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y = 152.65x - 6.70
R² = 0.98
-1
5
11
17
-0.010 0.010 0.030 0.050 0.070 0.090 0.110 0.130 0.150
Solid-p
hase P
(m
g k
g-1
)
Liquid-phase P (mg L-1)
Equilibrium Phosphorus Concentrations and Phosphorus Forms of Sediments in Walnut Creek , Iowa
Stream sediments that are derived from various sources mightrelease different forms of P (organic and inorganic) into streamwater.
The Equilibrium Phosphorus Concentration (EPC) is the value ofthe liquid-phase P concentration at which adsorption anddesorption processes are in equilibrium. P adsorption is favoredwhen EPC<DRP (Dissolved Reactive P) in the stream water.Conversely, P desorption is favored when EPC>DRP.
Exploring the relationship between EPC and sediment P fractions isan important first step to better predict the dynamics of P in theinterface of solid and solution phases.
Banks
In-stream deposit
Floodplain
Filtered stream water from Walnut Creek was used as a basesolution, spiked with 0, 0.05, 0.10, 0.20, 0.40, and 0.80 mg P L-1.
Three settings of physicochemical aspects.
EPC = 0.044 mg L-1
Organic and inorganic P were sequentially extracted using differentextractants.
Inorganic P (Pi) Organic P (Po)
Extractant Pi Fraction Extractant Po Fraction
1.0 M NH4Cl Soluble 0.5 M NaHCO3 Labile
0.5 M NH4F Al associated 1.0 M HCl Moderately soluble
0.1 M NaOH Fe associated 0.5 M NaOH Fulvic & Humic acid associated
CBD Reductant soluble 1.0 M H2SO4 Non labile
Sediment characteristics
Sediments CodepH H2O (1:1)
OM (%) % Sand/ Silt/Clay
Total P(mg kg-1)
CBD-Fe (mg kg-1)
DPS (%)
M3 Ox.
Banks
Camp Creek A 6.2 3.4 11/63/25 491 6,824 1.2 3.6
Roberts Creek B 6.3 4.5 13/60/27 588 5,862 1.0 3.8
Gunder C 7.4 1.5 6/72/22 484 3,813 1.0 5.7
Till D 8.1 1.5 49/31/21 473 10,124 0.0 10.8
In-stream deposit
Slump E 6.5 4.3 6/63/31 1,134 8,426 1.5 11.9
Stream bottom F 6.7 3.2 9/59/32 666 5,095 1.3 12.8
Debris dam G 7.2 3.6 22/53/25 966 15,571 1.4 6.0
Sand bar H 7.2 3.0 52/33/15 566 6,888 2.6 7.7
Floodplain
Forested floodplain I 6.1 6.4 4/70/26 730 8,615 1.4 5.3
Pasture J 5.6 5.2 1/81/18 567 7,341 1.1 3.0
Corn field K 6.2 4.7 23/57/21 617 9,195 2.5 4.1
Soybean field L 6.5 4.4 17/61/21 505 8,876 1.0 2.3
P fractionation
Sediment characteristics varied among the sampling locations.
Distribution of P among different organic and inorganic solidphases varied among the stream sediments.
Anaerobic incubation decreased redox potential and increased pHof the system after equilibrium.
Lowering redox potential significantly increased EquilibriumPhosphorus Concentration (EPC). EPC also tended to increase byincreasing shaking energy. The higher the EPC value, the morelikely stream sediments can act as a P source by favoringphosphate desorption into stream water.
Introduction
Materials and Methods
12 sediment samples (code A to L) from 3 groups (banks, in-stream deposit, floodplain) were collected from Walnut Creek,Jasper County, Iowa.
Results
Conclusions
Physicochemical aspects Setting 1 Setting 2 Setting 3
Solid to solution ratio of 1:20
Shaking speed Slow Fast Slow
30 days anaerobic incubation X X
24 hours shaking
EPC was determined by plotting solid and liquid phase-P afterequilibrium.
Note = OM: Organic Matter, CBD: Citrate Bicarbonate Dithionite, DPS-M3: Degree of PSaturation based on Mehlich-3 extraction; DPS-Ox : DPS based on ammonium oxalateextraction.
0
300
600
900
1200
A B C D E F G H I J K L
P c
oncentr
ation (
mg k
g-1
)
Sediments Code
Non Labile Po
Humic acid associated Po
Fulvic acid associated Po
Moderately labile Po
Labile Po
Ca associated Pi
Reductant soluble Pi
Fe associated Pi
Al associated Pi
Soluble Pi
Sampling
Fractionation study
Isotherm adsorption study
0.00
0.10
0.20
0.30
0.40
A B C D E F G H I J K L
EPC (
mg L
-1)
Sediments Code
Setting 1
Setting 2
Setting 3
Equilibrium P Concentration
EPC Means (mg L-1), n=12
0.047 b
0.084 b
0.156 a
Means of pH (1:20) and redox potential (Eh) after equilibrium
6.8
7.2
7.6
8.0
1 2 3
pH
(1:2
0)
Physicochemical Setting
0
200
400
600
1 2 3
Eh (
mV)
Physicochemical Setting
bb
aa a
bIOWA
Jasper County
Marion County
Red Rock
Reservoir
Walnut Creek Watershed
Walnut Creek
Neal Smith Refuge
Kilometer1 0 1
Suroso Rahutomo1, John L. Kovar2, and Michael L. Thompson1
1Agronomy Department, Iowa State University, 2USDA-ARS National Laboratory for Agriculture and the Environment
Ames, Iowa
Camp CreekA
Roberts CreekB
GunderC
TillD
Debris DamG Sand BarHStream BottomFSlumpE
ForestedI PastureJ Corn FieldK Soybean FieldL
A
B
C
A
B
D
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