Title: Influences of Fathead Minnows on Nutrient Partitioning, Water Clarity, and Ecosystem Structure in Prairie Wetlands

Focus Categories: Water Quality, Ecology, Wetlands

Project No. ND96-02

Principal Investigator: M. B. Butler - Department of Zoology, NDSU

Completion Report

Butler, M.D., K.D. Zimmer, M.A. Hanson and W.G. Duffy, 1998, Influences of Fathead Minnows on Nutrient Partitioning, Water Clarity, and Ecosystem Structure in Prairie Wetlands, Rept. No. ND96-02, North Dakota Water Resources Research Institute, North Dakota State University, Fargo, North Dakota, 72 pages.

Other Publications

Zimmer, K.D., M.A. Hanson, and M.G. Butler. In press. Factors Influencing Invertebrate Communities in Prairie Wetlands: A Multivariate Approach. Canadian Journal of Fisheries and Aquatic Science.

Butler, M.G., R.L. Rezanka, and K.M.Giovannielli. (in press), Utility Of Species-Level Identification Of Chironomus Larvae In Biological Assessment Of Prairie Lakes. Proceedings of the International Association for Theoretical and Applied Limnology, 27:xx-xx.

Noraker, T., K.D. Zimmer, M.G. Butler, and M.A. Hanson. (in press), Dispersion And Distribution Of Marked Fathead Minnows (Pimephales promelas), in Prairie Wetlands. Journal of Freshwater Ecology, 14: xx-xx.

Significant Findings

The mechanisms responsible for the observation that wetlands containing dense populations of fathead minnows have significantly higher turbidity and algal biomass than wetlands with few or no fish were examined. One prairie pothole wetland of each type, in conjunction with a separate, extensive study involving 22 additional wetlands was studied intensively. It was learned that phosphorus and nitrogen were concentrated in phytoplankton, seston, and fish in the pond with minnows, but these nutrients were tied up in macrophytes, epiphytes, and invertebrates in the fishless wetland. Bioenergetic modeling of the minnow population indicated that these fish serve as a short-term sink for nitrogen and phosphorus, but high mortality in these rapidly reproducing, fast-growing fish results in substantial recycling of these nutrients throughout the summer, enhancing algal biomass and increasing turbidity. When minnow populations attain high density, these native fish dramatically alter nutrient dynamics, water-quality, and other ecosystem characteristics in these prairie wetlands.