Institute of Food and Agricultural Sciences (IFAS)
Soil and Water Science Department
Baseline Soil Characterization of the Taylor Creek
Pilot Stormwater Treatment Area (STA) in
the Lake Okeechobee Watershed
Final Report
Submitted to:
South Florida Water Management District
3301 Gun Club Road
P.O. Box 24680
West Palm Beach, Florida 33416-4680
By:
K. R. Reddy, S. Grunwald, V. D. Nair, and Y. Wang
Wetland Biogeochemistry Laboratory
Soil and Water Science Department - IFAS
University of Florida
Gainesville, FL 32611-0510
Table of Contents
Table of Contents……………………………………………………
2
List of Figures ………………………………………………………..
3
List of Tables …………………………………………………………
5
Executive Summary…………………………………………………..
7
1. Introduction and Background………………………………………
9
1.1
1.2
Site description …………………………………………….
Project objectives ………………………………………….
2. Spatial Distribution of Phosphorus in Surface Soils………………
2.1
2.2
11
11
13
Soil sample and analysis …………………………………
Results and discussion …………………………………….
13
19
3. Fractionation of Soil Phosphorus …………………………………
50
3.1
3.2
Materials and methods ……………………………………
Results and discussion ……………………………………
50
53
4. Phosphorus Retention Properties of Soils…………………………
64
4.1
4.2
Materials and methods ……………………………………
Results and discussion ……………………………………
64
66
5. References ………………………………………………………..
73
6. Appendix ……………
75
2
List of Figures
Figure 1. Map showing landuse within Kissimmee and Taylor Creek hydrologic units of the
Okeechobee Drainage Basin
Figure 2. Taylor Creek Pilot STA located in north of Okeechobee, Florida. This two-celled
STA has a wetted treatment area of 169 acres.
Figure 3a. Sampling locations used to determine spatial distribution of soil properties
Figure 3b. Sampling locations in north and south sections of the wetland, used to determine
spatial distribution of soil properties.
Figure 4. Sampling locations of triplicate cores selected for phosphorus fractionation and
retention studies. At each location, soils were sampled at the 0-10 cm and 10-30 cm depths.
Figure 5. Spatial distribution of total phosphorus of soils collected from Taylor Creek STA
Figure 6. Spatial distribution of total inorganic phosphorus of soils collected from Taylor Creek
STA.
Figure 7. Spatial distribution of bulk density of soils collected from Taylor Creek STA.
Figure 8. Spatial distribution of pH of soils collected from Taylor Creek STA.
Figure 9. Spatial distribution of loss of ignition of soils collected from Taylor Creek STA.
Figure 10. Spatial distribution of total nitrogen of soils collected from Taylor Creek STA.
Figure 11. Spatial distribution of total carbon of soils collected from Taylor Creek STA.
Figure 12. Spatial distribution of water extractable phosphorus of soils collected from Taylor
Creek STA.
Figure 13. Spatial distribution of bioavailable phosphorus of soils collected from Taylor Creek
STA.
Figure 14. Spatial distribution of maximum phosphorus retention capacity of soils collected
from Taylor Creek STA, as estimated by the single point isotherm method.
Figure 15. Spatial distribution of 1M HCl-extractable calcium of soils collected from Taylor
Creek STA.
Figure 16. Spatial distribution of 1M HCl-extractable magnesium of soils collected from Taylor
Creek STA.
3
Figure 17. Spatial distribution of 1M HCl-extractable iron of soils collected from Taylor Creek
STA.
Figure 18. Spatial distribution of 1M HCl-extractable aluminum of soils collected from Taylor
Creek STA.
Figure 19. Phosphorus storage in soils collected from Taylor Creek STA. Stable pools (nonreactive P) was estimated by the difference between total soil phosphorus and inorganic
phosphorus extracted using 1 M HCl (Reddy et al., 1998b).
Figure 20. Sampling locations used to determine soil phosphorus forms and retention capacities.
Stations 20 and 37 were sampled in triplicate to determine the field variability within a sampling
location.
Figure 21. Soil phosphorus fractionation scheme used to determine labile and stable pools of
phosphorus (Reddy et al., 1998b).
Figure 22. Total P, inorganic P (measured using single extraction with 1 M HCl), and nonreactive P (not extracted with 1 M HCl) to include organic P and non-reactive inorganic P in
soils across the transect at Taylor Creek STA.
Figure 23. Distribution of labile P (KCl Pi), Fe/Al-P (NaOH Pi), and Ca/Mg Pi (HCl Pi)
fractions in soils collected along a transect in Taylor Creek STA.
Figure 24. Distribution of alkali extractable organic P, residual stable P, and total P of soils
collected along a transect in Taylor Creek STA.
Figure 25. A summary of labile and non-labile pools of phosphorus in soils collected along a
transect in Taylor Creek STA.
Figure 26. Relationship between Langmuir Smax and P sorbed at 100 mg P L-1 under (a) aerobic
and (b) anaerobic conditions.
Figure 27. Relationship between Langmuir Smax under aerobic and anaerobic conditions.
4
List of Tables
Table. 1. Site identification numbers (ID) of sampling locations with geographic coordinates.
Table 2b: Statistical properties of 0-10 cm soils (averaged replicates) [n: 52]
Table 2b: Statistical properties of 10-30 cm soils (averaged replicates) [n: 52]
Table 3. Range of 1 M HCl extractable metals in soils collected from Taylor Creek STA.
Table 4: Cross-validation results interpolations and spline parameters for 0-10 cm depth.
Table 5: Cross-validation results interpolations and spline parameters for 10-30 cm depth.
Table 6. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek
STA.
Table 7. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek
STA.
Table 8. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek
STA.
Table 9. Correlation matrix for soil variables measured at 0-10 cm and 10 – 30 cm depths.
Pearson correlation coefficients are significant at 0.05 level (>0.159) and 0.01 level (>0.208). n
=141. BD = Bulk density; LOI = Loss on ignition; TN = Total nitrogen; TC = Total carbon;
TPi = Total inorganic P; WEP = Water extractable P; M I-P = Mehlich I –extractable P; SPI =
Single point isotherm.
Table 10. Storage of labile and non-labile pools of phosphorus in Taylor Creek STA soils.
Table 11. Labile and non-labile pools of phosphorus expressed as percent of total phosphorus
stored in soils.
Table 12. Variability in selected soil properties measured on replicate soil cores from two
stations along a transect in Taylor Creek STA. Three cores were taken from each station.
Table 13. Total inorganic P recovered during repeated extractions with 1 M HCl.
Table 14a. Labile and non-labile pools of phosphorus in soils (0-10 cm depth) collected along a
transect in Taylor Creek STA.
Table 14b. Labile and non-labile pools of phosphorus in soils (10-30 cm depth) collected along
a transect in Taylor Creek STA.
5
Table 15. Variability in soil phosphorus forms measured on replicate soil cores from two
stations along a transect in Taylor Creek STA. Three cores were taken from each station.
Table 16. Relationship between soil phosphorus forms and total phosphorus in soils collected
along a transect in Taylor Creek STA. *Total inorganic P represents sum of inorganic P
extracted by alkali and acid. **Pi- [Me-TC] represents inorganic P complexed with metal and
organic matter
Table 17. Langmuir sorption parameters (P originally sorbed on the solid phase, So; equilibrium
P concentrations, EPC; the P retention maximum, Smax and the P bonding energy constant, k)
for the Taylor Creek STA soils at the nine selected locations under aerobic conditions.
Table 18. Langmuir sorption parameters (P originally sorbed on the solid phase, So; equilibrium
P concentrations, EPC; the P retention maximum, Smax and the P bonding energy constant, k)
for the Taylor Creek STA soils at the nine selected locations under anaerobic conditions.
Table 19. Correlation coefficients of aerobic P sorption parameters† with soil characteristics and
P fractionation data.
Table 20. Correlation coefficients of anaerobic P sorption parameters† with soil characteristics
and P fractionation data.
Table 21: Correlation coefficients of Langmuir parameters† under aerobic and anaerobic
conditions.
6
Executive Summary
Natural and constructed wetlands are used to treat nutrient enriched waters such as agricultural
drainage effluents, municipal, urban, and industrial waste waters. Constructed wetlands used as
buffers to retain nutrients and other contaminants are usually managed to improve their overall
performance, and to maintain expected water quality. The construction and operation of
Stormwater Treatment Areas (STAs) in the Lake Okeechobee Watershed (LOW) is a major
component of the Lake Okeechobee Protection Plan (LOPP). Required as part of Sec. 373.4595
(F.S.), the plan seeks to restore and protect Lake Okeechobee by achieving and maintaining
compliance with water quality standards in the lake and its tributaries, through an innovative
restoration program designed to reduce total phosphorus (TP) loads and implement long-term
solutions, in accordance to the lake’s Total Maximum Daily Load (TMDL).
The Taylor Creek and Nubbin Slough STAs are the first two pilot-scale STAs being
implemented north of the lake. Construction of the STAs was completed in July 2005 for Taylor
Creek, and October 2005 for Nubbin Slough. These prototype treatment wetlands will be
important for demonstrating effectiveness of the STA technology in the LOW area.
The overall objective of this work is to document the existing soil and vegetative conditions in
the Taylor Creek Pilot STA following construction but prior to operation. This work effort will
allow evaluation of changes in the physical, chemical, and biological functions of the STA over
time. This project has two main components. (1) collection and characterization of surface and
subsurface soils for various physical and chemical properties; and (2) characterization of the
existing vegetation and monitoring in the STA. This report focuses on soil characterization.
Specific objective of this portion of the study are to:
1. determine the spatial distribution of soil physico-chemical properties of soils.
2. identify relative partitioning of labile and non-labile pools of P in soils
3. determine the P retention capacity of soils.
The first objective was to determine the spatial distribution of soil physico-chemical properties
of soils. Spatial distribution of various soil properties showed high degree of variability. Total
P in the topsoil was dominant in the southern portion of the STA, whereas only few TP hotspots
remained with values > 500 mg kg-1 in 10-30 cm depth. High and low TP values in top and
subsoil were found in close proximity to each other. This high variability within the STA in TP
was confirmed by large ranges of 955 mg kg-1 (0-10 cm) and 873 mg kg-1 (0-30 cm),
respectively, and high standard deviations. Total inorganic P (TPi) hotspots in the topsoil
coincided with TP hotspot areas in the southern portion of the STA. Spatial distribution of TPi
was similar to the spatial distribution of HCl-extractable Al. Total P storage ranged from 4.3 to
44.7 g m-2 (mean value = 21.1 g m-2) in 0-10 cm soils and 3.1 to 90.3 g m-2 (mean value = 38.4 g
m-2) in 10-30 cm soils. Water extractable P, Mehlich 1 extractable P and TPi, respectively,
accounted for 0.18%, 4.2%, and 13% of the total P. A large proportion of P was stored in
organic P pool and as stable inorganic P.
The maximum P retention capacity of the soils was estimated using single point isotherms. This
estimate suggests that the soils are capable of adsorbing a maximum of 72 g P m-2. If one
7
assumes that the STA is loaded at a rate of 2 to 5 g P m-2 year-1, these soils potentially function
as sorption sinks for 14 to 36 years. Long term P retention in Taylor Creek STA depends not
only on soil P sorption capacity, but accretion of organic matter.
The second objective of the study was to identify relative partitioning of labile and non-labile
pools of P in soils. Labile Pi (as determined by Mehlich-1 extraction) accounted for 0.5% of the
total P. Total inorganic P accounted for <12% of the total P. A large proportion of soil
phosphorus is present in two major pools: alkali extractable organic P; and residual P stable
under both alkali and acid solutions. Approximately 40% of the total P is in stable pool, while
another 45% is present in organic P pool. Stability of these two pools under varying hydrologic
conditions needs further investigation.
The third objective of the study was to determine the P retention capacity soils. The Taylor
Creek STA soils exhibited P retention capacity within the top 30 cm. Significant correlation was
observed between P retention capacity and extractable Al and Ca. The P retention capacity of
the soils will not be adversely impacted during flooding of the soils as indicated by minimal
changes in Smax values under aerobic and anaerobic conditions.
Soils play a critical role during the initial establishment of STA. Once the STA starts accreting
organic matter and other particulate matter, the newly accreted material dictates the exchange of
P between soil and the water column. Soils of Taylor Creek STA have relatively high P
retention capacities. However, the P retention capacities are highly spatially variable. In certain
portions of STA where Al is high, P retention capacity is also high.
Additional studies are needed to determine the stability of P stored in these soils and determine
how P retention capacities change with period of operation of the STA.
8
1.0 Introduction
Natural and constructed wetlands are used to treat nutrient enriched waters such as agricultural
drainage effluents, municipal, urban, and industrial waste waters. Constructed wetlands used as
buffers to retain nutrients and other contaminants are usually managed to improve their overall
performance, and to maintain expected water quality. The extent of management required
depends upon the nutrient/contaminant retention capacity of the wetlands and the desired effluent
quality. Management scenarios can vary, depending on wetland type and hydraulic loading rate.
