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10/30/2019

Institute of Food and Agricultural Sciences (IFAS) . Biogeochemistry of Wetlands Science and Applications. Phosphorus Cycling Processes. Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida. Instructor K. Ramesh Reddy krr@ufl.edu. 10/30/2019.

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10/30/2019

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  1. Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands Science and Applications Phosphorus Cycling Processes Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor K. Ramesh Reddy krr@ufl.edu 10/30/2019 1 10/30/2019 WBL WBL 1

  2. DRP PP Water column DRP PP Soil • Institute of Food and Agricultural Sciences (IFAS) Phosphorus Cycling Processes 10/30/2019 WBL WBL 2

  3. Water Column Soil Phosphorus Cycling Processes Topic Outline • Introduction • Forms of phosphorus • Inorganic Phosphorus retention mechanisms • Organic phosphorus dynamics • Phosphorus exchange between soil and overlying water column • Regulators of phosphorus reactivity and mobility • Phosphorus memory in wetlands 10/30/2019 WBL 3

  4. Phosphorus Cycling Processes Learning Objectives • Identify sources, and inorganic and organic forms of phosphorus • Inorganic phosphorus retention mechanisms in soil • Descibe the influence of soil type on inorganic phosphorus retention • Role of enzymes and microorganisms in organic phosphorus mineralization • Biotic regulation phosphorus retention • Phosphorus exchange between soil and overlying water column • Draw the phosphorus cycle and indentify, storages, abiotic and biotic processes, and fluxes in soil and water column 10/30/2019 WBL 4

  5. Terminology • Total Phosphorus (TP) • Dissolved total P (DTP) • Total P in solutions filtered through 0.45 um membrane filter • Dissolved reactive P (DRP) or Soluble Reactive P (SRP) • Water samples filtered through 0.45 um membrane filter and analyzed for ortho-P. • Dissolved Organic P (DOP) • DTP – DRP = DOP • Particulate inorganic P (PIP) • Particulate matter or soil extracted with acid • Particulate organic P (POP) • TP-PIP = POP 10/30/2019 WBL 5

  6. Plant biomass P Runoff, Atmospheric Deposition Outflow Litterfall PIP DIP POP DOP DIP Periphyton P AEROBIC [Fe, Al or Ca-bound P] Peat DIP accretion DIP PIP Adsorbed IP DOP POP DOP ANAEROBIC Phosphorus Cycle WBL

  7. Fertilizers, Animal wastes Biosolids, Wastewaters Phosphorus Transfer Uplands [sink/source] Wetlands & Streams [sink/source] Lake [sink] Lake Okeechobee WBL

  8. Atmospheric Deposition Composts (?) Natural weathering of minerals (?) Animal Manures 0% 10% 8% 8% Fertilizers 69% Wastewater 5% Biosolids Total = 61,300 mt P per year 1996 Phosphorus Imports from Various Sources: Florida WBL

  9. Fertilizer Phosphorus Inputs [8%] [5%] [20%] Florida 42,660 metric ton year-1 [17%] North America 1.85 x 106 metric tons year-1 [Mullins et al., 2005] [50%] World 14 x 106 metric tons year-1 1996 Florida 2003 North America 2003 World [Mullins et al., 2005] WBL

  10. Phosphorus Loads from Uplands • Uplands have been a steady source of P to wetlands and aquatic systems, where substantial amounts of P has accumulated in soils and sediments • Best management practices and other remedial measures can significantly reduce P loads from uplands to wetlands and aquatic systems • How will wetlands and aquatic systems respond to P load reduction? • How long P memory lasts in wetlands and aquatic systems before they reach stable condition? WBL

  11. Water Column P Detritus P Soil Phosphorus Memory in a Watershed • Capacity for storing phosphorus in various ecosystem components (uplands, wetlands, and aquatic systems) • Transient pools • Stable pools • Capacity for showing effects as the result of past practices • Length of time over which phosphorus release extends before returning to a stable condition WBL

  12. Phosphorus Transfer [Lake Okeechobee Basin] [4157] Phosphorus Budget [tons/year] Uplands (82%) [754] • [415] (10%) Wetlands & Streams (8%) Lake Okeechobee 10/30/2019 WBL WBL 12

