the Looking Glass and the WI
The plants growing
in your lake fit into one of the following categories:
in the shallowest zone to about knee-deep. Here you'll find cattails,
bur-reed, blue-flag iris, bulrush, spikebrush, and sedges. These
plants can tolerate fluctuating water levels and dense stands
can dampen wave action.
going from knee-deep water out up to your waist and deeper. The
plants you'll find are white and yellow water lilies, watershield,
floating-leaved pondweeds, duckweeds, and some submergent species
like coontail, bladderwort and water milfoil.
- Open water
submergents- now you'll need to start swimming. These underwater
plants grow from the shallowest zones out to several meters deep.
There's a great diversity of plants out here; water milfoil, coontail,
bladderwort, water marigold, large-leafed pondweeds
Update 3/15/01: Hennepin Parks
has conducted aquatic plant composition surveys. Click here
for a map showing the lakes that were surveyed.
Aquatic plants perform
some of the same roles in your lake as trees do in a forest. While most
people are aware of the consequences of poor logging practices in a forest,
most are unaware of what changes in the aquatic plant community will do
to their lake. Like trees in a forest, aquatic plants provide structure
and food for other organisms. They also stabilize soft lake bottoms and
minimize shoreline erosion by dampening the effect of waves like trees
hold the soil and block the wind in a forest. These plants also absorb
and use nutrients like phosphorus and nitrogen, making less available
for algae. A healthy plant community in your lake also makes the lake
less susceptible to the spread of exotic plants like Eurasian water milfoil
(see Exotics section).
Let's go through
these benefits in a bit more detail:
Plants provide a refuge for small animals against predation by bigger
ones. Zooplankton and invertebrates use the plants to escape predation,
as do small fish. Lake vegetation can have a strong influence on the types
of fish and invertebrate communities present, different communities and
relationships exist between vegetated and unvegetated parts of the lake.
Stands of aquatic
plants tend to have a much richer invertebrate (aquatic insects and zooplanton)
than unvegetated stands, both in terms of number of species (diversity)
and total numbers of bugs (biomass). This is not only because fish have
a harder time catching bugs in plant beds but also because the plants
Aquatic plants are
usually coated with periphyton (attached algae), which is an important
food source for invertebrates. Decaying plant parts are also consumed.
In addition, the seeds/fruits of some plants and the invertebrates that
live within plant beds are important sources of food for waterfowl and
shorebirds. The plants often serve as nesting areas.
A number of mammals
also need aquatic plants. Muskrats and beavers feed on plant tubers and
often use plants for their construction projects.
Many aquatic plants are rooted and their roots help keep soft sediments
from being resuspended. Light limitation is one of the main problems for
submerged vegetation in many lakes. The resuspension of sediments by wind,
waves and boat traffic can cause turbidity in the water, which limits
the amount of sunlight that can reach the plant leaves. Once the plants
grow, the water clears up and they grow even better. Turbid (cloudy) unvegetated
shallow lakes tend to remain that way because wave action and bottom feeding
fish tend to keep resuspending sediments. Vegetated waters however tend
to stay vegetated because the resulting water clarity promotes more plant
growth, but also because the sediment is stable, the fish community is
shifted more towards piscivores instead of bottom feeder like suckers
and carp (Sheffer 1998). Predatory fish like northerns are highly dependant
on sight to catch their prey and obviously do much better in clearer waters.
Beds of aquatic vegetation often help dampen wave action and currents.
Water flow is slowed and wave energy absorbed by the stems and leaves
of the plants. Emergent vegetation near shorelines also keeps the lake
bottom more stable there.
Observations in many shallow lakes have shown that when vegetation reaches
its peak in the summer, algae or phytoplankton abundance declines. So
it becomes a trade-off. As long as nutrients and sunlight are available
either algae or aquatic plants or both are going to use them. If you remove
aquatic plants from a lake, algal growth will increase. This is an important
ingredient in determining how to approach plant management.
One reason exotic species are able to take over an ecosystem is because
that system has been perturbed. There is room for that new organism. Usually,
but not always, a healthy, unperturbed ecosystem can resist the invasion
of an exotic plant or animal. This provides another reason to try and
maintain a healthy aquatic plant community in your lake.
How do I Protect
the plants in my lake?
From Wisconsin DNR:
Aquatic plant protection
begins with us. We need to work to maintain good water clarity and healthy
native aquatic plant communities. How can we do it? The first step is
to limit the amount of nutrients and sediment that enter the lake. There
are other important ways to safeguard a lake's native aquatic plant
community. They may include developing motorboat ordinances that prevent
the destruction of native plant beds, limiting aquatic plant removal
activities, designating certain plant beds as sensitive areas and preventing
the spread of exotic plants, such as Eurasian watermilfoil. Most aquatic
plant communities have a dynamic balance. If plant management is needed,
it is usually in lakes significantly altered by humans. If we discover
how to use aquatic plant management techniques that blend with natural
processes rather than resist them, the forecast for healthy lake ecosystems
W. 1998. A Great Lakes Wetland Flora. Pocketflora Press, Calumet, MI.
Sheffer, Martin. 1998. Ecology of Shallow Lakes. Chapman and Hall, London,