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Aquatic plants are an often misunderstood and under-valued part of freshwater ecosystems. In fact, many people would rather not have them in their favorite swimming or fishing hole. The following points illustrate a few of the important roles that aquatic plants play in a water body.
Food
Aquatic plants provide important food for many animals. Ducks and geese
eat the seeds, leafy parts, and tubers of plants such as pondweeds (Potomogeten
spp.), watershield (Brasenia schreberi), arrowhead (Sagittaria
latifolia), water pepper (Polygonum sp.), and duckweed (Lemna
sp.). Songbirds use fluff from cattails (Typha sp.) as nest material and
eat the seeds of many emergent plants. Otter, beaver, muskrats, turtles, and
moose will also graze on a variety of aquatic plants.
Historically humans have also utilized aquatic plants as a food source. Cattails have edible shoots and roots and even the pollen has been used in making biscuits. Arrowheads form large edible tubers at the root ends, called duck potatoes, which were consumed by Native Americans. Watercress (Rorippa nasturtium-aquaticum) has many historic medicinal uses and its spicy vegetation continues to be used in salads and garnishes. Water lily roots are a common source of food in many parts of the world and have historic medicinal value. Even the submersed plant, coontail (Ceratophylum demersum) has been used for medicinal purposes.
Habitat
Aquatic plants provide important living space for small animals such as
aquatic insects, snails, and crustaceans, which in turn supply food for fish and
waterfowl. Many studies have shown that vegetated areas support many times more
of these tiny creatures than do unvegetated areas.
Cover
Young fish and amphibians will use aquatic plants as a source of cover from
predatory fish and birds. This, coupled with the abundant food supply, makes
aquatic plants important nurseries for baby fish (including our native salmon),
frogs, and salamanders.
Housing Supplies
The sturdy emergent plants provide nest and den-building materials for
many birds and mammals, including muskrats.
Humans also construct baskets, mats, boats, and even dwellings from cattail,
rush, and bulrush stems.
Erosion Control
Submersed and emergent plants protect shorelines from erosion due to wave action
or currents. They can also help stabilize the sediment which can increase water
clarity.
Nutrient Cycling
Aquatic plants form a vital part of the complex system of chemical cycling in a
waterbody. They can also influence the supply of oxygen in the water. Recently
aquatic plants have received a lot of attention for their ability to soak up
pollutants from contaminated water. They utilize nutrients that would otherwise
be used by algae, thereby improving water clarity. Increasing attention is being
paid toward their possible use as indicators of water quality.
Resist Invasion by Invasive Exotics
A diverse healthy native plant community is more resistant to invasion by
opportunistic exotic plants.
Why are Aquatic Plants Seen as a Problem?
If aquatic plants are so wonderful, why are they perceived as a problem? Most of
the time, problems arise when plants are so numerous they impede recreational
activities such as boating and swimming. When growth becomes very thick, they
also harm some fisheries, particularly juvenile salmon and trout habitat. The
causes of unnaturally high levels of plant growth are complex. Often it is
attributed to increased nutrients, which come from around the lake or in the
watershed. Contributing problems can include failing septic systems, fertilizer
run-off, or agricultural waste. These increased nutrients cause the natural
process of lake aging (eutrophication) to proceed at an accelerated rate, and
increased plant and algal growth is part of this process.
Another problem can arise if a nonnative species is inadvertently introduced to the lake. This often happens when recreational users unknowingly carry plants from one waterbody to another, or when someone discards aquarium plants into a lake. Several exotic species such as Eurasian watermilfoil (Myriophyllum spicatum) or Brazilian elodea (Egeria densa) are aggressive and can crowd out more desirable native vegetation. Changes in vegetation may take place slowly or quite rapidly.
What can individuals concerned about a waterbody do?
Along with preventing or eliminating pollution, you can monitor plant
community changes by collecting and identifying aquatic plants on a year-to-year
basis. This is also a good way to detect detrimental changes at an early stage
when control or elimination of the problem is both less complicated and less
costly. Collecting and preserving plants is not difficult, and the result is an
increased awareness of aquatic plants, as well as a valuable historic record of
what grows in the lake. However, proper identification of the plant can be
tricky and is essential, particularly if you believe any to be exotic invasive
species.
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
