Experimental manipulation of ponds to determine the impact of common carp (Cyprinus carpio L.) in Delta Marsh, Manitoba: Effects on water quality, algae, and submersed vegetation

Since their introduction to Canada in the late 1800s, common carp ( Cyprinus carpio L.) have lead to declines in the habitat quality of many aquatic systems. Carp re-suspend sediments, which leads to decreased water clarity, altered water chemistry, and shifts the ecosystem to a phytoplankton-dominated state. I monitored changes in water quality, and abundance of algae and submersed vegetation in Delta Marsh over two years. Ten ponds (1-13 ha) that had varying degrees of exposure to carp were used. Following one year of background characterization in 2001, manipulations were carried out prior to the second year of monitoring in 2002. New channels were created into two previously isolated ponds, while carp were excluded from four others ponds by screens or dikes. Four others remained unmanipulated. The results indicate that carp are contributing to the habitat degradation of Delta Marsh. Phytoplankton abundance, suspended solids, nutrients (P and Si), and turbidity increased with greater densities of young-of-the-year carp and the occurrence of large carp. Excluding large carp lead to a switch from a turbid, phytoplankton-dominated state to a clear, macrophyte-dominated state in peripheral ponds. Recommendations are made for further research and management of carp in Manitoba waters.