Presentation is loading. Please wait.

Presentation is loading. Please wait.

Biogeochemistry of Wetlands

Published byKathleen Berry Modified over 6 years ago

Similar presentations

Presentation on theme: "Biogeochemistry of Wetlands"— Presentation transcript:

1 Biogeochemistry of Wetlands
Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands Science and Applications Electrochemical Properties Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor K. Ramesh Reddy 9/17/2018 9/17/2018 WBL 1

2 Chemical Reactions in Natural Systems
Reactions in which neither protons nor electrons are exchanged Fe2O3 + H2O = 2 FeOOH Reactions involving protons H2CO3 = H+ + HCO3- Reactions involving electrons Fe2+ = Fe3+ + e- Reactions in which both protons and electrons are transferred 2Fe(OH)3 + 3H+ + e- = 2Fe2+ + 3H2O 9/17/2018 WBL 2

3 Electrons and Protons e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-
Institute of Food and Agricultural Sciences (IFAS) Electrons and Protons e- e- e- H+ e- e- e- e- e- e- H+ H+ e- H+ e- H+ e- H+ e- H+ e- H+ e- H+ e- e- H+ e- e- e- H+ e- e- e- e- e- e- H+ e- e- e- H+ e- e- H+ H+ e- e- e- H+ H+ e- e- 9/17/2018 WBL

4 Electrochemical Properties
Topic Outline Introduction Oxidation-reduction reactions Nernst Equation Eh - pH relationships Buffering of redox potential Measurement of redox potentials Soil and water column pH Redox couples in wetland soils Redox gradients in wetland soils Specific conductance Soil oxygen demand Walther Nernst The Nobel Prize in Chemistry 1920 9/17/2018 WBL

5 Electrochemical Properties
Learning Objectives Basic concepts related to oxidation-reduction reactions Use of Nernst Equation to calculate redox potential (Eh) Relationship between redox potential (Eh) and pH Laboratory and field measurements of redox potentials Diel changes in water column pH Redox couples and microbial metabolic activities in wetlands Redox gradients and aerobic/anaerobic interfaces in wetlands Soil oxygen demand and nutrient fluxes Source: D. R. Lovley, Nature Reviews 4: 9/17/2018 WBL

6 Oxidation-Reduction Reductant Oxidant + e- Reductant = Electron donor
[Organic matter, NH4+, Fe2+, Mn2+, S2-, CH4, H2, H2O] Reductant Oxidant + e- Oxidant = Electron acceptor [O2, NO3-, MnO2, Fe(OH)3, SO42-, CO2, and some organic compounds] 9/17/2018 WBL

7 Oxidation-Reduction C6H12O6 + 6H2O = 6CO2 + 24H+ + 24 e-
[Aerobic Respiration] C6H12O H2O = 6CO H e- 6O2 + 24H e- = 12H2O C6H12O O2 = 6CO H2O Oxidation Reduction Reductant Oxidant Oxidation - Reduction

8 Oxidation-Reduction 5C6H12O6 + 30H2O = 30CO2 + 120H+ + 120 e-
[Nitrate Respiration – Dentrification] 5C6H12O H2O = 30CO H e- 24NO H e- = 12N2 + 72H2O 5C6H12O6 + 24NO H+ = 12N2 + 30CO2 + 42H2O Oxidation Reduction Reductant Oxidant Oxidation - Reduction

9 Oxidation-Reduction C6H12O6 + 6H2O = 6CO2 + 24H+ + 24e-
[Sulfate Respiration] C6H12O H2O = 6CO H+ + 24e- 3SO H+ + 24e- = 3S H2O C6H12O SO42- = 3S2- + 6CO2 + 6H2O Oxidation Reduction Reductant Oxidant Oxidation - Reduction

10 Oxidation-Reduction Reduced Oxidized UPLAND SOILS FLOODED SOILS N NH4+
2 NH4+ Mn2+ Fe2+ S2- CH4 PH3 H2 H2O NO3- Mn4+ Fe3+ SO42- CO2 PO43- O2 Oxidized Reduced 9/17/2018 WBL 10 10

11 Eh = Eo - [0.059/n] log [Reductant/Oxidant]
Nernst Equation m (OXIDANT) + m H+ + n e- = m (REDUCTANT) Eh = Eo - [0.059/n] log [Reductant/Oxidant] [m/n] pH E = Electrode potential (volts) Eo= Standard electrode potential (volts) F = Faraday’s constant ( kcal/volt mole or 96.50 kJ/volt mole R = Gas constant ( kcal/mole degree or kJ/mole degree T = Temperature ( K ( oC)) n = number of electrons involved in the reaction 9/17/2018 WBL 11

