Lake Tips: Aquatic Plant
Management - Part I
Aquatic plants and algae are an integral part of the lake’s ecosystem, and
that is important to keep in mind as we address nuisance problems, such as
algal blooms and aquatic weeds. Inlake techniques for controlling algal blooms
and aquatic weeds differ, but the conditions that support their growth and
watershed measures used to prevent such conditions are similar. This Lake
Tips will help identify when aquatic vegetation becomes a problem and
factors that support the growth of these nuisances. (For information about nuisance
vegetation control measures, see Lake Tips: Aquatic Plant Management, Part 2).
A System Balance
Aquatic plants, algae (found on rocks, etc.) and free-floating algae (called
phytoplankton) are the primary producers in a lake. This aquatic vegetation
provides a food source for microscopic animals called zooplankton and
small fish. The smaller fish provide food for larger fish, etc. All these living
organisms are part of the lake ecosystem food web. Any action at one level ultimately
will affect all other levels of the system, so management must be tailored
to the lake and its watershed conditions.
Aquatic vegetation often becomes a problem when it tends to dominate the
system. At this point, it usually interferes with some intended lake usage. For
example, it may impair recreational activities like boating, swimming or
fishing. It may affect irrigation or hydropower generation or decrease lake
shore, and area property values. Algal blooms can lower dissolved oxygen levels
enough to kill fish, create offensive tastes and odors, and even be toxic to
wildlife, domestic animals and humans.
Plant species that are not native to a particular environment, so-called
exotic species, also can become a problem by out-competing native plants for
available nutrients and habitat. Eurasian watermilfoil, purple loosestrife and
southern naiad are among the exotic plants that have found their way into lakes.
(Though not a plant, zebra mussels are yet another example of an exotic species
that has become a lake nuisance in recent years.)
Who is creating the problem? We all are! If you live in a watershed (as we
all do), you are part of the problem and, more importantly, part of the
Have a Plan
The solution begins with awareness of the interconnected nature of humans
their activities, and a knowledge of how these activities impact the natural
environment. The next step is to develop a successful aquatic plant management
plan. The plan should include three major components:
- Understanding the source(s) of the problem;
- Prioritizing realistic goals and objectives to correct the problem; and
- Implementing the necessary actions to meet your goals and objectives.
This plan will be influenced by the watershed and lake ecology,
socio-economic factors, and regulatory considerations. Identifying the sources
of the pollution problem and determining feasibility of alternative measures to
address these sources are components of ecological evaluation. Identifying all
lake uses and user groups, forming working partnerships, and anticipating and
resolving conflicts are social elements in the overall plan. Economic factors
include creating a budget, and securing funding sources. To avoid costly delays,
local, state, and federal regulations that apply to environmental projects
should be identified early in the process.
A broad watershed perspective is needed for successful aquatic plant
management in a lake. This land area that drains into a lake directly relates to
the productivity of the lake. Inputs to the lake from both point sources
(municipal and industrial discharges) and nonpoint sources (runoff from
cropland, roadways) can carry nutrients and organic matter that spur the growth
of aquatic vegetation.
What Feeds Nuisance Vegetation?
The nutrient that is usually most crucial for the growth of lake vegetation
is phosphorus. In addition to watershed sources of phosphorus, in-lake sources
of phosphorus loading also can promote plant and algae growth. Usually in-lake
phosphorus remains bound to sediment on the bottom of the lake, but under
certain conditions, this nutrient is released and becomes available to support
plant production or algae blooms. For instance, underwater currents from
outboard motors can stir up bottom sediments in shallow lakes and release
nutrients to be available for algae. When bottom-dwelling plants are cut or die
off, phosphorus from the plants is released into the water column to be used by
suspended algae or phytoplankton and support algae blooms.
Because nuisance growths of both plants and algae can results from excessive
nutrient inputs from the watershed as well as from inside the lake, control
strategies need to target all potential sources. A nutrient budget, which
assesses phosphorus sources and sinks in the watershed and lake, can help
pinpoint those areas to target for nutrient control. Although the cost of a
detailed nutrient budget may seem high, in the long run, this up-front
investigation can save time and money.