An integrated trophic state assessment of a Mediterranean lagoon (Lake Manzala, Egypt) using chemical and rotifer indices

Lake eutrophication assessment is a metric that can contribute to increasing the effectiveness of future management strategies to control and reduce lake eutrophication problems. Therefore, this study aims to conduct an integrated assessment of the environmental state of Lake Manzala through chemical and biological indices of the lake eutrophication state (Trophic state index, TSI). Chemical trophic indices generally classify Lake Manzala from mesotrophic to hypertrophic. However, based on the rotifer indices results, the lake ranged between mesotrophic to eutrophic. Results indicated a significant correlation (p < 0.05) between TSI(TN), TSI(TP), TSI (chem) and TSIROT abundance, and TSIROT wet-mass. Moreover, total phosphorus (TP) and total nitrogen (TN) were the most important parameters that influenced on the rotifers, particularly in the east-south sector. The species that had the highest positive correlation with TN and TP were Brachionus quadridentatus, Philodina roseola, Brachionus calyciflorus, Lecane bulla, Keratella cochlearis, and Filinia longiseta. Based on chemical and biological indices, the water quality and ecological status of the northern and middle regions of the lake have relatively improved compared to previous periods due to the dredging and cleansing process that has been ongoing since 2017.