Aquatic Plant Control

Summary of 2016 Lake Mitchell RLS Aquatic vegetation Program

The 25 page report was prepared by Jennifer Jermalowicz-Jones CEO owner and water resources director of Restorative Lake Sciences and has been summarized by Dave Foley. The full report can be found at the bottom of this page. 

 

The overall condition of Lake Mitchell is ranked in the top 15% of developed lakes of similar size in the state of Michigan. Protection of the 26 native species of vegetation is paramount for the health of the lake fishery and these plants should not be managed unless they are a nuisance to the lakefront property owners creating navigational or recreational hazards (i.e. lily pads or nuisance pond weeds in the coves).


Invasion species such as hybrid Eurasian Watermilfoil (EWM) are able to grow in moderate nutrient waters and thus are a challenge to the Lake Mitchell ecosystem. In 2016 , a total of 33.5 acres of EWM were treated in the coves. No EWM was found in the canal. Approximately 71 acres of EWM was found in the main lake. Combined, this equaled approximately 4% of the lake surface area. EWM may have increased in 2016 due to the significantly higher water temperatures and sunlight relative to 2015. This occurrence was noted in many Michigan inland lakes. A total of $69,950 was spent on aquatic herbicide treatments in 2016.


The Purple Loosestrife beetles stocking occurred in 2016 and is still showing promise. Higher stocking levels are recommended for Big Cove in 2017.


Water Quality Parameters Measured
There are hundreds of water quality parameters one can use to measure an inland lake but several are the most critical indicators of lake health. These parameters include water temperature (measured in Fahrenheit), dissolved oxygen, pH, conductivity, total alkalinity or hardness, total dissolved solids, secchi transparency, total phosphorus chlorophyll-a, and algal species composition.


In 2016, water quality was measured in spring and late summer. Lake Mitchell would be considered eutrophic meaning it has much soft bottom and abundant vegetation. Oligotrophic lakes have hard bottom, and little vegetation. Mesotrophic lakes fall between the two categories.


Water clarity
The water clarity in 2016 averaged around 8.5 feet which is favorable and will allow abundant growth of algae and aquatic plants in the littoral (capable of growing vegetation) zone. Additionally, the lake has enough nutrients (phosphorus and nitrogen) to support some algae and submerged aquatic plant growth in the shallow littoral zone, but the nutrient levels are considered moderate. The water clarity has been improving since measurements were begun in 2009 when it was 4.5 feet.


Alkalinity
Lakes with high alkalinity are able to tolerate larger acid inputs with less change in the water column pH. Many Michigan lakes contain high concentrations of CaCO3 (marl) and are categorized as having “hard” water. Total alkalinity may change on a daily basis due to the re-suspension of sedimentary deposits in the water and response to seasonal changes due to cyclic turnover of lake water. The alkalinity of Lake Mitchell is quite low and is indicative of a “soft water” aquatic ecosystem.


PH
Most Michigan lakes have pH values that range from 6.5 to 9.5.Lake Mitchell is considered “neutral' on the pH scale. The pH of Lake Mitchell in 2016 was similar to previous years and ranged from 7.8-8.0 which is ideal for an inland lake.


Chlorophyll-a and Algal Species Composition
Chlorophyll-a is a measure of the amount of green plant pigment present in the water often in the form of planktonic algae. High chlorophyll-a concentrations are indicative of nutrient-enriched lakes. Chlorophyll-a concentrations greater than 6 are found in eutrophic or nutrient enriched lakes, whereas chlorophyll-a concentration less than 2.2 are found in nutrient-poor or oligotrophic waters. The mean chlorophyll-a concentrations in spring and late summer in Lake Mitchell did not exceed 2.9 which is quite low for an inland Michigan lake, especially given the extremely high water temperatures observed in 2016. Tests indicated a diverse algal flora and represent a good diversity of algae with an abundance of diatoms that are indicative of great water quality.


Native aquatic vegetation
With 26 varieties of aquatic vegetation, this biodiversity is a likely contributing factor to the lake's great fishery. These plants should be protected and not treated unless they become a nuisance in shallow coves or the Torenta Canal.

