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Biogeochemical Cycling of Phosphorus in Wetlands: Effect of Internal Load on Water Quality

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Title: Biogeochemical Cycling of Phosphorus in Wetlands: Effect of Internal Load on Water Quality


1
Biogeochemical Cycling of Phosphorus in Wetlands
Effect of Internal Load on Water Quality
John R. White Wetland Biogeochemistry
Institute Department of Oceanography Coastal
Sciences Louisiana State University jrwhite_at_lsu.ed
u
2
Phosphorus Transfer
Fertilizers Animal wastes Biosolids Wastewater
Rainfall
Wetlands
Uplands
Sink/Source
Sink/Source
Aquatic Systems
Sink
3
Water Quality Parameters
Phosphorus Dissolved reactive P (DRP) Water
samples filtered through 0.45 um membrane filter
and analyzed for ortho-P. Dissolved organic P
(DOP) Water samples filtered through 0.45 um
membrane filter and analyzed for organic P
Particulate inorganic P (PIP) Particulate
organic P (POP) Total P (sum of all the above)
4
Phosphorus Cycle (not like N)
Inflow
Outflow
Ca/Mg/Fe/Al-P
Recalcitrant P
5
Phosphorus Retention by Soils
  • Adsorption Desorption
  • Precipitation Dissolution
  • Immobilization - mineralization

Retention Adsorption Precipitation
Immobilization
6
Phosphorus Gradient in Wetlands
Phosphorus Outflow
Phosphorus Loading
Gradient in nutrient enrichment in soil and water
column
Distance from inflow
Soil vs Water Column
7
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8
South Florida
1900
1940
1970
9
Florida Everglades
P enriched soils in WCA
10
Impacted Area
11
Unimpacted Area
12
Total P concentration in WCA-2A soil (0-10 cm)
1998
1990
13
Stormwater Treatment Area Constructed Wetlands
14
Transfer to Water Column
Soluble P, mg L-1
Dissolved Fe, mg L-1
1
2
3
0
6
8
0
2
4
30
20
Water
10
Depth, cm
0
Soil
-10
-20
15
Internal Phosphorus Load Everglades -WCA-2A
6
5
4
P flux (mg P /m2 day)
3
2
1
0
0
2
4
6
8
10
12
Distance from inflow (km)
16
Internal Phosphorus Load
External Load Reduction
Water Column P
Background Level
Internal Load
Lag time for Recovery
Time - Years
17
Effect of Hydrology
Pulsed System vs Continuously Flooded
18
Experimental Design
  • Emergents vs no emergents
  • Continuously flooded vs periodic drawdown
  • One year

Randomized Block Design
Peat soil 7 x 1 m wide depth of 30 cm plumbed
40 cm water column HRT of 15 d
19
Mesocosms
  • Inflow and Outflow SRP, TDP and TP were
    determined on each tank, weekly.
  • Redox readings at 5 and 10 cm
  • Soils and plants were collected at time 0 and 1
    year analyzed for C, N, P

20
Mesocosms
21
Emergents
250
Mean Inflow
Mean Outflow
200
150
100
50
0
0
4
8
12
16
20
24
28
32
36
40
44
Time (week)
Mass of Dissolved Reactive Phosphorus (mg)
250
Mean Inflow
200
Mean Outflow
150
100
Drawdown
Drawdown
50
0
0
4
8
12
16
20
24
28
32
36
40
44
Time (week)
22
Submerged Aquatic Vegetation
23
Reduction of P in surface water
Drawdown
Flooded
Emergents No Emergents
Emergents No Emergents
SRP/DRP 90.2 90.1 81.4
81.4
DOP 24.4 10.4 -75.4
-53.1
PP 79.4 77.3
75.8 62.8
White et al., 2004 Hydrologic Processes White et
al., 2006 Soil Science Soc. Of Amer J
24
Internal Loads in the Eutrophic Northern
Everglades Large-scale Modeling of Phosphorus
Transport
J.W. Jawitz and K. Grace Soil and Water Science
Department University of Florida
25
Wetlands
  • Wetlands are typically low velocity systems with
    a significant biomass component
  • Large biomass means that biological uptake may be
    important and resultant accumulation of OM under
    anaerobic conditions
  • Low velocities mean deposition of suspended
    sediments is important

26
T 3, 15, 39, 66, 100, 133 years
27
T 3, 15, 39, 50, 66, 100 years
28
Depending on Modeling Scenario Not too
bad Disaster for Everglades Long-term For
Louisiana Surface Water Diversions Davis
Pond 10,000 cfs Mississippi River Water
29
Constructed Wetlands for P Removal
30
Soluble Phosphorus Removal
  • Loading rate 0.29 kg/ha day
  • Mass removal 41
  • Inflow concentration 1.8 mg/L
  • Outflow concentration 1.1 mg/L
  • Percent reduction in concentration 37