  13. Phosphorus Loading Phosphorus Outflow Gradient in nutrient enrichment in soil and water column [ Distance from inflow] Phosphorus Gradient in Wetlands 10/30/2019 WBL WBL 13

  14. 1 5 0 1 0 0 Total P (µg/L) 5 0 0 0 2 4 6 8 1 0 1 2 1 4 1 6 Distance from Inflow (km) Water column TP - WCA-2A transect 10/30/2019 WBL WBL 14

  15. 1.2 1.0 0.8 P ACCUMULATION (g m-2 y-1) 0.6 0.4 0.2 0 0 2 4 6 8 10 12 14 16 DISTANCE FROM INFLOW (km) Phosphorus accretion rates inEverglades WCA-2A 10/30/2019 WBL WBL 15

  16. Total P concentration in WCA-2A soil (0-10 cm) 1990 1998 10/30/2019 WBL WBL 16

  17. Everglades – Soil phosphorus 10/30/2019 WBL WBL 17

  18. Soil Phosphorus Blue Cypress Marsh-1992 0-4 0-4 4-8 8-12 8-12 12-16 16-20 Depth (cm) 16-20 24-28 20-24 Impacted 24-28 32-36 Unimpacted 32-36 36-40 40-44 0 1,000 2,000 0 1,000 2,000 Total P (mg /kg) 10/30/2019 WBL WBL 18

  19. Phosphorus Memory External Load Reduction Background Level Internal Memory Water Column Phosphorus Lag time for Recovery Time - Years WBL

  20. Ecological Significance – Phosphorus Loading N N C C P Labile DETRITUS Microbial Biomass Microbial Biomass P N P N P PLANTS WATER DETRITUS SOIL 10/30/2019 WBL WBL 20

  21. Plant biomass P Runoff, Atmospheric Deposition Outflow Litterfall PIP DIP POP DOP DIP Periphyton P AEROBIC [Fe, Al or Ca-bound P] Peat DIP accretion DIP PIP Adsorbed IP DOP POP DOP ANAEROBIC Phosphorus Cycle WBL

  22. Phosphorus in Wetlands Organic phosphorus Phosphorus loading Uptake by algae and plants Soil porewater phosphorus [dissolved] Metal oxides and clay mineral surfaces Discrete phosphate minerals 10/30/2019 WBL WBL 22

  23. Soil Phosphorus Forms • Inorganic P • KCl-Pi - Bioavailable P • NaOH-Pi - Fe-/Al- P [slowly available] • HCl-Pi - Ca-/Mg- P [slowly available] • Organic P • Microbial Biomass P - Bioavailable P • NaOH-Po - Fulvic Acid -P [slowly available] • NaOH-Po - Humic Acid -P [very slowly available] • Residual P -Highly resistant [unavailable] 10/30/2019 WBL WBL 23

  24. Phosphate ions and pH • H3PO4 = H+ + H2PO4- pK = 2.15 • H2PO4- = H+ + HPO42- pK = 7.20 • HPO42- = H+ + PO43- pK = 12.35 Oxidation number for P H3PO4 PO43- [+5] [+5] H2PO4- [+5] PH3 [-3] [+5] HPO42- 10/30/2019 WBL WBL 24

  25. Inorganic Phosphorus- Organic Soils - WCA-2A 3,000 Y = 0.01X1.54 R2 =0.897; n=390 1,000 300 100 Total Inorganic P (mg kg-1) 30 WCA1 WCA2 10 WCA3 3 HWMA EAA 1 50 100 200 500 1,000 2,000 5,000 Total Phosphorus (mg kg-1 ) 10/30/2019 WBL WBL 25

  26. 13% 2% 29% 50% 6% 10% 1% 7% 11% 71% Stream Sediments – Okeechobee Drainage Basin KCl-Pi (available) Fe- and Al-bound P Alkali extractable organic P Ca- and Mg-bound P Residual P DL-Stream Total P = 877 mg P/kg Rucks-Stream Total P + 93 mg P/kg 10/30/2019 WBL WBL 26

