Presentation on theme: "The Science Behind the Phosphorus Risk Index Wes Jarrell, Professor and Head Natural Resources and Environmental Sciences, UIUC March 2, 2005."— Presentation transcript:
The Science Behind the Phosphorus Risk Index Wes Jarrell, Professor and Head Natural Resources and Environmental Sciences, UIUC March 2, 2005
-from Robertson et al. EPA proposed Total P criteria for Upper Midwest water bodies
Forms of P - % of total Water Menomonee R, Armstrong Dissolved (PO 4 ) Sorbed Insoluble/ inorganic Ca, Fe, Al -P Organic 0.04% 15% 60% 25% 30% 3% 27% 40% TP =0.138 mg P/L TP= 500 mg P/L Soil ? Readily bioavailable Seasonably bioavailable ? e.g., Bray
Instantly bioavailable: dissolved PO4 and desorbable PO4 Seasonally bioavailable P: P in organic or inorganic particles that is released over a growing season Load vs concentration
Sources of water to water body Runoff - main source of P load Direct precipitation inputs Baseflow - seepage from groundwater: Wisconsin: 10 - 50 ppb total P Higher concentrations in some areas Point sources - discharges from municipal-industrial sources
Field Concentrated flow Particles – Entrainment Settling - enrichment Receiving water Precipitation P Transport – Land to Water Nonpoint sources Delivery zone Dissolved Dissolution Sorption/Desorption Rusle2 Bray vs total Bray vs soluble Soluble P in fert. Sediment delivery ratio Buffer effectiveness Settling - enrichment
SUMMARY Phosphorus that could cause problems in water occurs both in particles (PP) and dissolved in solution (SP) when it reaches surface water. We consider both particles and dissolved P.
Land/water/animal manager Researcher APEX - field/farm P index/ Rusle2 PI-EZ PALM - field/watershed SWAT - watershed Phosphorus Transport - Land to Water LEVEL OF DETAILUSER
Desirable Characteristics of P index - Accurately rank fields in order of their risk of supplying P to a water body - Based on best available science, easily modified to reflect improvements - Easy to use, interpret, and apply - Helps user understand factors affecting P movement to water - Direct user to improved management practices that effectively and economically lower the risk - Should be applied over the whole farm - Provide maximum flexibility to farmer, while decreasing P loading.
Total Risk Index for Phosphorus (PI): PI = PP + SP + LP PI = Total P index PP = Particulate P SP = Soluble P LP = Leached P
Total P in soils and clays, native soils, Wisconsin (Boerth and Helmke, 1997)
1,0002,0003,0004,000 5,000 0 Average P concentration in particulates, mg P/kg Wisconsin soils (Boerth and Helmke) Wisconsin soil clays (Boerth and Helmke) Runoff plot sediment (Bundy and Andraski) Small Wisconsin streams (Baum, WDNR) Wisconsin streams (Corsi et al., USGS) Living algal cell or crop plant leaf Soil organic matter Scenescent leaf Modeling land use effects (Panuska, others, WDNR) Manure To 11,000+
PP: Depends on (1) erosion, (2) fraction of eroded particles delivered to stream, and (3) P concentration in the soil particles Calculation: Particulate P = Rusle2 * Sediment Delivery Ratio * Enrichment Ratio * BufferEffectiveness* Soil particle P concentration (from Bray P1)
Also: Meyer, Lyne, Avila, Barak, UW Madison, Plano silt loam: Total P = 2.5 (Bray P1) + 875
“It appears that most of the sediment generated by a particulate erosion event is usually deposited in small or headwater tributaries.” - Glymph and Storey, 1967
Sediment Delivery Ratio S = SY 0 e – T (D)1/2 Where S = sediment yield at the down stream channel outlet, SY 0 = sediment yield at the upstream end of the channel, = (Beta) decay constant or routing coefficient, T = Travel time through the section in hours, D = the particle diameter in millimeters. From John Panuska – J.R. Williams original model
Soluble P: Depends on amount of runoff, P concentration in the soil, and soluble P concentrations in P-containing amendments/fertilizers Total soluble P = SP from soil P + SP from unincorporated nutrients on unfrozen soil + SP from unincorporated nutrients on frozen soil ( + SP release from crop residues?)