For example, small-scale wetlands can be managed effectively by altering hydraulic loading
rates or integrating them with a conventional treatment system, while large-scale systems can be
managed by controlling nutrient/contaminant loads.
Several biogeochemical processes regulate the retention of nutrients by wetlands. Some of these
processes include: accretion of particulate matter, uptake by vegetation, and chemical and
microbiological processes. Phosphorus (P) retention by soils and sediments, which store most of
the P relative to other ecosystem parts components include surface adsorption on minerals,
precipitation, microbial and immobilization. In treatment wetlands, such as the Stormwater
Treatment Areas (STAs) these processes may be combined into two distinct P retention pathways:
sorption and burial. Phosphorus sorption in sediments is defined as the removal of phosphate from
the soil solution to the solid phase, and includes both adsorption and precipitation reactions. When
plants and microbes die off, the P contained in cellular tissue may either recycle within the wetland,
or may be buried with refractory organic compounds.
The South Florida Water Management District (SFWMD) is using constructed wetlands
commonly known as STAs to abate P pollution. The STAs are now considered as key to
restoration of the Everglades. The construction and operation of STAs in the Lake Okeechobee
Watershed (LOW) is a major component of the Lake Okeechobee Protection Plan (LOPP).
Required as part of Sec. 373.4595 (F.S.), the plan seeks to restore and protect Lake Okeechobee
by achieving and maintaining compliance with water quality standards in the lake and its
tributaries, through an innovative restoration program designed to reduce total phosphorus (TP)
loads and implement long-term solutions, in accordance to the lake’s Total Maximum Daily
Load (TMDL).
9
Figure 1. Map showing landuse within Kissimmee and Taylor Creek hydrologic units of the
Okeechobee Drainage Basin
The Taylor Creek and Nubbin Slough STAs are the first two pilot-scale STAs being
implemented north of the lake. These prototype treatment wetlands will be important for
demonstrating effectiveness of the STA technology in the LOW area. Research and monitoring
data from these STAs will provide scientific basis for making management decisions to improve
design and operational guidance as additional STAs are planned in the watershed.
The design of the pilot STAs was based on TP removal performance data collected on the STAs
south of the lake in the Everglades Agricultural Area. Using the Everglades STA design model,
the average TP removal for Taylor Creek and Nubbin Slough STAs was estimated at 2.08 and
5.14 metric tons/year, respectively (Stanley Consultants Inc., 2000). There is some concern that
the Okeechobee STAs may perform differently from the Everglades STAs because of inherent
differences in water chemistry, soil and vegetation types, and expectations of effluent TP
concentrations. For this reason, research and management efforts and supplemental monitoring
beyond the normal permit monitoring requirements are being planned for these two pilot STAs to
optimize their performance. The primary goal of this project is to maximize effective removal of
TP in the STAs and minimize operational costs per pound of TP removed. The Research and
Management Plan developed in 2004 identified and prioritized thirteen supplemental research
and monitoring needs to address this goal (WSI, 2004).
10
The baseline characterization of the pilot STAs following construction but prior to operation is
the first project to be implemented under this plan. The current study documents soil and
vegetative conditions in the Taylor Creek Pilot STA.
1.1
Site description
The Taylor Creek Pilot STA is located about 1.4 miles north of the city of Okeechobee in central
Okeechobee County. It is bordered on the east by U.S. 441 and by Taylor Creek on the west.
The site is approximately 200 acres in total area and the STA has a treatment area of about 169
acres (Figure 1). The Taylor Creek Pilot STA is divided into two cells in series and is expected
to treat about 10% of the water flow rerouted from Taylor Creek. This would be accomplished
by allowing water to flow parallel to the creek for about 1.6 miles, before discharging back to
Taylor Creek, just upstream of US 441. The goal for water quality improvement is to reduce TP
loads to the maximum extent possible, given the limited area of the STA relative to the amount
of water in Taylor Creek. The Taylor Creek Pilot STA is expected to have a long-term average
TP removal rate of about 2.08 metric tons of TP per year.
1.2 Project objectives
The overall objective of this work is to document the existing soil and vegetative conditions in
the Taylor Creek Pilot STA following construction but prior to operation. This research effort
will allow evaluation of changes in the physical, chemical, and biological functions of the STA
over time.
This project has two main components. These include: (1) collection and characterization of
surface and subsurface soils for various physical and chemical properties; and (2)
characterization of the existing vegetation and monitoring in the STA.
This report presents the results of baseline characterization of surface and subsurface soils
including: (1) spatial distribution of soil phosphorus; (2) determination of labile and stable pools
of soil phosphorus; and (3) determination of phosphorus retention capacity.
11
Figure 2. Taylor Creek Pilot STA located in north of Okeechobee, Florida. This twocelled STA has a wetted treatment area of 169 acres.
12
2.0 Spatial Distribution of Phosphorus in Soils
The purpose of this task was to determine the spatial distribution of select physico-chemical
properties of soils in the STA.
2.1
Soil sampling and analysis
Soils are the dominant storage of TP in the STAs. In order to understand how this TP storage
changes through time, it is important to establish the baseline conditions for P in the STAs. This
task documents how the existing storage of TP in the Taylor Creek STA is partitioned into the
various inorganic and organic P forms. Soil samples within the STA footprint were collected
using grid sampling prior to system startup and operation (Figure 3). This sampling technique
allows for collection of equally spaced samples throughout the field and approximation of true
spatial variability of a number of soil nutrient levels.
In grid sampling, the field is divided with a grid using a field computer and GPS, with a sample
taken from the center of each grid section. A sampling density of one sample per four acres was
used. Soil samples were taken from 42 locations within the 169-acre treatment area of the
Taylor Creek STA at depth increments of 0-10 and 10-30 cm. Triplicate soil cores were
obtained at 9 stations (sampling stations # 9, 14, 17, 20, 34, 37, 42, 46, and 49, see Figure 4) to
determine the variability at the sampling station. Ten additional stations were added at random
to increase the spatial resolution. Core collection and handling followed the procedures outlined
in the FDEP SOPs (DEP-SOP-001/01, Revision Date: February 1, 2004).
Soil samples were transported to the UF-Wetland Biogeochemistry Laboratory and stored in a
refrigerator at 4 oC until analysis. Subsamples were air-dried for processing and analysis
13
Figure 3a. Sampling locations used to determine spatial distribution of soil properties.
14
Figure 3b. Sampling locations in north and south sections of the wetland, used to determine
spatial distribution of soil properties.
Northern section
Southern section
15
Table. 1. Site identification numbers (ID) of sampling locations with geographic coordinates.
Site ID
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Longitude
-80.83678
-80.83607
-80.83538
-80.83471
-80.83641
-80.83570
-80.83499
-80.83429
-80.83600
-80.83526
-80.83453
-80.83383
-80.83557
-80.83480
-80.83406
-80.83341
-80.83510
-80.83432
-80.83357
-80.83290
-80.83589
-80.83629
-80.83540
-80.83529
-80.83585
-80.83278
-80.83150
-80.83235
-80.83102
-80.83188
-80.83052
-80.83136
-80.82999
-80.83081
-80.82946
-80.83023
-80.82891
-80.82898
-80.82876
-80.82784
-80.82877
Latitude
27.31282
27.31298
27.31312
27.31329
27.31192
27.31209
27.31226
27.31245
27.31106
27.31125
27.31141
27.31160
27.31017
27.31036
27.31056
27.31074
27.30929
27.30945
27.30967
27.30987
27.31348
27.31281
27.31272
27.31328
27.31247
27.30677
27.30733
27.30581
27.30637
27.30487
27.30541
27.30393
27.30446
27.30297
27.30352
27.30206
27.30259
27.30064
27.30432
27.30361
27.29936
Site ID
41
42
43
44
45
46
47
48
49
50
51
16
Longitude
-80.82922
-80.83185
-80.83188
-80.83198
-80.83145
-80.83566
-80.82758
-80.83219
-80.83086
-80.83646
-80.83474
Latitude
27.30177
27.30655
27.30701
27.30562
27.30612
27.31271
27.30458
27.30655
27.30465
27.31239
27.31264
Soil samples were analyzed for pH, loss on ignition (LOI), bulk density, moisture content, and
extractable Fe, Al, Ca, and Mg, and total nitrogen. All samples were analyzed according to the
Wetland Biogeochemistry Laboratory (WBL) Standard Operational Procedure (SOP). The WBL
has NELAP certification E72949 by the Department of Health, Bureau of Laboratories. All
metals were analyzed by the UF-IFAS Analytical Research Laboratory, which is also NELAPcertified (E72850).
Figure 4. Sampling locations of triplicate cores selected for phosphorus fractionation and
retention studies. At each location, soils were sampled at the 0-10 cm and 10-30 cm depths.
Page 17
Soil pH: Soil pH was determined using soil:water ratio of 1:1 and glass electrode.
Bulk density (BD): A subsample of wet soil was dried at 70oC to determine dry weight and
moisture content. The bulk density was determined by calculating the dry weight of the sample
and dividing it by the volume of the corer.
Loss on ignition (LOI): Loss on ignition was determined by ignition a known amount of (ovendried soil) at 550oC. Loss in weight after ignition corresponds to organic matter content of the
soil. Results are expressed on percentage of over-dried basis.
Total carbon and nitrogen (TC and TN): Total carbon and nitrogen were determined on dried,
ground samples using Flash EA 1112 Elemental Analyzer (CE Instruments, Saddlebrook, NJ).
Results are expressed on a over-dried basis.
Total phosphorus (TP): Total P represents the amount of organic and inorganic P in soil
samples. Total phosphorus was determined by a combination of ignition at 550˚C and acid
digestion to dissolution convert organic P into inorganic P, followed by analysis for inorganic P
in digests by ascorbic acid techniques using an autoanalyzer (USEPA, 1993; Method 365.1).
HCl extractable inorganic phosphorus (HCl-TPi): Total inorganic P in soil was extracted
with 1 M HCl (soil to solution ratio = 1:50; 3 hours extraction time). Filtered solutions (0.45 μm
filter) are analyzed for P using an autoanalyzer (USEPA, 1993; Method 365.1).
Water extractable phosphorus (WEP): Water-soluble P concentrations provide an estimate of
the amount of P that is subject to vertical and/or lateral flow within the soil profile.
Water
extractable phosphorus in soil was extracted with deionized water using soil to water ratio of
1:10). Filtered solutions (0.45 μm filter) were analyzed for P using an autoanalyzer (USEPA,
1993; Method 365.1). .
Mehlich 1 extractable phosphorus (Mehlich 1-P): Mehlich 1-P provides an estimate of
bioavailable P in the soils (Kuo, 1996). Mehlich I extractable P was extracted with double acid
mixture ( 0.05 N HCl + 0.025 N H2SO4) using soil to solution ratio of 1:10. Filtered solutions
(0.45 μm filter) were analyzed for P using an autoanalyzer (USEPA, 1993; Method 365.1).
Single point phosphorus retention isotherm (SPI): Single point isotherms are used to
determine the maximum P retention capacity of soils. This procedure involves equilibrating a
known amount of air-dried soil with 0.01 M KCl solution spiked with 100 mg P/L at a 1:20 soil
to solution ratio on a mechanical shaker for 24 h at room temperature. The amount of P lost from
solution after 24h equilibration was used to determine the maximum P retention capacity of soils.
HCl-extractable metals: Extractable metals (Ca, Mg, Fe, and Al) in soils were extracted with 1
M HCl (soil to solution ratio = 1:50; 3 hours extraction time). Filtered solutions were analyzed
for metals using inductively coupled argon plasma spectrometry (ICAP) (USEPA, 1993; Method
200.7).
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Phosphorus storage in the soil: The mass of total phosphorus in the top 30 cm of the STA soils
was calculated using TP concentrations, bulk density, and soil depth. The mass of P that is
subject to leaching (water-soluble) and biovailable (Mehlich 1-P) was also calculated. The
amount of phosphorus stored was expressed on a mass per unit area basis.
Geostatistical analysis: Contour maps depicting spatial variability of the measured parameters
within the STA footprint were constructed.
We used completely regularized splines to
interpolate variables within the STA. Splines are a suite of interpolation methods that predict
values using a mathematical function that minimizes overall surface curvature, resulting in a
smooth surface that passes exactly through the input points (Burrough and McDonnell, 1998).
