Issue Profile
Maine's Wetlands: Their Functions and Values

August 2003     Phone: (207)-287-3901

Background

Our famous jagged coastline and generally rugged terrain statewide have provided Maine with an abundance and diversity of wetlands unequalled in the Northeastern United States. Fully 25 percent of Maine's land area is wetlands, four times the wetland area of the other five New England States combined.

Over five million acres of Maine's wetlands are freshwater types (wooded swamps, shrub swamps, bogs, freshwater meadows, freshwater marshes and floodplains). Only 157,500 acres are tidal types (tidal flats, salt marsh, brackish marsh, aquatic beds, beach bars and reefs).

Wetlands are valuable not only for their beauty and the recreation opportunities they support, but also for critically important functions they perform in our environment.

What natural functions do wetlands perform?

Important functions that wetlands provide include water storage, flood conveyance, groundwater recharge and discharge, shoreline erosion control, and water quality improvement. Perhaps most important, wetlands provide habitat vital to fish and wildlife, including many rare and endangered species. Wetlands are highly valuable to Maine's tourism, recreation, forestry and fishing and hunting industries.

How do wetlands serve as water storage areas?

Wetlands are characterized in part by abundant vegetation that slows and retains flows both above and below ground.  These qualities allow wetlands to serve as natural water storage areas. In Maine there are two major groups of wetlands, coastal and freshwater. These two groups receive water in different ways, but both store water.

Tidal flooding creates two readily identifiable zones in coastal wetlands: (1) regularly flooded areas which are alternately flooded and exposed at least twice daily (“intertidal areas”); and (2) irregularly flooded areas, the so-called high marsh, that is usually flooded for only brief periods but may be saturated near the surface during each high tide.

Freshwater wetlands receive their water mainly from surface water runoff, groundwater discharge and direct precipitation. Surface water runoff collects in isolated depressions surrounded by high ground, or overflows from rivers and lakes following snowmelt or periods of heavy rainfall. In other areas where the groundwater is close to the surface, water may pond on the surface when there is a period of sustained rainfall. Groundwater also discharges periodically to spring or seepage areas when groundwater recharge exceeds subsurface capacity.

In the case of coastal wetlands, the daily and seasonal flux of the tides means that this storage role has a major impact on the types and abundance of vegetation and wildlife. Similarly, the storage capacity of freshwater wetlands plays a vital role in releasing water to lakes and streams to help maintain water levels needed for fish and wildlife, especially during critical spawning seasons, and for recreation uses. The value of water storage is most easily recognized, however, in terms of flooding events.

How do wetlands help to control floods?

Because of their role as water storage areas, wetlands help to lessen the impacts of flooding by absorbing water and reducing the speed at which flood waters flow. Upstream wetlands can serve to store flood waters temporarily and release them slowly downstream. Along rivers, wetlands usually form natural pathways for flood waters from upstream to downstream points. If those pathways are altered or removed, flood waters can go elsewhere, potentially damaging property and threatening public safety. Without wetlands as a natural flood storage mechanism, flooding can become more severe and thus more dangerous.

How do wetlands contribute to shoreline erosion control?

Natural tidal action, river currents, seasonal flooding, waves and currents generated by wind on lakes, and waves and wakes from motorboats can all contribute to erosion. Erosion can result in loss of valuable beaches, other property damage and loss, increased sedimentation that is harmful to fish and wildlife, and other costly and harmful effects. By stabilizing soil, encouraging sediment deposit, and dampening the effects of wave action, the vegetation found in wetlands along the coast, around lakes and along the shorelines of rivers and streams help to control erosion.

What role do wetlands perform in groundwater recharge and discharge?

In a natural cycle, water moves from the atmosphere through rain and other precipitation to surface storage areas in the oceans, rivers and lakes, and to sub-surface storage areas known as groundwater aquifers. In Maine, fully half of the population depends on public or private wells drawing drinking water from such groundwater aquifers. Wetlands provide a key link in this cycle. Under specific circumstances, wetlands can provide a pathway for surface water to enter and thereby recharge groundwater. Wetlands also play an important role as the primary natural discharge path of some groundwater aquifers. Altering or filling wetlands can interfere with this natural cycle.

How do wetlands help to improve water quality?

