#10 Constructed Wetlands

Constructed wetland

built intentionally in an area that was not previously a wetland, typically for water treatment

Restored wetland

the return of a degraded or altered wetland to its original condition, usually by restoring hydrology

Enhanced wetland

an existing wetland that has been artificially improved to increase its functional capacity

• (e.g., more nutrient processing or habitat value)

Created wetland

an artificial conversion of upland or shallow-water habitat into a wetland

• essentially turning a non-wetland area into a wetland

Do constructed wetland always treats water?

No

• Although most are built for water treatment, some are constructed for other purposes such as seed production or fish rearing

What are some reasons to construct a wetland? (first 2)

• Recreation/ increase habitat for wildlife and wetland plants

• replace those lost→ mitigation banks

What are some reasons to construct a wetland? (last 3)

• replace nutrient and pollutant loads to waterways

  • nutrient processing

• remove contaminants from water for reuse

• groundwater return/ minimize runoff

What are some of the natural processes wetlands use to improve water quality? (first 2)

• Settling and processing of organic materials

• Filtration and chemical precipitation

  • Ways contaminates could get removed from water

What are some of the natural processes wetlands use to improve water quality? (last 3)

• Adsorption and ion exchange on plant surfaces and in substrate

• Chemical breakdown/ uptake/ transformation by plants and microorganisms

• Predation and natural die-offs of pathogens

What are some examples of contaminants or conditions that constructed wetlands commonly address? (first 3)

• excess nutrients (N, P)

• suspended solids

  • sediments

• pathogens

What are some examples of contaminants or conditions that constructed wetlands commonly address? (last 2)

• heavy metals

• organic pollutants

What are some hydrological considerations before constructing a wetland?

• Where the water will come from

• How much water will enter the wetland

• The quality of incoming water

• Appropriate flow rate and flow direction

• Required residence time of water

Why is surrounding land use important when planning a wetland?

It affects runoff quality, pollutant sources, suitability of the site, and potential risks such as contamination or disturbance

Greywater

Wastewater without fecal matter or high organic loads

• (e.g., laundry, sinks)

Blackwater

Wastewater containing fecal matter

• (toilets, some laundry)

Why are permits often required for constructed wetland systems?

Because they involve potential contamination risks, plumbing modifications, groundwater protection, and must meet public health regulations

What type of water would not require a permit?

water without strong pollutants

What is a “no-permit” greywater system example, and why doesn’t it require a permit?

Laundry-to-landscape systems; they do not alter existing plumbing and use relatively low-risk greywater

Why are constructed wetlands typically built downhill from wastewater sources?

To allow gravity to move water into and through the system, reducing or eliminating the need for pumps

Why must soils typically be compact in constructed wetlands?

To minimize groundwater seepage and prevent contamination

• (unless the wetland is specifically designed for groundwater recharge)

Give two reasons why a site in a floodplain is unsuitable for a treatment wetland

• Risk of spreading contaminated water

• Increased disease and pollutant transport during floods

What is the basic structure of a created wetland?

• Dikes hold water

  • Generally a bit less natural though

    • Only built for the function

  • like levee, but want to retain water for wetland creation/habitat not exclude it from areas

• Bottom usually sealed to prevent groundwater contamination

• Water controlled by flow structures

  • Flood gates

  • Flashboards

Why are water control structures more sophisticated in wastewater wetlands?

Because water quality, residence time, and contamination levels must be precisely managed for effective treatment and safety

Why are built-in testing points essential?

• to monitor contamination levels

• ensure treatment is occurring as intended

• to confirm water is safe before moving to the next stage

What are the 2 types of constructed treatment wetlands?

• Sub-surface flow treatment wetland

• Surface flow treatment wetland

Subsurface flow:

• Water flows horizontally through gravel or sand below the surface

  • go through a physical barrier

• No standing surface water

• Microbes on substrate do most pollutant breakdown

• Plants add oxygen and remove some nutrients

Surface flow

• Water flows above ground with standing water present

• Mimics natural marshes

• Plants and sunlight drive contaminant breakdown

Why are subsurface flow wetlands considered “more like a treatment plant”?

Because water moves through engineered media (gravel, sand), microbial biofilms do intensive nutrient processing, and the system is tightly controlled

What are the five vegetation-type categories used to classify treatment wetlands?

• Free-floating macrophyte systems

• Emergent macrophyte systems

• Submergent macrophyte systems

• Forested wetland systems

• Multispecies algal systems

Free-floating macrophyte system

Pull lots of N and produce lots of biomass

Emergent macrophyte system

• Provide lots of physical barriers

• Allows heavy metals to settle to the bottom of the wetland

What are some advantages of constructed wetlands over traditional water treatment plants?

• Lower cost and less energy-intensive

• Require only periodic labor rather than continuous staffing

• Ecological and wildlife benefits

• Generally popular and environmentally friendly

• Water supply is usually reliable

What are some disadvantages of constructed wetlands compared to treatment plants? (first 3)

• Performance affected by weather (drought, storms)

• Large land area requirements

• Inconsistent pollutant removal

What are some disadvantages of constructed wetlands compared to treatment plants? (last 3)

• Sensitivity to chemicals and plant die-off

• May require pre-treatment before entering the wetland

• Sometimes need additional water inputs

Why can weather reduce the performance of a treatment wetland?

• Drought reduces water volume and flow

• storms can overflow the wetland, flushing contaminants out

• temperature affects plant and microbial activity