Splines are piecewise (local) fitting functions (ArcGIS, Environmental Systems Research
Institute - ESRI, Redlands, CA). We also explored the option of semivariogram analysis and
kriging (weighted interpolations) (Webster and Oliver, 2001). This type of geostatistics assumes
that observations measured close to each other are more similar than the observations taken
further apart. This can be captured using semivariograms, which have the ability to characterize
the spatial autocorrelation structure of a measured property. However, almost all variables
showed an erratic spatial structure (fitted model in the semivariogram) or poor nugget effect
indicating that not enough samples were collected to derive robust semivariograms. This is
consistent with recommendations given in the geostatistical literature. Chilès and Delfiner (1999)
recommend to use > 50 and Webster and Oliver (2001) > 100 (better > 144) observations,
respectively. Thus, we used splines to interpolate measured variables.
The spline parameters, mean error (ME) and root mean square error (RMSE) derived using
cross-validation are listed in Table 4. The number of points identifies the number of observations
used in the calculation of each interpolated cell. The more input points, the more each cell is
influenced by distant points and the smoother the output surface. The spline parameters were
optimized using a heuristic approach with the goal to minimize ME and RMSE. Accurate
predictions show a small ME and RMSE.
2.2 Results and discussion
Spatial distribution of various soil properties are presented in Figures 5 -18 and Tables 1-3.
Interpolated maps on the following pages show the spatial distribution patterns of variables.
Total P in the topsoil was high in the southern portion of the STA, whereas only few TP hotspots
with values > 500 mg kg-1 were identified in the 10-30 cm depth. High and low TP values in top
and subsoil were found in close proximity to each other. This high variability within the STA in
TP was confirmed by large ranges of 955 mg kg-1 (0-10 cm) and 873 mg kg-1 (10-30 cm),
respectively, and high standard deviations. Inorganic P (HCl-extractable P) hotspots in the
topsoil coincided with TP hotspot areas in the southern portion of the STA. As expected bulk
densities were higher in the subsoil with means and (maximum) of 0.9 (1.54) g cm-3 in 0-10 cm
and 1.27 (1.79) g cm-3 in 10-30 cm depth. Interesting to note is that areas high in topsoil TP
showed inverse spatial patterns on the bulk density maps with low values of < 0.4 g cm-3
characteristic of wetland soils. This has implications for phosphorus storage assessment across
the STA. The pH spatial patterns showed heterogeneous spatial patterns in top and subsoil with
means of 6.3 (0-10 cm) and 6.5 (10-30 cm). Total N showed homogeneous patterns in the top
and subsoil which was also found in other wetland studies (Bruland et al., 2006; Corstanje et al.,
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2006). Only few hotspots in topsoil TN were found in the northern part and most southern tip of
the STA with maximum of 26.2 g kg-1 (0-10 cm). Those few TN hotspot areas became
insignificant in the subsoil with maximum TN of 16.6 g kg-1. The LOI and total C maps showed
the same spatial patterns which was confirmatory. Although TC showed a wide range of values
from 3.8 to 406.5 g kg-1 (0-10 cm) and 1.9 to 209.3 g kg-1 (10-30 cm) the map was relatively
homogeneous with highest values in the southern section. The most contrasting spatial patterns
between top and subsoil were found for water extractable inorganic P and Mehlich P. The spatial
patterns of Ca, Mg, Fe and Al-bound phosphorus showed similar patterns for HCl-extractable Ca
and Mg in top and subsoil. Spatial patterns of Ca and Mg-bound P diverged from those of Fe and
Al-bound P. In particular, HCl-extractable Al showed the same spatial patterns as TP within the
STA.
Soils of STA exhibited a wide range of Ca, Mg, Fe, and Al concentrations (Table 3). Calcium
concentrations ranged from 720 to 23,219 mg kg-1 (mean value = 6,064 mg kg-1) in 0-10 cm soils
and 123 to 17,873 mg kg-1 (mean value = 4,520 mg kg-1 ) in 10-30 cm soils. High Ca levels
were associated with the accumulation of organic matter. South end of STA showed highest Ca
levels. Similar trends were observed for Mg and Fe. Extractable Al concentrations ranged from
141 to 5,926 mg kg-1 (mean value = 1,389 mg kg-1) in 0-10 cm soils, and 65 to 8,350 mg kg-1
(mean value = 1,825 mg kg-1) in 10-30 cm soils. High Al levels were associated with the
accumulation of organic matter.
Maximum P retention capacity of soils was estimated using single point isotherm (Tables 2a and
2b). The maximum P retention capacity values ranged from 21 to 804 mg kg-1 (mean value = 167
mg kg-1) in 0-10 cm soils and 17 to 1,358 mg kg-1 (mean value = 211 mg kg-1) in 10-30 cm soils.
Phosphorus retention capacity was significantly correlated with HCl-extractable Al, Fe, Mg, and
Ca (Table 9). Approximately, 77% of the variability in SPI was explained by HCl extractable
Al.
SPI = HCl-Al 0.143 + 41.4
n = 140; R2 = 0.769
Where: SPI represents maximum P retention capacity using single point isotherm.
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Table 2a: Statistical properties of 0-10 cm soils (averaged replicates) [n: 52]
BD
pH
-3
LOI
TN
TC
-1
TP
-1
HCl-TPi
-1
-1
M1-P
g cm
-
%
g kg
g kg
mg kg
mg kg
mg kg
mg kg
mg kg-1
Mean
0.90
6.33
16.1
5.84
69.3
311.4
39.0
0.94
13.6
168.6
SE of mean
0.47
0.09
2.07
0.67
10.2
32.8
5.3
0.16
1.5
20.6
Median
0.89
6.24
13.8
5.30
56.2
284.2
31.3
0.42
10.8
123.0
Mode
2.20a
6.52a
14.3a
1.05a
3.8a
47.3a
6.9
0.026a
1.7a
21.0a
Std.dev.
0.34
0.68
14.9
4.84
73.63
236.4
38.3
1.16
10.7
146.0
Skewness
-0.134
0.61
2.8
2.54
3.0
1.4
4.2
2.03
2.98
3.09
Kurtosis
-0.453
0.20
9.5
8.44
11.2
1.8
22.5
4.49
11.26
11.3
Range
1.39
3.01
80.7
25.2
402.7
955.3
254.5
5.08
59.7
782.7
Minimum
0.15
4.98
1.8
1.05
3.8
47.3
6.9
0.03
1.68
21.0
Maximum
1.54
7.99
82.5
26.22
406.5
1002.6
261.4
5.1
61.4
803.6
Page
21
6/26/2007
-1
SPI
Units
a: Multiple modes exist. The smallest value is shown.
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WEP
-1
Table 2b: Statistical properties of 10-30 cm soils (averaged replicates) [n: 52]
BD
pH
LOI
TN
TC
TP
HCl-TPi
WEP
M1-P
SPI
Units
g cm-3
-
%
g kg-1
g kg-1
mg kg-1
mg kg-1
mg kg-1
mg kg-1
mg kg-1
Mean
1.27
6.47
10.7
3.7
39.3
191.3
25.0
0.24
7.2
224.9
SE of mean
0.05
0.08
1.2
0.4
5.7
23.8
3.4
0.05
1.1
34.1
Median
1.40
6.50
6.9
2.6
21.9
121.2
14.3
0.12
4.0
145.1
Mode
0.14a
5.49a
6.9
0.9a
1.9a
17.2a
2.6a
0.02a
0.9
17.1
Std.dev.
0.36
0.60
9.0
2.9
41.0
171.4
24.8
0.37
7.7
246.0
Skewness
-0.98
-0.28
2.1
2.2
2.1
1.9
1.9
3.8
2.3
2.6
Kurtosis
0.62
-0.03
5.1
6.8
5.4
4.6
3.1
15.2
6.1
8.5
Range
1.65
2.82
46.5
15.7
207.3
873.6
105.1
1.94
38.0
1,340.9
Minimum
0.14
4.94
1.5
0.9
1.9
17.2
2.6
0.02
0.9
17.1
Maximum
1.79
7.76
48.0
16.6
209.3
890.7
107.6
1.95
38.9
1,358.0
a :Multiple modes exist. The smallest value is shown
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Table 3. Range of 1 M HCl extractable metals in soils collected from Taylor Creek STA.
0-10 cm depth
Ca
10-30 cm depth
Mg
-1
Fe
-1
Al
-1
Ca
-1
Mg
-1
Fe
-1
Al
Units
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg-1
Mean
6,450
550
869
1,500
5,348
426
829
1,828
SE of mean
631
49
63
146
785
40
52
187
Median
5,091
501
761
1,022
3,185
375
750
1,555
Mode
750a
44a
138a
141a
123a
11a
40a
65a
Std.dev.
4,639
355
455
1,052
5,711
289
380
1,360
Skewness
1.6
1.5
3.0
2.6
3.2
1.9
1.3
2.5
Kurtosis
3.0
2.7
12.6
8.4
14.3
4.8
2.5
9.7
Range
22,468
1,645
3,007
5.785
35,294
1,505
2,004
8,285
Minimum
750
44
138
141
123
11
40
65
Maximum
23,219
1,689
3,145
5.926
35,417
1,516
2,045
8,350
a :Multiple modes exist. The smallest value is shown
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-1
Results indicate that RMSEs were relatively high for all variables indicating the large uncertainty
of predictions. This was due to the limited sampling size of 52. For example, the RMSE for TP
(0-10 cm) was relatively high with 239 mg kg-1 given a measured TP range of 955 mg kg-1 and
mean of 311 mg kg-1. The ME indicates which variables were under- and which ones were over
predicted. Overall, most variables in the topsoil, except for TN, TP, SPI, and HCl-Al, were
slightly under predicted (Table 3). The accuracy for all variables in the subsoil (10-30 cm) was
higher indicated by a lower RMSE when compared to the topsoil (0-10 cm) except for SPI and
HCl-Al (Table 3 and 4). Interestingly, most variables in the subsoil (except for TPi, Mehlich I P,
SPI and HCl-Fe) were slightly over predicted (Table 4 and 5).
Interpolated maps on the following pages show the spatial distribution patterns of variables. The
TP in the topsoil was dominant in the northern part of the STA, whereas these patterns shifted
and relatively high rates of TP were found in the subsoil (10-30 cm depth). Total inorganic P in
0-10 cm showed a very uneven spatial distribution that peaked at only few locations up to a
value of 1003 mg kg-1. Values jumped from very high TPi to extremely low TPi in the topsoil
indicating that soils are extremely variable in inorganic P.
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Table 4: Cross-validation results interpolations and spline parameters for 0-10 cm depth.
Variable
Spline
Parameters
Mean Error
RMSE
Moisture (%)
10(4)1
- 0.232
15.53
BD (g/cm3)
10(4)1
- 0.1269
0.3367
- 0.008467
0.6983
1
pH
10(4)
LOI (%)
12(7)1
- 0.1552
15.48
TN (g kg-1)
10(4)1
0.04441
7.05
TC (g kg-1)
10(7)1
- 1.132
75.61
TP (mg kg-1)
12(4)1
1.067
239.1
-1
1
- 0.8871
282.2
TPi (mg kg )
10(7)
Water Extractable P (mg)
12(7)1
- 0.00767
1.067
Mehlich I P (mg kg-1)
12(7)1
- 0.01961
10.52
SPI (mg kg-1)
12(7)1
0.2091
149
HCl-Ca (g kg-1)
10(7)1
- 78.45
47.25
HCl-Mg (mg kg-1)
10(7)1
- 4.962
366.5
HCl-Fe (mg kg-1)
10(7)1
-11.4
500.4
HCl-Al (mg kg-1)
10(7)1
1.558
933
1
Neighbors included; in parenthesis: minimum of neighbors
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Table 5: Cross-validation results interpolations and spline parameters for 10-30 cm depth.
Variable
Spline
Parameters
Mean Error
RMSE
Moisture (%)
10(4)1
0.04315
10.11
BD (g/cm3)
10(4)1
0.0008794
0.3372
12(7)
1
0.009733
0.5886
12(4)
1
0.06301
7.773
12(4)
1
0.04377
2.29
TC (g kg )
12(4)
1
0.3908
32.51
TP (mg kg-1)
12(4)1
5.095
148.9
-1
1
- 0.397
20.19
1
pH
LOI (%)
-1
TN (g kg )
-1
TPi (mg kg )
10(7)
Water Extractable P (mg)
10(4)
0.001243
0.3934
Mehlich I P (mg kg-1)
10(4)1
-0.3392
7.694
12(4)
1
-1.259
234.7
12(4)
1
1.107
30.23
12(4)
1
1.028
287.9
HCl-Fe (mg kg )
10(7)
1
- 3.001
390.3
HCl-Al (mg kg-1)
12(4)1
2.215
1289
-1
SPI (mg kg )
-1
HCl-Ca (g kg )
-1
HCl-Mg (mg kg )
-1
1
Neighbors included; in parenthesis: minimum of neighbors
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Figure 5. Spatial distribution of total phosphorus of soils collected from Taylor Creek STA
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Page
27
6/26/2007
Figure 6. Spatial distribution of total inorganic phosphorus of soils collected from Taylor Creek STA.