 

Management Recommendations for 2017
  Conduct aquatic vegetation surveys in late May /early June to determine precise locations of Eurasian Watermilfoil and Curly Leaf Pond Weed(CLP). Treat invasive plants with high doses of systemic herbicides due to the presence of hybrid EWM which is resistant to lower doses.
  Only treat native plants in coves and canal where they create navigational or recreational problems.
 
Monitor water quality parameters in Lake Mitchell.

 

In conclusion, Lake Mitchell is a healthy lake with excellent aquatic biodiversity, good water quality, moderate nutrients, and a healthy lake fishery. Management of EWM, CLP(Curly Leaf Pondweed), and Purple Loosestrife and protection of the water quality are paramount to the long term health of the lake. 


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Summary of 2015 Lake Mitchell RLS Aquatic Vegetation Program

 

This is a summary of the “Lake Mitchell Improvement Feasibility Study and Aquatic Vegetation Management Plan.” prepared by Jennifer Jermalowicz-Jones CEO of Restorative Lake Sciences, January 2016. Parts of this report are incorporated in newsletter features “Commonly asked questions” and “Lake Mitchell facts.” The full 57 page report can be downloaded below. Reports from previous years can also be downloaded below. 

 

Based on the most current study, Lake Mitchell has approximately 20 acres of invasive hybrid watermilfoil; however, that may change significantly within a single season as it has in previous years due to the aggressive and unpredictable growth of hybrid watermilfoil. This plant threatens the biodiversity of the submerged aquatic plants, as well as threatens navigation and recreational activities, and may harbor bacteria and other nuisance algae that are not beneficial to the lake's ecosystem. Waterfront property values may be reduced. The native plant diversity in Lake Mitchell is very high with 27 native aquatic plant species present.

 

Nature of the lake

Lake Mitchell has an average depth of 8.7 feet and water clarity averaging 7.5 feet during the year. This will allow aquatic vegetation to grow at depths less than 12 feet. The result is much of Lake Mitchell is shallow enough to grow weeds. The accumulated muck on the bottom created by years of decomposing plant makes for ideal conditions for growing weeds.

 

Water Quality

The overall water quality of Lake Mitchell was measured and found to be quite good with moderate amounts of nutrients such as phosphorus, nitrogen, which still allows for moderate water clarity. The pH and alkalinity of the lake indicates that it is a soft water lake with neutral pH and low conductivity. A prime source of nutrients comes from the three tributaries – Brandy Creek entering Little Cove, Gytta Creek entering the north side of the lake, and Mitchell Creek entering Big Cove.

 

Lakes that are high in nutrients (such as phosphorus and nitrogen) and chlorophyll-a, and high in transparency are classified as eutrophic; whereas those that are low in nutrients and chlorophyll-a and high in transparency are classified as oligotrophic (examples Crystal and Torch Lakes). Lakes that fall in between these two categories are classified as mesotrophic. Lake Mitchell is classified as eutrophic. Although Lake Mitchell has a fair level of nutrients, the water quality has been traditionally favorable for fish stocking of walleye (as recently as June 2014) by the DNR.

 

According to measures of water clarity made by a Secchi Disk over the last seven years, water clarity has improved ranging from 4.5 feet in 2009 to averaging 7.5 feet in 2015.

 

Lake Mitchell Plant management methods

Contact herbicides such as diquat and hydrothol cause damage to leaf and stem structures; whereas systemic herbicides are assimilated by the plant roots and are lethal to the entire plant. Whenever possible, it is preferred to use a systemic herbicide for longer-lasting aquatic plant control. There are often restrictions with usage of some systemic herbicides around shoreline areas that contain shallow drinking water wells. Contact herbicides are used in shallow water near-shore areas to kill nuisance native plants that can hinder boat navigation. Systemic herbicides are used to treat hybrid watermilfoil.

 

Mechanical harvesting was used to remove a build-up of algae and plant matter in the Torenta Canal in 2015.

The Galerucella beetle has been effective in the treatment of shoreline purple loosestrife and in July of 2012 beetles were reduced around the shoreline of Lake Mitchell where there were adequate stands of the plant. The beetles have significantly reduced the density of the loosestrife infestation. Loosestrife has showy magenta-colored flowers that bloom in mid-July. It grows and spreads rapidly and may out-compete plants such as cattails and other native plants which are necessary for the ecological health of an area and its population of fish and amphibians.

