Historically, the Great Lakes, in addition to their
lake ecology, were surrounded by various
forest ecoregions (except in a relatively small area of southeast Lake Michigan where
savanna or
prairie occasionally intruded). Logging, urbanization, and agriculture uses have changed that relationship. In the early 21st century, Lake Superior's shores are 91% forested, Lake Huron 68%, Lake Ontario 49%, Lake Michigan 41%, and Lake Erie, where logging and urbanization has been most extensive, 21%. Some of these forests are second or third growth (i.e. they have been logged before, changing their composition). At least 13 wildlife species are documented as becoming extinct since the arrival of Europeans, and many more are threatened or endangered. While the organisms living on the bottom of shallow waters are similar to those found in smaller lakes, the deep waters contain organisms found only in deep, cold lakes of the northern latitudes. These include the delicate opossum shrimp (order
Mysida), the deepwater scud (a crustacean of the order
Amphipoda), two types of
copepods, and the
deepwater sculpin (a spiny, large-headed fish). The Great Lakes are an important source of
fishing. Early European settlers were astounded by both the variety and quantity of fish; there were 150 different species in the Great Lakes. By 1801, the
New York Legislature found it necessary to pass regulations curtailing obstructions to the natural migrations of
Atlantic salmon from Lake Erie into their spawning channels. In the early 19th century, the government of
Upper Canada found it necessary to introduce similar legislation prohibiting the use of weirs and nets at the mouths of Lake Ontario's tributaries. Other protective legislation was passed, but enforcement remained difficult. On both sides of the Canada–United States border, the proliferation of
dams and impoundments have multiplied, necessitating more regulatory efforts. Concerns by the mid-19th century included obstructions in the rivers which prevented salmon and
lake sturgeon from reaching their spawning grounds. The Wisconsin Fisheries Commission noted a reduction of roughly 25% in general fish harvests by 1875. The states have removed dams from rivers where necessary. Overfishing has been cited as a possible reason for a decrease in population of various
whitefish, important because of their culinary desirability and, hence, economic consequence. Moreover, between 1879 and 1899, reported whitefish harvests declined from some 24.3 million pounds (11 million kg) to just over 9 million pounds (4 million kg).
The Great Lakes: An Environmental Atlas and Resource Book (1972) notes: "Only pockets remain of the once large commercial fishery." The last commercial fisherman left Milwaukee in 2011 because of overfishing and anthropogenic changes to the
biosphere. on Lake Superior in Minnesota near Silver Bay.
Invasive species Since the 19th century, an estimated 160 new species have found their way into the Great Lakes ecosystem; many have become invasive; the overseas ship ballast and ship hull parasitism are causing severe economic and ecological impacts. According to the Inland Seas Education Association, on average a new species enters the Great Lakes every eight months. The state of Michigan has had to develop legislation and regulations to help protect against these invasive species.