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28
6/26/2007
Figure 7. Spatial distribution of bulk density of soils collected from Taylor Creek STA.
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29
6/26/2007
Figure 8. Spatial distribution of pH of soils collected from Taylor Creek STA.
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30
6/26/2007
Figure 9. Spatial distribution of loss of ignition of soils collected from Taylor Creek STA.
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31
6/26/2007
Figure 10. Spatial distribution of total nitrogen of soils collected from Taylor Creek STA.
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Page
32
6/26/2007
Figure
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11.
Spatial
distribution
Page
of
total
carbon
33
of
soils
collected
6/26/2007
from
Taylor
Creek
STA.
Water extractable inorganic
phosphorus (mg/kg) 0-10 cm
Water extractable inorganic
phosphorus (mg/kg) 10-30 cm
Figure 12. Spatial distribution of water extractable phosphorus of soils collected from Taylor Creek STA.
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Page
34
6/26/2007
Figure 13. Spatial distribution of bioavailable phosphorus of soils collected from Taylor Creek STA.
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Page
35
6/26/2007
Figure 14. Spatial distribution of maximum phosphorus retention capacity of soils collected from Taylor Creek STA, as estimated by
the single point isotherm method.
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Page
36
6/26/2007
Figure 15. Spatial distribution of 1M HCl-extractable calcium of soils collected from Taylor Creek STA.
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Page
37
6/26/2007
Figure 16. Spatial distribution of 1M HCl-extractable magnesium of soils collected from Taylor Creek STA.
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Page
38
6/26/2007
Figure 17. Spatial distribution of 1M HCl-extractable iron of soils collected from Taylor Creek STA.
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Page
39
6/26/2007
Figure 18. Spatial distribution of 1M HCl-extractable aluminum of soils collected from Taylor Creek STA.
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Page
40
6/26/2007
Table 6. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek
STA.
Site
Depth
Cm
9
0-10
14
0-10
17
0-10
20
0-10
34
0-10
37
0-10
42
0-10
46
0-10
49
0-10
9
10-30
14
10-30
17
10-30
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Moisture
%
BD
g cm-3
pH
LOI
%
TN
g/kg
TC
g/kg
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
35.0
0.8
2.4
23.5
1.6
6.7
15.9
1.8
11.6
3.9
0.8
20.8
8.5
1.0
12.1
23.9
1.4
5.7
10.0
2.6
26.3
25.0
10.2
40.8
26.0
0.3
1.0
0.4
0.0
3.1
0.8
0.0
4.2
0.9
0.1
9.2
1.5
0.3
17.9
1.5
0.1
4.1
0.7
0.1
10.0
1.0
0.1
7.8
0.6
0.2
42.6
0.9
0.1
13.7
5.6
0.2
2.9
6.8
0.1
1.5
6.0
0.1
1.7
6.5
0.4
6.2
8.0
0.1
1.4
6.0
0.0
0.4
6.4
0.1
1.3
5.8
0.3
4.9
5.7
0.2
3.6
28.7
3.5
12.2
14.4
1.2
8.3
13.6
2.2
16.0
5.6
0.3
4.9
1.8
0.3
16.6
25.0
3.3
13.2
6.3
1.8
28.2
23.3
8.3
35.7
16.2
1.4
8.8
10.2
1.1
10.4
5.4
0.3
6.3
5.5
1.1
20.0
2.4
0.1
2.4
1.3
0.2
16.7
8.5
1.5
17.4
2.3
0.2
8.0
8.8
3.5
40.5
5.8
0.4
7.0
121.0
11.3
9.4
54.8
0.7
1.3
58.4
11.5
19.7
19.3
0.4
1.8
3.8
2.4
63.3
111.1
20.5
18.4
17.7
4.1
23.3
101.2
49.0
48.4
64.5
7.5
11.7
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
19.2
3.0
15.9
14.8
1.6
10.7
15.2
0.8
5.4
1.3
0.1
8.7
1.6
0.1
4.0
1.4
0.0
2.6
6.3
0.1
1.8
7.1
0.1
1.8
6.5
0.2
3.8
9.4
1.6
16.9
5.8
0.8
13.1
6.9
1.0
13.9
3.7
0.6
15.3
2.1
0.1
6.5
2.5
0.3
12.0
36.8
6.2
17.0
15.5
3.0
19.3
21.8
2.7
12.5
Page41
6/26/2007
Table 6. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek
STA.
Site
Depth
Cm
20
10-30
34
10-30
37
10-30
42
10-30
46
10-30
49
10-30
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Moisture
%
BD
g cm-3
pH
LOI
%
TN
g/kg
TC
g/kg
7.7
0.9
12.0
11.2
0.5
4.5
16.5
1.4
8.7
34.0
4.2
12.5
13.0
0.8
6.1
21.8
2.6
11.7
1.4
0.1
6.8
1.7
0.1
5.4
1.2
0.2
13.5
1.0
0.1
14.2
1.5
0.0
3.1
1.4
0.1
9.0
6.5
0.3
4.5
7.5
0.2
2.3
6.3
0.2
2.5
6.3
0.1
1.8
7.0
0.3
4.7
6.5
0.2
3.1
5.3
0.8
14.4
1.5
0.0
2.1
9.9
1.3
13.1
20.2
2.7
13.4
6.5
0.5
7.5
8.6
2.0
23.4
2.3
0.3
12.6
0.9
0.1
10.7
3.5
0.4
12.2
7.1
1.1
15.9
2.5
0.2
7.3
2.9
0.5
17.1
16.2
2.4
14.9
1.9
0.4
21.8
38.7
7.1
18.3
84.9
16.4
19.3
22.1
1.7
7.5
26.5
6.6
25.0
Data on variability among replicate cores at select stations is shown in Tables 6 and 7. For most
of the parameters measured, coefficient of variation was less than 20% among replicate cores.
However, for labile pools of phosphorus such as WEP and Mehlich 1- extractable P, a much
higher variability was observed.
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Table 7. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek
STA.
Site
Depth
Cm
9
0-10
14
0-10
17
0-10
20
0-10
34
0-10
37
0-10
42
0-10
46
0-10
49
0-10
9
10-30
14
10-30
17
10-30
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TP
mg/kg
TPi
mg/kg
TPo
mg/kg
WEP-P
mg/kg
M I-P
mg/kg
SPI
mg/kg
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
536.5
56.7
10.6
239.2
27.3
11.4
284.4
60.5
21.3
130.9
6.4
4.9
47.3
16.6
35.1
563.5
63.4
11.3
107.4
21.6
20.1
521.3
169.3
32.5
300.5
32.8
10.9
47.0
4.2
9.0
27.9
2.9
10.4
20.1
2.9
14.6
16.9
2.5
14.7
6.9
0.7
10.6
31.2
3.7
11.9
13.2
2.6
19.9
37.1
18.3
49.4
24.8
4.6
18.6
489.5
60.5
12.4
211.3
27.2
12.9
264.4
57.6
21.8
114.1
8.2
7.2
40.3
15.9
39.3
532.3
60.1
11.3
94.2
19.0
20.1
484.2
151.2
31.2
275.6
28.7
10.4
2.1
0.4
18.7
0.5
0.3
63.3
0.7
0.2
26.2
0.2
0.0
10.9
0.1
0.0
42.0
3.0
1.7
56.2
0.1
0.0
24.0
0.9
0.6
65.4
0.4
0.1
32.9
17.6
1.6
8.9
16.4
2.5
15.3
9.1
2.3
24.9
4.8
0.5
10.1
2.6
0.7
28.3
10.9
3.3
30.3
5.8
2.0
33.7
12.3
4.8
38.8
7.2
2.4
33.7
191.1
31.0
16.2
192.1
5.6
2.9
158.1
18.8
11.9
183.8
40.5
22.0
51.6
9.9
19.1
215.9
61.7
28.6
130.7
4.0
3.1
112.1
35.1
31.3
329.1
81.2
24.7
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
186.9
32.5
17.4
84.7
13.5
15.9
111.4
11.2
10.0
17.8
1.0
5.6
9.7
0.8
7.9
8.1
0.5
6.7
169.1
32.0
18.9
75.0
13.6
18.1
103.4
10.7
10.3
0.1
0.0
17.9
0.0
0.0
1.6
0.1
0.0
20.6
5.8
0.3
5.8
3.8
1.1
28.9
1.9
0.3
15.6
145.7
19.4
13.3
121.9
31.6
25.9
143.4
27.0
18.8
Page43
6/26/2007
Table 7. Variability in soil properties on triplicate soil cores along a transect in Taylor Creek .
STA
Site
Depth
Cm
20
10-30
34
10-30
37
10-30
42
10-30
46
10-30
49
10-30
krr
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
TP
mg/kg
TPi
mg/kg
TPo
mg/kg
WEP-P
mg/kg
M I-P
mg/kg
SPI
mg/kg
105.9
17.9
16.9
22.5
3.2
14.4
217.0
26.4
12.2
382.5
52.6
13.8
129.8
13.7
10.6
135.0
39.1
29.0
13.9
2.4
17.4
9.5
1.8
19.2
14.6
2.9
19.7
41.4
4.2
10.2
9.9
2.1
21.6
10.3
1.6
15.7
91.9
18.8
20.5
13.0
2.4
18.2
202.4
23.6
11.6
341.1
49.0
14.4
119.9
11.6
9.7
124.7
37.7
30.2
0.1
0.1
60.6
0.1
0.0
16.5
0.3
0.1
20.5
0.2
0.2
78.9
0.1
0.0
20.3
0.0
0.0
25.1
4.0
1.5
35.9
3.8
2.6
68.8
3.7
1.4
39.2
13.6
4.7
34.8
2.4
0.6
27.0
1.9
0.7
35.8
154.9
37.1
23.9
32.8
11.7
35.7
227.8
25.9
11.4
429.3
106.9
24.9
166.2
5.1
3.1
129.0
44.6
34.6
Page44
6/26/2007
Table 8. Variability in soil properties on triplicate soil cores along a transect in Taylor
Creek STA.
Site
Depth
Cm
9
0-10
14
0-10
17
0-10
20
0-10
34
0-10
37
0-10
42
0-10
46
0-10
49
0-10
9
10-30
14
10-30
17
10-30
krr
HCl-Ca
mg/kg
HCl-Mg
mg/kg
HCl-Fe
mg/kg
HCl-Al
mg/kg
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
7057
644
9
7074
597
8
4689
579
12
2138
342
16
1150
372
32
9022
981
11
3468
750
22
4256
1170
27
8250
1283
16
1128
278
25
653
117
18
490
38
8
293
4
1
44
17
39
918
50
5
273
25
9
570
178
31
660
47
7
1025
218
21
896
78
9
591
55
9
794
53
7
344
89
26
547
102
19
645
49
8
728
47
6
839
10
1
754
66
9
818
41
5
974
54
6
914
73
8
698
181
26
1584
490
31
1085
145
13
831
52
6
1962
106
5
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
3944
555
14
3075
486
16
3101
223
7
459
69
15
296
17
6
372
10
3
750
96
13
684
49
7
620
53
9
957
53
6
1395
325
23
1451
357
25
Page45
6/26/2007
Table 8. Variability in soil properties on triplicate soil cores along a transect in Taylor
Creek STA
Site
Depth
Cm
20
10-30
34
10-30
37
10-30
42
10-30
46
10-30
49
10-30
krr
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
Mean
SD
CV (%)
HCl-Ca
mg/kg
HCl-Mg
mg/kg
HCl-Fe
mg/kg
HCl-Al
mg/kg
2061
17
1
634
102
16
4224
164
4
9963
1522
15
2776
208
8
4384
704
16
317
25
8
87
8
10
629
24
4
592
51
9
390
19
5
409
60
15
937
123
13
706
63
9
564
123
22
801
99
12
918
43
5
583
38
6
1517
410
27
1834
171
9
2371
148
6
2974
435
15
1358
274
20
1981
72
4
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6/26/2007
Table 9. Correlation matrix for soil variables measured at 0-10 cm and 10 – 30 cm depths. Pearson correlation coefficients are
significant at 0.05 level (>0.159) and 0.01 level (>0.208). n =141. BD = Bulk density; LOI = Loss on ignition; TN = Total nitrogen;
TC = Total carbon; TPi = Total inorganic P; WEP = Water extractable P; M I-P = Mehlich I –extractable P; SPI = Single point
isotherm.
pH
LOI
TN
TC
TP
TPi
WEP
M I-P
SPI
HCl-Ca
HCl-Mg
HCl-Fe
HCl-Al
krr
BD
0.55
0.77
0.79
0.77
0.82
0.52
0.52
0.46
0.35
0.55
0.69
0.45
0.20
pH
LOI
TN
TC
TP
TPi
WEP
M I-P
SPI
HCl- HCl- HClCa
Mg
Fe
-0.51
-0.53
-0.52
-0.51
-0.22
-0.37
-0.09
-0.21
-0.13
-0.45
-0.30
-0.05
0.99
0.99
0.93
0.60
0.60
0.40
0.43
0.70
0.84
0.70
0.32
0.99
0.93
0.57
0.62
0.41
0.37
0.67
0.82
0.66
0.25
0.91
0.57
0.64
0.40
0.36
0.68
0.81
0.67
0.25
0.69
0.55
0.48
0.56
0.65
0.87
0.65
0.44
0.29
0.81
0.58
0.56
0.61
0.65
0.52
0.40
-0.09
0.28
0.44
0.21
-0.19
0.21
0.35
0.35
0.32
0.15
0.48
0.58
0.57
0.88
0.62
0.52
0.42
Page
47
6/26/2007
0.65
0.49
0.47
Phosphorus Storage in Soils
Table 10. Storage of labile and non-labile pools of phosphorus in Taylor Creek STA soils.