  27. KCl-Pi (available) Fe- and Al-bound P Alkali extractable organic P 1% <0.1% Ca- and Mg-bound P 4% 23% Residual P 72% 1% 7% 24% 47% 21% Organic Wetland Soils – Drainage Effects Peat Depth < 10 cm Total P = 836 mg P/kg Peat Depth > 30 cm Total P = 411 mg P/kg 10/30/2019 WBL WBL 27

  28. Inorganic Phosphorus • Pore water P • Exchangeable • Fe-/Al- bound P • Ca-/Mg-bound P • Residual P High Bioavailability Low 10/30/2019 WBL WBL 28

  29. Inorganic Phosphorus • Acid soils • AlPO4 . 2H2O [Variscite] • FePO4 . 2H2O [Strengite] • Alkaline soils • Ca (H2PO4)2 [Monocalcium phosphate] • Ca HPO4. 2H2O [Dicalcium phosphate] • Ca8 (H2 PO4)6 . H2O [Octacalcium phosphate] • Ca3 (PO4)2 [Tricalcium phosphate] • Ca5 (PO4)3 OH [Hydroxyapatite] • Ca5 (PO4)3 F [Fluorapatite] 10/30/2019 WBL WBL 29

  30. Phosphate Minerals 1 mm 5 mm Apatite Vivianite W. G. Harris, 2002 10/30/2019 WBL WBL 30

  31. Phosphate Availability • Readily available phosphates • Soil porewater. • Slowly available phosphates • Fe, Al, and Mn phosphates (acid soils) and Ca and Mg phosphates (alkaline soils) that have been freshly precipitated or are held mostly on the surface of fine particles in the soil. Labile organic compounds. • Very slowly available phosphates • Precipitates of Fe, Al, Mn, Ca, and Mg phosphates that have aged and are well crystallized. Phosphates that were held on particle surfaces have penetrated the particles, little remaining on the surface. Stable organic compounds 10/30/2019 WBL WBL 31

  32. Phosphorus • Is P one of the redox elements ? • HPO42- + 10H+ + 8e- = PH3 + 4H2O • Is P solubility affected by changes in redox potential? • FePO4 + H+ + e- = Fe2+ + HPO42- 10/30/2019 WBL WBL 32

  33. Phosphorus Retention by Soils • Adsorption –Desorption • Precipitation – Dissolution • Immobilization - mineralization Retention = Adsorption + Precipitation + Immobilization 10/30/2019 WBL WBL 33

  34. Sorption of Phosphate • Intensity factor : Concentration of phosphate in soil porewater. • Capacity factor : Ability of solid phases to replenish phosphate as it is depleted from solution. Solid phase Psolution Padsorbed 10/30/2019 WBL WBL 34

  35. Al OH2+ OH + H2PO4-= H2PO4 + OH- Al OH2+ OH OH Al + H2PO4- = + OH- Al OH OH OH H2PO4 Inorganic Phosphate Reactions • Precipitation by Al, Fe, Mn, Ca, and Mg ions • Al3+ + H2PO4- + 2H2O = 2H+ + Al (OH)2 H2PO4 (insoluble) (Variscite) • Anion exchange • Reaction with hydrous oxides • Fixation by silicate clays • Al2 SiO5 (OH)4 + 2H2PO4- = 2Al (OH)2 H2PO4 + Si2O52- 10/30/2019 WBL WBL 35

  36. pH- Dependent Charge on Solid Phase Negative charge [loss of H+] [-] Charge 0 ZPC [zero point charge] [+] Positive charge [gains H+] 3 4 5 6 7 8 9 10 pH 10/30/2019 WBL WBL 36

  37. Variable Charge on Solid Phase No charge Solid phase Soil Solution Negative charge Solid phase Al – OH + OH- = Al–O- + H2O COOH + OH- = COO- + H2O AlOH + H+ = AlOH2+ AlOH + H+ AlOH2+ AlO- + H+ Negative charge [high pH] No charge [Intermediate pH] Positive charge [low pH] 10/30/2019 WBL WBL 37

