Water
Quality: Management, Sanitation and Investigation
Limnological
Fundamentals
Aquatic
Plants
Aquatic plants
have true roots, stems, and leaves. They, too, are a vital part of the
biological community of a lake. Unfortunately, like algae, they can overpopulate
and interfere with lake uses.
Aquatic plants can
be grouped into four categories:
-
Emergent plants
are rooted and have stems or leaves that rise well above the water surface.
They grow in shallow water or on the immediate shoreline where water lies
just below the land surface. They are generally not found in lake water
over two feet deep.
-
Rooted floating-leaved
plants have leaves that rest on, or slightly above, the water surface.
These plants, whose leaves are commonly called lily pads or "bonnets,"
have long stalks that connect them to the lake bottom.
-
Submergent plants
grow with all or most of their leaves and stems below the water surface.
They may be rooted in the lake bottom or free-floating in the water. Most
have long, thin, flexible stems that are supported by the water. Most submergents
flower above the surface.
-
Free-floating
plants are found on the lake surface. Their root systems hang freely from
the rest of the plant and are not connected to the lake bottom.
Through photosynthesis,
aquatic plants convert inorganic material to organic matter and oxygenate
the water. They provide food and cover for aquatic insects, crustaceans,
snails, and fish. Aquatic plants are also a food source for many animals.
In addition, waterfowl, muskrats, and other species use aquatic plants
for homes and nests.
Aquatic plants are
effective in breaking the force of waves and thus reduce shoreline erosion.
Emergents serve to trap sediments, silt, and organic matter flowing off
the watershed. Nutrients are also captured and utilized by aquatic plants,
thus preventing them from reaching algae in the open portion of a lake.
Factors that
Affect Aquatic Plant Growth
There are many factors
that affect aquatic plant growth including:
-
the amount of light
that penetrates into the water;
-
the availability of
nutrients in the water (for free-floating plants) and in the bottom sediments
(for rooted plants);
-
water and air temperature;
-
the depth, composition,
and extent of the bottom sediment;
-
wave action and/or currents;
and
-
competition pressure
from other aquatic plants for nutrients, sunlight, and growing space.
The Overgrowth
of Aquatic Plants
Excessive growth
of aquatic plants is unsightly and can severely limit recreation. Submergents
and rooted floating-leaf plants hinder swimmers, tangle fishing lines,
and wrap around boat propellers. Fragments of these plants can break off
and wash up on beaches and clog water intakes.
For many species,
fragmentation is also a form of reproduction. An overgrowth problem can
quickly spread throughout a lake if boat propellers, harvesting operations,
or other mechanical actions fragment the plants, allowing them to drift
and settle in new areas of the lake.
Free-floating plants
can collect in great numbers in bays and coves due to prevailing winds.
Emergent plants can also be troublesome if they ruin lake views and make
access to open water difficult. In addition, they create areas of quiet
water where mosquitoes can reproduce.
Monitoring programs
designed to characterize the aquatic plant condition usually:
-
map the distribution
of plant beds in the lake;
-
estimate the density
of plants along a transect line in a selected area; and
-
collect specimens for
professional identification.