Wetlands improve the quality of water flowing over and through them, a critical role in nature's own water quality restoration process. Wetland vegetation slows water flow and captures sediment suspended in the water, reducing turbidity, that murky quality that makes some waters unattractive for swimming and other recreation uses. Wetlands also filter out, trap, and naturally recycle nutrients like nitrogen and phosphorous that run off from the land and might be harmful in excessive quantities in surface waters. This filtration process saves millions of dollars that might otherwise be required to build and operate facilities to perform this function. Wetlands can also capture pollutants like heavy metals, organic chemicals like pesticides and petroleum hydrocarbons, removing them at least temporarily and sometimes permanently from aquatic ecosystems. Unfortunately, when wetlands accumulate them, these harmful compounds can also enter the food chain through wetland vegetation and wildlife, ultimately finding their way into fish and wildlife people consume.

How are wetlands important to fish and wildlife?

With their diverse and abundant vegetation, wetlands support many valuable species of fish and wildlife that thrive only in a wetland habitat. Still other species that do not inhabit wetlands feed upon fish and wildlife that originate in wetlands. For example, coastal wetlands provide critical habitat for shellfish like clams and mussels and for migratory and nesting shorebirds like sandpipers, plovers and the endangered piping plover. Salt marshes are renowned as duck habitat.  Nesting birds like osprey, herons and the endangered bald eagle feed on both freshwater and saltwater wetland species.  Certain mammals, including furbearers, live in or near wetlands. Muskrat, for example, live on wetland banks in houses made from wetland vegetation.

Are there rare and endangered species that rely upon wetlands?

Researchers estimate that about 30 plant species have been extirpated, that is totally eliminated, from Maine since European settlement. Yet Maine wetlands are treasure troves of many rare plants, including some that botanists once thought extirpated. Studies of peatlands during the 1970s and 1980s, for example, resulted in the discovery of abundant collections of rare orchids that live only in rich wetland habitat. Similarly, certain wetland types are vital to endangered wildlife, including shore birds like the piping plover which nests in coastal wetlands and raptors like the bald eagle which feed in both marine and freshwater wetlands. Many species of endangered invertebrates, including dragonflies and butterflies, also require wetlands for survival.

How do wetlands contribute to Maine's economy and quality of life?

The functions wetlands perform are not only crucial to our environment, they contribute immeasurably to Maine's economy and to the quality of life Maine people and visitors to Maine enjoy. There are practical, economic and public health and safety values to each of the functions described above. Maine's wetlands save millions of dollars annually through erosion control, reduced flood damage and pollution abatement. Their water quality and flood control functions protect the public from otherwise harmful effects. Wetlands are also the source of over three million acres of productive timberland, vital to Maine's $8 billion forest products industry which provides jobs for 35,000 Maine workers (Maine Forest Products Council 2013 Report).

By far, however, the greatest contributions from Maine's wetlands are those associated with their importance to our fish and wildlife resources.

Countless commercial and sport fish species spend some portion of their life cycle in wetland habitat. Clam flats are one wetland habitat that coastal communities recognize as a critically important local economic asset. With the advent of mussel harvesting and emerging oyster and other commercial shellfish operations, the economic value of Maine's coastal wetlands continues to increase. Hunters and trappers know that wetlands mean valuable game, whether it is ducks in coastal salt marshes or deer, bear and small furbearers foraging in freshwater wetland habitat.

Commercial fishing in Maine is a $700 million a year industry that employs 26,000 Maine residents. Sport fishing and hunting are important attractions to the tourists and seasonal residents who make tourism a $1.5 billion a year industry employing another 25,000 Maine residents.

Even without their economic worth, wetlands have other values incalculable to Maine people. Hunting and fishing are traditional recreation stalwarts enjoyed by tens of thousands of Mainers. Other thousands of our citizens and visitors value wetlands for their beauty, the opportunity they afford to view rare plants and wildlife and as living laboratories for scientific studies.

For more information about Maine's wetlands, their functions and values, look for the following publications in your State library:

Maine Wetlands Conservation Plan, Maine State Planning Office, September 2001

Maine Wetlands and Their Boundaries: A Guide for Code Enforcement Officers by Ralph W. Tiner, Maine Department of Economic and Community Development, Office of Comprehensive Planning, June 1991

For more information about wetlands protection and Maine's Natural Resources Protection Act contact DEP staff at one of the following locations: