Conservation Minnesota

What Works (and Not) in Managing Lakes

A LAKE MANAGER’S NOTEBOOK-

The profession of managing lakes began about 40 years ago.  At that time, the United States was confronting huge water quality issues and the need to remedy these problems was compelling.  Due to this necessity, individuals, organizations and agencies passed laws and funded demonstration projects, thus birthing the profession of lake management.  Simply, we found what worked and what did not work to clean up lakes.

Today, the profession has evolved to a point where we have become less critical, systematic and scientific in our approach.  In short, we are using many tools, techniques and approaches that do not work and have set aside those that are tried-and-true.

Here, I provide an overview of categories of lake management tools, techniques and approaches using an objective, scientifically defensible guideline to list lake management that works.  In follow up columns, I will go into each one individually.

I use these definitions in my assessment of lake management techniques:

Works (W) – When applied in appropriate situations, this approach or technique provides predictable and measurable outcomes with a high level of reliability.

May work, beware (MW) – When applied in appropriate situations, this approach or technique may provide predictable and measurable outcomes, albeit with a low level of reliability.  This is considered under development.

Does not work (DNW) – This approach or technique is not likely to provide reliable outcomes.

Not recommended (NR) – This approach or technique cannot be recommended because it has unknown efficacy or it has not been tested (or both).

These ratings are based on a) efficacy, reliability and repeatability as determined by the level of scientific scrutiny they have received and b) the expectation of predictable and measureable positive outcomes.

For the ranking of what works, I consider common lake problems to be managed in these categories:

  • Eutrophication, including phosphorus impairments and nuisance algae.
  • Nuisance (native) plants
  • Aquatic invasive species (AIS) – Prevention
  • AIS – plant control
  • AIS – animal control

The list of lake management techniques includes:

Algaecides – Chemicals that kill algae.  Algaecide’s efficacy tends to be short-lived.

Artificial Circulation-I – AC-I refers to artificial circulation that is employed following carefully diagnosis, design, sizing and deployment.

Artificial Circulation-II – AC-II refers to artificial circulation that is employed uncritically.  There are many products that appear to be artificial circulators coming in the guise bubblers, fountains and machines that make water move.  There is an overall lack of objective assessment of these and what assessments that have been done are usually negative.

Biocontrols – are biological agents deployed to control unwanted invasive plants or animals.

Biomanipulation – The efficacy, reliability and repeatability of biomanipulation increases with decreased phosphorus levels in lakes, so it is most effective when least required.  There are documented cases where biomanipulation works well, however these involve ongoing maintenance and inputs of energy.  Long-term evaluations have a less complete record of documentation.  In light of the variable situations and management concerns, there is no single rating.

Drawdown – When practical, drawdown exposes shallow sediments thereby desiccating or freezing plant propagules.   Many rooted plants will be controlled for multiple seasons, however, some plant species may increase following a drawdown.

Dredging – Dredging (with removal) deep lake sediments has multiple benefits, including the removal of nutrient-enriched sediments and the deepening of the lake.  Suction dredging is a technique whereby nuisance rooted plants are hand-pulled and placed into a suction dredge for removal and collection.

Herbicides – are chemicals that kill unwanted plants.

Mechanical Removal – Nuisance plants and animals may be physically removed by various methods.  In most cases, mechanical removal may be very effective, however, removing sufficient numbers or amounts of biomass is challenging to remove and regrowth and repopulation is often rapid.

Microbes and Enzymes – Microbes and bacterial concoctions, sometimes augmented with enzymes, promise to facilitate algae control or nutrient manipulations.  Often bacteria or enzymes are proposed in combination with artificial circulation-II.

Oxygenation – is a kind of aeration that adds pure oxygen to the lake water.  This is most often added below the thermocline, called hypolimnetic aeration, using highly specialized equipment.

Public Education – is perhaps the most recommend, most used management approach and it is also the least objectively studied.  Public education is “untested,” at least in the context of evaluating measurable, tangible outcomes.

Watershed Management – includes the general category of best management practices.  Unfortunately there are few case studies that have demonstrable beneficial impacts for lakes.

Phosphorus Precipitants (Alum) – Alum has a long documented record of effective treatments to mitigate excess phosphorus through one of these approaches: phosphorus water column stripping, phosphorus inactivation, phosphorus interception and phosphorus maintenance.

Phosphorus Precipitants (Calcium & Iron) – Phosphorus precipitation using calcium or iron.

Phosphorus Precipitants (Other) – There are newer products available with claims they are effective phosphorus precipitants.  I am aware of no peer-reviewed or third party evaluations of field trails.

In summary, here is what works (or not):

Approach or Technique Eutrophication AIS Prevention AIS Plant Control AIS Animal Control

Nuisance Plants

Algaecides

 

W n/a n/a n/a n/a
Artificial Circulation-I

 

W n/a n/a n/a n/a
Artificial Circulation-II

 

DNW DNW n/a DNW n/a
Biocontrols

 

n/a n/a n/a MW DNW
Biomanipulation

 

See description n/a n/a n/a n/a
Drawdown

 

n/a W n/a W n/a
Dredging

 

Works W n/a W n/a
Herbicides

 

n/a W n/a W n/a
Mechanical Removal

 

Works n/a W n/a W
Microbes and Enzymes

 

NR n/a n/a n/a NR
Oxygenation

 

W n/a n/a n/a n/a
Public Education

 

NR NR NR n/a n/a
Watershed Management

 

NR n/a n/a n/a n/a
Precipitation (Alum)

 

W n/a n/a n/a n/a
Precipitation (Calcium, Iron)

 

W n/a n/a n/a n/a
Precipitation (Other)

 

NR n/a n/a n/a n/a

About Dick Osgood

Dick Osgood
Dick Osgood has authored numerous scientific journal papers, made hundreds of presentations at professional meetings, and recently co-authored his first book.  Now he’s working on his second book titled A Lake Manager’s Notebook.  Dick is a Certified Lake Manager and offers lake management consulting services through his business Osgood Consulting LLC.
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