Aquatic Plant Control

Summary of Lake Mitchell 2021 Annual Report 

by Dave Foley

(The entire report can be found below.)

 

This report was prepared by Jennifer Jermalowicz-Jones PhD Principal Limnologist of Restorative Lake Sciences (RLS). The entire report can be found at www.lakemitchell.org.  

The overall condition of Lake Mitchell in 2021 was good with favorable water clarity, reduced phosphorus concentrations, and reduced Eurasian watermilfoil (EWM) growth.  Water clarity averaged 9.5 feet. In 2021 RLS used the new systemic herbicide ProcellaCOR@ along with diquat.  The contact herbicide diquat and/or flumioazin will  continue to be used to control nuisance native weeds in coves. An additional Phoslock treatment may be desired in Franke South to reduce nutrients that are resulting in enhanced weed and algal growth. The Torenta Canal will be assessed for the need for a possible harvest and scheduled if necessary. Temporary algal blooms occur during hot windless periods or after intense rainfall events. RLS will monitor the lake for problematic algal blooms.

A survey on September 21, 2021 determined that there were a total of 26 native aquatic plant species in Lake Mitchell. This includes 17 submerged species, 4 floating leaved species and 5 emergent species. This indicates a high biodiversity of aquatic vegetation which is a significant reason for the great fishery in the lake. 

Analyzing water quality including clarity, phosphorus, alkalinity, pH, conductivity, chlorophyll-a and algal species composition leads to the conclusion that Lake Mitchell would be considered eutrophic. Eutrophic lakes have a good amount of vegetation which means ample phosphorus, nitrogen, aquatic vegetation and moderate algal growth.

Extensive surveys using GPS locate EWM which is then treated. In 2021, approximately 64.6 acres of EWM were treated throughout the lake. RLS recommends alternating use of different systemic herbicides to reduce the probability of herbicide tolerance which reduces efficacy.  Since 2015 the amount of EWM found each year has been less than 100 acres. In 2013 EWM became resistant to treatment and 400 acres appeared in Lake Mitchell. Alternating treatment chemicals have improved effectiveness of treatment. And extensive GPS surveys allow for better detection of invasive species locations. The amount of EWM varies each year and is dependent upon climatic conditions, especially runoff associated nutrients. Significant growth can occur when there is a large increase in air and water temperatures and high sunlight periods such as occurred in spring of 2021.

Phosphorus levels have remained consistent between .020 to .03. mg/L units Phosphorus is the primary nutrient necessary for abundant algae and aquatic plant growth. The alkalinity of Lake Mitchell is quite low and is indicative of a “soft water” aquatic system.

Most Michigan lakes have pH values that range from 6.5 to 9.5. Lake Mitchell measures as “8”  and is considered neutral on the pH scale. 

Chlorophyll-a is a measure of the amount of green plant pigment present in the water, often in the form of planktonic algae. Chlorophyll-a concentrations on September 21 was 7.5 micrograms per liter which was elevated for an inland lake and higher than in years past.  

Purple Loosestrife grows four to ten feet high and produces spikes of purple flowers. It is found on the shoreline of coves in Lake Mitchell. It negatively effects both wildlife by displacing native plants eliminating food, nesting and shelter for wildlife. By reducing habitat it has a negative effect on fish spawning and waterfowl habitat.  

The beetle, Galerucella sp., has been stocked in Lake Mitchell wetlands infested with Purple Loosestrife. The goal was to introduce enough beetles to create a sustainable population to manage this invasive plant.

Beetle counts were performed each year to evaluate the damage caused to plants. Recent evaluations show the beetle population is declining. Beetles have not been available so LMIB may consider topical treatment of the plants.

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Lake Mitchell 2020 Aquatic Vegetation and Water Quality Report

Summarized by Dave Foley. Prepared by Jennifer Jermalowicz-Jones CEO of Restorative Lake Sciences.

The entire report can be found below. 

