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==Overview of Microbial Ecology as it is known==
==Overview of Microbial Ecology as it is known==


Discuss the alpha and beta diversity of the system. Include some current research, with at least one figure showing data.<br>
The microbial ecology of Lake Michigan has been shown to be similar to the rest of the Great Lakes in composition. The same key taxa show up in studies of all five lakes.2 The five lakes exchange water and based on results of some studies, it seems as though they exchange microbes as well. In terms of beta diversity, Lake Michigan is closer in composition to oligotrophic Lakes Superior and Huron, than to the more productive Lakes Erie and Ontario2.<br>
 
<br>Looking at the alpha diversity of Lake Michigan, the main difference in composition seems to come from depth in the water column. Cell concentrations are found to be 5-10 x 106 cell/mL near the surface.2 As Lake Michigan gets deeper, cell concentrations progressively get smaller. Across the whole system dozens of oligotypes spanning Proteobacteria, Actinobacteria, Bacteroidetes can be found.2 In the deeper waters (below 83 meters), the environment is characterized by low light availability and low temperature. Enriched phyla in the deep waters include Chloroflexi, Nitrospirae, and Planctomycetes.2 In the surface waters, productivity is higher as well as temperature and light availability. Enriched phyla at this depth are Synechococcus and Methylophilaceae.2


==Expansion topic 1-3==
==Expansion topic 1-3==

Revision as of 15:18, 14 June 2020

Microbial Ecology of Lake Michigan

Overview


By David Pleta


Lake Michigan is one of the largest freshwater lakes in the world.[1] Its size makes it interesting area of study in terms of its microbial ecology. It can be seen as somewhere in the middle of the spectrum between highly productive small lakes and the oligotrophic ocean. Its importance to the surrounding communities also makes it an important area of study.


Detailed Environmental Description

Map of the Great Lakes region, showing temperatures and precipitation from the EPA.
Figure showing the seasonal trends in nutrient concentrations over 3 years in Lake Michigan from Brooks et al..

Lake Michigan is one of the five North American Great Lakes. It is the third largest of these by surface area. It is the second largest by water volume. The area of the lake is 57,800 km2. The volume of water in the lake is 4,920 km3. Its water retention time is 99 years. It is connected to Lake Huron via the Straits of Mackinac. At its deepest, Lake Michigan has a depth of 282 meters. The average depth of the lake is 85 meters.[1] The southern portion of the lake is more densely populated with the cities of Milwaukee and Chicago on its shore, as well as significant industrial activity and agricultural areas. The part has a more temperate climate. The northern portion is more sparsely populated with abundant forests surrounding it.[1] The lake is very important to the approximately 12 million people that live in the surrounding area. It is much colder on the northern portion. There are a number of small rivers that drain into Lake Michigan. The Chicago and Calumet rivers are the largest diversions of water from Lake Michigan.[1]


Lake Michigan becomes stratified during the summer months. The lower layer stays cooler and denser. This layer is referred to as the ‘hypolimnion’. The water closer to the surface is warmer and less dense. This layer is referred to as the ‘epilimnion’. There is a middle layer referred to as the ‘thermocline’ where a rapid temperature transition occurs. In the fall, turnover happens when the epilimnion cools and becomes denser. In the winter, ice cover on the top of Lake Michigan insulates the deeper water, which stays liquid. Turnover then occurs again in the spring when the top layer warms. The turnover and layering ensure that the lake stays oxygenated.[1]


The lake has been shown to be relatively plentiful in nitrate/nitrite and silica. Measurements have also shown low amounts of chlorophyll a and total dissolved phosphorus.[2] It has been shown that when turnover occurs total dissolved phosphorus increases in the lake. Following this nitrate and silica concentrations go down. In concert, the concentration of organic nitrogen and chlorophyll a increases.[3] This suggests that the system is phosphorus limited. Stable isotope data has been collected that suggests that nitrogen fixation is a significant source of nitrogen to the system.[4]

Overview of Microbial Ecology as it is known

The microbial ecology of Lake Michigan has been shown to be similar to the rest of the Great Lakes in composition. The same key taxa show up in studies of all five lakes.2 The five lakes exchange water and based on results of some studies, it seems as though they exchange microbes as well. In terms of beta diversity, Lake Michigan is closer in composition to oligotrophic Lakes Superior and Huron, than to the more productive Lakes Erie and Ontario2.


Looking at the alpha diversity of Lake Michigan, the main difference in composition seems to come from depth in the water column. Cell concentrations are found to be 5-10 x 106 cell/mL near the surface.2 As Lake Michigan gets deeper, cell concentrations progressively get smaller. Across the whole system dozens of oligotypes spanning Proteobacteria, Actinobacteria, Bacteroidetes can be found.2 In the deeper waters (below 83 meters), the environment is characterized by low light availability and low temperature. Enriched phyla in the deep waters include Chloroflexi, Nitrospirae, and Planctomycetes.2 In the surface waters, productivity is higher as well as temperature and light availability. Enriched phyla at this depth are Synechococcus and Methylophilaceae.2

Expansion topic 1-3

How you expand upon the basics will depend on your environment. Pick a couple or three of interesting subtopics and describe them in detail. Include some current research, with at least one figure showing data.


Key Microbial Players

In all of your systems there will be at least a couple of key microbial players. Describe these in detail. Where do they fall on the tree of life? Are they cultured? What do they do in general and as it relates to your target environment?


Conclusion

References



Authored for Earth 373 Microbial Ecology, taught by Magdalena Osburn, 2020, NU Earth Page.