 

Shoreline practices that promote nutrient source control

The construction of impervious surfaces (i.e. paved roads and walkways, houses) should be minimized and kept at least 100 feet from the lakefront shoreline to reduce surface runoff potential. In addition wetland areas around Lake Mitchell should be preserved to act as a filter of nutrients from the land and to provide valuable wildlife habitat.

 

The following procedures are recommended by RLS to reduce the input of phosphorus, which creates additional algal and aquatic plant growth, into the lake:

1. Don't allow raked leaves or empty grass clippings into the lake. Leaves or grass, once they decompose, will provide fertile areas to grow aquatic plants. Burning yard waste near the lakeshore is not a good solution either. Ashes contain phosphorous and nutrients that can easily make their way into the lake resulting in excess weed and algae growth.

2. Use phosphorus-free fertilizers and traditional fertilizers sparingly. Rain, lawn sprinkling, and snow melt all will wash fertilizers and sediments from yards into the lake unless there is a substantial greenbelt along the shoreline. The soil in the Lake Mitchell watershed generally has more than adequate amounts of phosphorus to grow lawns. With nitrogen, apply the correct amount at the right time to maximize plant uptake and minimize off target movement. You may purchase a soil sample kit at the Michigan State Extension in the Wexford County Lake Street Building in Cadillac. They will test your soil to determine what, if any, fertilizers are needed. If you must use fertilizers, select bags that are phosphorus-free and with slow release nitrogen. If the label on the package has a zero in the middle such as 12-0-20 then you know it contains no phosphorus. Excess nitrogen can add to weed growth while phosphorous can enhance algal blooms.

3. Preserve or plant riparian vegetation buffers along the shoreline around the lake such as cattails, bulrushes, and wild native plants. They act as a filter to catch nutrients and pollutants that occur on land and may run into the lake. As an additional bonus, Canada geese usually do not prefer lakefront lawns with dense riparian vegetation because they are concerned about potential of hidden predators within the vegetation.

 

Protecting the shoreline environment

Construction practices near the lake should minimize the chances of erosion and sedimentation by keeping land areas adjacent to the water stabilized with rock, vegetation and wood retaining walls. Sea walls should consist of rip-rap (stone, rock), rather than metal, because rip-rap offers a more favorable habitat for lakeshore organisms, which are critical to the to the ecological balance of the lake. Rip-rap should be installed in front of areas where metal seawalls are currently in use.

 

Recommendations

Restorative Lake Sciences (RSL) recommends that selective spot-treatments with highly selective granular systemic aquatic herbicides be used to treat the exotic hybrid watermilfoil within the lake and that strong contact herbicides be used to control the nuisance native aquatic plant and algae over growth in the Coves and in the Torenta Canal. Harvesting may be used to remove excessive plant or algae matter. A reduction in the herbicide treatment is projected for ongoing years of the program if no other invasives enter the Lake Mitchell ecosystem. Additionally, RLS recommends continued education of lake riparians on nutrient reduction to the lake and lake protection practices.


Download
2016 Lake Mitchell Annual Report
Lake Mitchell Annual Report RLS 2016.pdf
Adobe Acrobat Document 1.7 MB
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2016 Lake Mitchell Improvement Feasibility Study and Aquatic Vegetation Management Plan
January 2016 -- Full 57 page report
Lake Mitchell Feasbility Study RLS 2016F
Adobe Acrobat Document 3.8 MB
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2014 Lake Mitchell Annual Report
LakeMitchell 2014Annual Report REVISED.p
Adobe Acrobat Document 2.7 MB
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2013 Lake Mitchell Annual Report
LakeMitchell2013Annual Report.pdf
Adobe Acrobat Document 3.2 MB
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2012 Lake Mitchell Annual Report
LakeMitchell2012Annual Report.pdf
Adobe Acrobat Document 2.4 MB
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2011 Lake Mitchell Annual Report
LakeMitchell2011Annual Report.pdf
Adobe Acrobat Document 1.2 MB
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2010 Lake Mitchell Annual Report
Mitchell2010Annual Progress ReportLEI.pd
Adobe Acrobat Document 1.5 MB