Effects of common carp on water quality and submerged vegetation: results from a short-term mesocosm experiment in an artificial we and

Bioturbation by non-native common carp (carp) can facilitate an ecosystem phase shift from clear to turbid water in shallow lakes and ponds, with negative effects on abundance of aquatic animals and plants. Management of carp often involves reducing populations below a threshold biomass at which important components of the aquatic ecosystem, like submerged aquatic vegetation (SAV), recover. To evaluate control targets for a nuisance carp population in Malheur Lake in SE Oregon, USA, we conducted a mesocosm experiment in a small wetland within the lake's drainage basin. We stocked 200-m(2) enclosures with individual or multiple carp of different age classes at target biomasses of 50, 100, and 300 kg ha(-1). We measured turbidity, total suspended sediments, nutrients, chlorophyll-alpha, and surface coverage of SAV four times within a single growing season. Turbidity increased through time and soluble P was higher in 300 kg ha(-1) carp treatments compared to the control, but few changes were observed for any of the other variables at any biomass. Results suggest that with well established SAV, a maintenance carp biomass threshold of <200 kg ha(-1) will not result in a phase shift from a clear- to turbid-water state in the short-term.