0.10.20.30.126.96.36.199.80.9 1.0 0.0 P concentration in solution, mg/L Upper limit for oligotrophic lake (total) Lower limit for eutrophic lake (total) Lower limit for maximum crop growth in soil (soluble) Upper limit for oligotrophic stream (total) Soil solution [P] at 50 ppm Bray P-1 Lower target for wastewater discharge (total ) Manure: 10 - 30 mg P/L (100:1 dilution)
a.Soluble P load in runoff: For no fertilizer or incorporated fertilizer: Soil solution equilibrium [P] (from Bray P1) * Annual runoff volume (from Rusle2)
P index values for one field: Corn, 4% slope, 300 ppm Bray P1, 50% sol P in manure
Export coefficients – Model Panuska et al., WDNR
Preliminary Interpretation of risk associated with PI values: 0 – 2 Low risk: low probability of being a problem except for very sensitive water bodies 2 – 6 Intermediate risk: important for water bodies sensitive to P inputs 6 - 10 High risk: Likely excessive in most watersheds >10 Very high risk: Excessive for almost any water body
The Phosphorus Risk Index - Progressive Planning 1234567 Years Phosphorus Risk Index Case 1 - degradation Case 2 - balance Case 3 - restoration
The framework of the PI is in place. Now it needs (1)ADAPTATION to specific regional conditions in Wisconsin; (2)EVALUATION at a variety of scales, to see if it truly measures what we intend it to measure; (3)USABILITY for planners and plan implementers; (4)COMPARISON with other states
Summary -The PI should be part of a Systems Approach to Phosphorus Management in Wisconsin Agriculture - It provides a framework into which we can incorporate the best existing science and extend it to users -The PI should complement and be consistent with other models - Gaps in our understanding of the system are identified through applying the PI - Adaptation, Evaluation, Usability, and Comparability are needed to apply the PI more efficiently
Forms of Phosphorus in Water and Their Bioavailability Wes Jarrell, Senior Scientist Discovery Farms Program
"A river and its plankton are a flowing soil and its crop,...." (p. 147). Forbes, S. A. and R. E. Richardson. 1919. Some recent changes in Illinois River Biology. Bull. Ill. State Natural History Survey 13:141-156. (Thanks to Erwin Van Nieuwenhuyse, CA)
Corollary: "A soil is benthic sediment in an intermittent stream supporting emergent vegetation.” W.M. Jarrell, 2000, and likely someone else, circa 1940.
“It has been suggested that God must have been a limnologist or an oceanographer …” Harris, Phytoplankton Ecology, 1986
Regulations will be based on Total P in water; we have no easy ways of determining bioavailable P in the particle fraction Total P (mg P/L) = Particulate P (PP) + SRP
Loads Total P: All P in particles and all dissolved P entering water body Bioavailable P: Phosphorus that is, or can rapidly become, the PO 4 (ortho-P) form; from 10 to 90+% of total P
Follow the colloids! Colloid: - Particle less than 2 m in diameter (clays, organic matter) - Settles out of water very slowly - High surface to volume ratio - Often high concentrations of nutrients
Total P (mg P/L) = Particulate P (PP) + SRP Total P in water is comprised of (1) Particulate P, which does NOT pass through the 0.45 m filter, and (2) P that passes through a 0.45 m filter, also called “dissolved P”, “soluble reactive P” (SRP), “ortho-P”, “soluble P” (reminder: colloids at usually <2 m)
Actual analyses Total P: strong acid dissolution of entire water sample, determine ortho-P in digest. SRP: direct determination of water passing through a 0.45 m filter
SRP - Immediately bioavailable - Where did it come from? - How can we control it? Units ppb: g/L (for water), g /kg (particles, soil); or ppm: mg/L (for water) or mg/kg (particles, soils)
Minimum solution concentrations from which plants can extract P in flowing solution: Algae:0.3 - 0.6 - 1 g P/L (ppb), 0.001 ppm Rye:3 g P/L (ppb), 0.003 ppm Oats:7 g P/L (ppb), 0.007 ppm
Critical P concentrations and trophic state in water Periphyton streams (low flow) Trophic stateTotal P mg P/L Eutrophic0.020 Bioavailability
PARTICULATE PHOSPHORUS - Particulate P (PP) in water is organics, aluminum, iron, and calcium phosphates - How much PP is bioavailable in a given situation? - Where did it come from? - How can we control it?