Phosphorus pools
Total Phosphorus
Average
Minimum
Maximum
HCl-extractable P
Average
Minimum
Maximum
Mehlich I- P
Average
Minimum
Maximum
Water extractable P
Average
Minimum
Maximum
Stable Pool P
Average
Minimum
Maximum
SPI-Pmax
Average
Minimum
Maximum
0 – 10 cm
g P m-2
10 – 30 cm
g P m-2
0 – 30 cm
g P m-2
21.1
4.3
44.7
38.4
3.1
90.3
59.5
7.4
135.0
2.67
0.92
14.7
4.82
0.19
17.5
7.49
1.11
32.2
1.01
0.23
6.82
1.49
0.05
9.13
2.50
0.28
16.0
0.06
0.003
0.30
0.05
0.01
0.58
0.11
0.013
0.88
18.5
3.41
37.2
33.5
2.87
81.0
52.0
6.28
118.2
14.0
1.46
43.5
45.4
3.31
196.5
59.4
4.77
240
Table 11. Labile and non-labile pools of phosphorus expressed as percent of total phosphorus
stored in soils.
Phosphorus pools
Water extractable P
Mehlich 1-P
HCl extractable P
Stable P
krr
0 – 10 cm
% of TP
0.3
5.1
12.7
87.9
10 – 30 cm
% of TP
0.13
3.9
12.6
87.2
Page48
0 – 30 cm
% of TP
0.18
4.2
12.6
87.4
6/26/2007
Figure 19. Phosphorus storage in soils collected from Taylor Creek STA. Stable pools (nonreactive P) was estimated by the difference between total soil phosphorus and inorganic
phosphorus extracted using 1 M HCl (Reddy et al., 1998b).
Data on P storage in various pools are presented in Tables 10 and 11 and Fig. 19. Total P storage
ranged from 4.3 to 44.7 g m-2 (mean value = 21.1 g m-2) in 0-10 cm soils and 3.1 to 90.3 g m-2
(mean value = 38.4 g m-2) in 10-30 cm soils. Water extractable P accounted for 0.18% of total P
storage, while Mehlich 1 -extractable accounted for 4.2% of total P, and total inorganic P
accounted for 13% of the total P. A large proportion of P was stored in organic P pool and as
stable inorganic P. Stable inorganic P is operationally defined as Fe, Al, Ca, and Mg-bound P
not extracted with 1 M HCl.
The maximum P retention capacity of soils was estimated using single point isotherm. This
estimate suggests that the soils are capable of adsorbing a maximum of 72 g P m-2. If one
assumes that the STA is loaded at a rate of 2 to 5 g P m-2 year-1, these soils represent a P
retention expectancy of 14 to 36 years. Long term P retention in Taylor Creek STA depends not
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only on soil P sorption capacity, but the physico-chemical characteristics of newly accreted
organic and mineral matter.
3.0. Fractionation of Soil Phosphorus into Organic (Po) and Inorganic (Pi) Forms
Mobility and reactivity of P in wetlands under variable hydrologic conditions are controlled by
the chemical composition of P in soil and water, relative sizes of various P pools in the soil,
interactions of soluble fractions with solid phases, and decomposition of soil organic matter.
Phosphorus is present in both organic and inorganic forms, with organic forms present as the
dominant pool in many wetlands. Forms of inorganic P (Pi) in soils are usually determined by
sequential extractions with acid and alkaline reagents, as proposed by Chang and Jackson (1957)
and later modified by others for soils and sediments (Psenner et al., 1988; Ruttenburg,
1992; Olila et al., 1994). A modification of this scheme has been adopted for wetland soils
(Qualls and Richardson, 1995; Reddy et al., 1995, 1998b). These schemes typically identify P in
the following groups: (i) labile Pi loosely adsorbed; (ii) Pi associated with Fe and Al; (iii)
Pi associated with Ca and Mg; (iv) alkali-extractable organic P (fulvic- and humic-bound P); and
(v) residual organic P. In soils with high levels of organic P such as those impacted organic
waste loading, neutral salt extractions may include labile organic P. Forms of organic P (Po)
have also been distinguished using acid and alkaline extractions of soils. The objective of this
study was to quantify the labile and stable pools of phosphorus in soils collected from Taylor
Creek STA.
3.1 Materials and methods
The forms in which the existing P is held in the soils was evaluated by the Reddy et al., (1998a)
procedure. Total inorganic P was determined by extraction with 1.0M HCl and organic P
calculated as the difference between total P and inorganic P. Inorganic P was separated
sequentially into loosely bound P, Fe/Al-P, and Ca-P by extractions with 1M KCl, 0.1M NaOH
and 0.5M HCl . In addition, alkali extractable P was analyzed for organic P. All fractionations
were done on 26 samples (13 for each depth, 9 stations and 2 stations with triplicates) at the
selected sampling locations (Figure 20). The sampling scheme used is given in Figure 21.
Fractionation data for all samples on a weight basis is given in Appendix 1a and on a volume
basis in Appendix 1b.
Potassium Chloride extractable P (labile P): Phosphorus in field-wet soil (0.2 g dry-weight
equivalent) was extracted with 1 M KC1 solutions, with the P extracted representing the readily
available pool of P (KCl-Pi). Air-dried soils should not be used to determine labile pools, as
drying may affect the lability of P through oxidation of organic P. Soil suspensions were
equilibrated for a period of 2 h by continuously shaking on a mechanical shaker, followed by
centrifugation at 4066 x g for 10 min. The supernatant solution was filtered through a 0.45 μm
membrane filter. Solutions were analyzed for soluble reactive P (SRP) (U.S. EPA, 1993,
Method 365.2). The residual soil was used for the following sequential extraction.
Alkali (NaOH) extractable P: The residual soil was then treated with 0.1 M NaOH and
allowed to equilibrate for a period of 17 h on a mechanical shaker, followed by centrifugation
and filtration as described above. Filtered solutions were analyzed for both SRP and a separate
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6/26/2007
portion extract is digested and for TP (U.S. EPA, 1993, Method 365.1). These fractions are
referred to as NaOH-Pi and NaOH-TP, respectively, with NaOH-Pi considered to represent Feand Al-bound P. Extraction with 0.1 M NaOH also removes the P associated with humic and
fulvic acids. The difference between NaOH-TP and NaOH-Pi was assumed to be organic P
(NaOH-Po ) associated with fulvic and humic acids.
Acid (0.5M HCl) extractable P: Residual soil obtained from the above extraction was treated
with 0.5 M HCl and allowed to equilibrate for a period of 24 h followed by centrifugation and
filtration as described above. The filtered solutions were analyzed for SRP using an autoanalyzer
(U.S. EPA, 1993, Method 365.1). The HCl-Pi fraction is assumed to represent Ca- and Mgbound P.
Residual P and Total P: The residue from the above extraction was combusted at 550°C for 4
h. The ash was dissolved in 6 M HCl followed by analysis using an autoanalyzer (Andersen,
1976; U.S. EPA, 1993, Method 365.1). A similar method was also used to analyze total P of the
original soil.
Acid (1 M HCl) extractable P and Cations: Oven-dry soil samples were extracted with 1 M
HCl (soil/solution ratio of 1:50, w/v basis) after a 3-h equilibration, followed by centrifugation
and filtration, as described above. Filtered solutions were analyzed for P using the procedures
described above, and for Ca, Mg, Fe, and Al using inductively coupled argon plasma
spectrometry (U.S. EPA, 1993, Method 200.7).
All samples were analyzed according to the specifications described in the Wetland
Biogeochemistry Laboratory (WBL) Standard Operating Procedures (SOP). The WBL is
certified by the Department of Health, Bureau of Laboratories for NELAP certification
(E72949). All metals were analyzed by the UF-IFAS Analytical Research Laboratory. This lab
is certified by NELAP (E72850).
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Figure 20. Sampling locations used to determine soil phosphorus forms and retention
capacities. Stations 20 and 37 were sampled in triplicate to determine the field variability
within a sampling location.
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6/26/2007
Soi
1.0 M KCL extraction [2hr] hr]
Readily available P [Pi]
Residu
0.1 M NaO
extraction [17hr]
[TP]
[SRP
Alkali extractable
organic P [ Po]
[TP-SRP]]
Fe/A -bound P [Pi ]
Residu
0.5 M HC extraction [24hr]
[SRP]
Ca/Mg-bound P [Pi ]
Residu
Ashing [TP]
Residual P [Po ]
I
Figure 21. Soil phosphorus fractionation scheme used to determine labile and stable pools
of phosphorus (Reddy et al., 1998b).
3.2 Results and discussion
Total Phosphorus concentrations in soil samples across the STA Transect.
The total P (TP) concentrations within the STA transect at the 0-10 cm and 10-30 cm depths are
given in Figure 22. Stations #20 and 37 were sampled in triplicate. Data for all replicates are
plotted in Figure 22 and presented in Table 12. Total P concentrations in surface soils ranged
from 28 to 562 mg kg-1 with high values observed in stations at the south end of the transect. The
high TP concentrations are a reflection of lower bulk densities. Bulk densities ranged from 0.5
to 1.5 g cm-3. Lowest bulk density values in surface soil was observed at Station # 9, but TP
concentrations were not highest at this station. Highest TP concentrations were observed at
Station #34, where bulk density of soils was 0.65 g cm-3. Lowest concentrations were observed
at Station #34; total P concentrations in subsurface soils ranged from 19 to 242 mg kg-1.
Similarly, lowest TP concentrations were noted at Station #34. Total P concentration was higher
in surface soils than in subsurface soils.
Distribution of inorganic phosphorus across the STA transect: Distribution of inorganic P (as
determined by a single extraction with 1.0M HCl) within the STA transect at the 0-10 cm and
krr
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6/26/2007
700
0 -1 0 c m
600
T o ta l P
10 - 30 cm
500
R e p lic a te
c o res
400
300
200
R e p lic a te
c o res
Phosphorus [mg kg-1]
100
0
60
In o rg a n ic P
50
40
30
R e p lic a te
c o res
R e p lic a te
c o res
20
10
0
700
N o n -r e a c ti v e PR e p lic a te
600
c o res
500
400
300
R e p lic a te
c o res
200
100
0
20
20
20 46
9
14
17
42
49 34
37
37
37
S ta tio ns a lo ng the T ra ns e c t
Figure 22. Total P, inorganic P (measured using single extraction with 1 M HCl), and nonreactive P (not extracted with 1 M HCl) to include organic P and non-reactive inorganic P in
soils across the transect at Taylor Creek STA.
10-30 cm depths are given in Figure 22. Station #34 had lowest TP concentrations, as compared
to other stations along the transect. At this station, inorganic P accounted for 21 and 45% of the
total P in 0-10 and 10-30 cm depths, respectively. At the remaining stations, inorganic P
accounted for 6 to 15% of TP in 0-10 cm soil and 6 to 16% in 10-30 cm soils. Lower percentage
of inorganic P was found in soils with high organic matter content, suggesting P may be present
in organic pool. Since the soils in Taylor Creek STA were mineral in nature, we expected
higher recovery of TP as inorganic P. Lower inorganic P recovery in 1 M HCl suggests that P
may be present in non-reactive, stable pool.
Distribution of non-reactive phosphorus across the STA Transect:
Non-reactive
phosphorus represents P not extracted with 1 M HCl. This may include organic phosphorus and
stable inorganic phosphorus complexed with organic matter (Reddy et al., 1998b). Distribution
of non-reactive P (as determined by the difference between total P and total inorganic P) within
the STA transect at the 0-10 cm and 10-30 cm depths are presented in Figure 22. Station #34
had lowest TP concentrations, as compared to other stations along the transect. At this station,
non-reactive P accounted for 79 and 55% of the total P in 0-10 and 10-30 cm depths,
respectively. At the remaining stations, non-reactive P accounted for 85 to 94% of TP in 0-10
cm soil and 84 to 94% in 10-30 cm soils, respectively. High percentage of non-reactive P in
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6/26/2007
these soils was surprising observation and further investigation is needed to determine the forms
of P stored in this pool.
