Freshwater Wetland Restoration

Freshwater Wetland Restoration

I. Types of systems, based upon hydrology:

Riparian

Water level: High variation
Water supply: Dependable
Characteristic vegetation: fast growing, disturbance associated

Vernal

Water level: Cycling, dries out or dries down every year
Water supply: Variable; years of high supply and low supply
Characteristic vegetation: annuals, endemics

Constant water level

Beaver ponds, ground-water fed, lacustrine, low ET environments, montane
Water level: narrow range
Water supply: constant
Characteristic vegetation: emergents, aquatics

High fluctuation

Stormwater-associated, or natural drainage ponds in arid environments
Water level: may vary across season or fluctuate with each precipitation event.
Water supply: highly variable
Characteristic vegetation: weedy species, disturbance opportunists

Oligotrophic

Fens, bogs, peatlands
Water level: may be constant or quite variable; some bogs get quite dry
Water supply: dependable
Water quality: low nutrient; minimal contact with mineral soil
Characteristic vegetation: Slow growing, stress-tolerators, nutrient-intolerant
systems, acid-loving, sedge or sphagnum dominated, dwarfed

Saturated soils

Areas adjacent to wetlands, streams and lakes often have continually saturated
soils. Wet meadows, pastures and prairies may also be saturated much of the year.
Water level: low but constant; soil saturated for much of growing season.
Water supply: constant
Characteristic vegetation: because of grazing, many areas of saturated soils are
highly susceptible to invasive species, esp. grasses like reed canarygrass.

II. Functions, and how you get your wetland to perform them.

Functions that are commonly attributed to wetland ecosystems

    Water quality improvement
        -sediment removal
        -nutrient removal
    Hydrology
        -flood flow attenuation
        -recharge
        -bank stabilization and erosion control
    Habitat
        -specific habitat types
        -primary productivity

How is each function generated in a restoration project?

            Vegetation
            Shaping the land
            Modifying or controlling hydrology
            Using landscape ecology
            Engineering
            Location
            Organic material
            Structures

Sediment removal

            Wetland or stream
                -Accomplished by slowing down flowing water
                    Vegetation
                    Increased cross-section
                    Increased sinuosity of stream path
                    Increased residence time

Nutrient removal

         Wetland or stream
                - Denitrification
                - Flushing or leaching of nitrates
                - Nitrogen uptake
                - Phosphorus removal requires soil contact

Flood-flow attenuation

            Wetlands and streams
                - Sinuosity
                - Vegetation (woody best)
                - Constrictions
                - Bottom friction (many shallow channels)
                - Storage capacity

Recharge

            Wetland
                In a wetland, you need
                -A permeable layer
                -Water source
                -Adequate head

Bank stabilization and erosion control

            Wetland
                Fast-growing, energy absorbing woody vegetation good
                In coastal wetlands, stabilization is achieved by
                    - Energy-absorbing vegetation
                    - Shallow water (frictional dissipation of energy)
                    - Minimal fetch

Primary production

            Wetlands and streams
                Production encouraged by growth of vegetation along streams and by
                contributions of detritus to aquatic systems.
                    - Shallow shorelines with sunlight are very productive
                    - Many aquatic systems are very leaky and have flow-through of detritus,
                        nutrients, water

Habitat

            Wetland
                Wetland types are many, but you usually have little choice as to type you restore
                Wetlands often differ in plant composition from site to site
                    - So multiple wetlands can increase diversity
                Maximize shallow-water area
                Minimize open water
                Constructed habitat features also common

            Streams
                Pool/riffle ratios
                In-stream wood
                Overhanging vegetation
                In-stream shelters
                Side channels

III. Problems encountered in the restoration of each wetland hydrologic type

Riparian

Wetlands associated with riparian systems often depend on river flooding for
recharge. The return interval of flooding may be variable. Flood control
practices often minimize minor flooding and result in catastrophic floods.

Floodplains may have spotty soils with areas of very quick drainage and poor
nutrients.

High flood energy may cause disturbance, loss of biomass.

Compromised buffers.

Water level: High variation
Water supply: Dependable, but at varying intervals
Characteristic vegetation: fast growing, disturbance associated

Vernal

Vernal systems, because they dry out, have often been drained and plowed, and
are regularly grazed. Grazing is often associated with an increase in invasive
plant species in vernal ponds. Endemism is high in vernal ponds, so restoration
efforts must observe guidelines that protect the genetic integrity of such
systems. Because they often cascade across the landscape, they may cross
property lines; restoration in multiple ownerships is difficult.

Water level: Cycling, dries out or dries down every year
Water supply: Variable; years of high supply and low supply
Characteristic vegetation: annuals, endemics

Constant water level

Wetlands with constant water levels are susceptible to changes in watersheds
caused by development, road construction, drainage projects, forest harvest,
beaver eradication, and a number of other factors that can alter the delivery of
water from a system or its retention in the wetland.
Systems that retain a constant water level are often very good candidates for
restoration, unless there is a particular weedy plant that thrives in a constant
water level. For instance, if the site is highly disturbed, cattail may invade
and dominate the site.

Beaver ponds, ground-water fed, lacustrine, low ET environments, montane
Water level: narrow range
Water supply: constant
Characteristic vegetation: emergents, aquatics

High fluctuation

High fluctuation systems can be very difficult to restore, but can have a high
level of functional performance with a low level of species diversity.
Diversity tends to drop as water level variation increases (either depth or
frequency of variation).

Oligotrophic

Oligotrophic systems exist because of a disconnection between mineral soil
(source of nutrients), and the water in the wetland. These kinds of conditions
exist in fens and bogs, where peat has built the wetland up and separated it
from the soil, and in montane wetlands, where there is little weathered soil to
release nutrients. Most degradation in oligotrophic systems happens when
nutrients are released into them. Watershed-level modifications, most of them
difficult to reverse, are usually the main culprit. Increased nutrients allow
invasive species to enter wetlands formed under low-nutrient conditions and
outcompete existing vegetation. Restoration may involve fixing watershed
problems, or separating nutrient-rich water from the flow into the fen or bog.

Saturated soils

Flat areas on flood plains may be intermittently flooded or may have poor
drainage. Alluvial soils often make them attractive for agricultural use,
particularly for grazing. Because they are wet, have moderately fertile soils,
and often have a continuing history of disturbance and importation of non-native
plant species, such sites are often heavily invaded by quite persistent invasive
plants. Removal of such species is difficult. In riparian areas, conversion
back to riparian forest may be a sensible objective.

Areas adjacent to wetlands, streams and lakes often have continually saturated soils.
Wet meadows, pastures and prairies may also be saturated much of the year.
Water level: low but constant; soil saturated for much of growing season.
Water supply: constant
Characteristic vegetation: because of grazing, many areas of saturated soils are
highly susceptible to invasive species, esp. grasses like reed canarygrass.