Chapter
Five - Lake Management
EVERY
LAKE is unique. Specific strategies to address a lake's water quality
problems should focus on activities in the watershed and/or in-lake
restoration techniques, depending on the nature and extent of the
problem.
Lake management
approaches fall into two categories, the "quick-fix" and
long-term management. The quick-fix offers a short-term solution such as
the application of herbicides to kill unwanted algae or macrophytes
(large plants). It treats the biological symptoms of a lake problem, but
does not address the underlying causes. Plant and fish productivity are
dependent on the chemical and physical processes going on in and around
the lake, and these must be considered in any plan to change the biology
of a lake.
Long-term
management considers all of the environmental, cultural, and biological
factors affecting the lake and sets a priority on finding lasting
solutions. If immediate in-lake restoration techniques are necessary,
they should be followed by appropriate long-term management actions to
control sediment, nutrient, and toxic inputs.
Lake management
is a complicated job and likely will be a joint effort of community
groups, individuals, landowners, and government. To be effective, lake
management is a long-term commitment and investment. This and following
sections briefly summarize various methods to improve a lake's water
quality and indicate necessary permits and possible grants and loans.
In-Lake
Restoration: Cleaning up problems
Controlling
pollution sources will not improve lake water quality immediately in
many cases. Years may pass before lakes cleanse themselves of
accumulated nutrient loads and wastes. For this reason, in-lake
restoration techniques have been developed to accelerate recovery.
In-lake restoration techniques are briefly described in the table below.
Consult the references at the end of this web-site for more details on
these techniques.
In-Lake
Restoration Techniques
| Method |
Advantages |
Drawbacks |
| Dilution:
Flush with low nutrient water |
Reduces
nutrient levels. Washes out surface algae. |
Requires
large volumes of water.Does not eliminate sources of
phosphorous from sediments or watershed. |
| Aluminate
sulfate (alum) treatment |
Lowers
lake phosphorus content. Inhibits release of phosphorous from
sediment. Increases water column transparency. |
Temporary
measure. Potential toxic impacts during application. Increased
macrophyte growth due to water clarity. |
| Artificial
circulation |
Disrupts
or prevents stratification. Provides aeration and oxygenation.
Increases aerobic habitat. |
Does
not decrease algal biomass. May decrease water clarity. Adverse
impact on cold-water fish. No effect on macrophytes.
|
| Hypolimnetic
aeration |
Maintains
oxygen in hypolimnion. Limits release of phosphorous from sediments.
Increases habitat and food supply. |
Difficult
to supply adequate oxygen. Potential for destratification and subsequent
algal blooms. No effect on macrophytes. |
| Dredging |
Controls
aquatic vegetation, deepens lake. Increases lake volume. May improve water
quality. |
Temporary
resuspension of sediments. Temporary destruction of habitat. Disposal
concerns. High cost. |
| Water
level drawdown |
Controls
macrophytes. Consolidates sediments. Facilitates dredging or excavation.
Facilitates dock repairs. |
Poor
effectiveness in mild, wet climates. Short-term benefit. Intensifies algal
blooms. Temporary adverse impacts on fish and invertebrates. May leave
docks high and dry. |
| Biomanipulaton:
Adjust fish species composition |
Encourages
growth of zooplankton, which eat algae. |
Considered
experimental. Not effective where blue-green algae dominate. |
Aquatic Plant
Control
 Many
techniques have been developed for controlling aquatic plants and are
briefly described in the table below. Additional information on
advantages, disadvantages, permits, costs, and contacts for each technique
are available at
this link and in references provided at the end of this web-site.
Aquatic Plant
Control Techniques
| Method |
Advantages |
Drawbacks |
| Manual
Methods: (Handpulling, raking
and cutting) |
Inexpensive.
Flexible. Easy to use around docks, swim areas. |
Not
practical for large areas. Stirs up sediment. Disturbs
bottom-dwellers. |
| Sediment
Covers
(Bottom
barriers)
|
Inhibits
or prevents growth. Nontoxic. Low environmental impact in small
applications. Ability to target problem areas. Can be installed in
areas that are inaccessible to harvesters. |
High
cost. Prone to damage, displacement, and plant regrowth. Must be
correctly installed to prevent flotation. Maintenance required. |
| Weed
Rolling:
Rolls plants flat or detaches them from bottom sediment |
Inexpensive,
easy to operate. Can give season-long control. |
Detached
plants need to be removed from water. Good only for limited area
around dock. |
| Mechanical
Cutting:
Cutters clip plants several feet below surface |
Hand-held
cutters easily maneuvered. Fish habitat retained. Low cost for
individuals/associations. |
Plant
fragments must be removed to prevent rerooting. Several cuts
required in growth season. |
| Mechanical
Harvesting |
Removes
plant material from lake. Requires no toxic substances. Vegetation
may be composted. |
Labor
intensive, seasonally dependent. Access constraints. May facilitate
colonization of new areas due to fragmentation. High costs. Repeat
treatments needed. Depth restriction (.5m-5ft.) Plant disposal
needed. |
| Rotovation:
"Roto-tilling" to dislodge plants and roots |
2-3
acres can be rotovated daily. Removes roots. |
Large
equipment, high costs. Disrupts sediment, causing turbidity,
nutrient and toxic release. Disturbs bottom dwellers. For milfoil
control. |
| Sterile
Grass Carp |
Controls
some aquatic vegetation. Requires no toxic substances. |
Potential
impacts on other organisms. May increase nutrient cycling and
stimulate algal blooms due to grazing and digestive activities.
Possible escape and infestation of nontarget areas. Introduction of
parasites. May prefer native plant species over exotics. |
| Herbicides:
Apply chemicals to kill or control plants. |
Inexpensive.
Easy to apply. May control macrophyte and algae growth. |
Potential
toxic effects. Decomposing plant material releases nutrients to
water column. Short-term benefit may require temporary restriction
on recreational activities. Dissolved oxygen depletion due to
decomposing plants. Repeat applications needed. |
Next
Chapter - Permits
1.
Lake Characteristics | 2. Lake Problems | 3.
Watershed Management | 4. Shoreline
Management | 5. Lake Management | 6.
Permits | 7. Lake Organizations | 8.
Sources of Money | 9. References | WALPA
Return to Washington Lake Book Table of
Contents |
