Forms of Phosphorus in Water and Their Bioavailability

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Forms of Phosphorus in Water and Their
Bioavailability Wes Jarrell, Senior
Scientist Discovery Farms Program
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It has been suggested that God must have been a
limnologist or an oceanographer Harris,
Phytoplankton Ecology, 1986
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"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 13141-156. (Thanks to
Erwin Van Nieuwenhuyse, CA)
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Corollary "A soil is benthic sediment in an
intermittent stream supporting emergent
vegetation. W.M. Jarrell, 2000, and likely
someone else, circa 1940.
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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

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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
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EPA proposed Total P criteria for Upper Midwest
water bodies
-from Robertson et al.
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Loads Total P All P in particles and all
dissolved P entering water body Bioavailable P
Phosphorus that is, or can rapidly become, the
PO4 (ortho-P) form from 10 to 90 of total P
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Load vs concentration
Instantly bioavailable dissolved PO4 and
desorbable PO4 Seasonally bioavailable P P in
organic or inorganic particles that is released
over a growing season
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Readily bioavailable
Forms of P - of total
Seasonably bioavailable
Water Menomonee R, Armstrong
Soil
0.04 10 60 25
Dissolved (PO4)
30 3 27 40
Sorbed
Insoluble/ inorganic Ca, Fe, Al -P
Organic
TP 0.138 mg P/L
TP 500 mg P/L
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Follow the colloids! Colloid - Particle less
than 2 mm in diameter (clays, organic matter) -
Settles out of water very slowly - High surface
to volume ratio - Often high concentrations of
nutrients
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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 mm filter, and (2) P that passes through a
0.45 mm filter, also called dissolved P,
soluble reactive P (SRP), ortho-P, soluble
P (reminder colloids at usually lt2mm)
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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 mm filter
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SRP - Immediately bioavailable - Where did it
come from? - How can we control
it? Units ppb mg/L (for water), mg /kg
(particles, soil) or ppm mg/L (for water) or
mg/kg (particles, soils)
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Minimum solution concentrations from which
plants can extract P in flowing
solution Algae 0.3 - 0.6 - 1 mg P/L (ppb),
0.001 ppm Rye 3 mg P/L (ppb), 0.003 ppm
Oats 7 mg P/L (ppb), 0.007 ppm
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Bioavailability
Critical P concentrations and trophic state in
water Periphyton streams (low flow)
Trophic state Total P mg P/L
Eutrophic 0.020
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Bundy and Andraski
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Lower target for wastewater discharge (total )
Soil solution P at 50 ppm Bray P-1
Lower limit for maximum crop growth in soil
(soluble)
Lower limit for eutrophic lake (total)
Upper limit for oligotrophic lake (total)
Manure 5 - 50 mg P/L (saturation extract)
Upper limit for oligotrophic stream (total)
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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?
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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)
PP (mg P/L) TSS (mg solids/L)
mg P mg solids
P concentration in suspended solids


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P concentrations in water particulates
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P concentrations in water particulates
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P concentrations in water particulates
Watershed water quality monitoring, Panuska and
others, WDNR
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- How do TP concentrations in soil compare with
PP in water? - Does this explain why we cant
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?
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Why doesnt 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
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(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 gt 1 year In turbulent
water, water energy keeps larger particles in
suspension, especially colloids
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(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.
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(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
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Total P in soils and clays, native soils,
Wisconsin (Boerth and Helmke, 1997)
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Runoff plots TSS in runoff vs P in solids
(Bundy and Andraski)
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Average P concentration in particulates, mg P/kg
1,000
2,000
3,000
4,000
0
5,000
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
To 11,000
Soil organic matter
Manure
Scenescent leaf
Modeling land use effects (Panuska, others, WDNR)
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103 ug/L
37 ug/L
125 ug/L
286 ug/L
Mean Conc.
Stratification from Robertson, Saad, and Wieben,
2001
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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

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Load vs concentration
Movement from land to water
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)
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Movement from land to water - BMP function
Algae
Dissolved
Desorption
Dissolved
Bulk soil
Sorbed
Uptake
Particulate
Particulate
Smaller, lighter colloids
Settled heavy/large
enrichment
Filtered
Settled heavy/large
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Load vs concentration
Issues
- 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?
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Load vs concentration
Issues (contd)
- 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
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Load vs concentration
Issues (contd)
- 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
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Load vs concentration
Issues (contd)
- 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
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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.
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Land to water transport - It IS a continuum!
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