Habitat description
Freshwater marshes are a diverse group of wetlands characterized by emergent, soft-stemmed, tall aquatic plants such as grasses, sedges, rushes, and reeds. Freshwater marshes generally form on mineral soils and are seasonally inundated and permanently saturated. Some freshwater marshes may accumulate minor amounts of peat, but they are often differentiated from fens by their mineral-based rather than peat-based soils. Freshwater marshes may occur along the banks of slow-moving rivers and streams, within shallow backwaters of lakes and ponds, and shallow depressions marking the transition between aquatic and terrestrial habitats. Freshwater marshes may also form temporarily when beaver impound a forested swamp or fen raising the water level and causing shifts in the hydroperiod of the wetland.
Wet meadows, sometimes referred to as sedge meadows, draw down seasonally so the mineral soil is permanently saturated but not generally inundated. These wetlands reflect the local hydroperiod and are fed primarily by groundwater seepage, runoff, and precipitation. They are often characterized by a diverse group of wetland plants including tussock sedges, bulrushes, blue-joint grass, joe pye-weed, blue-flag iris, sweet flag, and white-topped aster. These wetlands are often vulnerable to channelization, drainage, and hydrologic perturbations causing shifts in plant composition and encroachment of woody plants.
Characteristic natural communities
Learn more about the natural communities found in marshes and wet meadows:
- Kettlehole wet meadow (S3)
- Deep emergent marsh (S4)
- Shallow emergent marsh (S4)
- Wet meadow (S4)
Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled).
Characteristic plants and animals
Freshwater marshes and wet meadows provide important habitat for many species of native plants, waterfowl, wading birds, songbirds, mammals, invertebrates, amphibians, reptiles, and fish. Many species are uniquely adapted to seasonally or fully inundated hydrologic conditions found within these wetlands. Marshes and wet meadows are home to many rare and declining species, such as northeastern bulrush, a Massachusetts endangered and regionally declining aquatic plant in the sedge family; wild rice, a native aquatic grass important to Indigenous cultures; and the American bittern, a secretive marsh nesting bird.
Freshwater marshes are important for muskrat, which find shelter and nesting habitat in bank burrows and abundant vegetation to feed upon within the marsh. Ducks, geese, and wading birds also rely on wet meadows at different stages of their annual cycle including breeding, wintering, and/or refueling during their migration.
Freshwater, saltwater, and euryhaline fish species use freshwater marsh habitats for reproduction, foraging, spawning and rearing. Individual fish communities will depend on water chemistry, connectivity to saline and freshwater habitats and the magnitude, duration, and timing of inundation. Freshwaters may contain typical warmwater fish species such as pumpkinseed, largemouth bass, perch, and bullhead. Euryhaline or anadromous fish such as herring, shad, eels, striped bass, smelt and white perch may also be found throughout.
View a complete list of Species of Greatest Conservation Need associated with this habitat.
Associated habitats
As marshes typically demarcate the transition between aquatic and terrestrial habitats, they are closely associated with lake, riverine, and streamside habitats. Marshes associated with inland rivers and streams are closely associated with riparian and floodplains, shrub swamps, and other adjacent terrestrial habitats through which a river or stream flows. Marshes and wet meadows are also associated with inland lakes and ponds, kettlehole depressions, forest swamps and seeps.
Ecological processes
Hydrology determines the ecological character of freshwater nontidal marshes and wet meadows. Deep emergent marshes generally form in flat broad areas with standing or running water averaging 6 inches to 3 feet during the growing season or most of the year. These wetlands have permanently saturated soils. Shallow emergent marshes occur in similar hydrologic settings but the standing or running water depth during most of the year is usually less than 6 inches. Both deep emergent and shallow emergent marshes form on mineral soil and develop a layer of muck. These marshes have permanently saturated soil. While wet meadows are also characterized by permanently saturated soils, they tend to flood or have standing water only occasionally. They may intercept groundwater and do not usually develop a muck layer.
Freshwater marshes are generally characterized as having high pH substrates, moderately available soil calcium, medium loading rates for nutrients, high productivity, and high soil microbial activity that leads to rapid decomposition, recycling, and nitrogen fixation. Most of the primary productivity is routed through detrital pathways but herbivory by muskrats and Canada geese can be seasonally important. Freshwater marshes are significant carbon sinks, storing large amounts of carbon in their soils and plant matter.
Marshes serve as important buffer zones against erosion and flooding from storms while filtering and absorbing nutrients and sediments washed in from upstream watershed sources. Together these characteristics and functions make marshes and wet meadows some of the most productive and diverse habitat types in Massachusetts.
Threats
Hydrologic alterations such as ditching, tile drains, dikes, and levees impact the integrity of freshwater marshes. Historical damming of rivers and streams results in channel incision which decreases connectivity to floodplains, marshes and wet meadows altering the magnitude, duration, and timing of inundation intervals. Finally, lake and pond management techniques such as seasonal water drawdowns denude backwater marsh habitats unnecessarily. Wetland conversion, degradation, and warming can lead to rapid losses of ancient carbon and methane emissions, moving carbon from the soil to the atmosphere as carbon dioxide and methane.
Water carrying runoff or dissolved minerals, chemicals, and nutrients such as road salt, construction debris, fertilizers, and detergents can impact natural marsh vegetation, increase sediment loads and nutrient levels, cause algal blooms, and create oxygen depleted environments unhealthy for aquatic plants and wildlife living in marshes.
Invasive plants often spread in freshwater marshes and wet meadows following disruption of the natural hydrologic regime and dispersal of sediment, nutrients, or chemicals into the wetland corridor. Invasive plants such as common reed, purple loosestrife, and reed canary grass are invasive plants which spread and outcompete native marsh plants.
Restoration & management recommendations
The biggest need for conservation of these habitats is to restore hydrologic connectivity in marshes and wet meadows. Actions which aim to restore natural flow regimes that by their nature reconnect rivers and streams to floodplains and marshes are recommended. Actions that benefit these habitats include dam removals; culvert removal, replacement and enlargements; installation of retention basins in watersheds with high quantities of impervious cover; and prevention of unnecessary lake and pond management techniques which seasonally dewater backwater habitats. Artificial lake drawdowns and structures that manipulate water levels and impact freshwater marsh plant composition should be avoided. Marsh habitats lost due to draining by removing berms and dikes, when possible, should be restored to allow streams and rivers to meander naturally.
Activities which carry particulate-laden runoff or dissolved chemicals or nutrients into freshwater marshes and wet meadows should be avoided. Understanding how water enters a freshwater marsh or wet meadow and travels through these habitats will help identify conservation and management strategies.
Strategies to remove invasive plants within wetlands should be closely coordinated with hydrologic restoration to avoid their dispersal into wetlands and in order to achieve long-term restoration goals for improving wetland integrity.
Wet meadows may require mowing, prescribed fire, and invasive species control to reduce encroachment of woody vegetation from the surrounding uplands. These areas are prone to invasion by glossy buckthorn and shrub honeysuckle from surrounding agricultural fields. Removal of ditches and tiles from these areas often helps restore hydrologic flow within these wetlands.
All activities within regulated wetlands and their protective buffers should follow the Massachusetts Regulated Wetlands Protection Act (Massachusetts General Laws (MGL) Chapter 131, Section 40).
Additional resources
Principles of Wetland Restoration
Wetlands of the Northeast: Results of the National Wetlands Inventory
Mitsch, W. J. & Gosselink, J. G. in Wetlands 5th edn Wiley (2007).
Vepraskas, M. J., Craft C. B. (eds) in Wetland Soils 2nd edn CRC Press (2016).