Particulate Soil Phosphorus and Eutrophication in Lakes and Streams Paul R. Bloom Soil, Water, & Climate Department University of Minnesota With contributions by John Moncrief, Carl Rosen and David Mulla
Particulate Soil Phosphorus and Eutrophication in Lakes and
Streams
Paul R. BloomSoil, Water, & Climate DepartmentUniversity of Minnesota
With contributions by John Moncrief, Carl Rosen and David Mulla
Outline
EutrophicationPhosphorus Chemistry in SoilTransport of P from Soil to Surface WaterSoil P: a P Source for Algae in Surface Waters
http://www.ars.usda.gov/is/np/Phos&Eutro2/agphoseutro2ed.pdf
Eutrophication
Creation of high nutrient status of a lake or stream.Results in:
Excess algal growth Lower productivity of game fish If severe - fish kills.
Generally P is the limiting nutrient.
Algal Growth
Temperature is a factor in all biological production
Excess algae generally most apparent in late summer.
Total P and Growth of Algae
< 0.02 ppm (20 ppb )Little algal growth Clear water
> 0.02 ppmAccelerated algal growthLower water clarity
Log total phosphorus (ppb) vs. log chlorophyll-a (ppb). (Eco-region reference lakes in MN, summer-mean measurements.)
0.02 ppm
http://lakeaccess.org/lakedata/datainfotsi.html
0.02 ppm
http://lakeaccess.org/lakedata/datainfotsi.html
Total Phosphorus (ppb) vs. Secchi depth (m).
EutrophicationP stimulates algal productivity.Light penetration limited at depth.
Less algae and plant growth at depth.
Decay of surface algae further depletes oxygen.
Dead algae fall through the water.
HypolimnionO2 depletion
EpilimnionAquatic plants
Role of Suspended Sediment
Other sources of suspended sediment make the problem worse.
Soil particles from erosion.
Severe Conditions Lead to Blue-Green Algae
Excess production of algae can lead N depletion.
Blue-green algae are N fixers.Produce their own N
Stink and produce toxins
Lake Pepin, drought of 1988
Phosphorous Chemistry in Soil
Solu
ble
P (<
1%)
Non Labile P
inorganic
organicinorganic
organic
Labile P
slow
Soil Phosphorus Forms____Solid_______
Soluble P
Inorganic + Some organic PThis is the form taken up by plants,
> 0.2 ppm in highly fertile soilsCompare to 0.02 ppm in a clear water lake
Mobile formSmall fraction of total P (< 1 lb/A)
Inorganic Soluble P
Sometimes called ortho-P Reacts rapidly with molybdate reagent:
Molybdate reactive P (MRP)Dissolved reactive P (DRP)Soluble reactive P (SRP)Dissolved molybdate reactive P (DMRP)
H-O-P-O-H
:O:
:O:H
::
::
:
Labile P
The most reactive P in soil solids.
Mostly inorganic.
Estimate with P soil test Varies with soil test used.A bioreactive form of P.
Bound to Al-P, Fe-P, Ca-P.Some adsorbed on surfaces.
< 10 lb/A to > 300 lb/A
Labile P
Buffers P in soil solutionPlant uptake lowers soluble concentration.Replaced from labile P.
Non labile
Relatively insoluble and unreactiveOrganic and inorganic compoundsOrganic can be 30 - 60 % of the P in surface soils
In Minnesota typically 50%Slow equilibrium with labile and soluble P300 lb/A to 3000 lb/A
Fate of P Added to Soil
P in fertilizer and manure initially solubleWith time
Fast SlowDissolved P ⇔ Labile P ⇔ Non labile P
Most soils have a high capacity to retain P in labile and non labile forms
Soil P Transport to Surface Waters
Soil Phosphorus Transport to Surface Waters
Surface RunoffDissolved-P Sediment-P (erosion)
Leaching into subsurface drain tiles Dissolved-P (leaching)Minor in most cases.
P in Surface Runoff
Particulate P (sediment P) Typically 75-90% of runoff P for row cropsOrganic and inorganic P
Typically 50 % organic in fertile Minnesota soilsAnalysis after hot acid digestion.
