Wetlands Ecology in the Lake Erie Basin
Overview
• What is a wetland?
• Case study
• Types of treatment wetlands
• Wetlands for water quality
• Important variables in wetland design
• Management after construction
Case Study
Wolf Creek Watershed
Maumee BayMaumee Bay SP Lodge
Beach advisories due to high coliform counts…..
• Coliform bacteria: Rod-shaped, gram-negative organisms which ferment lactose with the production of acid and gas when incubated at 35-37°C.
• Coliforms are generally not the cause of sickness, but are easy to culture. Their presence indicates that other pathogens of fecal origin may be present.
• Escherichia coli (E. coli), is an example of a coliform bacterium. Found in the intestine of warm-blooded animals. Most E. coli strains are harmless, but some can cause serious food poisoning.
• E coli’s ability to survive outside the body makes them an ideal indicator to test environmental samples for fecal contamination
0
10
20
30
40
50
0 200 400 600 800 1000
5
4
3
2
1
0
E. coli from Rain Flush(Berger Ditch, Maumee Bay SP, Aug 24, 2001)
Time (minutes)
E.
coli
, F
lush
Co
nd
itio
ns
(Th
ou
san
ds
cfu
/100
ml)
E.
coli
, B
ackg
rou
nd
Co
nd
itio
ns
(Th
ou
san
ds
cfu
/100
ml)
Source: University of Toledo/Lake Erie Center, June 2003
Recreational use (primary contact) is impaired if the mean fecal coliform content exceeds 1000 CFU/100ml (for no less than five samples/month)
Maumee Bay 2004: E. Coli
High E. coli in Maumee RiverSettle out in shipping channelLow E. coli levels between CDF & parkHigh E. coli levels at Berger DitchLow E. coli levels at other ditches
Design considerations for E. coli removal
…..go to the literature (case studies)
• Ecological Engineering
• Wetlands Ecology and Management
• Wetlands
• Environmental Science and Technology
Source: Hull and Assoc. 2007
Source: Hull and Assoc. 2007
Wetland Design Considerations for
E. coli Removal• Retention time
– Longer retention promotes removal
• Aquatic macrophytes– Planted systems have higher removal efficiency
• Substrate conditions– Gravel works better than sediments
• Water depth– Shallow systems remove more E. coli
• UV light– High UV (summer) kills E. coli
Overview
• What is a wetland?
• Case study
• Types of treatment wetlands
• Wetlands restoration for water quality
• Important variables in wetland design
• Management after construction
In-stream constructed wetlands
Rain gardens
After Kadlec and Knight (1996)
Soil cross section of a surface and a sub-surface flow wetland
Surface water
Sand, soil or gravel
Overview
• What is a wetland?
• Case study
• Types of treatment wetlands
• Wetlands restoration for water quality
• Important variables in wetland design
• Management after construction
What can be treated?
• Municipal wastewater
• Mine drainage
• Stormwater runoff, non-point-source pollution
• Landfill leachate
• Agricultural wastewater (dairy, swine, feedlot)
How can wetlands transform pollutants in runoff?
• Sedimentation (including filtration, adsorption, and precipitation)
• Volatilization
• Microbial decomposition
• Uptake by plants
Water Quality
Organic Carbon Export from Wetland-dominatedWatersheds Compared with Non-wetland Watersheds
0
4
8
12
16
0 50 100 150 200 250
Annual Runoff (cm)
Exp
ort
(g C
m-2 y
r-1)
Wetland-dominatedWatersheds
Non-WetlandWatersheds
Summary of effectiveness data for constructed and natural wetlands (after Strecker et al. 1992)
Total Suspended Solids (TSS)
Ammonia (NH3)
Total Phosphorus
(TP)
Lead (Pb)
Zinc (Zn)
Constructed Wetlands – Median Removal Rate (%)
80 44 58 83 42
Coefficient of Variation (%) 28 49 48 56 39
Natural Wetlands – Median Removal Rate (%) 76 25 5 69 62
Coefficient of Variation (%) 62 168 1,900 67 47
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60
80
100
0 20 40 60 80 100
Removal of P from wastewater by several wetlandsP
rem
ove
d (
%)
P loading (g m-2 yr-1)
> 25 years ofwastewater applied
< 2 years of wastewater applied
Removal of N from wastewater by several wetlandsN
rem
ove
d (
%)
N loading (g m-2 yr-1)
0
20
40
60
80
100
0 100 200 300 400 500
< 5 years of wastewater applied
> 25 years ofwastewater applied
Potential drawbacks of diverting runoff into natural wetlands
• Changes the hydrology!
• Eutrophication (inorganic nutrients and organic matter)
• Habitat loss (herbicides)
• Ecotoxicological effects (trace metals, organochlorines)
• Pathogenic effects (coliform bacteria and other agents)
Houghton Lake treatment wetland (Michigan) where treated sewage has been applied to a natural peatland since 1978.
a & b. Visually-affected area in 1998 (vegetation changes)
c. Dissolved inorganic nitrogen levels in inflow and outflow
d. Ditto for total phophorus
Overview
• What is a wetland?
• Case study
• Types of treatment wetlands
• Wetlands restoration for water quality
• Important variables in wetland design
• Management after construction
Design requires attention to…
• Hydrology (“First, get the water right”)– drawdowns, rates of inflow/outflow, detention times,
groundwater recharge
• Basin morphology– gentle slopes (6:1 or better) to maximize the littoral
zone, (wetland plants)
– multiple inflow locations and avoid flow channelization
– variety of deep and shallow areas
• Chemical loading– loading graphs, retention rates, empirical models
• Soil physics and chemistry– organic content, soil texture, depth and layering
• Wetland vegetation– establishment, growth form, species
Overview
• What is a wetland?
• Case study
• Types of treatment wetlands
• Wetlands restoration for water quality
• Important variables in wetland design
• Management after construction
After wetlands are constructed and wastewater has been applied, management may include:
• Plant harvesting– harvest multiple times per growing season.
• Wildlife habitat– ancillary goal, but often welcomed
• Mosquito and pathogen control– adjusting hydrology, introducing chemical or biological
control agents
• Water-level management– pulse stability
• Sediment dredging– expensive; also removes seed bank and rooted plants.
Best done during drawdown
New UT treatment wetlands(aka “rain gardens”)
Honors rain garden
Lot-10 rain garden
Carolyn Edwards Memorial Rain Garden (July 2010)
Carolyn Edwards Memorial Rain Garden – July 2010
Carolyn Edwards Memorial Rain Garden – July 2010
May Sue Cave Honors Rain Garden (July 2010)