Microalgae as indicators to assess trophic status and organic pollution in the Seven Brackish Lakes, North of Benghazi, Libya الطحالب الدقيقة كمؤشرات لتقييم الحالة التغذوية والتلوث العضوي في البحيراتالسبع قليلة الملوحة شمال بنغازي، ليبيا

Abstract

This study investigates the use of microalgae as bioindicators to assess the trophic status and organic pollution levels in the Seven Brackish Lakes located north of Benghazi, Libya. Microalgae, due to their rapid response to environmental changes and their central role in aquatic ecosystems, serve as effective indicators of water quality. Over four seasons sampling period, qualitative and quantitative analyses of microalgae communities were conducted across 6 sites within the lakes. Key ecological indices, including Nygaard index, Palmer Pollution Index and trophic diatoms index were employed to evaluate trophic status and pollution levels. During the four seasons from October 2022 to July 2023, 33 species following to 27 genera and 5 divisions were recorded from in the seven lakes north of Benghazi. The most diverse group was Chlorophyta (49%), followed by Cyanobacteria (21%), Bacillariophyta (12%), Euglenophyta (9%) and Dinophyta (9%) as well. Results revealed significant organic pollution conditions based on palmer index (score = 36) with higher abundances of eutrophication based on the compound Nygaard index indicated(score =9) and trophic diatoms index ( score = 4 to 4.5). These findings suggest a gradient from mesotrophic to hypereutrophic conditions within the lake system, corresponding to varying degrees of anthropogenic impact, particularly domestic and agricultural runoff.

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