Voyageurs National Park was established in 1975 to preserve the scenery and remote system of interconnected waterways along a portion of the US-Canada border. The complexity of the waterways increased with the installation of dams in the early 1900s. Subsequently, the International Joint Commission set rules governing dam operation (rule curves) for this system of lakes, with the most recent adjustment in 2018. The U.S. Geological Survey and National Park Service collaborated on several studies to evaluate the rule curves and how they are related to a wide range of hydrologic, environmental, and cultural resources observed in park lakes.
Within Voyageurs National Park, along the Minnesota-Canadian border, water levels are controlled by a series of dams to support a
variety of uses. Previous research has indicated a relation between these artificially maintained water levels and water-quality and aquatic biological effects in these lakes (Christensen et al. 2011, 2013; Cole 1979, 1982; Kallemeyn et al. 1993). Relations were documented between water levels and chlorophyll-a concentrations in the most eutrophic lakes in the system (Christensen et al. 2011) and a link was established between water-level fluctuations and mercury concentrations in fish (Wiener et al. 2006, 2013) due to the drying and rewetting of wetlands and other near-shore areas, which may release methylmercury into the water when inundated.
A better understanding of water-level effects on water quality and biology was needed. To address this need, the U.S. Geological Survey, National Park Service, and other agencies cooperated in a series of studies to assess the importance of water-level fluctuation and other factors affecting water-quality and mercury concentrations of fish in lakes of Voyageurs National Park. The purpose of this paper is to summarize the findings of these studies where international water-level regulation was a major factor.
Our research has shown a decrease in chlorophyll-a concentration and an increase in Secchi depth in two of the most eutrophic water bodies in the park. However, significant improvements were not seen for total phosphorus. A follow-up study suggested a possible link between frequent recirculation and internal recycling of phosphorus. Additional studies evaluated trophic state, flow direction, fish mercury concentrations, cyanobacterial harmful algal blooms, and cultural resources. These collaborative studies provided useful information for a review of previous rule curves leading to the 2018 Supplementary Order issued by the International Joint Commission, which prescribes a new method of regulating water levels of international border lakes.
- Overview
Voyageurs National Park was established in 1975 to preserve the scenery and remote system of interconnected waterways along a portion of the US-Canada border. The complexity of the waterways increased with the installation of dams in the early 1900s. Subsequently, the International Joint Commission set rules governing dam operation (rule curves) for this system of lakes, with the most recent adjustment in 2018. The U.S. Geological Survey and National Park Service collaborated on several studies to evaluate the rule curves and how they are related to a wide range of hydrologic, environmental, and cultural resources observed in park lakes.
Within Voyageurs National Park, along the Minnesota-Canadian border, water levels are controlled by a series of dams to support a
Sources/Usage: Public Domain.Photo of water flowing into Voyageurs National Park (by Victoria G. Christensen, August 2019). USGS and academic scientists examined cyanotoxins and cyanobacterial communities from recurring algae blooms in Kabetogama Lake in Voyageurs National Park. They documented the presence of 7 understudied toxins and identified correlations among toxins and cyanobacteria, revealing potential competitive relations among cyanobacteria. Christensen, V.G., Olds, H.T., Norland, Jack, and Khan, Eakalak, 2022, Phytoplankton community interactions and cyanotoxin mixtures in three recurring surface blooms within one lake: Journal of Hazardous Materials, vol. 427, April 2022, 128142 variety of uses. Previous research has indicated a relation between these artificially maintained water levels and water-quality and aquatic biological effects in these lakes (Christensen et al. 2011, 2013; Cole 1979, 1982; Kallemeyn et al. 1993). Relations were documented between water levels and chlorophyll-a concentrations in the most eutrophic lakes in the system (Christensen et al. 2011) and a link was established between water-level fluctuations and mercury concentrations in fish (Wiener et al. 2006, 2013) due to the drying and rewetting of wetlands and other near-shore areas, which may release methylmercury into the water when inundated.
A better understanding of water-level effects on water quality and biology was needed. To address this need, the U.S. Geological Survey, National Park Service, and other agencies cooperated in a series of studies to assess the importance of water-level fluctuation and other factors affecting water-quality and mercury concentrations of fish in lakes of Voyageurs National Park. The purpose of this paper is to summarize the findings of these studies where international water-level regulation was a major factor.
Our research has shown a decrease in chlorophyll-a concentration and an increase in Secchi depth in two of the most eutrophic water bodies in the park. However, significant improvements were not seen for total phosphorus. A follow-up study suggested a possible link between frequent recirculation and internal recycling of phosphorus. Additional studies evaluated trophic state, flow direction, fish mercury concentrations, cyanobacterial harmful algal blooms, and cultural resources. These collaborative studies provided useful information for a review of previous rule curves leading to the 2018 Supplementary Order issued by the International Joint Commission, which prescribes a new method of regulating water levels of international border lakes.
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