Presentation on theme: "Ecological Engineering: Nutrient Uptake Patrick Corbitt Kerr University of Notre Dame It has been said that streams are the gutters down which flow the."— Presentation transcript:
Ecological Engineering: Nutrient Uptake Patrick Corbitt Kerr University of Notre Dame It has been said that streams are the gutters down which flow the ruins of continents. L.B. Leopold et al. 1964.
Stormwater Management: The Industry Direction Quantity (-) Water Supply (Irrigation, Drinking Water,…) (+) Flooding (Rate or Volume?) Quality Importance Safe for humans (Acute vs Chronic) Ecosystem Conscious Aesthetics Components Groundwater vs Surface Water Type of Pollutants Pollutant Source: Urban or Rural Sediment & Watercourse Stability Image from http://www.the-macc.org/wp-content/uploads/2009/04/storm2.jpg
Nutrients Nutrients: Chemicals that an organism needs to live and grow. Macronutrients: Carbon (C) Nitrogen (N) Phosphorus (P) If the aquatic ecosystem requires nutrients, why then are nutrients considered a pollutant? An oversupply of nutrients to a certain species can result in excessive growth; thereby choking out other species. The Solution is …. Balance.
Algae (Phytoplankton) Blooms Upper left: Cyanobacterial (blue-green algal) bloom in the Gulf of Finland region of the Baltic Sea. Upper right: Dinoflagellate red tide bloom near the Japanese Coastline (Sea of Japan). Lower left: Cyanobacterial bloom in the St Johns River Estuary, near Jacksonville, Florida. Lower right: Mixed cyanobacterial-chlorophyte bloom in North Island, New Zealand Image from http://lepo.it.da.ut.ee/~olli/eutr/html/htmlBook_78.html
Hypoxia Means “Low Oxygen” Algae blooms consume oxygen (0 mg/L) is “anoxia” Called “Dead Zones” because animals can’t survive Kills mobile animals like fish Kills shellfish and other less mobile animals Nursery habitat is destroyed Releases stored pollutants Chemical reaction between hypoxic water and bottom sediments Overall ecosystem is stressed (Birds, mammals, too!) Image from: srwqis.tamu.edu/hot-topics/hypoxia.aspx
Gulf of Mexico Hypoxia Image from: http://water.usgs.gov/nawqa/sparrow/gulf_findings/hypoxia.html
The Mississippi River Basin: N & P Yield Image from: http://water.usgs.gov/nawqa/sparrow/gulf_findings/delivery.html
Percent N & P Contribution by State Image from: http://water.usgs.gov/nawqa/sparrow/gulf_findings/by_state.html
Macro-Scale vs Micro-Scale: Hydrosphere, Lithosphere, Atmosphere, Biosphere Water Cycle Conservation of Mass & Energy Ecosytem Components: Solar Energy ( Light / Temperature ) Producers Consumers Decomposers Water Soil / Water / Air Chemistry The Nutrient (Biogeochemical) Cycle Image from: ga.water.usgs.gov/edu/watercyclehi.html
Nutrient Transport: Spiraling Concepts and Methods for Assessing Solute Dynamics in Stream Ecosystems Stream Solute Workshop Journal of the North American Benthological Society, Vol. 9, No. 2. (Jun., 1990), pp. 95-119.
