User:Dovaleca/Lake Michigan

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Lake Michigan Limnology and Environmental Issues[edit]

Salinity (Under Hydrology)[edit]

A study conducted by PNAS (Proceedings of the National Academy of Sciences of the United States of America) found that 44% of lakes, including Lake Michigan, are becoming more susceptible to increased levels of NaCl (Sodium chloride) being dissolved in freshwater lakes^[1]. This is influenced by the amount of impervious surfaces surrounding bodies of water. NaCl that is utilized during the winter season to melt snow on these surfaces, such as roadways, is being deposited into Lake Michigan, among thousands of other lakes. Land in Michigan State is approximately 45.9% covered by impervious surfaces, such as asphalt ^[1]. Elevated levels of NaCl can have an immense impact on a number of different biological variables including zooplankton and phytoplankton levels, fish survival rates, density of water in relation to stratification ^[1]. These biological impacts will further impact human-related services that the lake provides such as recreational fishing, quality of drinking water, swimming, and boating ^[1]. Another study found that Lake Michigan currently varies between 50-600 mg/l of dissolved sodium^[2], while the threshold for harmful levels of dissolved sodium begins at 250 mg/l^[3].

Drinking Water Addition[edit]

Drinking water in Lake Michigan is primarily sourced from ground water discharge (as much as 79%)^[4]. Overuse of water from this lake though is creating lower levels of groundwater which is affecting the western basin enough to cause a reversal of flow in groundwater ^[4]. Another issue impacting drinking water in this lake is the contamination of Microplastics. There are a number of different measures that can be taken on the personal individual level, such as different additions to washing machines like filters, recycling plastics, and avoiding littering ^[5]. Ultimately though, microplastics will need to be addressed on a large-scale, starting with how products are manufactured ^[5].

Another issue with drinking water contamination comes from failing septic systems^[5]. Michigan as a state does not have state-wide standards that regulate how septic systems are designed or how they are maintained ^[5]. Because of this, over half of the rivers and streams in Michigan are estimated to have Escherichia coli or E.Coli levels that are above the safe level for human consumption^[5]. Recent studies, July 2021, found E.coli contamination high enough to restrict swimming at certain beaches^[6].

Hydrology Addition[edit]

One study modeled the Stratification (water) of Lake Michigan during two periods, one from 1982-1983 and another during 1994-1995. The modeling completed in this study found that Lake Michigan is a Dimictic lake, with inverse stratification occurring in the winter, where water columns are coldest at surface level, with extensive amounts of ice coverage^[7]. Then normal stratification during the summer months, and mixing of water columns during the spring and the fall^[7]. The layers or water columns that separate during stratification are the Epilimnion, Thermocline, and Hypolimnion^[7]. Stratification regimes have an effect on Dissolved Oxygen within lakes. Dissolved oxygen increases with decreasing temperature levels and is needed for aquatic life such as Zooplankton, Phytoplankton, and Fish. A study conducted from 2001-2003 compared the overwinter survival and growth rates of Alewife (fish) in Lake Michigan and Muskegon Lake and found that fish in the latter ecosystem had higher survival rates, indicating that conditions for this species in Lake Michigan are less ideal^[8].

Impact of Invasive Species[edit]

Since around the 1970's studies have been completed to understand and analyze the impacts on lower-level food webs^[9]. Changes to the food web within Lake Michigan has been changing, with the most influential drivers of change being increases of invasive species. Specifically, Zebra Mussel (D. polymorpha) and Quagga Mussels (D. rostriformis) have had the largest impact on a multitude of factors, including lower food-web resource availability^[9]. Both groups of mussel utilize filter-feeding to consume phytoplankton which leaves little available for other aquatic life ^[10]. The first documented case of D. polymorpha in the state of Michigan was in 1997^[11]. The first documented case of D. rostriformis was in 1989. A study from 2010 documented that when comparing levels of phytoplankton from 1983 and 1998 to levels in 2008, there was a 66-87% decrease in phytoplankton, which is a primary food source for zooplankton^[10]. Decreases in phytoplankton had a documented impact in 2008 that was observed as a decrease in cyclopoid copepods and large omnivorous calanoid copepod species^[11]. In addition to decreases in zooplankton and phytoplankton, the presence moreso of D. rostriformis causes a decrease in primary production overall, which negatively impacts nutrient loads in the lake, leading portions to become oligotrophic^[9].

Water Quality Standards[edit]

All lakes need a certain amount of nutrients such as phosphorus, nitrogen and silica for proper primary production and build up of sediment in appropriate amounts. Soils in Michigan contribute to phosphorus concentration in waterways, including in Lake Michigan^[10]. In addition to phosphorus concentration from soils, a known source of excess phosphorus is from agricultural chemical run-off, water treatment processes, and industrial or municipal discharge^[10]. Adverse effects from excess phosphorus include eutrophication of water ways, increases in cyanobacteria, poor tasting drinking water. Because of this, Michigan created a set of water-quality standards in 1968^[10]. This set of standards regulates and controls the allowable amount of phosphorus discharge from the previously listed sources, and was renewed in 1972, 1978 and 1986^[10]. The main component of this list of standards as it currently stands is to keep discharge amounts below 1 mg/l and has shown significant success to keeping Lake Michigan in a healthy range of nutrient load.