 

Water quality

Overall condition of Lake Mitchell in 2020 was good considering heavy spring rains. Water clarity averaged around 8 feet which continues an overall trend of improved clarity. In 2009 clarity was just over 4 feet. Water tends to be clearer in spring  and decreases as more aquatic plants and algae appears. Clarity may vary depending on turbidity and amount of suspended particles in the water caused by wind.

 

Phosphorus

Although 2020 recorded higher levels of phosphorus than in recent years, nutrient levels are still considered moderate. Lake Mitchell is eutrophic (meaning it supports a good amount of plant growth) since it contains ample phosphorus, nitrogen, and aquatic vegetation growth. 

Phosphorus levels, after dropping for several years, went up slightly.

 Phosphorus is the primary nutrient necessary for algae and plant growth.

 

Alkalinity 

The alkalinity of Lake Mitchell is quite low and is indicative of a “soft water” aquatic system. Lakes with high alkalinity are able to handle lager acid inputs. High concentrations of CaCO3 with high alkalinity are categorized as “hard water”. 

 

Ph values

Most Michigan lakes have pH values that range from 6.5 to 9.5. Acidic lakes (pH less than 7) are rare in Michigan. Lake Mitchell is considered “neutral” on the pH scale. The pH of Lake Mitchell in 2020 was similar to previous years and was 8.0 S.U.

 

Conductivity 

Conductivity is a measure of the number of mineral ions present in the water, especially those of salts and other dissolved in organic substances. Conductivity generally increases as the amount of dissolved minerals and salts in a lake increases and also increases as water temperature increases. The conductivity values of Lake Mitchell are moderately low for a  large shallow inland lake. Mitchell's levels were slightly higher during the 2020 sampling and were recorded at 227-271 mS/cm. Severe water impairments do not occur until values exceed 800 mS/cm.  Conductivity may be increasing due to more road salt applications during harsh winters.    

 

Chlorophyll-a

Chlorophyll-a  is a measure of the amount of green plant pigment 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 Hg/L are found in eutrophic  or nutrient enriched aquatic systems, whereas chlorophyll-a concentrations less than 2.2  Hg/L are found in nutrient poor or oligotrophic lakes. In mid-August Lake Mitchell did not exceed 3.0 Hg/L which is quite low for an inland Michigan lake but higher than in recent years.

 

Native aquatic vegetation 

Native aquatic vegetation is essential for overall health of the lake and the support of a fishery. An August 6, 2020 survey found 26 native species in Lake Mitchell, including 17 submerged species, 4 floating- leaved species, and 5 emergent species. The results were similar to recent year surveys. This indicates a very high biodiversity of aquatic vegetation in Lake Mitchell is likely a significant reason for the great fishery in the lake. The overall percent of cover of the lake by native aquatic is low relative to the lake size. These plants should be protected and not treated unless they become a nuisance in shallow coves or the Torenta Canal. In these cases RLS may recommend the use of mechanical harvesting in some areas of Big Cove, Little Cove and/or Franke Coves and the Torenta Canal.

 

Status of invasive aquatic plant species  

The amount of Eurasian Watermilfoil (EWM) varies each year and is dependent upon climatic conditions, especially runoff-associated nutrients. A June survey found 27. 3 acres of EWM. A late season August 6 survey found an additional 36 acres of EWM.

 

Evaluation of purple loosestrife beetles 

The beetle,  Galerucella, is stocked each season in Lake Mitchell areas infested with purple loosestrife. The goal has been to introduce enough beetles each season to create a sustainable population, that will control the infestation of purple loosestrife. Beetle counts are performed to evaluate number of beetles along with  the damage to plants. The beetle population is declining and did not have marked effects on the purple loosestrife. More stocking is recommended for 2021 as the budget allows or the LMIB may consider topical treatment of the plants with triclopyr. Beetles will not be available in 2021

 

Management recommendations for 2021

Surveys will be done in  May and June to locate invasive and nuisance plants. Bottom scans will be done to determine the changes in aquatic biovolume and distribution of aquatic vegetation.  Post treatments will be scheduled to see if additional treatment is needed. Restorative Lake Science staff will oversee all treatments as in previous years. 

