Introduction:

Wetlands are those areas where land and water meet. Whether water is slightly above or below the surface of the land, the single controlling feature that makes the difference when identifying whether or not an area is a wetland is the presence of water.

Land does not have to be wet all of the time in order to be defined as a wetland. In some cases, it will not be immediately obvious that a wetland exists. Water present in or on the land will, however, cause a number of physical and biological characteristics to develop and these characteristics can be used to identify and locate wetlands.

Because laws define wetlands by the actual interaction of land and water, there is no map or information source that overrules what any particular area is really like. Wetlands depend on the actual interaction between land and water, not on any particular maps or descriptions. As a result, the actual conditions present on a property will always take precedence over any information source.

Despite this, there are a number of information sources about the physical and biological characteristics of land that can assist you in identifying whether an area is likely to be wetland. While none of these sources are foolproof, when used together they can help you understand where wetlands are likely to be found and not found. In many cases, only expert analysis of on site information can suffice if you need an absolute wetland boundary or confirmation about the presence or absence of a wetland on a parcel. If you need only to know where wetlands are likely to exist, the following information sources will help.  (Some of the following information is available through our Wetland Assessment Program.)

Wetland Plant Information:

Although it requires specific on site information, knowledge about the plants in an area can be particularly helpful. Wetlands normally contain distinctly different kinds of plants than those found in uplands. Correctly identifying the most common plants is an important first step in recognizing wetlands.

Wetlands generally have water at or near the surface of land for some period during the plant growing season. Because many types of plants have their roots die after even brief periods in "water logged" soils, the types of plants found in wetlands will generally be different than those found outside wetlands. Wetland plants have adaptations or responses that allow them to survive, grow, and reproduce with their roots in water or saturated soils for at least part of a year.

On a relatively undisturbed site, plants can be one of the best ways to identify wetland areas. If they are predominantly wetland plant types, the area is very likely to be a wetland. People skilled in identifying plants can use a reference that will help determine whether or not the predominant plants on a site indicate the presence of a wetland.

The National List of Plant Species That Occur in Wetlands by Porter B. Reed, Jr. identifies and classifies wetland plants. In addition to giving the names of wetland plants, it includes information about how commonly each plant occurs in wetlands (many wetland plants can also survive in uplands and visa versa) and other useful information. The list can be obtained at the National List of Wetland Plants Web Page.

There are several limitations to using this reference. The most critical is that you must have correctly identified the plants to the species level. Simply knowing that a tree is an oak will not work unless you know precisely which species it is. Also, the list will not help unless it is used to classify the predominant plants in the vegetative community. Using less common plants may give an inaccurate picture of the area. Therefore, one must first determine which plants are the most common and then apply the plant list to those species. Reliance on common names is risky. Some plants have more than one common name and sometimes different plants are known by the same name. Just because you may not find a plant listed under the name you know it by does not mean that it is not somewhere else on the list. Finally, it must be realized that the plant community is only an indicator of the presence of water and may, in some cases, be misleading. This is particularly true when a site has been disturbed or planted with species that would not exist there naturally.

Wetland Soils Information:

In Michigan, the State's legal definition of wetland makes no mention of soils. As an indicator of the presence of water, however, soils can provide valuable information. There are many different types of soils that are found in wetlands including mucks, peat, loams, clays, and sands. Mucks and peat are obvious wetland soils but even loam, clay, and sandy soils can be wetland soils if they were frequently saturated or inundated while they were being formed. Soil scientists can interpret soils in a way that describes the history of water exposure.

Short of hiring someone to do detailed borings across a site, an excellent overview of the types of soils likely to be found can usually be obtained through the use of a Modern Soil Survey produced by the U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS). Soil surveys are available for most counties in Michigan and those unavailable will be completed soon. Check with your county office of the NRCS (phone number is in the government section of the phone directory) or the Michigan Soil Information Page for soil survey availability.

Modern Soil Surveys have been produced by detailed field work translated into coded areas on aerial photographs. Each major soil series is identified throughout the county and described in text. Reviewing descriptions for soils on a parcel can provide a great deal of information about the likely presence or absence of wetland conditions. Descriptions such as "poorly," "somewhat poorly," or "very poorly" drained soils, "unsuitable for building because of wetness," etc., should provide immediate flags that wetlands are likely to be present. Other useful information is seasonal depth to groundwater, typical vertical profiles, suitability of the soil for various purposes, etc.

To assist in identifying soils developed under conditions sufficiently wet to support wetlands, the NRCS, along with other federal agencies, developed a definition and listing of those soils termed "hydric." If the name of a soil series or subgroup is included on this list, it should be considered to be a wetland soil. Other useful information included with the listing is the drainage class, high water table depth, likelihood of flooding, and permeability.  Contact the National Technical Committee for Hydric Soils, Soil Conservation Service, P.O. Box 2890, Washington, DC 20013 or visit the Hydric Soils of the United States Web Page to determine availability.

