A
E
Bh
Bw
Phosphorus Issues and Protocol Development for Risk
Assessment in Florida Watersheds
V.D. Nair, W.G. Harris, D.A. Graetz, R.D. Rhue, M. Chrysostome, and L.R. Ellis
Soil and Water Science Department
University of Florida
February 27, 2008
A
The Suwannee River Basin (SRB)
E
Bh
Bw
•Complex hydrologic system
•Zones of surface and subsurface
(karst) drainage
•Cody scarp between the 2 zones
2
2
A
Springs of the Lower SRB
E
Bh
Bw
• High concentration of springs; haven for species; manatee,
gulf sturgeon
• Combination of sandy soils over limestone constitutes a
scenario of high vulnerability for ground- and surface water
contamination
Photo credit: David Hornsby
3
3
A
Water Quality Concerns - SRB
E
Bh
Bw
#
S
#
S
#
S
#
S
S
##
S
#
S
#
S
#
S
#
S#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
T
$
#
S
#
S
#
S
#
S
#
S
#
S
S
#
S#
#
S
T
$$
T
T
$
#
S
#
S
#
S
#
S
#
S
S
#
S #
#
S
T
$
# #
S
S
#
S #
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S#
S
#
S
#
S#
S
#
# #
SS
S
S
S#
##
S
#
S
#
S
#
S
#
S
#
S
T
$
#
S
TS
$
#
S
T# $
$
T#
#
S
S $
T$
T$
T
#
S
#
S
#
S
T
$
#
#
S
S
#
S $
T$
T
#
S
T#S$
#
#
S
S $
T
T$
#
S
T
$
T#S #S
$
#
S
T
#
S $
T$
#
T
S
#
S $
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
#
SS
#
S
#
S
#
S
#
S
T
$
T
$ $
T
#
S
#
S
S
#
S #
#
S
#
#
SS
S
#
S#
#
S
#
S#
S
#
S
#
S
#
S
#
S
#
S
#
S
T
$
#
S
#
S
#
S #
S
#
#S
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
SS
TS
$
##
#
S#
S
#
S
#
S
#
#S
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
Maximum Spring TP (ppb)
T
$
0 - 100
#
S
T
$
100 - 1000
T
$
> 1000
0 - 100
#
S
100 - 1000
#
S
#
S
#
S
#
S
#
#
S S
T
$
#
S
#
S
#
S
#
S
#
S #
S#
T
$
#
#
S
S
S
# #
S
S#
S
#
S
#
#
#
S
S
S#
S
#$
S
S#
##
T#S
S
S
Miocene not Present (Karst)
#
S
#
S
#
S
#
#
S
S#
S
#
S
#
S
#
S
#
S
#
S
N
Agriculture
Miocene Present
#
S #
S
#
S
#
S
#
S
W
#
S
E
S
##
S
S
5 0 5 Kilometers
#
S
#
S
#
S
> 1000
Water
#
S
#
S
S #
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
#
S
$#S
T
T$
$
T
#
S
#
S
#
S
#
S
Maximum Groundwater TP (ppb)
#
S
#
S
#
S
T$
$#S$
T
T#S
#
S
#
S
T
$
#
S
T
$
#
S
# #
S
SS
S #
##
T S
$
#
#
S$
TS #S
#
S
T
$
#
S
S#
T
$
#
S
#
S
#
S
#
S
#
S
#
S #
S
#
S
#
S
#
S
#
S
#
S
• Average spring P
concentrations generally in
0-100 ppb (0-0.1 mg P L-1 )
range
• Several instances where
maximum spring water P is
between 0.1 and 1.0 mg L-1
(Environmental concerns
about P are often based on
a P concentration of ≥0.1
mg P L-1).