Table 12. Variability in selected soil properties measured on replicate soil cores from two
stations along a transect in Taylor Creek STA. Three cores were taken from each station.
Parameter
Station
Bulk density
g cm-3
LOI
g kg-1
Total C
g kg-1
Total N
g kg-1
Total P
mg kg-1
Inorganic P
mg kg-1
Non-reactive P
mg kg-1
20
37
20
37
20
37
20
37
20
37
20
37
20
37
0-10 cm
Mean
1.54
0.65
56
250
19
111
2.4
8.5
131
563
17
31
114
532
SD
0.28
0.07
2.7
33.1
0.4
20.5
0.1
1.5
6.4
63.4
2.5
3.7
8.2
63.2
CV (%)
18
11
5
13
2
18
4
18
10
11
15
12
7
12
10-30 cm
Mean
1.39
1.19
53
99
16
39
2.3
3.5
106
217
14
15
92
202
SD
0.10
0.16
7.6
12.6
2.4
7.1
0.3
0.4
17.9
26.4
2.4
2.0
18.8
23.6
CV (%)
7
13
14
13
15
18
13
11
17
12
17
13
20
12
Table 13. Total inorganic P recovered during repeated extractions with 1 M HCl
Station
23
52
111
128
138
Total 1M HCl-Pi
mg kg-1
46.2
10.3
34.6
61.3
103.8
% of Total HCl-Pi recovered during each extraction
First
Second
Third
57.6
73.1
80.0
81.2
81.5
13.2
14.7
9.0
10.8
9.6
26.3
12.1
11.0
8.0
9.0
To determine the efficacy of 1M HCl in extracting inorganic P, we selected soil samples from
five stations and subjected them to sequential extractions with the acid. The purpose of this
sequential extraction was to determine how reactive is the residual inorganic and organic P.
During each extraction, soils were equilibrated with acid for a period of 3 hours. Results are
presented in Table 13. With the exception of soil from Station #23, approximately 80% of the
TPi was extracted during the first extraction, and the remaining 20% was extracted in the next
two extractions. These results suggests that the P not extracted after repeated extractions is
either in stable inorganic P pool (stable mineral form) or organic P form. Further analysis of
residual organic P (using more modern techniques such NMR spectroscopy) is needed to
document the forms of organic P forms. If the residual P contains inorganic P, that can
documented by X-ray diffraction. These analysis is beyond the scope of this project.
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Labile and Non-labile Pools of Soil Phosphorus
The P fractionation scheme used (Figure 21) sequentially separated P into: (i) loosely bound P
(ii) Pi associated with Fe and Al ; (iii) Pi associated with Ca and Mg; (iv) alkali-extractable
organic P (fulvic- and humic-bound P); and (v) residual organic P. Data are presented in Tables
14 and 15.
KCl-extractable P: Inorganic P extracted with salts such as 1 M KC1 represents loosely
adsorbed P, which is bioavailable and can be readily released into the water column. Labile Pi
content of surface soils (0-10 cm) was in the range of 0.14 to 2.8 mg kg-1, which accounted for
0.12 to 0.54% of total P (Figure 23). At Station #34, a larger proportion of TP (2 to 6%) was
labile. On an average, 0.3% of the total P was labile, as estimated by the regression equation
presented in Table 16.
3 .0
R e p li c a t e c o r e s
2 .5
0-10 cm
10 - 30 cm
2 .0
E xch -P
1 .5
Phosphorus [mg kg-1]
1 .0
0 .5
0 .0
70
60
50
40
30
20
10
0
30
R e p lic a t e
co re s
F e - / A l- P
R e p l ic a t e
co re s
C a -/M g -P
25
R e p lic a t e
co re s
20
15
10
R e p l ic a t e
co re s
5
0
20
20
20
46
9
14
17
42
49
34
37
37
37
S ta tio n s a lo n g th e T ra n s e c t
Figure 23. Distribution of labile P (KCl Pi), Fe/Al-P (NaOH Pi), and Ca/Mg Pi (HCl Pi)
fractions in soils collected along a transect in Taylor Creek STA.
Iron - and Aluminum bound P: Inorganic P extracted with 0.1N NaOH represents Fe-and Albound P. This pool accounted for 8 to 14% of TP in 0-10 cm soils and 7 to 15% in 10-30 cm
soils, respectively. There was no distinguishable trend among the stations sampled. On an
average, Fe- and Al-bound P accounted for 9% of total P (Table 16).
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Calcium and Magnesium bound P: Inorganic P extracted with 0.5M HCl (after alkaline
extraction) represents Ca-and Mg-bound P. This pool accounted for 2 to 9% of total P in
surface soils and 2 to 13% in soils from 10 -30 cm depth (Figure 25, Tables 14, 15 and 16).
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Table 14a. Labile and non-labile pools of phosphorus in soils (0-10 cm depth) collected along a transect in Taylor Creek STA.
Site
9-1
14-1
17-1
20-1
20-2
20-3
34-1
37-1
37-2
37-3
42-1
46-2
49-1
krr
NaOHNaOHResidual Sum
TP
HCl-TPi
BD
KCl Pi
Pi
HCl-Pi
Sum TPi Po
P
TPo
Sum TP
-1
-1
-1
-1
-1
-1
-1
-1
-1
mg kg
mg kg
g cm-3 mg kg
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg-1
---------------------------------------------------------Soil Depth 0-10 cm-------------------------------------------------------------507.1
51.1
0.384
2.80
59.4
25.97
88.1
199.8
231.1
430.9
519.0
223.4
24.8
0.843
0.57
22.6
18.75
41.9
56.4
114.4
170.8
212.7
273.2
19.8
0.925
0.31
29.9
6.83
37.0
119.5
115.9
235.4
272.4
123.6
18.6
1.853
0.14
17.2
4.07
21.4
53.6
45.0
98.6
120.0
134.9
14.0
1.338
0.18
16.7
3.08
20.0
66.2
46.6
112.8
132.8
134.3
18.0
1.428
0.35
18.1
3.63
22.0
64.0
44.5
108.5
130.6
28.9
6.1
1.498
0.43
1.6
1.52
3.5
4.4
12.2
16.7
20.2
627.6
35.5
0.628
2.52
50.8
17.03
70.4
314.8
257.8
572.6
643.0
562.1
29.1
0.603
1.17
44.1
12.47
57.7
254.3
233.8
488.1
545.8
500.8
28.9
0.727
2.09
38.8
11.39
52.3
224.2
221.9
446.2
498.5
103.0
13.1
1.017
0.32
6.0
4.94
11.3
22.0
43.9
65.9
77.2
447.9
26.2
0.774
0.47
33.7
9.77
43.9
164.9
161.2
326.1
370.0
266.3
19.5
0.935
0.25
20.5
6.93
27.7
95.8
98.7
194.5
222.2
Page
58
6/26/2007
Table 14b. Labile and non-labile pools of phosphorus in soils (10-30 cm depth) collected along a transect in Taylor Creek STA.
Site
9-1
14-1
17-1
20-1
20-2
20-3
34-1
37-1
37-2
37-3
42-1
46-2
49-1
krr
NaOHNaOHResidual Sum
TP
HCl-TPi
BD
KCl Pi
Pi
HCl-Pi
Sum TPi Po
P
TPo
Sum TP
-1
-1
-1
-1
-1
-1
-1
-1
-1
mg kg
mg kg
g cm-3 mg kg
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg
mg kg-1
---------------------------------------------------- Soil Depth 10-30 cm -------------------------------------------------------151.2
17.6
1.433
0.25
16.2
5.64
22.1
45.1
60.8
105.9
128.1
84.8
8.8
1.596
0.35
5.5
4.29
10.2
17.4
44.1
61.5
71.7
110.4
7.9
1.390
0.15
8.1
3.27
11.5
32.0
55.0
87.0
98.5
86.8
13.7
1.303
0.12
13.0
3.42
16.5
34.3
33.1
67.4
83.9
108.5
16.5
1.492
0.15
15.0
3.86
19.0
43.9
41.9
85.8
104.8
122.3
11.6
1.387
0.14
11.3
2.81
14.3
53.6
44.8
98.4
112.6
18.9
8.5
1.774
0.93
1.5
1.95
4.4
2.1
8.3
10.3
14.7
220.1
15.6
1.277
0.28
23.9
4.68
28.9
137.3
79.7
216.9
245.8
241.6
16.9
1.009
0.35
22.3
4.25
26.9
123.4
82.7
206.2
233.1
189.1
11.4
1.298
0.30
13.4
3.74
17.4
82.2
65.4
147.6
165.1
385.7
44.0
0.938
0.22
33.8
19.40
53.4
121.7
168.5
290.2
343.6
116.1
8.0
1.445
0.27
10.4
3.66
14.3
47.0
60.7
107.7
122.0
89.9
8.6
1.535
0.17
4.4
3.58
8.2
18.3
33.3
51.6
59.7
Page
59
6/26/2007
Table 15. Variability in soil phosphorus forms measured on replicate soil cores from two stations along a transect in Taylor Creek
STA. Three cores were taken from each station.
Parameter
Station
Loosely bound P,
mg kg-1
Fe-/Al-P, mg kg-1
20
37
20
37
20
37
20
37
20
37
20
37
Ca-/Mg-P, kg kg-1
Organic P, mg kg-1
Residual P, mg kg-1
Sum TP, mg kg-1
krr
0-10 cm
Mean
0.23
1.93
17.3
44.6
3.6
13.6
61.3
264
45.4
238
128
562
Page
SD
0.11
0.69
0.68
6.0
0.5
3.0
6.7
46.1
1.1
18
6.8
73.7
CV (%)
47
36
4
13
14
22
11
17
2
8
5
13
60
10-30 cm
Mean
0.14
0.31
13.1
19.9
3.4
4.2
43.9
114
40.0
75.9
100
215
6/26/2007
SD
0.01
0.04
1.9
5.7
0.53
0.47
9.6
28.6
6.1
28.6
14.8
43
CV (%)
7
13
15
29
16
11
22
25
15
37
15
20
Table 16. Relationship between soil phosphorus forms and total phosphorus in soils collected
along a transect in Taylor Creek STA. *Total inorganic P represents sum of inorganic P
extracted by alkali and acid. **Pi- [Me-TC] represents inorganic P complexed with metal and
organic matter
Regression equation: P form = m TP + b
R2
n
KCl-Pi = 0.0033 TP + 0.124
0.609
26
Fe-/Al-bound P = 0.086 TP + 3.76
0.924
26
Ca-/Mg-bound P = 0.029 TP + 1.22
0.608
26
Total Inorganic P (Pi)* = 0.116 TP + 3.86
0.887
26
Extractable Organic P = 0.463 TP + 6.46
0.963
26
Residual P = 0.421 TP + 2.6
0.976
26
[NaOH-HCl]Pi = 1.802 [HCl]Pi - 5.6
0.907
26
Pi- [Me-TC]** = 0.06 TP - 3.9
0.871
26
Total Inorganic P: Total inorganic P (TPi) is the sum of P extracted with KCl, NaOH, and HCl.
Total Pi was also estimated by a single extraction with 1 M HCl. Both methods showed similar
trends and were highly correlated (P = 0.0001), but showed varying extraction efficiencies. The
following empirical relationship was observed between TPi and Pi extracted with 1 M HCl:
TPi = 1.802[HCl-Pi] – 5.6; R2 = 0.907; n = 26
In other studies, Reddy et al., (1998b) showed 1:1 relationship between these extraction methods.
Their results suggested that 1 M HCl is strong enough to dissolve mineral and amorphous forms
of P bound to iron, aluminum, calcium, and magnesium. For Taylor Creek STA soils, only 55%
of the inorganic P was extracted with 1 M HCl, suggesting presence of other forms of P that are
resistant to HCl treatment. A sequential extraction with alkali and acid, resulted in solubilization
P held in the soil. It is hypothesized that P in the Taylor Creek STA soils was probably bound to
metal-organic matter complexes. With this assumption, we estimated P bound to metal-organic
matter (Me-TC) as follows:
Pi- [Me-TC] = TPi [alkali-acid extraction] – HCl-Pi
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Where: Pi- [Me-TC] is the inorganic P bound to metal-organic matter complexes; TPi [alkaliacid extraction] is the total inorganic P extracted during the sequential alkali and acid extraction
(Figure 21); HCl-Pi is the single extraction with 1 M HCl (Reddy et al., 1998b). The estimated
Pi- [Me-TC] showed strong correlation with total carbon (TC) of soils.
Pi- [Me-TC] = 0.282 TC + 2.7; R2 = 0.893; n = 26
This pool accounted for approximately 6% of the total P in both surface and subsurface soils
(Table 15).
