Wetland Creation

• Why?• Can it be done?• Does a created

wetland serve the same ecological purposes as a natural wetland?

Why Build Treatment Wetlands?

• Improve water quality

• Secondarily, provide wildlife and other wetland functions.

Ecological Services

• biological filters• “nature’s kidneys”• “yada-yada-yada”-fact or more

environmental hype from tree huggers?

Not a new concept:– Germany in early 1950s– US in late 60s, dramatically increasing in

1970s

What’s the Goal?• Removal of contaminants from water

– contaminant-any undesirable constituent in the water that may directly or indirectly affect human or environmental health

– anything that degrades the water so that it cannot be used for its natural or intended purpose.

– might include:• toxic organics and metals• non-toxics-nutrients• thermal pollution

Uses

• Municipal wastewater

• Acid mine drainage (AMD)

• Landfill leachate

• Nonpoint urban/agriculture runoff

Municipal Wastewater Wetland

Acid Mine Drainage

Landfill Leachate Wetland

Agricultural Runoff Wetland

Types of Treatment Wetlands

1. natural wetlands-use for this often prohibited by laws created to protect them

2. surface flow wetlands

3. subsurface flow wetlands

What Can Be Treated?

• municipal wastewater (sewage)-residential and commercial sources; may range from single homes to regional scale– Iron Bridge wetland (FL) is 1200 A (480 ha)

• agricultural wastewater-runoff from cropland, pasture, milking and washing barns, and feedlots.

• industrial wastewater-pulp & paper manufacturing, food processing, slaughtering and rendering, chemical manufacturing, refining, and landfill leachate

Overview of Mechanisms of Contaminant Removal

Contaminant Removal Mechanisms

• Physical– especially good for sedimentation of particulates;

low velocity laminar flow– results in accumulation of solids– may be resuspended by wind-driven turbulence,

bioturbation (by humans or animals), and gas lifting (bubbling of methane, CO2, etc.)

• Biological• Chemical

Contaminant Removal Mechanisms

Biological-perhaps most important?– Plant uptake

• nutrients (NO3, PO4, ammonium)• toxics (bioremediation) e.g., lead, cadmium• rate of removal dependent on growth rate and

concentration of the contaminant in the tissue– woody plants sequester more and for longer times– herbaceous plants (e.g., Typha) have higher rates– Algae can be significant but are more susceptible to

toxicity of metals; however, have rapid turnover

• where does the contaminant go?– re-release; accumulation in peat

Contaminant Removal Mechanisms

Biological (continued)• Microbial processes

– may uptake contaminants in their biomass;– conversions by metabolic processes probably

more important• carbon -> CH4 or CO2; offgassing removes this C• inorganic Nitrogen (nitrate & ammonium)

– nitrate: denitrification facilitated by Pseudomonas spp.

NO3 -> N2; offgassing removes this N– ammonium: nitrification and denitrification facilitated by Nitrosomonas and Nitrobacter spp

NH4+ -> NO3 (aerobic) -> N2 (anaerobic)

Contaminant Removal Mechanisms• Chemical

– sorption (most important)• transfer of ions from solution phase (water) to solid

phase (soil)• includes adsorption and precipitation

– adsorption-attachment of ions to soil particles, either by cation exchange (weak attachment to negatively charged clay or organic particles); effective with ammonium and most trace metals (e.g., Cu2+)

» or chemisorption-stronger bonding attachment of some metals and organics to clays, iron or aluminum oxides, and organic matter; effective with phosphate

– precipitation-combine with iron and aluminium oxides forming new, stable, solid compounds; also production of highly insoluble metal sulfides, a way of immobilizing many toxic metals

Contaminant Removal Mechanisms• Chemical

– volatilization-diffusion from water to atmosphere

• e,g, ammonia (NH3) (aq) -> ammonia (gas)

iff pH > 8.5; if pH is less than that, N is in the form of ammonium which is not volatile

• many other organics are volatile

• increases air pollution?

Examples and Case Studies

Olentangy River Wetlands

at

The Ohio State University

It’s Good to be a

Buckeye!