---

---

Influences of Fathead Minnows on Phosphorus and Nitrogen Cycling in a Prairie Wetland

by
Kyle D. Zimmer¹
Walter G. Duffy²
Malcolm G. Butler¹
Mark A. Hanson

---

Abstract

A current issue in aquatic ecology is the functional role of fish in the nutrient cycles of aquatic ecosystems. A substantial amount of research on this topic has been done in lake ecosystems, but the role and influences of fish in nutrient cycles of wetlands is unknown. Here we examine the influences of fathead minnows on phosphorus and nitrogen cycling in a semipermanent wetland in west-central Minnesota. We hypothesized that consumption and subsequent excretion of nutrients by fathead minnows increases nutrient recycling rates, and this "internal" loading facilitates increased nutrient and algal levels in the water column of the wetland. To test this hypothesis, we used a bioenergetic model to measure nutrient consumption, allocation to growth, excretion, and amounts of nutrients released through fish mortality. Our results show that the minnow population served as an important short-term sink for nitrogen and phosphorus, but also played a significant role as a source of nutrients via high recycling rates. High consumption rates resulted in large amounts of nutrients being sequestered from various prey pools, but consumed nutrients were rapidly returned (recycled) to the water column. An unexpected result was that most of the recycled nutrients resulted from fish mortality and decomposition, not from excretion by the fish as we had hypothesized. The quantities of nutrients (phosphorus in particular) recycled from fish death likely increase nutrient concentrations in the water and may be an important mechanism for increasing levels of nutrients and algae in wetlands with fathead minnows.

---

Table of Contents

• Introduction
• Methods
• Results
• Dicussion
• Acknowledgments
• Literature Cited
• Tables
  • Table 1
  • Table 2
  • Table 3
  • Table 4
  • Table 5
• Figures
  • Figure 1
  • Figure 2
  • Figure 3
  • Figure 4

---

¹Department of Zoology, North Dakota State University, Fargo, ND 58105
²California Cooperative Fisheries Research Unit, Humboldt State University, Arcata, CA 95521

---

NPWRC Home | Site Map | About Us | Staff | Search | Contact | Web Help | Copyright