Alkali Extractable Organic Phosphorus: This fraction includes both living and dead sources
of organic P associated with humic and fulvic acids. The NaOH-Po, fraction was estimated as the
difference between total P of the NaOH extract and SRP concentration in the NaOH extracts.
This pool is termed as Organic P. At all locations, organic P was higher in surface layers and
decreased with depth (Figure 24 and Tables 14, 15 and 16). Alkali extractable organic P
accounted for 22 to 50% in surface layers and 14 to 56% in 10-30 cm soils.
350
300
0-10 cm
10 - 30 cm
250
200
R e p lic a t e
co re s
R e p lic a t e
co re s
150
100
Phosphorus [mg kg-1]
O r g a n ic P
50
0
700
R e s id u e P
600
500
400
300
R e p lic a t e
co re s
R e p lic a t e
co re s
200
100
0
300
R e p lic a t e
co re s
250
T o tal P
200
150
R e p lic a t e
co re s
100
50
0
20
20
20
46
9
14
17
42
49
34
37
37
37
S ta tio n s a lo n g th e T ra n s e c t
Figure 24. Distribution of alkali extractable organic P, residual stable P, and total P of soils
collected along a transect in Taylor Creek STA.
Results suggest that a major proportion of P is stored in the organic pool (22-56% of the total P
in surface soils). Similarly, 14 to 56% of the total P was present in alkali extractable organic P in
subsurface soils (10-30 cm depth). Alkali solutions are used to extract humic and fulvic acids
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and organic P recovered in such extracts is considered to have been bound to humic substances.
However, the relative stability of organically bound P is unknown.
Residual Non-reactive P: Residual P is highly refractory and may not be bioavailable. This
pool is not soluble either in alkali or acid. Residual stable P accounted for 34 to 60% of total P
in 0-10 cm soil and 32 to 62% in the 10 -30 cm soil (Figure 24; Tables 14, 15 and 16). Stability
of residual P under different hydrologic conditions is unknown and needs further investigation.
0 – 10 cm depth
Residual P
44.6%
Exch- P
0.4%
Fe-/Al-P
10.1%
Ca-/Mg- P
4.0%
Organic P
40.9%
10 – 30 cm depth
Residual P
46.3%
Exch- P
0.7%
Fe-/Al-P
10.1%
Ca-/Mg- P
4.5%
Organic P
38.4%
Figure 25. A summary of labile and non-labile pools of phosphorus in soils collected along a
transect in Taylor Creek STA.
In conclusion, a large proportion of soil phosphorus is present in two major pools: alkali
extractable organic P; and residual P stable in both alkali and acid solutions (Fig. 25).
Approximately 40% of the total P is in stable pool, while another 45% is present in organic P
pool. Stability of these two pools under varying hydrologic conditions needs further
investigation.
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4.0
Phosphorus Retention Properties of Soils
Phosphorus (P) sorption/desorption reactions in wetland soils are important because they buffer
soil porewater P concentrations and regulate P availability to plants, microorganisms and
overlying waters (Axt and Walbridge, 1999). Phosphorus sorption is often characterized by an
initial rapid P uptake by solid from solution (processes such as ion exchange, ligand exchange)
followed by a slower P uptake, which is governed by diffusion and precipitation processes
(Reddy et al. 2004). The objectives of this study were to: (1) describe P sorption parameters of
soils in the proposed STA under aerobic and anaerobic conditions; and (2) determine the
maximum P retention capacity of soils using adsorption isotherms.
4.1
Materials and methods
To evaluate the P retention properties of the soils, batch incubation studies were conducted on
selected soils at the 9 locations (18 soils at two depths; Figure 21) and single-point isotherms
were performed at all 42 locations (Figure 3). The batch incubation studies were conducted
under aerobic and anaerobic conditions.
Batch incubation under aerobic conditions
Phosphate sorption was measured using one gram of an air-dried, homogenized soil treated with
10 mL of 0.01M KCl solution containing various levels of P (ranging from 0 to 100 mg P L-1) in
50 mL centrifuge tubes. The tubes were placed on a mechanical shaker for a 24-hour
equilibration period. At the end of the period, the soil samples were centrifuged at 6000 rpm for
10 min and the supernatant filtered through a 0.45 µm membrane filter and the filtrate analyzed
for soluble reactive P (Murphy and Riley, 1962) using a TechniconTM Autoanalyzer (EPA 365.1).
All extractions and determinations were at room temperature.
Batch incubation under anaerobic conditions
One gram each of soil samples were pre-incubated anaerobically with 5 mL of deionized water
for four weeks and the samples were purged with N2 weekly to maintain anaerobic conditions. At
the end of incubation, 5 mL of graded series of P solutions in 0.02M KCl from 0 to 200 mg P L-1
was added so the final concentrations were the same as for the aerobic studies. The samples were
equilibrated on a mechanical shaker for 24 hours at room temperature. The amount of P that
disappeared from solution after 24-h equilibration represents the fraction of P sorbed by the soil.
Single point isotherms
Single point isotherms (SPI) were determined for the surface and subsurface soils collected in
this study (Figure 3). The procedure involves equilibrating a known amount of air-dried soil with
deionized water spiked with 100 mg P L-1 at a 1:20 soil to solution ratio on a mechanical shaker
for 24h at room temperature. The amount of P lost from solution after 24h equilibration was used
to determine the maximum P retention capacity of the soils.
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Calculations
The total amount of P adsorbed on sediments can be calculated as follows:
[1]
S = S’ + So
Where, S = total adsorbed P in sediment (mg kg-1), S’ = amount of added P retained by sediment
(mg kg-1), and So = initial or native sorbed P in sediment (mg kg-1).
Since at low equilibrium concentrations the relationship between S’ and C (equilibrium
concentrations) is typically linear (Rao and Davidson 1979), the So can be estimated by a least
square fit using the following equation (Reddy et al., 1998):
S’ = Kd*Ct – So
[2]
Where, Ct = solution P concentration measured after 24-h equilibration (mg L-1).
By plotting the linear form of equation [2], i.e., S’ vs. Ct, the intercept is equal to So and slope is
equal to Kd, a linear adsorption coefficient (L kg-1) estimated without taking into account initially
sorbed P (So). So was estimated using a least square fit of S' measured at low (< 10 mg P L-1)
equilibrium concentrations, C. At these concentrations, the linear relationship between S' and C
can be described by S' = bC - So where b is the linear adsorption coefficient (Gale et al., 1994;
Graetz and Nair, 1995; Reddy et al., 1998a). The linear portion of the graph used in the
calculations had r2 values of at least 0.95. The method used for calculations of So using actual
data points was illustrated by Graetz and Nair (1995).
A frequently used term in P sorption phenomena, EPCo, an equilibrium P concentration
(mg L-1), can be defined as the concentration of P in solution where no net adsorption or
desorption of P occurs, i.e., S’ = 0.
Thus, by substituting the values of S’ and Ct in equation [2], EPCo can be calculated as
follows:
EPCo = So/Kd
[3]
The P sorption parameters, sorption maxima (Smax) and bonding energy constant (k) were
estimated using Langmuir equation:
Ct/S = 1/k*Smax + Ct/Smax
[4]
where:
S = S' + So, the total amount of P sorbed, mg kg-1
S' = P sorbed by the solid phase, mg kg-1
So = P originally sorbed on the solid phase, mg kg-1
C = concentration of P after 24 h equilibration, mg L-1
Smax = P sorption maximum, mg kg-1
k = a constant related to the bonding energy, L mg-1 P
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4.2
Results and discussion
Langmuir Sorption Parameters under Aerobic and Anaerobic Conditions
The Langmuir sorption parameters for the nine selected soils for the two depths (0-10 cm and 1030 cm) are provided; Table 17 for aerobic conditions and Table 18 for anaerobic conditions.
Details of the calculations are given in Appendix 3 (aerobic conditions) and Appendix 4
(anaerobic conditions). Other pertinent information including replications can be found in
Appendix 5 for aerobic conditions and in Appendix 6 for anaerobic conditions. Correlation
coefficients of aerobic P sorption parameters with soil characteristics and P fractionation data are
given in Table 19 for aerobic conditions and Table 20 for anaerobic conditions.
Smax-aero (mg/kg)
500
y = 1.1143x + 4.5232
2
R = 0.8881
400
a
300
200
100
0
0
100
200
300
400
500
P100 Sorbed-aero (mg/kg)
Smax-anaero (mg/kg)
600
y = 0.9304x + 1.1784
500
2
R = 0.9265
400
b
300
200
100
0
0
100
200
300
400
500
600
P100 Sorbed-anaero (mg/kg)
Figure 26. Relationship between Langmuir Smax and P sorbed at 100 mg P L-1 under (a) aerobic
and (b) anaerobic conditions.
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Relationships for Smax with P sorption as determined by the single point isotherm procedure
indicate that Smax can be predicted with reasonable accuracy under aerobic and anaerobic
conditions using single-point isotherms (Figure 26). This relationship is well documented for
upland soils (Nair et al., 1998) as well as wetland soils and stream sediments (Reddy et al.,
1998a). Relationships for other Langmuir sorption parameters under aerobic and anaerobic
conditions are provided in Table 21.
The P sorption maximum (Smax) values under aerobic conditions (Table 17) for both the 0-10
cm depth and the 10-30 cm depth do not show a definite trend from the inflow to the outflow.
Values of Smax under aerobic conditions range from approximately 400 mg kg-1 at the 10-30 cm
depth at the beginning of Cell 2 (Site 42) to <20 mg kg-1 at both soil depths at Site 34 in the same
Cell. Based on the retention capacity parameters of the STA soils, it appears likely that a part of
the surface horizons may have been removed during the STA construction, and the present
“surface” 0-10 and 10-30 cm soils could be a mixture of A, E, and Bh horizon soils with
properties that are not typical of surface horizons of other upland soils within the Basin. It is
assumed that the STA was constructed on Spodosols, which is the predominant soil order in the
Lake Okeechobee Basin.
Stepwise regression of Smax with HCl-Ca, Mg, Fe, Al and TC under aerobic conditions gave the
following:
Smax-aero (mg/kg) = 0.026*[HCl-Ca] + 0.111*[HCl-Fe] + 0.025*[HCl-Al] - 58.82
(R2 =0.82, p<0.0001, n=26)
Smax values for soils and sediments of the Lake Okeechobee Basin are usually associated with
Fe, Al and organic matter (Nair et al., 1999; Reddy e al., 1998a). The STA stepwise regression
equation suggests Ca as a contributor to Smax as well.
Definite trends from inflow to outflow were not found for the other Langmuir parameters, So,
EPC or k. The situation was similar under anaerobic conditions (Table 18). So and EPC were
correlated to both HCl-extractable Ca and Mg under aerobic conditions (Table 19). Under
anaerobic conditions, EPC values were correlated to Ca and Mg; there were no significant
correlations of So to any of the metals. The presence of Ca and Mg reduces k, the bonding
capacity of the soil as noted by negative significant correlations (Table 19). Previous studies on
Spodosols of the Lake Okeechobee Basin (Nair et al. 1998) showed that So was significantly
correlated to Mehlich 1 extractable Mg, particularly for soils of the spodic (Bh) horizon. The
study also showed that k was significantly correlated to Mehlich 1-extractable Ca in the surface
A and E horizons, and negatively to Mg concentrations in the Bh horizons. Smax appeared to
change minimally under anaerobic conditions (Figure 27). The retention capacity of the STA
soils will therefore be little affected by flooded conditions.
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Table 17. Langmuir sorption parameters (P originally sorbed on the solid phase, So; equilibrium
P concentrations, EPC; the P retention maximum, Smax and the P bonding energy constant, k)
for the Taylor Creek STA soils at the nine selected locations under aerobic conditions.
Cell #
Site
From
inflow
outflow
Depth
So
EPC
to
Smax
k
cm
mg kg-1
mg -1 L
mg kg-1
L mg P-1
1
20†
0-10
5.0 0.04
160 0.22
1
10-30
5.6 0.03
135 0.30
1
46
0-10
12.1 2.32
141 0.05
1
10-30
2.8 0.02
101 0.42
1
9
0-10
17.1 1.47
267 0.04
1
10-30
2.7 0.04
88 0.50
1
14
0-10
1.1 0.05
263 0.06
1
10-30
3.4 0.02
89 0.85
1
17
0-10
4.2 0.36
221 0.04
1
10-30
1.6 0.02
109 0.22
2
42
0-10
3.2 0.02
107 0.23
2
10-30
16.1 0.04
407 0.25
2
49
0-10
6.3 0.07
221 0.15
2
10-30
4.0 0.02
152 0.21
2
34
0-10
0.1 0.01
18 0.18
2
10-30
0.0 0.00
12 1.06
2
37
0-10
18.9 2.56
252 0.03
10-30
4.2 0.07
204 0.15
† Mean of triplicates
‡ SPI = P sorption as measured by the single-point isotherm method
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Page68
SPI‡
mg kg-1
158
129
101
96
196
81
239
83
182
104
101
388
209
149
22
9
162
192
6/26/2007
Table 18. Langmuir sorption parameters (P originally sorbed on the solid phase, So; equilibrium
P concentrations, EPC; the P retention maximum, Smax and the P bonding energy constant, k)
for the Taylor Creek STA soils at the nine selected locations under anaerobic conditions.