12 Oxidation-Reduction Potential (mV) Wetland Soil
-300 700 300 500 100 -100 Oxidation-Reduction Potential (mV) Highly Reduced Moderately Oxidized Anaerobic Aerobic Wetland Soil Drained Soil 9/17/2018 WBL 12 12

13 Oxidation-Reduction Electron Pressure -300 -100 100 300 500 700
Strongly reduced Strongly oxidized -300 -100 100 300 500 700 Oxidation-Reduction Potential (mV) 9/17/2018 WBL

14 Electron donors e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-
[Organic matter, NH4+, Fe2+, Mn2+, S2-, CH4, H2, H2O] e- e- e- e- e- H+ e- e- e- e- e- H+ e- e- e- H+ H+ e- H+ e- H+ e- e- H+ H+ e- H+ H+ e- e- H+ e- e- e- H+ e- e- e- e- NO3- Mn4+ Fe3+ SO42- CO2 H2 O O2 e- 600 -300 200 -100 100 300 Oxidation-Reduction Potential (mV) -400 Energy Electron acceptors 9/17/2018 WBL

15 How much energy is released during oxidation - reduction reactions?
Electrode Potentials Ease of Reduction CO2 SO42- Fe (III) Mn (IV) N-Oxides O2 Energy Yield [+] [-] 9/17/2018 WBL

16 Oxidation-Reduction Redox Potential, mV (at pH 7) Mn4+ Mn2+ CO2 CH4
SeO Se(0); Se2- SeO SeO32- SO S2- Fe Fe2+ NO N2 O H2O -200 -100 +100 +200 +300 +400 Redox Potential, mV (at pH 7) 9/17/2018 WBL 16 16

17 Iron Redox Couple and Eh-pH
1200 800 400 -400 pH Redox Potential (mV) Fe2+ Fe3+ Fe2O3 Fe3O4 FeS2 FeCO3 O2 H2O H2

18 Oxidation-Reduction Wetlands and Aquatic Systems Uplands
Electron acceptor non-limiting Electron donor limiting Electron acceptor limiting Electron donor non-limiting 9/17/2018 WBL

19 Sequential Reduction of
Electron Acceptors Organic Substrate [e- donor] Fe2+ S2- SO42- Relative Concentration CH4 NO3- Mn2+ O2 Oxygen Nitrate Iron Methanogenesis Manganese Sulfate Time or Soil Depth 9/17/2018 WBL 19 19

20 Redox Zones with Depth WATER Oxygen Reduction Zone
Aerobic SOIL I Eh = > 300 mV Nitrate Reduction Zone Facultative Mn4+ Reduction Zone II Eh = 100 to 300 mV Fe3+ Reduction Zone III Depth Eh = -100 to 100 mV Sulfate Reduction Zone Anaerobic IV Eh = -200 to -100 mV Methanogenesis V Eh = < -200 mV 9/17/2018 WBL 20 20

21 Regulators of Eh Water-table fluctuations.
Activities of electron acceptors. Activities of electron donors. Temperature pH 9/17/2018 WBL

22 Field Redox Electrodes
Copper wire Volt meter Heat shrinking tube Calomel Reference Water Epoxy Soil Platinum wire Platinum electrodes 9/17/2018 WBL

23 Laboratory Redox Electrodes
Platinum Glass Electrode Copper wire Saturated KCl Heat shrinking tube Glass tube Glass tube Calomel + Mercury Mercury Platinum wire Salt bridge Epoxy Mercury Platinum wire Calomel Reference Electrode 9/17/2018 WBL

24 Okeechobee Basin Wetland Soils and Stream Sediments
9/17/2018 WBL

25 Flooded Organic Soils: Everglades Agricultural Area
9/17/2018 WBL

26 Flooded Paddy Soils: Louisiana
Aerobic Anaerobic Redox Potential, mV Time, days 9/17/2018 WBL

27 Electron Acceptors - Redox Potential
-300 -200 -100 100 200 300 400 500 600 700 Oxygen Eh (mV) Nitrate Sulfate Bicarbonate Time (wk) 9/17/2018 WBL

28 Electron Donor [Organic Matter] –
Redox Potential 300 200 Low Organic Matter Soil 100 Redox potential (mV) -100 High Organic Matter Soil -200 Time after flooding 9/17/2018 WBL

