Multi-condition evaluation of floating treatment islands for eutrophication control and water quality improvement in Zhaveh Dam reservoir, Iran

Eutrophication is a major environmental problem in reservoirs, particularly in mountainous regions where shallow inflows and agricultural runoff increase nutrient loading. Floating Treatment Wetlands (FTWs), as a general nature-based treatment technology, have been investigated for nutrient removal. This study evaluated Floating Treatment Islands (FTIs) for improving water quality in the Zhaveh Dam reservoir, Iran, targeting total phosphorus (TP), total nitrogen (TN), and organic matter. Experiments were conducted under contrasting hydraulic conditions in barrel, pool, canal, and reservoir-edge systems. Results showed reductions in TP, TN, and organic matter, with observed removal efficiencies varying across hydraulic conditions and generally tending to be higher under longer retention times and lower flow conditions. Native species such as Sparganium erectum demonstrated high adaptability and effective nutrient uptake under the tested conditions. The findings indicate that FTIs may provide a sustainable approach for eutrophication control and reservoir water quality improvement. This study presents a comparative multi-condition evaluation of FTIs under contrasting hydraulic conditions in a reservoir transition zone.