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Supplementary Map 7:

Wetlands Characterization

About Map | Data Components | Background Information | Strategies for Local Action


About Map : Map 7: Wetlands Characterization

The Wetlands Characterization model is a planning tool intended to help identify likely wetland functions associated with significant wetland resources and adjacent uplands. Using GIS analysis, this map provides basic information regarding what ecological services various wetlands are likely to provide. These ecological services, each of which has associated economic benefits, include: floodflow control, sediment retention, finfish habitat, and/or shellfish habitat. Forested wetlands and small wetlands such as vernal pools are known to be underrepresented in the National Wetlands Inventory (NWI) data used to create this map. The model developed to estimate the functions provided by each wetland could not capture every wetland function or value. Therefore, it is important to use local knowledge and other data sources when evaluating wetlands, and each wetland should be considered relative to the whole landscape/watershed when assessing wetland resources at a local level.

This map depicts all wetlands shown on National Wetland Inventory (NWI) maps, but categorizes them based on a subset of wetland functions. This map and its depiction of wetland features neither substitute for nor eliminate the need to perform on-the-ground wetland delineation and functional assessment. In no way shall use of this map diminish or alter the regulatory protection that all wetlands are accorded under applicable State and Federal laws. For more information about wetlands characterization contact Elizabeth Hertz at the Maine Dept. of Agriculture, Conservation, and Forestry (207- 287-8061, elizabeth.hertz@maine.gov).


Data Components: (Data Sources)

Impervious/Developed- Areas of impervious surfaces including buildings and roads.

Subwatersheds- Areas that drain to a particular lake, pool, river, stream, or the ocean.

Wetlands- Based on the National Wetlands Inventory (NWI) with wetland class (type) and wetland functions predicted on the BwH paper maps and increasing number of wetland functions depicted in the BwH Map Viewer.

Wetland Class-

  • (A) Aquatic Bed (floating or submerged aquatic vegetation), Open Water
  • (E) Emergent (herbaceous vegetation), Emergent/Forested Mix (woody vegetation >20 ft tall), Emergent/Shrub-Scrub Mix (woody vegetation <20ft tall)
  • (F) Forested, Forested/Shrub-scrub
  • (S) Shrub-scrub
  • (R) Other (rocky shore, streambed, unconsolidated shore, reef, rocky bottom)

Wetland Functions-

  • Runoff/Floodflow Alteration- (HYDRO)- Wetlands provide natural stormwater control capabilities. As natural basins in the landscape, wetlands are able to receive, detain, and slowly release stormwater runoff. Wetland shelves along stream banks naturally regulate flood waters by providing an area for swollen stream flows to expand and slow, thereby protecting downstream properties. This map assigns Runoff/Floodflow Alteration functions to wetlands that are (a) contained in a known flood zone, (b) associated with a surface water course or waterbody, and (c) with slope <3%.
  • Erosion Control/Sediment Retention- (HYDRO)- Wetlands act as natural sponges that can hold water, allowing suspended particles such as sediment to settle out. The dense vegetation in most wetlands helps to stabilize soil and slow water flows, thereby reducing scouring and bank erosion. This map assigns Erosion Control / Sediment Retention functions to wetlands with (a) slope <3%; (b) emergent vegetation; and (c) close proximity to a river, stream, or lake.
  • Finfish Habitat- (FISH)- Wetlands with documented finfish populations, including wetlands adjacent to a river, stream, or lake.
  • Shellfish Habitat- (FISH)- Inland wetlands and streams can directly affect the status of coastal shellfish harvest areas. Fecal coliform bacteria and waterborne nutrients resulting from land use changes away from the coast can travel via surface water to harvestable flats. One failed septic system near a stream could close a mudflat several miles away. Excessive nutrients can reduce water clarity and stimulate epiphytic growth that degrades eelgrass meadows. Conservation of freshwater wetlands and stream buffers in coastal watersheds is a key component in marine resource conservation. This map assigns a Shellfish Habitat function to wetlands within 0.5 miles of (a) identified shellfish habitat, (b) identified shellfish closure areas, or (c) mapped eelgrass beds OR palustrine wetlands directly connected by a stream of <0.5 mile in length to (a) identified shellfish habitat, (b) identified shellfish closure areas, or (c) mapped eelgrass beds.
  • Plant and Animal Habitat- (PLANT)- Nearly all wildlife species, and many of Maine's plant species, depend on wetlands during some part of their life cycle. For the purposes of this map, wetlands containing open water or emergent vegetation, 3 or more wetland vegetation classes, and within 1/4 mile of a known rare, threatened, or endangered plant or animal occurrence, within 1/4 mile of a mapped significant or essential habitat, or within 1/4 mile of a rare or exemplary natural community have been assigned this function. Rare element occurrences and mapped habitats can be found on Map 2 High Value Plant and Animal Habitats.
  • Cultural/Educational- (OTHER)- Wetlands within 1/4 mile of a boat ramp or school have been assigned this value as these wetlands are likely candidates for use as outdoor classrooms, or similar social benefit. Wetlands rated for other functions listed above may also demonstrate cultural/educational values although not expressly shown.
  • No Documented Function- (OTHER)- The basis of this characterization is high altitude aerial photos. Photo quality often limits the information that can be interpreted from small wetland features, or those with dense canopy cover. Although not assigned a function under this study, ground surveys may reveal that these wetlands have multiple functions and values.

