Constructed Wetlands and the soil properties and biogeochemical processes

that increase efficiency in Nitrate removal

Mark Campbell

Brief Intro of Wetlands

Turkey Creek WetlandA restored floodplain wetland at a private farm in rural McLean

County, Illinois

Characteristics of Wetlands

Wetlands are transitional areas between land and water

Main Characteristic present of surface or near-surface water, at least periodically

The hydrology of wetlands is generally one of slow flows and either shallow waters or saturated substrates

Also forms an Anaerobic environment

Benefits CostsProvides the removal of

contaminants: Nitrates, Phosphorous, metalloids

Allows for sedimentation to occur

Low Cost Removal as opposed to Ion-Exchange

Control of FloodingEcosystem for wildlife

Loss of Land use $$$$

Aesthetic Value

Soil Profile

Per

mea

bilit

y

Differences between Soils in Constructed and Natural Wetlands

5 cm Depth20 cm Depth

Variable CW Reference

Organic (%)

4.8 11.5

Sand Content (%)

52.1 23.7

Clay (%) 22.0 30.0

Silt (%) 20.0 45.2

CW Reference

2.8 7.2

54.3 21.9

30.1 31.4

15.0 39.5

Campbell et al (2002)

ComparisonIt was also found that the diversity of plant

communities were higher in reference sites

Even in long-term CW’s the organic matter did not reach levels of reference sitesThis has shown to be an indicator of removal of

nitrogen (Reddy and D’Angelo 1997).

Another comparative study

O’Geen et al (2007)

What is the chemistry that goes on that in hydric soils

that helps with denitification?

Factors that affect Denitrification rates

Temperature With season, can not control, lower temp. lower

rate

pH pH in natural waters is in the between 6 to 8,

optimal pH for denitrifying bacteria

Redox Potential Organic Carbon and Dissolved Oxygen

Retention time/Flow Rate

Biochemistry Organic Material is oxidized by aerobic

respiration use Oxygen as the electron receptor, while anaerobic conditions use Nitrogen as receptor (Metcalf and Eddy 2003).

Corganic + 4 NO3- + 4H+ = 2N2 + 5CO2

+ 2H2O

PseudomonasThiobacillus 

Constructed wetlands have found to remove ≈40% of NO3- ther is

a high degree of variability there have been reports of up to 75% and low of 15% (Kovacic et al. 2000)

Effects of DO and TN Removal

H. C. Kim et al. (2010)

Flow Rate and Retention TimeDuring pulse flows, in the case of storm

events the amount of denitrification is greatly reduced (Kovaic 2006).

Still wetlands need slow flow, to have some mixing in the water. Need to create anaerobic environment.

The average retention time 6-8 days for optimal conditions (Zedler 2003).

Horizontal substrate is more important, while increase in depth lowers efficiency(Garcia et al 2010).

Substrate soils for CWSince high levels of nutrients

Sand and Gravel- cheap

Soils with high clay content- good at retaining phosphorous

Organic Substrate- sawdust, compost, or hay.

USDA-NRCS Handbook for constructed wetlands