This year RLS is recommending treatment of large offshore areas with Sculpin (2, 4-D)as well as some small isolated areas. Navigate (2, 4-D)  will be used where Sculpin was applied in 2020. Changing chemicals helps deter EWM from forming hybrid plants that are resistant to chemicals.  Near shore areas will continue to be treated with Renovate OTF (triclopyr). Diquat and/or Clipper will continue to be used in the cove areas for nuisance natives. The canal will be assessed for the need for possible harvest and scheduled if necessary. 

Water quality will continue to be monitored in the lake and tributaries. Lake Mitchell is a healthy lake with excellent aquatic plant diversity. Nutrients are at acceptable levels and there is a robust fishery. Temporary algal blooms will occur during hot windless periods or after intense rainfall events. RLS will continue to monitor the lake for any problematic algal blooms.   

 

 

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What happened on Lake Mitchell?

A summary of 2019 RLS aquatic vegetation

and water quality program

 

By: Dave Foley, Lake Mitchell Improvement Board

 

I have put together this summary of the annual report prepared by Dr. Jennifer Jermalowicz-Jones CEO of Restorative Lake Science. The full report can be found at www.lakemitchell.org.

 

Overall, Lake Mitchell is doing well. Water clarity, which in 2009 was less than 5 feet, now averages about 9 feet. Additionally, the lake has nutrients (phosphorus and nitrogen) which result in some algae and submersed aquatic plant growth in shallow soft bottomed areas. Overall nutrient levels are considered moderate with higher concentrations in the tributaries.

 

Status of native aquatic vegetation

 

Lake Mitchell has 26 native species of native aquatic plants. This hasn't changed over the years. This high biodiversity is likely a significant reason for the great fishery in the lake. The overall % cover of the lake by native plants is low relative to the lake size. These plants should be protected and not treated unless they become a nuisance in shallow coves or the Torenta Canal. In these cases, RLS may recommend harvesting.

 

The invasive Eurasian watermilfoil (EWM) has been a challenge to Lake Mitchell's ecosystem since the late 1980s. In 2019, approximately 53 acres of EWM were treated throughout the entire lake. (There are 2,580 acres in Lake Mitchell.) The Torenta Canal was not treated in 2019 as it was not needed. Approximately 28 acres were treated in Big Cove and 3.3 acres in Little Cove. Franke North and South Coves received 8.1 acres of treatment. Whereas only EWM was treated in the main lake, the coves were treated for both EWM and nuisance pondweeds. A new systemic herbicide product, ProcellaCOR® was successfully in used in Big Cove. (A systemic product kills the entire plant including the roots. A contact herbicide just kills the leaves and stems.)

 

The purple loosestrife beetle stocking is recommended in 2020 to increase control of the plant or spot-treatments with an aquatic herbicide for emergents.

 

 

Water quality parameters measured

 

Lake Mitchell is considered a eutrophic lake because it has more weed growth than most lakes in the shallows as well as ample phosphorus or nitrogen. It has good water clarity and moderate algal growth.

 

Phosphorus is the primary nutrient necessary for abundant algae and aquatic plant growth. Phosphorus concentrations are usually higher at increased depths due to higher release of phosphorus from lake sediments under low oxygen conditions. Phosphorus may also be released from sediments as pH increases. Fortunately, even though phosphorus levels in Lake Mitchell are moderate, the dissolved oxygen levels are good enough at the bottom to not cause release of phosphorus from the bottom. Phosphorus, during the sampling event in 2019, was about the same as it has been in 2011.

 

Alkalinity determines whether lakes are “hard water”, having high concentrations of CaCO3, or “soft water.” Total alkalinity may change on a daily basis due to the re-suspension of sedimentary deposits in water and respond to seasonal changes due to the cyclic turnover of the lake water. Lake Mitchell's alkalinity is quite low making it a soft water lake.

 

pH in most Michigan lakes ranges from 6.5 to 9.5 S.U.. Acidic lakes (pH less than 7) are rare in Michigan but are more common in the UP. Lake Mitchell's 8.3 S.U. pH is considered “neutral” on the pH scale.

