Influences of Fathead Minnows on Nutrient Partitioning and Ecosystem Structure in a Prairie Wetland
by
Kyle D. Zimmer1
Mark A. Hanson2
Malcolm G. Butler1
Walter G. Duffy3
Abstract
We compared ecosystem structure and sizes of nutrient pools in two wetlands in west-central Minnesota in 1997, one supporting a population of fathead minnows and the other fishless. We hypothesized that the fishless wetland would typify the clear-water state, the wetland with fish the turbid-water state, and that sizes of nutrient pools would differ between the two wetlands. We assessed water transparency, water-column sedimentation rates, and quantified the amount of phosphorus and nitrogen in periphyton, macrophyton, phytoplankton, aquatic invertebrates, fathead minnows, seston, interstitial water, and the water column. Results showed that nutrients were apportioned quite differently between these two wetlands. Major phosphorus and nitrogen pools in the wetland with fish were phytoplankton, seston, fathead minnows, and macrophyton, while macrophyton, periphyton, and aquatic invertebrates were the largest pools in the fishless site. We believe that direct and indirect activities of fathead minnows and submerged aquatic plants probably mediate the size and dynamics of major nutrient pools in these semipermanent prairie wetlands. Our results support the hypothesis that high-density populations of fathead minnows may favor turbid conditions in deep, semipermanent prairie wetlands by translocating phosphorus to water-column nutrient pools.
Key Words: prairie wetland, phosphorus, nitrogen, phytoplankton, periphyton, macrophytes, aquatic invertebrates, fathead minnows
Table of Contents
- Introduction
- Methods
- Results
- Discussion
- Acknowledgments
- Literature Cited
- Figures
- Figure 1 -- Sedimentation rates of phosphorus and nitrogen.
- Figure 2 -- Interstitial-water concentrations of phosphorus and nitrogen.
- Figure 3 -- Concentration of nitrogen and phosphorus in sediment.
- Figure 4 -- Turbidity, phytoplankton, total phosphorus, and total nitrogen concentrations in water column.
- Figure 5 -- Dry-weight biomass of macrophyton, periphyton, metaphyton, and aquatic invertebrates.
- Figure 6 -- Numbers and biomass of fathead minnows and total phosphorus and nitrogen in fathead minnows.
- Figure 7 -- Results of phosphorus and nitrogen partitioning of the seven nutrient pools.
- Figure 8 -- Results of phosphorus and nitrogen partitioning for six nutrient pools.
1 Department of Zoology, North Dakota State University, Fargo, ND 58105
2 Wetland Wildlife and Populations Research Group, Minnesota Department of Natural Resources, Bemidji, MN 56601
3 California Cooperative Fisheries Research Unit, Humboldt State University, Arcata, CA 95521
