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Transcript
Aquatic Plants and the Environment
(SWES, ECOL, WFSc 474/574)
Constructed Wetlands
Dr. Kevin Fitzsimmons
Professor – University of Arizona
Terminology of constructed
wetlands
• 1. Restored wetlands - those under
rehabilitation. Put back into working order
(fixed) hydrology of wetland either by dredging
or by taking out a dike (common in small areas).
• 2. Constructed wetlands - built where none
existed before (usually for water treatment).
Usually well engineered.
• 3. Created wetlands - developed where none
existed before (usually for wildlife habitat).
Normally done with little engineering.
Reasons for constructed wetlands
• 1. Waste Treatment
• 2. Hydraulic modification - for flood control,
water storage
• 3. Water quality changes
• 4. Erosion protection
• 5. Open spaces and aesthetics
• 6. Mitigation
• 7. Habitat for wildlife
1. Waste Treatment
• Municipal waste (sewage): secondary/tertiary
treatment of wastewaters. To reduce the
nitrogen, phosphorus, TSS (Total Suspended Solid),
BOD (Biological Oxygen Demand), TFC (Total Fecal
Coliforms).
• CAFO treatments (Concentrated Animal Feeding
Operations): treat wastes from dairies, feedlots, hog
sheds, chicken ranches, and fish farms.
1. Waste Treatment
• Acid Mine Drainage: Absorb heavy metals and
increase the pH.
• Highway Runoffs: Effective for cleaning the water
that runs off roads carrying oil, gas, dirt, etc.
• Specific Pollutants: Wetlands put in to treat or
absorb a heavy metal or organic. Often, the
plants will accumulate chemicals inside the plant
stem and leaves (concentrating the pollutants).
The plant can then be disposed of.
• Storm Water: Handle storm waters in developed
areas where runoff is a problem. Cleans up
runoff as well.
2. Hydraulic modification
• Flood control – reduce flood waters and
impacts
• Water storage – reservoir
• Groundwater recharge
3. Specific water quality changes
• Reduce sediment loading
• Raise or lower extremes of pH
• Add or remove organics (remove in the case of
paper mills, add in acid mine drainage).
4. Erosion and flood protection
•
•
•
•
Bank or shoreline stabilization
Dissipation of wave energy
Dissipation of flood flows
Alter flow patterns of stream or river
5. Open spaces and aesthetics
• Used by resorts or new developments to increase
land value.
• Adds nature values
• Property owners will pay extra for sounds, smells
and sights of wildlife and wetland plants
6. Mitigation
• Intended to replace the function of lost wetlands.
• In US, when developers destroy wetlands they
must replace them by a 1 to 2 or 1 to 3 ratio.
• The developer is not only responsible for
replacement, but the function as well.
• Usually replaced wetlands do not function as well.
Lots of problems occur with how to build and
maintain them.
7. Habitat as life support
• Habitat specifically for threatened and
endangered species
• Habitat for other wildlife.
Design of constructed wetlands
•
A. Free water surface
systems (FWS): have open
water surfaces, water is
exposed, covering the
substrate, submerged and
emergent plants.
•
B. Subsurface flow
systems (SFS): water
below surface level, the
substrate is exposed to air
at the surface. Only
emergent plants
Design of constructed wetlands
•
A. Free water surface
systems (FWS): have open
water surfaces, water is
exposed, covering the
substrate, submerged and
emergent plants.
•
B. Subsurface flow
systems (SFS): water
below surface level, the
substrate is exposed to air
at the surface. Only
emergent plants
Typical construction for a small
sub-surface wetland
Constructed wetlands can be
customized for the task
• Select submerged flow or free surface
• Determine volume of anaerobic vs aerobic
needed
• Select plants that will accomplish task
- fast growing plants that scour nutrients
- plants that bio-accumulate heavy metals
- plants that accumulate or break down organics
- plant community that drops leaves to add
organics to water
Typical subsurface flow systems
Treating grey water
from a house in Italy
Treating municipal waste
in Virginia, USA
Typical free water surface flow
Municipal waste treated
In Florida, USA
Farm animal waste treated
In Pennsylvania, USA