Kadlec and Knight (1995)
31
Total Phosphorus Removal
  • Loading rate 0.5 kg/ha day
  • Mass removal 34
  • Inflow concentration 3.8 mg/L
  • Outflow concentration 1.6 mg/L
  • Percent reduction in concentration 57

Kadlec and Knight (1995)
32
Orlando Easterly Wetland
  • City of Orlando
  • Iron Bridge Water
  • Reclamation Facility

33
OEW Facts
  • 1,200 acre wetland constructed in 1986
  • 18 cells, 32 water control structures
  • Treats up to 35 mgd from Iron Bridge Wastewater
    Treatment Plant

34
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35
The Problem
Inflow TP
Outflow TP
TP (mg L-1)
Jan-96
Jan-97
Jan-98
Jan-99
Jan-00
Jan-01
Jan-02
Jan-03
Jan-04
Jan-05
Jan-06
Concern over P binding capacity
36
Management Strategies
  • Prescribed burning
  • Cell 1,3,8,9,10,11
  • Dredging
  • Cell 1,3,4,7,8, 13
  • Chemical amendments

37
Alum (Al2(SO4)314H2O)
  • pH of 2.4
  • Dissociates in water forming Al3 ions that are
    immediately hydrated
  • Al3 H2O ? Al(OH)2 H
  • Al(OH)2 H20 ? Al(OH)2 H
  • Al(OH)2 H20 ? Al(OH)3(s) H
  • For P sequestration need system pH 6 to 8

38
Chemical Amendment
Water Column
Al Floc
Sediment surface
Sediment SRP
39
Mesocosm Study Emergents and SAV Alum drip vs
Control
40
Outflow Phosphorus
Dissolved Reactive P
n3
41
Outflow Phosphorus
Total P
42
Plant Biomass
n3
SAV
Scirpus californicus
Typha spp.
43
Plant Nutrient Content
Mg
Ca
TP
Plant
Fe
Al
mg kg-1
mg kg-1
mg kg-1
 
mg kg-1
mg kg-1
532 289
2949 749.7
13372 6390
3315 1823
28296 8575
SAV
Alum
69.8 79.7
411.7 75.14
1516 154
59.2 33.2
15493 1909
Scirpus
 
85.4 54.7
485.1 49.49
5337 604
176 52.9
14351 1614
Typha
 
371 134
1853 167.3
28989 6771
66.3 32.6
23345 7116
SAV
Control
75.8 44.6
373.0 32.76
1474 486
25.6 13.7
20678 9721
Scirpus
 
155 117
558.8 67.53
4466 804
44.6 19.4
15822 1549
Typha
 
Time 84d, n3
44
  • Alum effectively sequestered P in SAV and
    emergent continually loaded mesocosms
  • Soil amorphous Al concentration increased,
    reducing soil pH, microbial biomass
  • SAV biomass decreased due to Al toxicity while
    emergent vegetation was relatively unaffected

45
Conclusions
Phosphorus storage in organic matter in
wetlands Stored Phosphorus (Internal Load) can
be mobilized Saturation no more
capacity Fluctuating Hydrology Restoration
low water concentrations Need to decrease
mobility of internal load to prevent eutrophicatio
n downstream Manage Hydrology Chemical
Amendments Fire Physical Removal
46
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47
  • DRP attenuation was greatest in the continuously
    flooded treatments (90 yr).
  • Periodic drawdown led to a net release of P, in
    particular, dissolved organic P.
  • Plants and algae took up more P than was
    removed from the water column, mining the soil.
  • White et al., 2004 Hydrologic Processes
  • White et al., 2006 Soil Science Soc. Of Amer J

48
Phosphorus
  • Forms of phosphorus
  • Inorganic phosphorus
  • Organic phosphorus
  • Phosphorus retention mechanisms
  • Adsorption
  • Precipitation
  • Mineralization of organic phosphorus
  • Phosphorus exchange between soil and overlying
    water column

49
Sorption of Phosphate
Solid phase
Solution phase
I
I Initial equilibrium condition
Phosphate ions
II
II Increase in solution P concentration
--- Rapid adsorption to solid surface
Time seconds to minutes
III
III Diffusion into solid phase
Time hours to days
50
Organic Phosphorus
Detrital Matter Phytin Phospholipids Nucleic
acids Sugar phosphates
Plants Animals Microbes
Humus
Inorganic Phosphate
51
Phosphorus in Wetlands
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