Data: Suwannee River Water Management District
4
4
A
Lake Okeechobee Basin (LOB)
E
Bh
Bw
• 98% of P imported to the
watershed supports
agriculture (Fluck et al.,
1992)
Lake Okeechobee
5
– Fertilizers 73%
– Dairy feed 16%
5
A
Water Quality Concerns - LOB
E
Bh
Bw
• Four Priority Sub-basins
• 12% of watershed area
• 35% of P load
6
6
A
Phosphorus Transfer
E
Bh
Bw
Fertilizers, Animal wastes
Biosolids, Wastewaters
Uplands
[sink/source]
Wetlands &
Streams
[sink/source]
Lake
Lake [sink]
Okeechobee
Credit: K. Ramesh Reddy
7
7
A
Soils of Florida Watersheds
E
Bh
Bw
makes a big
difference in
P retention capacity
their presence or absence,
Sand grain coatings,
8
8
A
Development of a New Tool
•
•
•
•
E
Bh
Bw
Based on extractable P of soil
Also on P retention capacity of soil (related to Fe+Al)
New tool: “Safe” Soil P Storage Capacity (SPSC)
Calculations based on oxalate-extractable P, Fe and Al
Developed using soils of the SRB in Florida.
USDA-IFAFS
9
9
A
The Need for a New Protocol
E
Bh
Bw
• Low value of soil test P (STP) is not necessarily an
indicator of low environmental risk if P is added to a soil
• Some sandy soils, such as those of the LOB, could have
99% quartz sand in the upper horizons and negligible P
retention
• STP does not convey the amount of P that can be safely
added to a soil in an absolute sense
10
10
A
E
Water Soluble P (mg kg-1)
Water Soluble P (mg kg-1)
P Saturation Ratio (PSR)
25
(Ex = Extractable)
15
10
5
0
0
0.125
0.25
PSROX
Bw
• Ex-P/ [ExFe + ExAl]
Surface Horizon
Subsurface Horizon
20
Bh
0.375
0.5
• Change point ~ 0.10
• Confidence intervals: 0.05
– 0.15
• Threshold PSR: 0.15
25
Surface Horizon
Subsurface Horizon
20
15
10
5
0
0
.125
.025
.375 0.5 .625
PSR M1
.75 .875
Nair, V.D., K.M. Portier, D.A. Graetz, and
M.L. Walker. 2004. J. Environ. Qual. 33:107-113.
FDEP
11
11
A
The Approach – “Safe” Soil Phosphorus
Storage Capacity (SPSC)
E
Bh
Bw
⎡ Oxalate Fe Oxalate Al ⎤
* 31
+
SPSC = (0.15 – Soil PSR) * ⎢
⎥
56
27
⎦
⎣
-1
(mg P kg )
• SPSC can also be expressed in mmoles P kg-1, or kg P ha-1
• SPSC is additive; SPSC for horizons within a sandy soil can be
added providing a single value for a designated depth
Nair, V.D., and W.G. Harris. 2004. New Zealand J. Agric. Res. 47:491-497.
12
12
A
SPSC and Water Soluble P (WSP)
E
Bh
Bw
Initial SPSC (mg P kg -1)
300
200
Lab
100
0
-100
0
1
2
3
4
5
6
-200
-300
y = -65.89x - 25.41
R2 = 0.88
-400
-500
-600
Average leachate P concentration (mg L -1)
Column Study Set-up
•
400
400
300
300
SPSC (mg kg -1 )
200
200
Field
n = 604
100
100
00
-100
-1000
10
20
30
40
50
60
•
-200
-200
-300
-300
-400
-400
y =-11.6x
–0.9
-500
-500
R2 = 0.84
n = 147
•
-600
-600
WSP (mg--1)kg -1 )
Soil is a P sink when SPSC is
positive and a source when SPSC
is negative
Similar observation under field
conditions
95% of samples with positive
SPSC (soil is a P sink) indicate less
than 0.1 mg L-1 P in solution
Chrysostome, M, V.D. Nair, W.G. Harris, and R.D. Rhue. 2007. Soil Sci. Soc. Am. J. 71:1564–1569.
13
13
A
-1(mg
predicted
P )kg
SPSCSPSC
predicted
(mg P
) kg-1
Laboratory Verification of SPSC
20
0
-140 -120 -100 -80 -60 -40 -20-20
-40
y =20.98x
-8.96
- 8.96
-60
R2= 0.81
-80
-100
-120
-140
E
Bh
Bw
20
SPSC observed (mg P kg-1 )
SPSC observed -1
(mg
) P kg
Predicted PSR =
Initial Ox P + P gained or lost
Ox ( Fe + Al )
SPSCpredicted = (0.15 – predicted PSR) x Ox (Fe + Al) x 31
Chrysostome, M, V.D. Nair, W.G. Harris, and R.D. Rhue. 2007. Soil Sci. Soc. Am. J. 71:1564–1569.