Ecosystems change spatially Seeks a dynamic balance between form & function The watercourse changes Width, Depth, Velocity, Sediment Load, Canopy Cover, Temperature, Flow Characteristics The stream community & biogeochemical processes conform to the new structure. River Continuum Concept (RCC) www.tcnj.edu/~bshelley/EcolTCNJ.htm
Nutrient Uptake (U) Image from: http://www.biol.vt.edu/faculty/benfield/freshwater/freshwaterlocked/fredfigs.html Definition: The total flux of nutrient from the water column to the stream bottom, expressed on the basis of stream bottom area (e.g., mg/m²/hr) Biotic & Abiotic Element Cycling Rate Pathways Residence Time
Abiotic Uptake Some nutrients adsorb to sediment particles. Adsorption capacity varies By nutrient and chemical state: Phosphorus (H 2 PO - 4 ) is most adsorptive By Media: Capacity dependent on makeup and chemical properties pH, total and reactive calcium, total and reactive Fe, Al oxide Capacity also increases as: Size & Density decreases Porosity and Surface Area increases Not Permanent -> Desorption Image from: http://www.phosphoreduc.com/fr/our-technology/technical-info/25-phosphorus-adsorption-capacity.html
How does this relate to us as Professional Civil Engineers?
The Design Process: What conditions are we considering? Existing or Pre-Existing Proposed or Ultimate What is our design criteria? Quantity: Typically: Peak Discharge (Match α -yr Post to ß-yr Pre) But sometimes ….Volume Recharge (Re V ), Channel Protection (CP V ), Overbank Flood Protection (Q p ), Extreme Flood (Q f ) Quality: Water Quality Standards: What Format? Waterbody Type or Waterbody Specific? Concentration, Load, or Indicator (Clarity or Chl-a)?
The Water Quality Challenge Who’s leading the charge? Environmental Groups EPA Coastal States: Maryland, Florida, etc. Who/What is being targeted? Point versus Non-Point Sources Urban Areas (Agricultural/Rural has largely been avoided) Construction Practices: Erosion & Sediment Control Stormwater BMPs: New Construction & Retrofits Stream Restoration How do we design stormwater BMPs? Uniform Sizing Criteria: (Performance Based?) Water Quality Volume (WQ V )
WQv ( A Standard Solution?) Methods: Post-Conditions vs Pre-Conditions Difference Post-Conditions Total Regression Equation: function of P, I, and A WQ V = [(P)(R V )(A)]/12 Where: WQ V = Water Quality volume (acre-feet) P = Precipitation (inches) Rainfall necessary to facilitate full movement of pollutants (“First Flush”) A = Drainage Area (acres) R V = Volumetric Runoff Coefficient = 0.05 + 0.009(I) I = Percent Impervious Area (%) Function of Load and BMP Performance (Pollutant Specific)
The Water Quality Volume Issues: Regression equation doesn’t account for non-impervious area Are nutrient-laden areas being considered? For storms greater than P, can WQ V be targeted? Consider a 100% Impervious Site, designed for P = 1”: P is a function of Duration, Time of Concentration, and Land Cover Peak Water Quality Flowrate (Q WV ) P = 1”P > 1” 100% Treated Any Duration Duration Dependent WQV”
What to do with the Water Quality Volume? Suppose we account for the “First Flush” and can isolate all the pollutants by that WQ V, what are our goals? Ideally we wish to TREAT the water? In Water/Wastewater: We have effluent criteria defined by concentration and load We measure (sample) both influent and effluent We alter it chemically and mechanically But, most importantly, though, we can remove mass (SLUDGE) Why is sludge removal so important? Some pollutants can be broken down but unless N, P, Heavy Metals, etc. are removed from the system and assuming steady flow the load in will equal the load out. If removal is the ultimate goal, then how?
Removing N & P N & P come in many different forms. Which do we target? Perhaps, we should first identify ways to remove nutrients, and maybe that will decide for us… Image from: http://www.biol.vt.edu/faculty/benfield/freshwater/freshwaterlocked/fredfigs.html
General Ways to Remove Pollutants Separation is the first step to pollutant removal. Methods of separation we know from water/wastewater treament: 1) Screening 2) Skimming 3) Settling 4) Filtering Can’t use active treatment systems or mechanical means Typically referred to as a Pre-Treatment. Pollutants are separated WITHIN the system. Full Removal requires maintenance (Typically considerable). These methods will often FAIL under HIGH flows.
