Evaluation of Pollution Levels in the Ologe Lagoon Using Macroalgae as Bioindicators, Lagos State

Macroalgae are effective bioindicators of nutrient enrichment and heavy metal pollution in coastal lagoons due to their sedentary nature and capacity to accumulate contaminants from the surrounding water. This study evaluated pollution levels in Ologe Lagoon, Lagos State, South West Nigeria, using macroalgal bioaccumulation of nitrogen, phosphorus, and heavy metals. Macroalgae samples were collected from five stations over three seasons. Dominant species were identified, and their tissue concentrations of total nitrogen, total phosphorus, lead, cadmium, copper, and zinc were determined by standard analytical methods. Concurrent water and sediment samples were collected for comparison. Five macroalgal species were identified, with Cladophora glomerata and Spirogyra spp. most abundant. Tissue nitrogen and phosphorus concentrations exceeded reference values at three stations, indicating eutrophication-driven nutrient enrichment. Lead concentrations in Cladophora thallus tissue ranged from 3.1 to 11.8 milligrams per kilogram dry weight, significantly exceeding background values at stations nearest to industrial discharge zones. Strong correlations were found between water metal concentrations and tissue metal levels in Cladophora, validating its bioindicator potential. Seasonal patterns showed highest tissue metal and nutrient levels during the dry season, linked to reduced water dilution. The Cladophora pollution index was applied and classified two stations as heavily polluted. The study recommends the adoption of standardised macroalgal bioassessment protocols for routine pollution monitoring in Nigerian coastal lagoons. Keywords: macroalgae, bioindicators, Ologe Lagoon, heavy metals, eutrophication.