14
14
A
E
Application: Soils of the SRB
Bh
Bw
High intensive dairy soils vs less P-impacted pasture soils
Soil P Storage Capacity, kg P ha- 1
Depth, cm
-2800 -1400
Depth, cm
-2800 -1400
0
0
20
40
60
80
100
120
1400
0
0
20
40
60
80
100
120
1400
2800
2800
4200
4200
5600
5600
• High dairy manure-impacted soils (top); negative SPSC in surface; soil is P source
• Low manure-impacted soils (bottom) have remaining capacity
Nair, V.D. and W.G. Harris. 2004. NZ J Agric. Res. 47:491-497.
15
15
A
E
Application: Soils of LOB
0
A
Depth (cm)
E
20
40
0
SPSC (kg ha- 1)
2000 3000 4000 5000
1000
A
A
EE
20
Depth (cm)
Spodosol Profile
Minimally impacted
80
Bw2
B ’h
-400 -200 0
0
0
Bw
6000
Bw1
100
Bh
Bw
a
Bh
Bh
60
Bh
200
A
AE
AE
20
40
40
60
60
60
400
600
800
1000
b
E1
E1
80
80
80
100
100
Impacted
EE2
2
Bh
Bh
Bw
Bw
FDACS
16
16
A
E
Applications
Bh
Bw
Tree-based vs tree-less pasture
Soil P Storage Capacity, kg P ha-1
Depth, cm
- 200
200
400
600
800
1000 1200 1400
0
200
400
600
800
1000 1200
0
10
20
30
40
50
60
70
80
90
100
- 200
Depth, cm
0
1400
0
10
20
30
40
50
60
70
80
90
100
Nair, V.D. P.K.R. Nair, R.S. Kalmbacher, and I.V. Ezenwa. 2007. Ecol. Eng. 29:192-199.
Michel, G.-A., V.D. Nair, P.K.R. Nair. 2007. Plant Soil. 297:267-276.
USDA/IFAFS, through the Center for Subtropical Agroforestry
17
17
A
Other Field Applications
E
Bh
Bw
• Predict reduction in P storage capacity of soil with time if
P loading known, such as in dairy spray fields
• Evaluate how much P can be safely applied to soil before
soil becomes an environmental risk if manure application
is based on N requirement of crop
• Use SPSC in P-Index as a replacement for STP
• Use SPSC to estimate how long a P loaded site would
continue to release P at environmentally elevated levels
• Identify suitable areas for animal-based agriculture by
selecting soils which have greater capacity to retain P
• Verify suitability of potential locations for the
construction of stormwater treatment areas.
18
18
A
Summary and Conclusions
E
Bh
Bw
• SPSC is a better indicator of environmental P risk than STP
• Provides estimate of amount of P that can be safely applied to
the volume (or mass) of soil represented by depth of
sampling
• SPSC is additive; may be added across depths to obtain P
storage within a soil profile
• SPSC is a P sink when positive and a source when negative
• Negative SPSC linearly related to WSP
• SPSC has potential to serve as indicator that balances
agronomic requirements with environmental risk
considerations
19
19
A
Acknowledgments
E
Bh
Bw
Funding agencies:
• USDA - Initiative for Future Agriculture and Food Systems (IFAFS)
– UF Soil and Water Science Department
– UF Center for Subtropical Agroforestry
• Florida Dept. of Environmental Protection (FDEP)
• Florida Dept. of Agriculture and Consumer Services (FDACS)
Personnel:
• Dawn Lucas, Greg Means, and Bill Reve for analytical and field
assistance
• Students: Daniel Herrera, Manohardeep Josan, Ravindra Ramnarine,
TJ Rew, Leighton Walker
• Faculty: Jerry Kidder, Rao Mylavarapu, Ken Portier
20
20
A
E
Bh
Bw
Thank you!
21
21