Soluble P Passes 0.4 micron or 0.2 micron filter.Mostly inorganic P
Determined by molybdate reaction (MRP)
Example 1P Lost from Fall Rainfall Simulation Experiment
Following CornNo-tillMoldboard
Following beanChiselMoldboard
D. Ginting, J.F. Moncrief, S.C. Gupta, M.R. Zumwinkle, M. A. Dittrich ,and M.J. Hanks
Fall runoff - Rainfall simulation- 4 in 1.5 hrP lost, g/ha
RESIDUE COVER & TYPE
PHO
SPH
OR
US
LO
SS (g
ha-1
)
0
5
10
15
20
25
30
35
40
45Particulate PDMRP
CORN RESIDUE SOYBEAN RESIDUE
25% 7% 13% 4%
PHOSPHURUS LOSS FROM 100 mm SIMULATED RAIN
Le Sueur Co. Surface Inlet 6Storm Event July 4th 1998
Example 2Runoff via Surface Tile Inlets
201 202 203 204 205 206
TS
Con
. (g
L-1
)
0
1
2
3
CO
D c
on. (
mg
L-1
)
0
100
200
300
400
201 202 203 204 205 206
TP
Con
. (m
g L
-1)
0
2
4
DM
RP
Con
. (m
g L
-1)
0
2
4
COD
TS
TPDMRP
21 Ju
ly
24 Ju
ly
Day of Year
Deposition of Particulate P Before Delivery to Surface Waters
Sedimentation: Sedimentation pondsIn ponds that form at tile inlets (80% loss)During transport in ditches.
Trapped by:Grassed edge of field buffers stripsRiparian buffers
Minnesota P Index Assesses Relative Risk of Delivery of P to Surface Waters
Rainfall Runoff(DP) c Soil P
Applied P c PracticeFactors RISK=
Erosion(PP) c Soil P c
BMPsStructuresDelivery
RISK=
OverallRisk
Snowmelt Runoff(DP) c Biomass
Applied P c PracticeFactors RISK=
TransportMechanism
PhosphorusSource
ManagementEffects
Soil P: a P Source for Algae in Surface Waters
Labile P Provides an Easily Accessible Source of P for Algae
Labile P tries to buffer at soluble P at 0.2- 0.3 ppm soluble P
Algae can draw soluble P down to < 0.01 ppm
P Mobilized in 2 Weeks by Algal Growth:0.6 ppm soil P added to algal culture (Ohio soil)
Dorich et al., 1984, JEQ pp. 82 - 86
Bioavailable P
Mobilized by algaeEstimated by
0.1 M NaOH extractionExtraction with Fe(OH)3 impregnated filter paper strips
Half of the Labile P Dissolves without the Algae
Bioavailable P was twice the DMRP in the no algae control after 2 weeks
DMRP about 0.2 ppm
Response of Algae to Soil P in Minnesota Soils
y = 0.078x + 4.75R2 = 0.68p < 0.001
0
2
4
6
8
10
0 10 20 30 40 50 60
Fe-oxide paper P (ppm)
Chl
-a re
spon
se
Soil Particles Can Also Supply P Over Longer Time Periods
Slow dissolution of non labile inorganic PEnzymatic hydrolysis of organic P
Organic P → Soluble PAlgae release alkaline phosphatase
Reactions in bottom sedimentHydrolysis of organic PLow redox
Iron P → Soluble P
Fate of P in particulate organic matter (POM)
Wat
er C
olu m
nA
c tiv
e Se
d im
e nt
Flux of POM
Fluxes of O2, H2S, NH4,
NO3, PO4, Si
Aerobic LayerAnaerobic
LayerDiagenesis of POM: Production of
H2S, NH4, PO4, Si
Modeling of P Transformations in Water
Source: HydroQual, Inc.
Internal loading
Total P: Is it the Best Predictor of Negative Impacts of Sediment P?
Most experts agree it is the best single parameter.
Most other measures like soluble P (DRP) and “bioavailable P” underestimate the effects of sediment P.
Conclusions
Particulate P in runoff from row crops contributes to eutrophication in lakes and streams.Labile P (bioreactive P) is can have a rapid impact on growth of algae.Non labile P can contribute to eutrophication over the long term.Total P is a reasonable parameter to estimate impact of P in runoff.Preventing erosion and transport to surface waters is very important in reducing impact.
Thank You for Your Attention
Questions?