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?