Aquatic invasive species regulations in Michigan have been put in place to combat the influx of species. from Lake Michigan. The
alewife first entered the system west of Lake Ontario via 19th-century canals. By the 1960s, the small silver fish had become a familiar nuisance to beach goers across Lakes Michigan, Huron, and Erie. Periodic mass die-offs result in vast numbers of the fish washing up on shore; estimates by various governments have placed the percentage of Lake Michigan's biomass which was made up of alewives in the early 1960s as high as 90%. In the late 1960s, the various state and federal governments began stocking several species of salmonids, including the native lake trout as well as non-native
Chinook and
coho salmon; by the 1980s, alewife populations had dropped drastically. The
ruffe, a small
percid fish from Eurasia, became the most abundant fish species in Lake Superior's
Saint Louis River within five years of its detection in 1986. Its range, which has expanded to Lake Huron, poses a significant threat to the lower lake fishery. Five years after first being observed in the St. Clair River, the
round goby can now be found in all of the Great Lakes. The goby is considered undesirable for several reasons: it preys upon bottom-feeding fish, overruns optimal habitat, spawns multiple times a season, and can survive poor water quality conditions. The influx of parasitic
sea lamprey populations after the development of the Erie Canal and the much later Welland Canal led to the two federal governments of the United States and Canada working on joint proposals to control it. By the mid-1950s, the
lake trout populations of Lakes Michigan and Huron were reduced, with the lamprey deemed largely to blame. This led to the launch of the bi-national
Great Lakes Fishery Commission. Several species of exotic
water fleas have accidentally been introduced into the Great Lakes, such as the spiny waterflea,
Bythotrephes longimanus, and the fishhook waterflea,
Cercopagis pengoi, potentially having an effect on the
zooplankton population. Several species of
crayfish have also been introduced that may contend with native crayfish populations. More recently an electric fence has been set up across the Chicago Sanitary and Ship Canal in order to keep several species of invasive
Asian carp out of the lakes. These fast-growing planktivorous fish have heavily colonized the Mississippi and Illinois river systems. Invasive species, particularly zebra and quagga mussels, may be at least partially responsible for the collapse of the deepwater demersal fish community in Lake Huron, as well as drastic unprecedented changes in the zooplankton community of the lake.
Microbiology Scientists understand that the micro-aquatic life of the lakes is abundant but know very little about some of the most plentiful microbes and their environmental effects in the Great Lakes. Although a drop of lake water may contain 1 million
bacteria cells and 10 million
viruses, only since 2012 has there been a long-term study of the lakes' micro-organisms. Between 2012 and 2019 more than 160 new species have been discovered.
Flora Native habitats and ecoregions in the Great Lakes region include: •
Alvar •
Boreal rich fen (such as in
Door County) •
Eastern forest-boreal transition •
Eastern Great Lakes lowland forests •
Southern Great Lakes forests •
Central forest-grasslands transition •
Upper Midwest forest-savanna transition •
Western Great Lakes forests •
Central Canadian Shield forests •
Laurentian Mixed Forest Province •
Beech-maple forest •
Habitats of the Indiana Dunes Plant lists include: •
List of Michigan flowers •
List of Minnesota wild flowers •
List of Minnesota trees Logging Logging of the extensive forests in the Great Lakes region removed
riparian and adjacent tree cover over rivers and streams, which provide shade, moderating water temperatures in fish spawning grounds. Removal of trees also destabilized the soil, with greater volumes washed into stream beds causing siltation of gravel beds, and more frequent flooding. Running cut logs down the tributary rivers into the Great Lakes also dislocated sediments. In 1884, the New York Fish Commission determined that the dumping of sawmill waste (chips and sawdust) had impacted fish populations.
Pollution The first U.S.
Clean Water Act, passed by a Congressional override after being vetoed by U.S. President
Richard Nixon in 1972, was a key piece of legislation, along with the bi-national
Great Lakes Water Quality Agreement signed by Canada and the U.S. A variety of steps taken to process industrial and municipal pollution discharges into the system greatly improved water quality by the 1980s, and Lake Erie in particular is significantly cleaner. Discharge of toxic substances has been sharply reduced. Federal and state regulations control substances like
PCBs. The first of 43 "
Great Lakes Areas of Concern" to be formally "de-listed" through successful cleanup was Ontario's Collingwood Harbour in 1994; Ontario's Severn Sound followed in 2003.