  38. Inorganic Phosphate Reactions Alkaline pH conditions: • Ca2+ + 2H2PO4- = Ca (H2PO4)2 • Ca (H2PO4)2 + Ca2+ + 2OH- = 2CaHPO4 + 2H2O • 2CaHPO4 + Ca2+ + 2OH- = 2Ca3 (PO4)2 + 2H2O 10/30/2019 WBL WBL 38

  39. 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] 10/30/2019 WBL WBL 39

  40. Phosphorus Sorption Isotherm Smax Adsorption EPCo slope = KD Water Pw Pad Ps Pret Desorption Soil P desorption under So ambient conditions Phosphorus in Soil Porewater 10/30/2019 WBL WBL 40

  41. Phosphorus Sorption Isotherm Low P Load Adsorption EPCo High P Load EPCo P Retention Desorption P Release Phosphorus in Soil Porewater 10/30/2019 WBL WBL 41

  42. Influence of Phosphorus Loading on EPC0 [Nair et al. 1997] Land use Total P (mg/kg) EPCo (mg/L) Intensive 2,330 5.0 181 1.4 Holding Pasture 0.1 31 Beef 0.1 31 Forage 23 0.2 Native 18 0.1 10/30/2019 WBL WBL 42

  43. Influence of Phosphorus Loading on EPC0 [Everglades – WCA-2a] 2 Anaerobic 0-10 cm 1.5 Aerobic 0-10 cm 1 EPCo (mg P/L) 0.5 0 0 2 4 6 8 10 12 Distance from inflow (km) 10/30/2019 WBL WBL 43

  44. Phosphorus Sorption [Richardson, 1985] 3000 Swamp forest Mineral/peat soil 2400 Houghton fen Peat soil 1800 P sorbed, mg/kg Pocosin bog Mineral/peat soil 1200 600 Pocosin bog Peat soil 0 0 30 90 150 210 P in solution, mg/L 10/30/2019 WBL WBL 44

  45. P Sorption by WCA-2A soils 2,000 Ambient PW-P 1,500 Site 1 Desorption 1,000 [Anaerobic] 500 Sorption 0 Sorbed P (mg P/kg) 0.01 0.1 1 10 100 Site 8 Ambient PW-P 1,500 [Anaerobic] 1,000 Desorption 500 Sorption 0 0.001 0.01 0.1 1 10 100 Solution P concentration (mg P/L) 10/30/2019 WBL WBL 45

  46. Phosphorus Sorption Isotherm • Linear Equation • S = KL C • where: S = mass of P sorbed per mass of solid phase; C = P concentration in solution; KL = adsorption coefficient related to binding strength • Freundlich Equation • S = KF CN [log S = N log C + log KF] • where: S = mass of P sorbed per mass of solid phase; C = P concentration in solution; KF = adsorption coefficient related to binding strength; N = empirical constant 10/30/2019 WBL WBL 46

  47. Phosphorus Sorption Isotherm • Langmuir Equation • S = [k C Smax]/1 + k C • C/S = [1/Smax] C + 1/k Smax • where: S = mass of P sorbed per mass of solid phase; C = P concentration in solution; k = constant related to binding strength; Smax = maximum amount of P sorbed per mass of solid phase Slope = 1/Smax (C/S) 1/kSmax C 10/30/2019 WBL WBL 47

  48. Phosphorus Sorption Isotherm Adsorption Smax Adsorption Precipitation EPCo slope = KD Desorption P desorption under ambient conditions So Phosphorus in Soil Porewater 10/30/2019 WBL WBL 48

  49. Saturation Index (SI) Ca Ab = aC + bA [C]a [A]b K = [Ca Ab] [C]a [A]b Ion Activity Product (IAP) = Saturation Index (SI) = IAP/K SI < 1 = Solution is “undersaturated” SI > 1 = Solution is “supersaturated” SI = 1 = Solution saturated (near equilibrium) 10/30/2019 WBL WBL 49

  50. Precipitation of Phosphate P in solution; t = 0 1 Supersaturation with respect to B 2 Intensity Factor Supersaturation with respect to C A 3 B C Capacity Factor 10/30/2019 WBL WBL 50

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