This is the second in a series of articles about eutrophication that have been contributed by Nathan Wilson, a PhD candidate of Lakehead University. The previous article can be found here: Classifying Lakes: Eutrophication in the Boreal Forest Ecozone. It goes over basic terminology for classifying lakes, which is used in the following article that examines how changes in the Lake Superior watershed are impacting Lake Superior itself.
We like to believe that Lake Superior is unaffected by human impacts, especially in comparison to other Great Lakes. Unfortunately, this may not be so true. In fact, Lake Superior has a long history of human impacts from legacy issues like the industrial revolution and the collapse of commercial fisheries, to more recent issues of phytoplankton blooms, high water levels, and reduced ice cover. Some historical, yet often overlooked, human impacts on Lake Superior include the Long Lac and Ogoki diversions and the damming of Lake Nipigon and the Nipigon River to provide more water to the Great Lakes. The subsequent sea lamprey introduction, which contributed to the near-loss of the lake trout fishery in Lake Superior, is a good example of how alterations in one area can have resulting impacts in connected systems. Humans altering the connectivity within Lake Superior, as well as the Great Lakes as a whole, has had significant and long-lasting impacts.
Lake Superior Ability to Buffer Against Impacts Overestimated
In the 1980’s, degraded environmental conditions in Lake Superior led to the establishment of four areas of concern (AOC) – Thunder Bay, Nipigon Bay, Jackfish Bay and Peninsula Harbour, as well as the St. Marys River at Sault Ste. Marie. Today, the historic impacts of direct industrial related degradation to Lake Superior have for the most part been addressed; however, it is no longer possible to restore the ecosystem to its former function in areas like Thunder Bay where ecosystems, such as coastal wetlands within the harbour, were filled in to allow for industrial development. This is a permanent loss of ecosystem function within Lake Superior that was justified due to the assumption that Lake Superior’s vast size gave it the inherent ability to buffer change. A more recent indication that human impacts continue to afflict Lake Superior would be last year’s (2018) extensive cyanobacteria (also known as blue-green algae) bloom at the Duluth Harbour on the southwest shore of Lake Superior. Because Lake Superior is an oligotrophic lake, with minimal nutrients and productivity, the observation of cyanobacteria, which is normally associated with higher nutrient contributions, was unexpected.
Lake Superior is the largest freshwater lake by surface area at 82,000 km2, with an average depth of 147 m and a maximum depth of 406 m, and holds around 12,000km3 of freshwater. It takes approximately 191 years for a drop of water entering Lake Superior today to exit into Lake Huron via the St. Mary’s River at Sault Ste. Marie. Lake Superior’s catchment area, or watershed, is 127,000km2—this includes the two diversions, Ogoki and Long Lac, on the north shore. The Lake receives water from about 200 rivers around the basin, the largest of which include the Nipigon River, St. Louis River, White River, Pic River, and Kaministiquia River. Lake Superior is classified as a dimictic oligotrophic lake. It is home to more than 80 different fish species, although it has fewer dissolved nutrients and is less productive when compared to the other Great Lakes.
We assume the massive size and volume of water in Lake Superior and it’s oligotrophic characteristics buffer the lake from small changes resulting in major impacts, but there is an emerging shift in our understanding of Lake Superior’s sensitivity to change. The scientific community has shown that Lake Superior is warming faster than any other great lake. This is very important as the temperature has major impacts on a number of other ecological and environmental factors such as fish growth and reproduction. Dr. Jay Austin of the Large Lake Observatory in Duluth has shown that Lake Superior is actually very sensitive to small changes. Dr. Austin’s work focuses on the long-term effects of climate change on lakes. Much of his recent work has specifically looked at the variation of ice cover on Lake Superior and seasonal temperature changes.
Understanding Nutrient Contribution in Lake Superior Important
If Lake Superior is, in fact, more sensitive than previously thought, it is important to re-examine the state of lakes and rivers that feed into Lake Superior. There are a large number of headwater lakes in Lake Superior’s watershed that are connected via rivers to the lake proper. If there is a contamination issue within a headwater lake, eventually that water will be transported to Lake Superior. Although it is a massive lake, we are already seeing signs and symptoms that inland problems are potentially causing problems for Lake Superior. Because of the connection of aquatic systems and the fact that Lake Superior receives and provides water for such a massive area, it is essential that we pay attention and take responsibility for the small inland lakes and water systems that may be at risk.
This past summer, Ontario’s Ministry of Environment Conservation and Parks (OMOECP) reported several cyanobacteria blooms, in lakes within Lake Superior’s watershed. At least one of these blooms was confirmed to be producing cyanotoxins. In 2012 and 2018, on the south shore of Lake Superior, the U.S. waters around Duluth experienced cyanobacteria blooms, something few thought possible. The blooms were the result of significant rain events in the area, described as 500-year rain events by the U.S. National Weather Service. Infosuperior also reported a cyanobacteria bloom in the northern waters of Lake Superior after a rainy fall season this year. As previously discussed in Classifying Lakes: Eutrophication in the Boreal Forest Ecozone, increased precipitation events result in more nutrients from the surrounding catchment area being picked up by surface water and eventually deposited into Lake Superior.
Unfortunately, because cyanobacteria blooms in Lake Superior were not anticipated, there was no equipment in place to record the exact conditions leading up to and during the blooms in Lake Superior’s south shore. Now researchers such as Dr. Robert Sterner from the Large Lakes Observatory along with his Ph.D. student Kaitlyn Reinl are working to understand the land-lake connection and where the bloom cells originate. There have been other reports of nuisance blooms around Lake Superior specifically of didymosphenia geminata (AKA Didymo or rock snot), a diatom that can have significant ecological impacts as it forms dense mats on the bottom of rivers. Didymo blooms can get so bad that they displace fish from the river.
There are differences around Lake Superior when it comes to the ecological inputs and potential contaminants that are transported from the watershed to the lake. If you have travelled around Lake Superior you may have noticed a significant difference in the abundance of human development between the northern and southern catchment areas. There is very little agricultural development along the northern region of the lake; however, around Duluth and the St. Louis River in the south, the human development, both urban and agricultural, increases. As previously mentioned, human developments are significant sources of anthropogenic eutrophication driving nutrients. It should be noted that although reports of cyanobacteria and other algae blooms appear to be increasing, it is important to acknowledge there is not enough data to verify the cause of the increase. Northwestern Ontario is an understudied region with respect to eutrophication and cyanobacteria blooms and as people become more educated and conscientious about ecological health there is an increasing likelihood that reporting from the public will increase.
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