29 Redox Gradients in Sediments
-20 Aerobic Layer -40 Anaerobic Layer -60 Depth (mm) -80 -100 -120 -140 -160 100 200 300 400 500 600 700 Redox Potential (mV) 9/17/2018 WBL

30 Sediment Microbial Fuel Cell
Source: D. R. Lovley, Nature Reviews 4: 9/17/2018 WBL

31 Redox Potential and pH Eh mv] pH 1000 800 600 400 200 -200 -400 -600
-200 -400 -600 pH 9/17/2018 WBL Baas Becking et al. 31

32 Limitations of Redox Potentials
Most of the redox couples are not in equilibrium except in highly reduced soils. In biological systems, electrons are added and removed continuously. Platinum electrodes respond favorably to reversible redox couples. Redox potential is closely related to pH. Platinum electrode surface can be contaminated by coatings of oxides, sulfides and other impurities. 9/17/2018 WBL

33 Soil and Water Column - pH
Reactions involving protons CO2 + H2O = H2CO3 H2CO3 = H+ + HCO3- HCO3- = H+ + CO32- Reactions in which both protons and electrons are transferred 2Fe(OH)3 + 3H+ + e- = 2Fe2+ + 3H2O 9/17/2018 WBL

34 Water Column pH: Experimental Ponds – Lake Apopka Basin
10 Algae 9 pH 8 Cattails and Egeria 7 Water hyacinth 6 Time, hundred hours 9/17/2018 WBL

35 Effect of Flooding on Soil pH
8 Clay loam [ pH = 8.7; OM = 2.2%; Fe = 0.63%] 7 6 pH Clay [ pH = 3.4; OM = 6.6%; Fe = 2.8%] 5 4 Clay [ pH = 3.8; OM = 7.2%; Fe = 0.1%] 3 Time after flooding 9/17/2018 WBL

36 Effect of Flooding on Soil Porewater Ionic Strength
Ca2+ Soil Fe2+ NH4+ Mn2+ K+ Solid Phase Soil Solution B Ionic Strength 9/17/2018 WBL Time after flooding

37 Redox Couples in Wetlands
C6H12O6/CO2 and NO3-/N2 C6H12O6/CO2 and FeOOH/Fe2+ C6H12O6/CO2 and MnO2 /Mn2+ C6H12O6/CO2 and SO42- /H2S H2/H+ and CO2 /CH4 C6H12O6/CO2 and O2/H2O 9/17/2018 WBL

38 Aerobic Respiration and Energy Yield
C6H12O O2 = 6CO H2O Gr = kcals/mole ADP + Pi = ATP Gr = -7.7 kcals/mole 9/17/2018 WBL

39 Biogeochemistry of Wetlands
Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands Science and Applications Soil Oxygen Demand Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor K. Ramesh Reddy 9/17/2018 9/17/2018 WBL 39

40 Oxygen Oxygen is an electron acceptor Reduction [Electron acceptor]
O2 + 4H+ + 4e- = 2H2O : Oxidation [Electron donor] C6H12O6 + 6H2O = 6CO2 + 24H e- Oxidant Reductant 9/17/2018 WBL

41 Oxygen Consumption Heterotrophic microbial respiration
C6H12O6 + 6O2 = 6CO2 + 6H2O Chemolithotrophic oxidation of reduced inorganic compounds NH O2 = NO3- + H2O + 2H+ Chemical oxidation of reduced inorganic compounds 4Fe H2O + O2 = 4Fe(OH)3 + 8H+ 9/17/2018 WBL

42 Oxidation-Reduction Carbon Nitrogen O2 O2 Floodwater Aerobic soil
Anaerobic soil Floodwater Aerobic soil Anaerobic soil CO2 O2 + CH4 NO3 O2 + NH4 OM CH4 OM NH4 9/17/2018 WBL

43 Oxidation-Reduction Iron Manganese O2 O2 Floodwater Aerobic soil
Anaerobic soil Floodwater Aerobic soil Anaerobic soil Fe3+ O2 + Fe2+ Mn4+ O2 + Mn2+ FeOOH Fe2+ MnO2 Mn2+ 9/17/2018 WBL

44 Oxidation-Reduction Carbon Sulfur O2 O2 Floodwater Aerobic soil
Anaerobic soil Floodwater CO2 O2 + OM SO4 O2 + H2S Aerobic soil Anaerobic soil SO4 H2S 9/17/2018 WBL

45 Oxygen Consumption Low organic matter soil [C/Co]
during chemical oxidation Consumption during biological oxidation [C/Co] High organic matter soil Time (hours) 9/17/2018 WBL