 

Conductivity is a measure of the number of mineral ions in the water, especially those of salts and other dissolved inorganic substances. Conductivity generally increases as the amount of dissolved minerals and salts in a lake increases as water temperature rises. The conductivity values for Lake Mitchell are relatively low for a large inland shallow lake, ranging from 148-214 mS/cm during 2019 sampling. Severe water quality impairments do not occur until values exceed 800 and are toxic to wildlife at around 1000. Conductivity may be increasing due to more road salt applications during harsh winters.

 

Chlorophyll-a measures green plant pigment present in water often in the form of planktonic algae. High chlorophyll -a are indicative of nutrient enriched lakes. Chlorophyll-a readings of greater than 6 are found eutrophic lakes. Readings of less than 2.2 µg/L are found in nutrient poor lakes. Lake Mitchell recorded a 1.8 µg/L reading in mid-August.

 

Toxic blue-green algae vs tree pollen Blue green algae can be found in many lakes including Lake Mitchell. When it grows in high abundance, it may produce a toxin that humans and animals should avoid contact with when swimming. Animals and humans should avoid surface water algal scums when present as they can be toxic.

 

Tree pollen which appears more yellow and may coat the lake surface in some areas, is not harmful and will soon dissipate.

 

Management recommendations for 2020

 

As in past years, detailed aquatic vegetation surveys will be done by GPS in late May or early June to locate invasive plants as well as nuisance species that may be causing imbalance or recreational issues. Along with the surveys, bottom scans will be conducted to determine changes in aquatic bio-volume and distribution of aquatic vegetation. Post-treatment surveys will be conducted and these may result in additional treatments. The Torenta Canal will be assessed for the need of a possible harvest and scheduled if necessary.

 

Detailed information on chemicals that will be used in 2020 treatments is available in the full RLS report that can be found on the LMIB website:(www.lakemitchell.org )

 

Water quality will continue to be monitored in the lake and tributaries. Lake Mitchell is a healthy lake with excellent aquatic plant diversity. Nutrients are at acceptable levels and there is a robust fishery indicated by the many fishing tournaments held on the lake. Temporary algal blooms occur during hot windless periods or after intense rainfall events. RLS will continue to monitor for any problematic algal blooms.

 

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Lake Mitchell Improvement Plan 2019 -- Full Report

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Summary of 2018 RLS aquatic vegetation and water quality program

Dave Foley 

 

I have put together this  summary of the annual report prepared by Dr. Jennifer Jermalowicz-Jones CEO of Restorative Lake Science. The full report can be found  at  www.lakemitchell.org.  

 

The overall condition of Lake Mitchell in 2018 was very good. Water clarity is improving and the lake has enough nutrients (phosphorus and nitrogen)to support some algae. Nutrient levels are considered moderate with higher concentrations in the coves near the tributaries. 

Protection of the 26 native aquatic plant species is vital for the health of the lake and should not be managed unless they are a nuisance to lakefront property owners and create navigational and recreational hazards (i.e. lily pads or nuisance pond weeds in the coves).

Invasive plants such as Eurasian Watermilfoil (EWM) are able to grow in moderate nutrient waters and thus are a challenge to the Lake Mitchell ecosystem. In 2018 approximately 60.8 acres of EWM was treated throughout the entire lake. The coves and Torenta Canal required contact herbicide for nuisance pond weeds with a total of 22.1 acres. Additionally 20 acres of nuisance Cladophora and nuisance pond weeds were harvested in the coves and canal. A small area of phragmites was treated on August 22, 2018. 

The stocking of Galerucella beetles to control purple loosestrife is recommended to continue in 2019.

 

Lake Mitchell Water Quality   

In late summer of 2018 water quality was measured in the deepest basins of Lake Mitchell.  Parameters were measured for water temperature, dissolved oxygen, pH, conductivity, total alkalinity, total dissolved solids, Secchi transparency, total phosphorus chlorophyll and algal species composition. The results of these studies are found in the full  report on our website. Lake Mitchell would be considered eutrophic since it does contain ample phosphorus, nitrogen, and aquatic vegetation growth but also good water clarity and moderate algal growth. Here are highlights of the water quality report:

 

    Water clarity averaged around 6.0 feet which is lower than average  due to the higher water temperatures persisting later into the season and as a result of the late season heavy rainfall events. Earlier season measurements ranged from 9-12 feet.  