Presque Isle Bay in Pennsylvania is formally listed as in recovery, as is Ontario's Spanish Harbour. Dozens of other Areas of Concern have received partial cleanups such as the
Rouge River (Michigan) and Waukegan Harbor (Illinois). Phosphate detergents were historically a major source of nutrient to the Great Lakes algae blooms in particular in the warmer and shallower portions of the system such as Lake Erie,
Saginaw Bay,
Green Bay, and the southernmost portion of Lake Michigan. By the mid-1980s, most jurisdictions bordering the Great Lakes had controlled phosphate detergents. Blue-green algae, or
cyanobacteria blooms, have been problematic on Lake Erie since 2011. "Not enough is being done to stop fertilizer and phosphorus from getting into the lake and causing blooms," said Michael McKay, executive director of the Great Lakes Institute for Environmental Research (GLIER) at the
University of Windsor. The largest Lake Erie bloom to date occurred in 2015, exceeding the severity index at 10.5 and in 2011 at a 10. In early August 2019, satellite images depicted a bloom stretching up to 1,300 square kilometers on Lake Erie, with the heaviest concentration near
Toledo, Ohio. A large bloom does not necessarily mean the cyanobacteria ... will produce toxins", said Michael McKay, of the University of Windsor. Water quality testing was underway in August 2019.
Sewage The amount of raw sewage dumped into the waters was the primary focus of both the first Great Lakes Water Quality Agreement and federal laws passed in both countries during the 1970s. Implementation of secondary treatment of municipal sewage by major cities greatly reduced the routine discharge of untreated sewage during the 1970s and 1980s. The
International Joint Commission in 2009 summarized the change: "Since the early 1970s, the level of treatment to reduce pollution from waste water discharges to the Great Lakes has improved considerably. This is a result of significant expenditures to date on both infrastructure and technology, and robust regulatory systems that have proven to be, on the whole, quite effective." The commission reported that all urban sewage treatment systems on the U.S. side of the lakes had implemented secondary treatment, as had all on the Canadian side except for five small systems. Though contrary to federal laws in both countries, those treatment system upgrades have not yet eliminated
combined sewer overflow events. This describes when older sewerage systems, which combine storm water with sewage into single sewers heading to the treatment plant, are temporarily overwhelmed by heavy rainstorms. Local sewage treatment authorities then must release untreated effluent, a mix of rainwater and sewage, into local water bodies. While enormous public investments such as the
Deep Tunnel projects in Chicago and
Milwaukee have greatly reduced the frequency and volume of these events, they have not been eliminated. The number of such overflow events in Ontario, for example, is flat according to the International Joint Commission. are encased within a
silicate cell wall. The fish of the Great Lakes have anti-depressant drugs meant for humans in their brains, which has caused concerns. The number of American adults who take anti-depressant drugs rose from 7.7% of all American adults in 1999–2002 to 12.7% in 2011–2014. As the anti-depressant drugs pass out of human bodies and through sanitation systems into the Great Lakes, this has resulted in fish in the Great Lakes with twenty times the level of anti-depressants in their brains than what is in the water, leading to the fish being exceedingly happy and hence less risk-averse, to the extent of damaging the fish populations.
Plastic Researchers have found that more than of plastic end up in the Great Lakes each year. Plastics in the water break up into very small particles known as
microplastics. Microplastics can also come from synthetic clothing washed down the drains.
Plastic waste found in the lakes include
single-use plastics, plastics used in packaging, takeout containers as well as
pre-production pellets produced by
plastics industry. High concentrations of microplastics were discovered in 100 percent of the fish that were studied by researchers from the Rochman Lab. About of fish is harvested each year from Great Lakes which has raised concerns on how this might affect human health.
Impacts of climate change on algae Algae such as
diatoms, along with other
phytoplankton, are
photosynthetic primary producers supporting the
food web of the Great Lakes, and have been
affected by global warming. The changes in the size or in the function of the primary producers may have a direct or an indirect impact on the food web. Photosynthesis carried out by diatoms constitutes about one fifth of the total photosynthesis. By taking out of the water to photosynthesize, diatoms help to stabilize the
pH of the water, as would react with water to produce
carbonic acid. : Diatoms acquire
inorganic carbon through passive diffusion of and Bicarbonate|, and use
carbonic anhydrase mediated active transport to speed up this process. Large diatoms require more carbon uptake than smaller diatoms. There is a
positive correlation between the surface area and the chlorophyll concentration of diatom cells. ==History==