IMPACT OF MACROPHYTES ON PHYTOPLANKTON IN EUTROPHIC PERI-URBAN PONDS, IMPLICATIONS FOR POND MANAGEMENT AND RESTORATION

Abstract

A 4-year monitoring of 16 eutrophic peri-urban ponds located in the south eastern periphery of Brussels has shown that different aquatic plants have different interrela tionship with phytoplankton. Extensive submerged macrophytic vegetation has shown the strongest effect on phytoplankton biomass and composition and seems to be crucial for the maintenance of the clear-water state through its capacity to buffer the effects of nutrient enrich ment. Restoration of submerged macrophytes seems to be essential for successful biomanipu lation of eutrophic ponds. Biomanipulation induced revegetation with submerged macrophytes resulted in the restoration of the clear-water state in the two biomanipulated ponds. Fish removal not accompanied with the restoration of submerged macrophytes in the third bioma nipulated pond did not lead to the decrease in phytoplankton biomass. The removal of sub merged macrophytes from a clear-water pond invariably led to a shift towards the turbid state often accompanied with cyanobacterial bloom formation. Profuse growth of filamentous green algae also had a negative effect on phytoplankton growth, albeit less strong than that of sub merged macrophytes. Floating-leaved plants did not show a significant effect on phytoplank ton biomass outside their stands.