    Phosphorus is primary nutrient necessary for abundant algae growth and aquatic plant growth. Even though phosphorus levels are moderate, the dissolved oxygen levels are good enough at the bottom to not cause release of phosphorus from the lake bed.

Total alkalinity - The alkalinity of Lake Mitchell is quite low and is indicative of a “soft water” aquatic system.

PH - Most Michigan lakes have pH values that range from 6.5 to 9.5. Lake Mitchell is considered “neutral” on the pH scale and ranges from 7.7 to 8.4. 

Conductivity – Conductivity is a measure of the amount of mineral ions in the water, especially of those of salts and other dissolved inorganic substances. Lake Mitchell measured 161-163. Severe water impairments do not occur until values exceed 800 and are toxic to wildlife at around 1000.  

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 concentrations (greater than 6) are found in eutrophic (nutrient rich lakes). Concentrations of less than 2.2 are found in oligotrophic (nutrient poor lakes). In 2009 Lake Mitchell was 5.2. Last fall it was 2, which is quite low for an inland lake. This decline may be resulting in increased transparency.  Tests show Lake Mitchell has a good diversity of alga which indicates good water quality.

Toxic blue-green algae – Blue-green alga can be found in many lakes in Michigan, including the Great Lakes. When it is growing in high abundance, it can result in surface scums that produce a toxin that humans and animals should avoid contact with when swimming. The alga flourishes and may congregate near shore during periods when water temperatures are high. RLS is in the process of developing an immediate watershed plan for Lake Mitchell to help reduce runoff associated nutrients which could improve water quality in the lake.  

 

Status of native aquatic vegetation in Lake Mitchell 

The most recent survey determined there were 26 native aquatic plant species in Lake Mitchell. This is similar to to recent years and means that the lake is maintaining its biodiversity. Biodiversity is key to maintaining a productive fishery in a lake. The overall % cover of the lakes by native plants is low relative to the lake size and thus these plants should be protected and not treated unless they become a nuisance in shallow coves or the Torenta Canal. RLS may recommend the use of mechanical harvesting in some areas of Big and/or Little Cove  and along the Torenta Canal. 

 

Status of invasive aquatic plant species in Lake Mitchell

The amount of Eurasian Watermilfoil present in Lake Mitchell varies each year depending on climatic conditions and runoff associated nutrients.  The whole lake June 6 survey determined there was 60.8 acres of milfoil. Both Franke South and the Torenta Canal were harvested in addition to chemical treatments. 

 

Evaluation of Galerucella beetles on purple loosestrife reduction

Beetles have been stocked where loosestrife is growing in order to create a sustainable population around the lake that will manage the presence of this plant. While loosestrife is still commonly seen around the lake, the beetle population is making progress at controlling this invasive plant.

 

Management recommendations for 2018

Surveys of the lake will be done in May and/or June and from that a treatment plan will be developed. Treatments will occur in June and post-treatment surveys will determine if further treatment will be needed.

This year RLS is recommending that we treat large offshore areas with Sculpin@ (2, 4-D). Sculpin@ is recommended  for a change from Navigate@(2, 4-D) since the latter was used in 2018 and so that plant tolerance does not become established. Near shore areas will continue to be treated with Renovate OTF@ (triclopyr). Diquat and/or Clipper will continue to be used in the cove areas for nuisance natives. The canal will be monitored for a possible harvest and scheduled if necessary.

Maintaining EWM at existing low levels will be the top priority to keeping a healthy balance and continuing to maintain a low assessment for the lakefront owners.

Water quality will continued to be monitored in the lake and tributaries. New water quality data from2019 will be compared to historic data to establish any long-term trends.   

Lake Mitchell is a healthy lake with excellent aquatic plant diversity. It has acceptable water clarity that is somewhat reduced by tannins and lignins coming from extensive wetland drainage. RLS is working on an immediate watershed plan to reduce future nutrient contributions. Temporary algal blooms occur during hot windless periods but do not tend to become established but may aggregate near shoreline if hot weather persists for an extended period of time. RLS will continue to monitor the lake for any problematic blooms.  