Screening Typically refer to as trash racks We focus on the Inlet Image from: http://www.waterwatchadelaide.net.au/index.php?page=how-does-a-wetland-work Image from: http://www.mitchamcouncil.sa.gov.au/site/page.cfm?u=1496
Skimming Solution: Submerged Outlets High flow overflow? Use Bypass Control Structures Reduces both size of structure and effectiveness Image from: http://www.ene.gov.on.ca/envision/gp/4329eimages/ figure4.41.gif Image from: http://www.baysaver.com/products/BaySeparators/index.html
Settling Theoretical Solutions: Force it with a vortex Inhibit (re-)suspension Slow Flow (Long Release Time) Not Turbulent (Wide/Deep) Long Paths (Baffles, Islands, L:W) Design Options: SW Manual Criteria Length to Width Ratio 1.5:1 to 3:1 Forebay (Typically at least 10% WQ v ) Use Stoke’s Law Need to know influent load
Stoke’s Law Equation: V S = settling velocity (cm/s) g = gravity (m/s²) ρ S and ρ W = densities of the particle and water (g/cm³) µ = dynamic viscosity d = effective particle diameter Particle TypeDensity (g/cm³)Diameter (µm) Settling Velocity (m/d) Phytoplankton1.0272 – 840.08 – 1.9 Particulate Organic Carbon1.02 – 1.271 – >64,0.2 - >2.3 Clay2.652-40.3-1 Silt2.6510-203-30
Resuspension Bed Scour is a function of shear stress Shear Stress is a function of velocity gradient, therefore consider the : Velocity of the flow path Orbital Velocity (from wind forced waves) Wind Velocity Depth Fetch Affects both aeration and suspension Image from: http://www.ozcoasts.org.au/glossary/images/resuspension.jpg
Sediment Transport Sediment Balance Bed Load Suspended Load Costly to Model Image from: cals.arizona.edu/.../riparian/chapt4/p7.html Image from: medinaswcd.org/streams.htm
BMP Performance How do we measure performance? Load or Concentration How do we rate performance? Reduction % or Final Effluent Result
Comparing Pollutant Removal Efficiencies among Different BMPs
Dry versus Wet methods Dry > Wet Filtration/Infiltration Groundwater Recharge In-basin vegetation in addition to perimeter BioRetention Dry < Wet Less effective for oils, greases, & hydrocarbons Disturbance of Bottom Sediments Leaching
Combination Facilities 2+ facilities Target different pollutants Pre-Treat for Next BMP Start at Source Grass Channels instead of Curb, Gutter, & Sewers Image from: http://h2o.enr.state.nc.us/wswp/images/wet_pond.gif Image from: www.fhwa.dot.gov/environment/ultraurb/3fs5.htm
Pond Depth (Shallow or Deep) Shallow: Pros: More Vegetation Higher oxygen content Greater Wetted Contact Area Cons: More bottom disturbance -> Greater Turbidity Thermal Increase Wider Pond: Less Canopy Cover Deep Pros: Cooler Water Less Disturbance Cons: Stratification and Anoxia Less Wetted Contact Area Less Vegetation
State Requirements (Min, Max) (GA) Max Depth: (GA: 8 ft ) Min Depth: (GA: 3ft to 4ft) Design for maximum depth to avoid Anoxia (FL) If TP is known, calculate chyl-a: TP = total P concentration (µg/l) Chyl-a = chlorophyll-a (mg/m³) Calculate Mean Secchi Disk Depth SD = Secchi disk depth (m) Calculate Depth of DO For Deeper Depths Aeration or Mixing is Required Pond Depth Design
Maximizing Nutrient Uptake Summary Pre-Treat Screen, Skim, Settle, Filter (abiotic Uptake) Treat (Biotic Uptake) Healthy Ecosystem Biodiversity Vegetation (Diversify) Plan Form Features (Abnormal Geometry) Habitat (In-Pond Features) Pore Diffusivity Bed/Bank Material Construction Methods Can’t rely on maintenance!