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Scientific Investigations Report 2011–5096

Prepared in Cooperation with the National Park Service

Relation of Nutrient Concentrations, Nutrient Loading, and Algal Production to Changes in Water Levels in Kabetogama Lake, Voyageurs National Park, Northern Minnesota, 2008–09

By Victoria G. Christensen, Ryan P. Maki, and Richard L. Kiesling

Thumbnail of and link to report PDF (2.2 MB)Abstract

Nutrient enrichment has led to excessive algal growth in Kabetogama Lake, Voyageurs National Park, northern Minnesota. Water- and sediment-quality data were collected during 2008–09 to assess internal and external nutrient loading. Data collection was focused in Kabetogama Lake and its inflows, the area of greatest concern for eutrophication among the lakes of Voyageurs National Park. Nutrient and algal data were used to determine trophic status and were evaluated in relation to changes in Kabetogama Lake water levels following changes to dam operation starting in 2000. Analyses were used to estimate external nutrient loading at inflows and assess the potential contribution of internal phosphorus loading. Kabetogama Lake often was mixed vertically, except for a few occasionally stratified areas, including Lost Bay in the northeastern part of Kabetogama Lake. Stratification, combined with larger bottom-water nutrient concentrations, larger sediment phosphorus concentrations, and estimated phosphorus release rates from sediment cores indicate that Lost Bay may be one of several areas that may be contributing substantially to internal loading. Internal loading is a concern because nutrients may cause excessive algal growth including potentially toxic cyanobacteria. The cyanobacterial hepatotoxin, microcystin, was detected in 7 of 14 cyanobacterial bloom samples, with total concentrations exceeding 1.0 microgram per liter, the World Health Organization’s guideline for finished drinking water for the congener, microcystin-LR. Comparisons of the results of this study to previous studies indicate that chlorophyll-a concentrations and trophic state indices have improved since 2000, when the rules governing dam operation changed. However, total-phosphorus concentrations have not changed significantly since 2000.

First posted August 11, 2011

For additional information contact:
Director, USGS Minnesota Water Science Center
2280 Woodale Drive, Mounds View, MN 55112
(763) 783-3100
http://mn.water.usgs.gov

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Suggested citation:

Christensen, V.G., Maki, R.P., and Kiesling, R.L., 2011, Relation of nutrient concentrations, nutrient loading, and algal production to changes in water levels in Kabetogama Lake, Voyageurs National Park, northern Minnesota, 2008–09: U.S. Geological Survey Scientific Investigations Report 2011–5096, 50 p.



Contents

Abstract

Introduction

Methods

Nutrient Concentrations and Loading, Algal Production, and Their Relation to Changes in Water Levels

Synopsis of Water-Quality Conditions at Lake Kabetogama, 2008–09

Summary

References Cited

Appendix—Algal species composition, density, and biovolume for samples collected from Kabetogama Lake, 2008–09


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