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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