Monitoring of algal species growth in drinking water reservoirs using onsite fluorescent probe: impact of suspended solids composition on cell counting

Evaluation of algal growth potential (AGP) is critical to prevent reservoir eutrophication. However, accurately and promptly monitoring algal species and counts via the microscopic method is challenging due to interference from suspended solids (SS). The study aims to determine the composition and the impact of SS in six major drinking water reservoirs in Taiwan over a 6-month period (November to April). A fluorescent probe was used to quantify algal cells and to determine species diversity. Pearson's correlation was employed to assess the relationship among various indicators, including chlorophyll-a, total phosphate (TP), and SS. The results indicate that TP significantly enhances AGP, showing a moderate correlation (γ = 0.54) with algal suspended solid (ASS). The ASS can serve as an alternative and more robust indicator for assessing AGP in reservoirs. However, algal cell counting may be hindered by inorganic particles, resulting in lower accuracy compared to microscopic enumeration. Consequently, the ‘relative algae count’ emerges as a practical indicator to reach cost-effective species-specific monitoring for reservoir management. Furthermore, the fluorescence probe proved effective in distinguishing algal species fractions (e.g., diatoms, green algae, cyanobacteria, and cryptophyta), even under the impact of SS. It is concluded that fluorescent probing is a rapid-response method for AGP monitoring across diversified drinking reservoirs.