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Summary of 2017 Lake Mitchell RLS Aquatic Vegetation Program

 

The 26 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 o the website www.lakemitchell.org

 

The overall condition of Lake Mitchell is ranked in the top 15% of developed lakes of similar size in the state of Michigan. In 2017, 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

Protection of the 26 native species of vegetation is vital 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 2017 approximately 78 acres of Eurasian water milfoil (EWM) was treated in the entire lake. This represents a decrease from the 105 aces that was found in 2016. Rigorous treatments in 2016 and the mild summer weather may have accounted for the reduction in acreage. 

 

The water clarity in Lake Mitchell is improving and has been measured to be 9 feet. This is adequate to allow abundant growth of algae and aquatic plants. The improved clarity cannot be attributed to presence of zebra mussels since their population is not strong in Lake Mitchell due to low alkalinity. They are much more prevalent in Lake Cadillac. 

 

Phosphorus

Measurements for phosphorus in Lake Mitchell showed a decrease.  This may due to the long dry spells where no runoff occurred. Hopefully it also comes from a reduction in fertilizers containing phosphorus being put on lawns. Phosphorus is the primary nutrient necessary for abundant algae growth and aquatic plant growth.   

 

Alkalinity

Lakes with high alkalinity are able to tolerate larger acid inputs with less change in pH. The alkalinity of Lake Mitchell is quite low and indicative of a “soft water” aquatic ecosystem.

 

pH

  Most Michigan lake have pH values from 6.5 to 9.5 Acid lakes  with greater than 7 pH are rare. Lake Mitchell had a higher pH at 8.8 to 9.0. This may due to less tannins from inlets reaching the lake.

 

Chlorophyll and algal species

Chlorophyll-a is the measure of the amount of green plant pigment in the water, often in the form of planktonic algae. Mitchell has a low rating and  a diverse crop of algae and plant life, an indicator of great water quality.  

 

Toxic blue-green algae

When growing in high abundance, blue-green algae can result in a surface scum that produces a a toxin that humans and animals should avoid contact with when swimming. Cause of this bloom may be nutrient enrichment, abundance of zebra mussels which filter out good algae and then expel blue-greens and possibly the enrichment of CO2 since this phenomena is occurring globally. The preferred treatment is not to apply copper based algaecides which may cause further blooms. RSL will focus on this problem this year.   

 

Purple Loosestrife control

The Galerucella beetle is stocked each season around areas of Lake Mitchell infested with Purple Loosestrife. The goal has been to introduce enough beetles each season to create a sustainable population around the lake to naturally  reduce the acreage of over management of the invasive Purple Loosestrife.

 

Management Recommendations for 2018 

Detailed surveys done in late May or early June will pinpoint location of EWM and Curly Leaf Pondweed. Chemical treatments will follow and be overseen by RSL staff. 

 

This year RLS is recommending that we treat offshore areas with  Navigate (2,4-D), at 200 pounds/per acre  and small areas with 240 pounds per/acre. Navigate is recommended for a change from  Sculpin (2, 4-D)so that plant tolerance does not become established. Near shore areas will continue to be treated with Renovate OTF. Diquat and/or Clipper will be continued to be used in the cove areas for nuisance natives. The canal will assessed for the need for a possible harvest and scheduled if necessary. 

 

Water quality will continue to be monitored in lakes and tributaries. 

 

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2017 Annual Report
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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.


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2018 Annual Report
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Lake Mitchell Annual Report RLS 2018.pdf
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2017 Lake Mitchell Annual Report
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2016 Lake Mitchell Annual Report
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2016 Lake Mitchell Improvement Feasibility Study and Aquatic Vegetation Management Plan
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2014 Lake Mitchell Annual Report
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2013 Lake Mitchell Annual Report
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2012 Lake Mitchell Annual Report
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2011 Lake Mitchell Annual Report
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2010 Lake Mitchell Annual Report
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