Non-point Pollution Control: Relating Wetland Functions to Stormwater Nitrogen Load Removal in Bioretention Areas Sharkey 2001 NC STATE UNIVERSITY The Problem Increased Runoff Short Circuit Groundwater Nutrient Addition From Stormwater 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 InflowOutflowReductio n Conventi onal 5.06 kg/acre Kg/acre 40.19% Annual Loadings Research By Hunt (2003) Addition to Surface Water Particulate Organic Nitrogen (PON) Soluble Organic Nitrogen (SON) Ammonia-N (NH4-N) Ammonium-N (NH3-N) Nitrate-N (NO3-N) Vegetative N Nitrogen Transformations In Wetland Soils 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 24 mm 8 16 mm Sandy loam Loamy Sand fill soil 1 1.2 m 5 10 mm Top layer: Mulch Washed Gravel Envelope Corrugated Plastic Underdrain (typically 4 diameter) Outlet pipe (RCP or CMP typ) for overflow and drainage. Allowable Ponding Concrete Drop Box with Standard Inlet Aerobic zone throughout. Water freely drains from entire soil profile. Bottom portion of bio-retention i anaerobic due to elbow in drain pipe. 350 mm Cross Sections of Bioretention Area From Hunt 2003 Soil Surface Anaerobic Zone: Denitrification (NO3 to N2) Aerobic Zone: Nitrification (NH4 to NO3) Site Excavation Elbow used to induce anoxic conditions Drainage Layer/ Washed Stone Backfill Soil Overflow Drain Photos: Bill Lord, 2001 Greensboro Bio-retention Sites August, 2003 Cell #1Cell #2 Sharkey 03 Reductions by Bioretention Areas InflowOutflowReduction Conventional5.06 kg/acre Kg/acre 40.19% Lab Studies of Induced Anaerobic Layer Conclude Higher Reductions Complications in relating these to Field studies. The Problem SOURCES Martin, Jay F, Reddy, K R Interaction and Spatial Distribution of Wetland Nitrogen Processes. Ecological Modeling. 105: Hunt, WF Pollutant Removal Evaluation and Hydraulic Characterization for Bioretention Stormwater Treatment Devices. Unpublished Thesis Document. Wu, Jy S., Allen, C. J Characterization and Pollutant Loading for Highway Runoff. J. of Environmental Engineering. July, 1998: Sharkey 2000 QUESTIONS? Nitrogen Model for Wetland Soil Reactions NH OH - H 2 O + NH3 NH O2 NO3 2NO3 N2O N2