PREDICTIONS ON THE EFFECT OF COMMON CARP (CYPRINUS-CARPIO) EXCLUSION ON WATER-QUALITY, ZOOPLANKTON, AND SUBMERGENT MACROPHYTES IN A GREAT-LAKES WETLAND

We conducted a study to examine the relationship between common carp ( Cyprinus carpio) exclusion, water quality, zooplankton, and submergent macrophytes. Twelve 50-m(2) in situ experimental enclosures were inst alled in degraded Cootes Paradise Marsh during the carp spawning perio d in 1995. Enclosures were stocked with two or three carp of similar s ize, ranging from 13 to 59 cm and in total biomass from 23 to 2100 kg/ ha. Turbidity, total phosphorus, and total ammonia concentrations incr eased predictably with total carp biomass in the enclosures. Although carp had no direct effect on zooplankton community structure, increase d turbidity and nutrient load associated with carp activity resulted i n reduced total zooplankton biomass. We developed a relationship betwe en species richness and water turbidity for 19 wetlands in the Great L akes basin which indicated that above an apparent threshold of 20 NTU, there were less than five species of submergent plants, while a more diverse community existed in less turbid systems. We predict that wate r turbidity in Cootes Paradise Marsh may not be reduced below this thr eshold value of 20 NTU following carp exclusion. We emphasize the need to consider other factors that may contribute to increases in water t urbidity and nutrient concentrations, including wind resuspension and substrate characteristics.