To estimate average P concentration in suspended particles in water: (1) Calculate Particulate [P]: PP(mg P/L) = TP - SRP (2) Divide PP concentration by TSS concentration: (Total suspended solids (TSS) in water: mg solids/L) P concentration in suspended solids PP (mg P/L) TSS (mg solids/L) = = mg P mg solids
Watershed water quality monitoring, Panuska and others, WDNR P concentrations in water particulates
- How do TP concentrations in soil compare with PP in water? - Does this explain why we can’t simply add up RUSLE across a watershed and get good quality water? - How does this help us compare different P pollution sources - P credit trading?
Why doesn’t it work to add up all the RUSLE values for a watershed to get total lost? - Sediment delivery ratio - Enrichment ratio - Unknown relationships between Bray P1 and total P
(1) Sediment delivery ratio (SDR) As water and sediment moves from land to water, larger particles drop faster e.g., in perfectly still water, to drop 20 cm requires sand: 2 minutes silt: about 2 hours clay (colloids): 8 hours to > 1 year In turbulent water, water energy keeps larger particles in suspension, especially colloids
(2) Enrichment ratio As heavy particles drop out, lighter particles (especially colloids) stay in suspension: “bed load”: heavy sandy particles “wash”: particles that are light, colloidal - organics, clays - that move with water NOTE: Colloids and most organic matter have much higher P concentrations than do sands and some silts.
(3) Different soils have different TP concentrations - Very little known about total P in Wisconsin soil particles - For same soil type, should be a correlation between Bray P-1 and total P in the soil - Reactive clay-sized particles have a much higher [P] than silts and sands
Runoff plots: TSS in runoff vs [P] in solids (Bundy and Andraski)
Stratification from Robertson, Saad, and Wieben, 2001 103 ug/L 37 ug/L 125 ug/L 286 ug/L Mean Conc.
Movement from land to water What determines how much P is mobilized? Breaking away from aggregates: strength of aggregate bonds (organic matter); energy of water Movement energy of water size of particles; density of particles
Movement from land to water Load vs concentration Soil has a wide range of particle sizes and density Most of bioavailable P is associated with (1) small particles, colloids; and (2) light particles, organic matter (about 1/3 the density of clay)
Bulk soil Dissolved Particulate Dissolved Particulate Algae Settled heavy/large Filtered Smaller, lighter colloids Sorbed “enrichment” Movement from land to water - BMP function Desorption Uptake Settled heavy/large
Issues Load vs concentration - If soluble levels are increasing in the environment, will our current BMPs work? - If clays and small organics are the primary runoff particulates, where will BMPs work?
Issues (cont’d) Load vs concentration - If soluble levels are increasing, which of our current BMPs will work? - Lower soil soluble P: P management, chemical treatments? - Lower manure soluble P: feed and chemical management - Increase infiltration/lower runoff: organic matter, plant management
Issues (cont’d) Load vs concentration - If clays and small organics are the primary runoff particulates, which BMPs work best? - Increase infiltration - Improve aggregation, wet strength - Increase residue BETTER USE OF ORGANIC MATERIALS AND PERENNIAL PLANTS
Issues (cont’d) Load vs concentration - QUESTION: Will buffers work to decrease the problems with runoff? - Yes, for physical effects: sands and silts, bottom deposition, abrasion - Not for removing colloids: except by increased infiltration
Recommendations - Determine actual forms of particulate phase P in runoff, manures, water column, and bottom sediments - Evaluate current BMPs based on their effects on colloidal particle transport and soluble P transport - Develop new BMPs for manure, land management, and in-water management targeted at mitigating colloidal and soluble P impacts.