There are several limitations to using soil surveys and lists of hydric soils. First, they generally do not map "inclusions" of different soil types if the map units are less than 2 acres in size. These inclusions can be wetland soils within an upland soil series. Sometimes, the description will include the types of soils that are the most common inclusions in the series. Also, as for all information sources, there are occasional errors. Finally, as noted above, having a wetland soil present is not a legal requirement to be a wetland. There are wetland soils that have been historically been so severely drained that they no longer have wetland characteristics, and there are non wetland soils that now support wetlands because of additional flow into the water table.

National Wetland Inventory Maps:

The U.S. Department of Interior, Fish and Wildlife Service, is attempting to delineate and classify all wetlands of the United States to better manage and protect these resources nationally. The products that are being assembled to achieve this goal are the National Wetland Inventory (NWI) maps.  Mapping is done by interpreting aerial photographs and overlaying apparent wetland areas onto standard topographic maps (topographic maps were produced by the U.S. Geological Survey - USGS - in geographical units called "quads").

Information contained on the maps include a map scale, approximate wetland locations, wetland types, (e.g. forested, scrub, shrub, emergent, etc.) and the probable frequency and duration of water that will occur for each mapped wetland. Since they are drawn over USGS maps, the topography of the land and many other features are also apparent. Although available for much of Michigan, a portion of the state has not been completed.  To determine availability of the NWI maps, check  the National Wetland Inventory (NWI) Web Page.

There are several limitations to using NWI maps. Since they are produced by mass scale aerial photograph interpretation, there is a significant source of error. Some areas have been interpreted from black and white photographs, others from color infrared photographs which are easier to interpret. Interpretations within especially flat areas and in forested areas have greater error than in other areas and land forms. Most areas have not been field checked to confirm aerial interpretations. Also, due to the scale of the aerials, small wetlands may be missed. Finally, an aerial photograph reflects the specific year and season when taken and may not reflect a "typical" situation.

Local Wetland Maps:

Some townships and municipalities have mapped their wetlands for use in administering local wetland ordinances. There are many different mapping methods used and the variability is too great to review here. It is recommended, however, that the appropriate local government be contacted to determine whether or not there are wetland ordinances in effect and, if so, whether or not there are local wetland maps available. When available, local wetland maps will generally be located in the planning or building departments of the township or the municipality. When reviewing such maps, you should determine what limitations or sources of error may exist for the mapping method used by the particular local government.

Statewide Land Cover/Land Use Maps:

The Michigan Resource Information System (MIRIS) is a digitized computer mapping of land cover types compiled from interpretation of aerial photographs. The entire state is included in this System. The primary purpose of the inventory was to locate the land and water resources of Michigan. It is not intended to locate wetland regulatory jurisdiction. Included in the current land cover/use categories, however, are several classifications that pertain to wetlands.

These maps can serve as an excellent regional planning tool, especially since the pattern of wetland distribution over large areas is readily discernible. Other land cover categories are also mapped and can provide additional information about the overall setting of probable wetland areas. Each county has been provided with a complete set of maps for that particular county. The maps can be viewed at the appropriate local government offices. In most cases, these are county agencies such as county planning departments, building and zoning departments, etc. Additional information about this inventory can be obtained from the Center for Geographic Information website. 

There are several limitations to using these maps. Like the NWI maps (see above), land cover maps were compiled from interpretation of aerial photographs and there is some degree of error inherent in accomplishing this on a large scale. Again, the information has not been field checked. Other limitations include the fact that the classification system was, in forested areas, meant to identify harvestable timber rather than wetlands. As a result, many areas which are classified as "lowland" hardwoods and conifers are also wetlands. In addition, some marshes and wet meadows that are used as pastures are classified as "agricultural land" although they are also wetlands. Finally, only cover types that include more than 2 1/2 acres are mapped, consequently small wetlands are not included.

Aerial Photographs:

Experts qualified at interpreting aerial photographs are usually able to identify wetlands by their appearance. Water features and vegetation types are often discernible, particularly on color infrared photographs. Aerial photographs are useful even for non experts, particularly when used with other information sources. Often the extent of a wetland is apparent on an aerial photograph and when topography and soil types are also known, one can get an excellent idea of the location of wetland areas. Aerial photographs are often on file with County planning agencies.

Limitations in using aerial photographs are fairly obvious. Lacking expert interpretation, photographs can be misleading, particularly in wetland areas that lack standing water. They are also limited to showing the condition at a particular season and year and may not reflect normal conditions.

Summary And Conclusion:

All of the information sources indicated above have significant limitations that must be taken into account when using them. Due to limitations and possible error, extreme caution should be used in making assumptions based upon these sources, particularly if only one or two sources are used. When used together, however, these sources can be excellent planning tools to help screen properties for possible wetlands. When it is vital to have a correct answer or when a wetland boundary must be set, these tools are not fully definitive and it is necessary to obtain expert on site analysis from a qualified consultant or MDEQ.