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
Acid Mine Drainage Municipal Wastewater Wetland Landfill Leachate Wetland Agricultural Runoff Wetland
Types of Treatment Wetlands • natural wetlands-use for this often prohibited by laws created to protect them • surface flow wetlands • 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 gaslifting (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!