Cell #
Site
From
inflow to
outflow
Depth
cm
So
mg kg-1
EPC
mg -1 L
Smax
mg kg-1
k
L mg P-1
1
20†
0-10
14.6
0.02
239
0.35
1
10-30
5.3
0.01
210
0.29
1
46
0-10
1
10-30
9.1
0.02
184
1.21
1
9
0-10
10.9
0.20
368
0.05
1
10-30
2.0
0.02
148
0.30
1
14
0-10
8.3
0.14
326
0.16
1
10-30
8.1
0.01
105
0.39
1
17
0-10
7.2
0.26
263
0.08
1
10-30
3.0
0.01
59
-0.67
2
42
0-10
1.3
0.01
100
0.24
2
10-30
39.7
0.15
519
0.10
2
49
0-10
1.9
0.02
225
0.15
2
10-30
0.2
0.00
70
0.96
2
34
0-10
2
10-30
2
37†
0-10
2
10-30
1.7
0.09
180
0.10
† Mean of triplicates
‡ SPI = P sorption as measured by the single-point isotherm method
SPI‡
mg kg-1
208
182
173
332
150
299
100
232
54
96
488
280
67
180
Note: Data are not provided for some of the samples since it was not possible to obtain Langmuir
isotherms for some soils under anaerobic conditions. These soils are likely P sources and not P
sinks.
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Table 19. Correlation coefficients of aerobic P sorption parameters† with soil characteristics and
P fractionation data.
n
So
EPC
Smax
k
SPI
pH
1M HCl-Ca
1MHCl-Mg
1MHCl-Fe
!MHCl-Al
Loss on ignition
Total N
Total C
Total P
Total inorganic P
Water soluble P
Mehlich 1-P
KCl Pi‡
NaOH Pi‡
HCl Pi‡
Sum TPi‡
NaOH Po‡
Residue P‡
Sum TPo‡
So
26
1
0.803
0.686
-0.412
0.509
-0.571
0.794
0.774
0.085
0.149
0.881
0.870
0.889
0.894
0.825
0.851
0.738
0.738
0.862
0.717
0.851
0.877
0.885
0.894
EPC
26
Smax
26
k
26
SPI
26
1
0.334
-0.429
0.055
-0.466
0.609
0.691
-0.163
-0.143
0.800
0.778
0.800
0.854
0.591
0.857
0.511
0.785
0.754
0.535
0.722
0.851
0.843
0.860
1
-0.572
0.883
-0.648
0.862
0.769
0.191
0.411
0.763
0.776
0.774
0.723
0.794
0.486
0.786
0.363
0.751
0.761
0.772
0.678
0.722
0.709
1
-0.417
0.536
-0.506
-0.592
0.066
0.091
-0.560
-0.566
-0.559
-0.580
-0.454
-0.402
-0.397
-0.252
-0.583
-0.414
-0.546
-0.578
-0.548
-0.572
1
-0.531
0.713
0.588
0.181
0.570
0.531
0.532
0.537
0.497
0.627
0.184
0.578
0.081
0.515
0.541
0.530
0.447
0.486
0.472
correlation coefficient: r=0.381 at α=0.05
correlation coefficient: r=0.487 at α=0.01
† So= Native Sorbed P; k=constant related to bonding energy; Smax=P sorption
maximum; SPI=Single Point P Isotherm (100 mg L-1)
‡ Parameters from the fractionation studies (see Task 3.0)
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Table 20. Correlation coefficients of anaerobic P sorption parameters† with soil characteristics
and P fractionation data.
n
So
EPC
Smax
k
SPI
pH
1M HCl-Ca
1M HCl-Mg
1M HCl-Fe
!M HCl-Al
Loss on ignition
Total N
Total C
Total P
Total inorganic P
Water soluble P
Mehlich 1-P
KCl Pi‡
NaOH Pi‡
HCl Pi‡
Sum TPi‡
NaOH Po‡
Residue P‡
Sum TPo‡
So
22
1
0.267
0.708
0.022
0.570
-0.037
0.402
0.064
0.269
0.147
0.326
0.328
0.335
0.343
0.552
0.067
0.566
0.088
0.358
0.423
0.389
0.220
0.363
0.306
EPC
22
1
0.565
-0.284
0.360
-0.471
0.602
0.609
0.203
0.052
0.709
0.732
0.748
0.729
0.617
0.582
0.625
0.452
0.750
0.620
0.731
0.744
0.741
0.774
Smax
22
1
-0.112
0.765
-0.404
0.686
0.493
0.529
0.156
0.702
0.729
0.728
0.737
0.860
0.407
0.860
0.361
0.757
0.750
0.779
0.619
0.735
0.708
k
22
SPI
28
1
-0.099
0.302
-0.266
-0.308
0.163
-0.026
-0.288
-0.298
-0.301
-0.310
-0.254
-0.185
-0.266
-0.132
-0.295
-0.214
-0.276
-0.307
-0.289
-0.310
correlation coefficient: r=0.413 at α=0.05
correlation coefficient: r=0.526 at α=0.01
† So= Native Sorbed P; k=constant related to bonding energy; Smax=P sorption maximum;
SPI=Single Point Isotherm (100 mg/L) (1:20)
‡Parameters from the fractionation studies (see Task 3.0)
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1
-0.531
0.713
0.588
0.181
0.570
0.531
0.532
0.537
0.497
0.627
0.184
0.578
0.081
0.515
0.541
0.530
0.447
0.486
0.472
Smax-anaero (mg/kg)
600
y = 1.1835x + 4.1579
2
R = 0.7188
500
400
1:1
300
200
100
0
0
100
200
300
400
500
600
Smax-aero (mg/kg)
Figure 27. Relationship between Langmuir Smax under aerobic and anaerobic conditions.
Table 21: Correlation coefficients of Langmuir parameters† under aerobic
conditions.
n
SPI‡
So (aerobic) Smax (aerobic)
28
28
28
n
So (aerobic)
28
1
0.506
EPC (aerobic)
28
0.055
0.804
Smax (aerobic)
28
1
0.881
0.688
k (aerobic)
28
-0.417
-0.409
-0.569
So (anaerobic)
22
0.568
0.544
0.571
0.423
EPC (anaerobic)
22
0.362
0.665
Smax (anaerobic)
22
0.731
0.713
0.816
k (anaerobic)
22
-0.026
-0.006
-0.069
and anaerobic
k (aerobic)
28
1
0.037
-0.440
-0.321
0.169
†
So=native sorbed P; k=constant related to bonding energy; Smax=P sorption maximum;
SPI=single point isotherm.
n=28
r=0.367 at α=0.05
r=0.470 at α=0.01
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n=22
r=0.413 at α=0.05
r=0.526 at α=0.01
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Results of this study show that the physico-chemical properties of Taylor Creek STA soils
exhibit significant P retention capacity within the top 30 cm. Low EPC values suggest that these
soils potentially function as sinks for P at relatively low concentrations. The P retention
capacity of these soils was not be adversely impacted by flooding as indicated by minimal
differences in Smax values under aerobic and anaerobic conditions. Long-term effectiveness of
STA soils depends on P loading and contact of water column P with underlying soils. In
addition several other factors such as vegetation and extent of particulate matter accretion can
also affect the overall capacity of soils to retain P.
The biogeochemical processes occurring in a wetland soil are dependent on its chemical
composition, mineral components, and physicochemical and biological factors. Phosphorus
reactivity in soils, for example, changes drastically, depending on whether the soil is calcareous
or non calcareous, as moisture regime and hydrology shifts from unsaturated to saturated and
prolonged submerged conditions. The complexity of P biogeochemistry in wetlands is
compounded by the presence of high organic matter. Hence, chemical characterization and
quantification of soil P fractions (organic and inorganic) and other components in wetlands, such
as those in STAs, constitute an important component in understanding P dynamics and the
effects of hydroperiod on P stability in accreted material.
Burial or accretion of organic matter has been reported as a major mechanistic long-term sink for P
in wetlands. Wetland soils tend to accumulate organic matter due to the production of detrital
material from biota and the suppressed rates of decomposition. Soil accretion rates for constructed
wetlands can range between a few millimeters to more than one centimeter per year. Accretion
rates in productive natural wetland systems such as the Everglades have been reported as high as
one centimeter or more per year. The genesis of this new material is a relatively slow process,
which may affect the nutrient retention characteristics of the wetland. With time, productive
wetland systems will accrete organic matter that has different physical and biological characteristics
than the underlying soil. Management of newly accreted material by consolidation, hydrologic
manipulation (water level drawdown), application of soil amendments and/or soil removal can
improve the overall longevity of STAs to maintain water quality.
Phosphorus management in STAs has been a major focus of the SFWMD. In wetlands, P
cycling is tightly coupled to organic matter turnover and cycling of other nutrients such as
nitrogen and sulfur. A recent series of papers on STA-1W published in a special issue of
Ecological Engineering (Reddy et al., 2006) indicates the importance of hydrology, vegetation,
periphyton, and biogeochemical processes regulating long-term retention of P in wetlands.
However, to understand the long-term performance of STAs it is critical to determine the
fundamental processes and the linkages between those processes for effective long-term P
management.
5.0 References
Axt, J. R., and M. R. Walbridge. 1999. Phosphate removal capacity of palustrine forested
wetlands and adjacent uplands in Virginia. Soil Sci. Soc. Am. J. 63:1019-1031.
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Campbell, K. 1999. A written summary report on the use of New Palm Dairy as
a site for STA development.
Chang, S.C., and M.L. Jackson. 1957. Fractionation of soil phosphorus. J. Soil. Sci. 84:133144.
Gale, P.M., KR. Reddy, and D.A. Graetz. 1994. Phosphorus retention by wetland soils used for
treated wastewater disposal. J. Environ. Qual. 23:370-377.
Graetz, D.A., and V.D. Nair. 1995. Fate of phosphorus in Florida Spodosols contaminated with
cattle manure. Ecol. Eng. 5:163-181.
Nair, V.D., D.A. Graetz, and K.M. Portier. 1995. Forms of phosphorus in soil profiles from
dairies of south Florida. Soil Sci. Soc. Am. J. 59:1244-1249.
Nair, V. D., D. A. Graetz and K. R. Reddy. 1998. Dairy manure influences on phosphorus
retention capacity of Spodosols. J. Environ. Qual. 27:522-527.
Olila, O.G., K.R. Reddy, and W.G. Harris, Jr. 1995. Forms and distribution of inorganic
phosphorus in sediments of two shallow eutrophic lakes in Florida. Hydrobiologia.
302:147-161.
Psenner, R., B. Bostrom, M. Dinka, K. Pettersson, R.Pucsko, and M. Sager. 1988. Fractionation
of phosphorus in suspended matter and sediment. Arch. Hydrobiol. Beih. Ergebn.
Limnol. 30:98-103.
Reddy, K.R. 1999. A written evaluation and recommendations on the efficacy of
New Palm Dairy as a site for STA development.
Reddy, K. R., O. A. Diaz, L. J. Scinto, and M. Agami. 1995. Phosphorus dynamics in selected
wetlands and streams of the Lake Okeechobee Basin. Ecol. Eng. 5:183-208.
Reddy, K.R., G.A. O’Connor, and P.M. Gale. 1998a. Phosphorus sorption capacities of wetland
soils and stream sediments impacted by dairy effluent. J. Environ. Qual. 27:438-117.
Reddy, K.R., Y. Wang, W.F. Debusk, M.M. Fisher, and S. Newman. 1998b. Forms of soil
phosphorus in selected hydrologic units of the Florida Everglades. Soil Sci. Soc. Am. J.
62:1134-1147.
Reddy, K.R., R.H. Kadlec and M.J. Chimney. 2006. Editorial: the Everglades Nutrient Removal
Project. Ecological Engineering 27(4): 265-267.
Ruttenberg, K. C. 1992. Development of sequential extraction method for different forms of
phosphorus in marine sediments. Limnol. Oceanogr. 37:1460-1482.
Stanley Consultants, Inc. 2002. Lake Okeechobee Water Retention/Phosphorus
Removal Project. Design Analysis Report. Final Submittal. Volume I. August
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9, 2002.
Wetland Solutions, Inc. 2004. Okeechobee Stormwater Treatment Areas (STAs)
Research and Management Plan for Performance Optimization. January 2004.
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