Marshes are shallow-water areas that sustain water-loving plants such as cattail, sedge, arrowhead, bulrush, water lily, and pondweed. Marshes found in Michigan include wet meadows with grasses and sedges, potholes with cattails, and shallow vegetation zones along Great Lakes shorelines. While marshes are generally covered by standing or slow-moving water, certain marshes dry out late in the growing season or during dry years. This fluctuating water level is part of the natural process, which increases plant and habitat diversity, and productivity of the marsh.
Less than an acre or as large as several thousand acres, marshes have appeared and disappeared since the beginning of time. When the glaciers slowly melted about 12,000 years ago, they left behind depressions that formed lakes and potholes. As these bodies of water became shallower and warmer, many turned into marshes--an evolutionary step in the long natural succession process from water to dry upland. Also, when rivers change course in their serpentine march to the Great Lakes, they also leave old isolated sections of a channel, called oxbows, many of which become marshes over time. Marshes may also occupy slow-moving shallow zones of active rivers or develop at river mouths along the Great Lakes as coastal marshes. Fluctuating water levels in the Great Lakes create, maintain, and continually alter these marshes.
The Importance of Marshes
Like most wetlands, marshes are dynamic systems that are important to wildlife and also provide other valuable functions. On average, marshes produce at least three times more biomass than lakes, upland grasslands, and farmland. Their high rate of productivity allows marshes to support complex food chains and a broad diversity of wildlife. For example, about 80 percent of Great Lakes fish use coastal marshes during at least one stage of their life cycle. Marshes also store and collect nutrients and sediments from surface water run-off, and they reduce flooding by temporarily storing water.
All wetlands provide food, water, shelter, and living space to many kinds of wildlife. Mammals such as muskrats, raccoons, mink, and deer feed, rest, and hide in marshes. Herons, shorebirds, waterfowl, red-winged blackbirds, sedge wrens, common yellowthroats, and other songbirds also seek shelter, nesting habitats, and food. Marshes with dense cattail stands provide choice winter habitat to ring-necked pheasants. Further, they supply food and cover to leopard and chorus frogs, snapping turtles, and northern water and ribbon snakes. Uncommon wildlife species that live in marshes include black terns, American and least bitterns, king rails, and massassauga rattlesnakes. Arrowhead and marsh mallow are examples of unique plants that may grow there.
Many human activities can harm marshes. Construction projects, some farming practices, and logging methods may increase silt loads into marshes. Draining marshes to create farmland and filling marshes to make building sites are activities that most commonly have destroyed these wetlands. Streams that provide water to marshes may also deliver pollutants and fertilizer runoff, which eventually alters marsh vegetation. Some marshes are accidentally ruined by well-intentioned landowners who dig ponds in the existing marsh and then deposit the spoils in the surrounding marsh. Because marshes are such a valuable natural resource, they should be preserved, restored, or enhanced whenever possible.
The general rule for wetland management is to protect those that are healthy, restore those that have been damaged, and actively manipulate only those that are too disturbed to function naturally. If a marsh on your property is not currently being affected by human activities, the best way to protect it for future generations may be to leave it alone, or conduct small management activities. In addition to avoiding harmful practices like draining or filling, consider the following:
Restoring a marsh on your property is one of the most satisfying of all habitat management projects because the results are usually immediate and dramatic. Normally too shallow to support fish, the restored marsh will become an oasis for other wildlife, and the amount and diversity of animals that quickly move in may surprise you.
The most important consideration is restoring the wetland depression or basin with a stable supply of water. Most likely the marsh has been drained by a ditch or field tiles. If the marsh has been drained by a ditch, plugging the ditch with soil will restore the natural water source. If drainage has occurred from buried field tiles, removing at least 50 feet of tile will also bring water back to the marsh. Some landowners also add water-control structures to allow periodic draw-downs and re-flooding. The Michigan Department of Natural Resources, U.S. Fish & Wildlife Service, and Natural Resource Conservation Service (NRCS), and County Conservation Districts are among several organizations and agencies that offer assistance to landowners interested in wetland restorations. For additional information, see the Wetland Restoration Techniques chapter.
Although many landowners are interested, creating a marsh can be expensive and hard to do, especially if the site is not on hydric soils. In addition, quality wet meadows, sedge marshes, wooded swamps, and uplands may be destroyed by landowners trying to create deep water marshes or ponds. Careful planning is required, along with securing government permits. Remember, most private and government groups provide only technical assistance to wetland creation, whereas financial assistance is provided to projects that restore natural wetland systems.
The topography of your property and the surrounding land -- along with the soil type, watershed size, and drainage patterns--are important points to consider before actual construction begins. The U.S. Department of Agriculture maintains a NRCS office in nearly every Michigan County. Agency staff can help you evaluate the water-holding capability of the soil, the elevation of the present water table, and whether or not there will be adequate runoff or spring flow to maintain desired water levels in a constructed basin. Also, they can help you design the project.
In your design, think small and shallow. Areas as small as one-half acre or less will support a marsh. However, two to five acres would be productive for wildlife, especially waterfowl. Various water depths result in a mosaic of vegetation zones and increased diversity of both plant and animal species. A general rule worth noting is to provide water depths in the following proportions: 50 percent at less than 1-1/2 feet, 30 percent at 1-1/2 to 3 feet, and 20 percent at 3 to 6 feet.
No simple guidelines exist that cover all the construction methods possible. Site characteristics, available funding, water source, and total size of the marsh to be created all must be considered. The project design may include excavations below the water table and the use of berms to catch surface water.
Great care should be taken in planning any excavation projects--including soil probing--to ensure that you can reach your goals without destroying desirable natural conditions. Digging too deep, for example, could cause many problems. A thin layer of clay or other impermeable soil may be the only reason water exists above the surface at the project site. Breaking this subsurface seal by digging too deeply would remove existing water, much like pulling a bathtub plug. Also, you need to be careful that you are not creating a pond that is too deep for maximum wildlife benefit. Another consideration is the side-slope grade of the excavation. This grade should range from a 4:1 to 6:1 horizontal distance:vertical drop to ensure that a variety of marsh-loving plants will grow in various patterns.
When excavating, be sure to scrape and stockpile the topsoil, then replace the upper six to eight inches on the berm and excavated basin to take advantage of seed sources already in the soil. In general, planting aquatic plants is not necessary because seeds are naturally transported in the environment and are usually already in the soil. But if vegetation is slow to respond on a new site (after 2-3 years) or you wish to add diversity to a present site, you might consider planting duck potato, pickerelweed, bulrush, and cattailall of which are available from specialty growers. Water depths between one and two feet are ideal for these species. In addition, sago pondweed, coontail, and wild celery are common submergent plants able to grow at a variety of water depths.
Other Management Considerations
The following are general options to consider when managing a marsh:
In summary, marshes are an important part of Michigan's natural landscape. Identifying any that exist or historically existed on your property is the first step toward developing a management plan. By protecting, restoring, enhancing, or successfully creating marshes using the above management practices, these dynamic wetlands will provide critically important wildlife habitat.
Last Revised: December 30, 1999