells ml^-1 for Microcystis and 20 – 400 cells ml^-1 for Anabaena. The biovolume of these genera was 0.010 – 0.071 mm³ l^-1, which was at a safe level for aquaculture or even domestic-supply water. These ponds had a medium risk level and the results of biovolume were strongly correlated with the level of eutrophication and water quality (expressed through N, P, pH, and total coliform).