Relating wetland functions to stormwater nitrogen load removal in bioretention areas
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Relating Wetland Functions to Stormwater Nitrogen Load Removal in Bioretention Areas. Non-point Pollution Control:. Sharkey 2001. NC STATE UNIVERSITY. The Problem. Increased Runoff. Short Circuit Groundwater. Nutrient Addition From Stormwater. NH3-N .22mg/L NO3-N .25mg/L*

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Relating wetland functions to stormwater nitrogen load removal in bioretention areas
Relating Wetland Functions to Stormwater Nitrogen Load Removal in Bioretention Areas

Non-point Pollution Control:

Sharkey 2001


The problem
The Problem Removal in Bioretention Areas

Increased Runoff

Short Circuit Groundwater

Nutrient addition from stormwater
Nutrient Addition From Stormwater Removal in Bioretention Areas

  • NH3-N .22mg/L

  • NO3-N .25mg/L*

  • TKN .88mg/L

  • OP .10mg/L

  • TP .14mg/L

    From J.S. Wu (1996),

    *Greensboro data.

Concentrations in Runoff

Annual Loadings

Research By Hunt (2003)

Addition to surface water

Particulate Organic Nitrogen ( Removal in Bioretention AreasPON)

Soluble Organic Nitrogen (SON)

Ammonia-N (NH4-N)

Ammonium-N (NH3-N)

Nitrate-N (NO3-N)

Vegetative N

Addition to Surface Water

Nitrogen transformations in wetland soils
Nitrogen Transformations In Wetland Soils Removal in Bioretention Areas

  • Enzymatic Hydrolosis of Organic N

  • Mineralization

  • Nitrification in Aerobic Zone (NO3 Reduction)

  • Adsorption/Desorption of NH4-N

  • Volatization of NH3-N

  • Denitrification in Anaerobic zone

  • Vertical Flux by Vegetative Assimilation and Decay, Settling of PON

Bottom portion of bio-retention i anaerobic due to elbow in drain pipe.

Aerobic zone throughout. Water freely drains from entire soil profile.

Allowable Ponding

24 mm

Concrete Drop Box with Standard Inlet

350 mm

Top layer: Mulch

8 – 16 mm

Sandy loam –

Loamy Sand fill soil

1 – 1.2 m

5 – 10 mm

Outlet pipe (RCP or CMP typ) for overflow and drainage.

Washed Gravel Envelope

Corrugated Plastic Underdrain (typically 4” diameter)

Soil Surface

Cross Sections of Bioretention Area

From Hunt 2003

Soil Surface

Aerobic Zone: Nitrification (NH4 to NO3)

Anaerobic Zone:

Denitrification (NO3 to N2)

From Hunt 2003

Site Excavation drain pipe.

Elbow used to induce anoxic conditions

Overflow Drain

Drainage Layer/

Washed Stone

Backfill Soil

Photos: Bill Lord, 2001

Greensboro bio retention sites
Greensboro Bio-retention Sites drain pipe.

Cell #2

Cell #1

August, 2003

Sharkey ‘03

Reductions by bioretention areas
Reductions by Bioretention Areas drain pipe.

Lab Studies of Induced Anaerobic Layer Conclude Higher Reductions

Complications in relating these to Field studies.

The problem1
The Problem drain pipe.

SOURCES drain pipe.

Martin, Jay F, Reddy, K R. 1997. Interaction and Spatial Distribution of Wetland Nitrogen Processes. Ecological Modeling. 105: 1-21.

Hunt, WF. 2003. Pollutant Removal Evaluation and Hydraulic Characterization for Bioretention Stormwater Treatment Devices. Unpublished Thesis Document.

Wu, Jy S., Allen, C. J. 1998. Characterization and Pollutant Loading for Highway Runoff. J. of Environmental Engineering. July, 1998: 584-592.

QUESTIONS? drain pipe.

Sharkey 2000

Reactions drain pipe.

  • NH4+ + OH-  H2O + NH3

  • NH4+ + O2  NO3

  • 2NO3  N2O  N2