Assessment of seasonal variation in water quality and organic pollution: A case study of Ouled Mellouk Dam in northern Algeria

Lentic and lotic ecosystems provide essential services for environmental development but are particularly vulnerable to pollution, mainly caused by anthropogenic activities. This study assesses the water quality of the Ouled Mellouk Dam in northern Algeria over a 15- month period, using physicochemical parameters, and index-based methods to evaluate organic pollution. Key indicators, such as pH, Electrical Conductivity, Suspended Matter, Dissolved Oxygen, BOD5, COD, and various nitrogen and phosphorus compounds were periodically measured to understand pollution levels influenced by human activities. Results for mineralization indicators such as Ca??, Mg??, Na?, K?, Cl?, and SO??? indicate that the dam's water generally maintains moderate mineral quality, consistent with standard surface water guidelines. Organic pollution indicators suggest water quality ranging from good to moderate, with average BOD? and COD values of 4.16 mg/L and 18.08 mg/L, respectively. However, elevated concentrations of nitrites (NO??), exceeding the acceptable threshold (0-0.01 mg/L), signal significant nitrogen pollution. Orthophosphate (PO???) levels indicate low phosphorus-related contamination, with an average of 0.05 mg/L, except during September 2016, when a notable increase in organic load was recorded. The Organic Pollution Index (IPO) indicates that surface water quality generally ranges from low to moderate levels of organic contamination. These results underscore the urgency of implementing effective and sustainable management strategies to reduce pollution risks and safeguard the long-term resilience of this vital water resource.