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Background Information:

Wetlands play a variety of important roles in the landscape in which they are found. Healthy wetland systems offer incalculable benefits to us including water quality buffering, water discharge and recharge, shoreline stabilization, nutrient and sediment retention, floodflow alteration and control, habitat for a wide variety of plant and animal species, and recreational opportunities. Preserving and protecting wetlands in the landscape makes good economic sense as well as good environmental sense, as replacing wetland benefits after they have been lost is an expensive and uncertain undertaking. Wetland systems and their associated uplands are the anchors that give our Maine landscape many of the qualities that make it so unique.

The Maine State Planning Office, in conjunction with other state and federal agencies, developed the Wetlands Characterization, a planning tool intended to help identify likely wetland functions associated with significant wetland resources and adjacent uplands. Using GIS analysis, the Wetlands Characterization, provides basic information regarding what ecological services various wetlands are likely to provide. These ecological services, each which has associated economic benefits, include: hydrologic function (floodflow alteration), biogeochemical function (sediment retention), biological function (plant and animal habitat, finfish habitat and shellfish habitat) and cultural value (education and research). There are other important wetland functions and values, however, that are not depicted on the map.

A wetland that is found to provide multiple functions by the characterization may contribute more ecologically than a wetland characterized as providing fewer of the target functions. However, when incorporating this analysis into the planning process, it is important to look beyond the total number of functions identified and consider which individual functions are predicted by the characterization. For example, a wetland that is identified by the characterization as providing only the function of floodflow control may in fact be critical in the landscape context for exactly that function.

The results of the characterization process provide information that enriches our understanding of the roles that wetlands play in the landscape and how they interconnect with other resources. This information is useful in a planning context but may not be appropriate for site-specific analysis.

Forested wetlands and small wetlands such as vernal pools are known to be under represented in the National Wetlands Inventory (NWI) data used to create this map and the model developed to estimate the functions provided by each wetland could not capture every wetland function or value. Therefore, it is important to use local knowledge and other data sources when evaluating wetlands and each wetland should be considered relative to the whole landscape/watershed when assessing wetland resources at the local level.

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Strategies for Local Action:

  • In the context of the "Beginning with Habitat" model, use the characterization to inform your decisions and choices when assessing the adequacy of shoreland zoning and large unfragmented blocks in your town. Using local knowledge, identify those wetlands that are highly valued by citizens for their recreational and commercial values. Bring this information to your town planning process and incorporate these wetlands and their values into decisions made about how your town will grow and develop.
  • Starting with the characterization, add local knowledge of wetlands and affiliated uplands to produce a more detailed picture of the role that these systems play in maintaining the environmental integrity of your town. Remember that wetlands provide natural floodflow control and sediment retention, both vital functions in maintaining water quality. They are also nursery areas for fish and shellfish and support commercial fisheries.
  • Using local knowledge and interested citizens, consider adding information that may be missing from the characterization, due to the conservative nature of the base maps used. For example, local knowledge about the true extent of a wetland may indicate connections to nearby waterways not identified in the NWI base maps. Also, vernal pools, tiny ponds which are often present for only part of the year, are very likely to be missed by the characterization, and local information about these pools can help inform the process of identifying important contributors to amphibian habitat. Contact Maine Audubon for citizen guides to identifying and characterizing vernal pool habitats and their associated uplands.
  • In the land use planning process, compare your designated growth zones with the characterization and local knowledge to determine if you are inadvertently promoting growth in an area at the expense of a highly functioning wetland or wetland complex. Use this comparison to consider reshaping growth zone locations.
  • Review and, if necessary, strengthen your town's definition and enforcement of Maine's Mandatory Shoreland Zoning Act. Consider creating additional local protections along important wetlands and adopting shoreland and buffer guidelines. See the BwH Toolbox section on Wetland and Shoreland Zoning Tools for examples.
  • Conduct an information and outreach effort to educate landowners about the value of shoreline and wetland habitats; alert landowners to their responsibilities under the Shoreland Zoning Act.
  • Develop a town-based wetland compensation fund that requires those applying for permits and altering wetlands to provide compensation for their impacts beyond that required by State and Federal regulations. Focus this fund on town-identified goals and priorities for wetland protection, restoration, and stewardship. Visit the Wetland and Shoreland Zoning Tools section of the BwH Toolbox for more information on wetland compensation and other wetland related tools.
  • Review the kind of development allowed in designated rural areas. If it is predominately 1-to-5-acre lots, cumulative infringement on wetlands and related habitat is likely. Consider very low densities in these areas (1 or fewer units per 10 acres) in combination with open space zoning to maintain large blocks of unfragmented land.
  • In coastal areas, use Maine Audubon's "Maine Citizen's Guide to Evaluating, Restoring, and Managing Tidal Marshes" to assess the condition of your coastal wetland resource and to identify restoration opportunities.
  • Work with your local school system to develop a wetlands-based curriculum to promote awareness and understanding of the crucial role wetlands play across our landscape.
  • Create an "adopt-a wetland program" within your town to develop stewardship of these important resources.
  • Ask your local government to develop a citizen wetland award to recognize those individuals who voluntarily protect their privately-owned wetland resources, and help to elevate the appreciation of these resources within your community.
  • Identify potential wetland restoration opportunities that could be implemented with private funds.

To learn more about specific strategies for local action, visit the Beginning with Habitat (BwH) Toolbox or contact BwH.

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