Aquatic Plants and the Environment (SWES, ECOL, WFSc 474/574)

Constructed Wetlands

Dr. Kevin FitzsimmonsProfessor – 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 treatedIn Florida, USA

Farm animal waste treatedIn Pennsylvania, USA