By Wisconsin Lakes staff
Native aquatic plants are at the root of healthy lakes, and are essential for good fishing and clean water. Plants provide a place to live and food for fish, birds, frogs, turtles, insects, and many other kinds of wildlife. They also produce the oxygen needed by fish and other underwater animals. They also help preserve water quality by using nutrients—like phosphorus—that would otherwise be available for algae growth, protecting shorelines from erosion, and holding down lake-bottom sediments with their roots.
Role of Aquatic Plants in Lakes
Plant growth is important to the character of the lake, and to all other organisms that live in the lake. Emergent and floating-leafed plants are valued for their aesthetic qualities and help provide a more “natural” buffer between a developed shoreline and the open water.
Plants are primary producers, that is, they take sunlight and nutrients in the water and convert them into energy to grow and produce oxygen—necessary for fish and many other underwater creatures—as a byproduct.
A lake’s “littoral zone” describes the shallow water area where rooted and floating aquatic plants (also called macrophytes) can grow because sunlight can penetrate to the lake bottom. Large algae are also included in the macrophyte community. In lakes where the lake bed is too rocky or sandy for rooted plants to anchor themselves, or wave action is too severe, there may be few macrophytes
Algae constitute the other main group of primary producers. Algae come in countless forms and live in nearly all kinds of environments. Most are microscopic, growing as single cells, small colonies, or filaments of cells. Algae suspended in the water are called phytoplankton. Phytoplankton grows suspended in open water by taking up nutrients from the water, and energy from sunlight. If their populations are dense, the water will become noticeably green or brown and will be turbid (have low transparency). Sunlight may not reach the lake bed bottom even in shallow areas if the concentration of algae or silt is high.
In many lakes (especially shallow ones) submerged plants grow in abundance, performing a critical role: they compete with algae for nutrients and help maintain better water clarity. In shallow, clear lakes, macrophytes may represent most of the green plant material present and may account for most of the photosynthesis. The major threat to lakes involves the excessive growth of primary producers due to excessive nutrients entering lakes in polluted runoff.
What Affects Aquatic Plant Growth?
To grow, plants need sunlight, water, nutrients, proper temperature and a stable soil to root in. Usually these elements are found in abundance in the shallow waters and surrounding marsh edges of lakes. Fluctuations in lake levels—caused by drought, floods, or deliberate lake management—can affect where plants can grow and which species can survive.
Summer temperatures are conducive to plant growth anywhere in Wisconsin and plants growing underwater are not subjected to the wide temperature variations that affect land plants. Nutrients are important, but they are usually abundant enough in the water or bottom soils to support abundant plant growth. Most often lakes have problems with too many nutrients, such as phosphorus, rather than not enough.
Plants can’t root in extremely hard bottoms, and they are easily uprooted in very soft bottoms. Some shorelines are high-energy. That is, they are constantly buffeted by high winds, waves, or currents so plants can’t root. Lack of sunlight can limit rooted plant growth to shallow water. How shallow depends on water clarity. In clear water lakes plants will grow in deeper water than in turbid waters. Some lakes are so turbid no plants will grow.
Human activities can affect where and what plants will grow in a lake too. Disturbing shorelines by clearing vegetation for shoreland projects (from installing piers to constructing buildings) can impact lake water quality and open up opportunities for invasive species to establish themselves. Waves and scouring of the lake bed in shallow areas caused by motorized watercraft can also impact lake plants.
Protecting Native Aquatic Plant Communities
Leaving aquatic plants and along your shoreline and fallen trees and branches in the water provides habitat for fish and wildlife. The plants filling in the distance between the edge of intensely managed property (lawns, buildings, walkways etc.) and the water’s edge is called a shoreland buffer. While the ideal width of a shoreland buffer may vary based on the sensitivity of the lake ecosystem, any amount of natural shoreland is better than none, and the more the better.
Many local governments have passed boating ordinances to create slow or no-wake zones and restricted motor areas in order to reduce the impact of boats on aquatic plants.
Limiting boat traffic in areas with sensitive species or where there are many floating plants may be a good way to guide boat activity to more appropriate parts of a water body. Basing no-wake zones on water depth or the maximum depth of plant growth may be more useful than those based upon fixed distances from shore. While no-wake zones do not prevent all impacts, they do serve to reduce the overall amount of boat activity in a given area.
Controlling Nuisance Aquatic Plant Growth
Since aquatic plant communities are the foundation of lake ecosystems, aquatic plant management and nuisance control activities require an aquatic plant management plan and permits issued by the Department of Natural Resources. Many lake groups have used lake grants to fund development of aquatic plant management plans.
Chemical, mechanical, and biological (for example, introducing insects that feed on undesired plant species) control methods of aquatic plants always require a permit. Manual control (hand-pulling or raking) may require a permit, depending on the specifics of the proposed project and the site. Generally, a permit is required when plants are removed mechanically or manually from an area greater than 30 feet in width along the shore.
Physical aquatic plant control methods include activities such as bottom plant barriers and water level draw-downs. Because they involve placing structures on the bed of a lake and/or affect lake water levels, Chapter 30 or Chapter 31 permits are required.