46 Dissolved organic C, mg/kg
Aerobic Respiration 100 200 300 400 500 600 700 Impacted Everglades, FL Unimpacted Everglades, FL Talladega, AL Houghton Lake Oxygen consumption, mg/kg day marsh, MI Salt marsh, LA Belhaven, NC y= ln(x) R2=0.84 Lake Apopka marsh, FL Prairie pothole, ND Crowley, LA 500 1,000 1,500 2,000 2,500 3,000 3,500 Dissolved organic C, mg/kg 9/17/2018 WBL

47 Impacted Unimpacted DEPTH (cm) DISSOLVED OXYGEN (% SATURATION) -2 -1 1
1 2 3 4 5 6 7 8 9 10 DEPTH (cm) DISSOLVED OXYGEN (% SATURATION) 12N 6P 12M 6A FILAMENTOUS ALGAE PERIPHYTON Peat Unconsolidated Peat WATER MACRO-LITTER AND ALGAE 20 40 60 80 100 Impacted Unimpacted 9/17/2018 WBL

48 Oxygen - Periphyton % O2 Saturation Depth (mm) Irradiance
50 100 150 200 250 19 36 68 192 306 593 - 1 2 Depth (mm) 4 6 8 10 Irradiance (μmol m-2 s-1) S. Hagerty, SFWMD unpublished results 9/17/2018 WBL

49 Lake Apopka Marsh Depth, cm Soluble P, mg L-1 Dissolved Fe, mg L-1 2 4
2 4 6 8 1 2 3 30 Phosphorus Iron 20 Depth, cm 10 Water Soil -10 -20 9/17/2018 WBL

50 Mobile and Immobile Iron
Insoluble Fe Fe2+ Aerobic 2 4 Depth below soil surface Anaerobic 6 8 1 2 3 % Fe 9/17/2018 WBL

51 OXYGEN: Sources and Sinks
Water Air Plants and Algae Release by Plant Roots Soil Oxygen Oxidation of Reductants Chemical oxidation Respiration Chemolithotrophic oxidation 9/17/2018 WBL

52 Electrochemical Properties &
Soil Oxygen Demand Summary Oxidation-reduction reactions regulate several elemental cycles Wetland soils are limited by electron acceptors and have abundant supply of electron donors. Upland soils are usually limited by electron donors, and have abundant supply of electron acceptors (primarily oxygen). Nernst Equation is used to calculate redox potential (Eh) Redox potentials (Eh) are inversely related to pH (59 mV/pH unit) Redox potential of soils are affected by (i) activities of electron donors (ii) activities of electron acceptors and (iii) temperature Laboratory and field electrodes can be used to measure redox potentials of soils 9/17/2018 WBL

53 Electrochemical Properties &
Soil Oxygen Demand Summary Distinct Eh gradients are present at (i) the soil-floodwater interface, (ii) root-zone of wetland plants, and (iii) around soil aggregates in drained portions of wetlands during low water-table depths. Water column pH is affected by photosynthesis Soil pH is affected by reduction of electron acceptors The rate of oxygen consumption is related to the concentration of reductants Oxygen consumption at the soil-floodwater interface regulates nutrient fluxes 9/17/2018 WBL

54 9/17/2018 WBL

Download ppt "Biogeochemistry of Wetlands"

Similar presentations

Iron and Manganese Cycling

Iron and Manganese Cycling
Oxidation-Reduction (Redox) Reactions 1. Measuring voltage Standard potentials (E°) have been determined for how much voltage (potential) a reaction is.

Oxidation-Reduction (Redox) Reactions 1. Measuring voltage Standard potentials (E°) have been determined for how much voltage (potential) a reaction is.
A galvanic cell is made from two half cells. In the first, a platinum electrode is immersed in a solution at pH = 2.00 that is 0.100 M in both MnO 4 -

A galvanic cell is made from two half cells. In the first, a platinum electrode is immersed in a solution at pH = 2.00 that is M in both MnO 4 -
Electricity from Chemical Reactions

Electricity from Chemical Reactions
How are soil properties affected when soil is submerged?

How are soil properties affected when soil is submerged?
Soil Chemical Properties

Soil Chemical Properties
Redox Geochemistry. Oxidation – Reduction Reactions Oxidation - a process involving loss of electrons. Reduction - a process involving gain of electrons.

Redox Geochemistry. Oxidation – Reduction Reactions Oxidation - a process involving loss of electrons. Reduction - a process involving gain of electrons.
Bacterial Metabolism and Biogeochemical Cycles. Redox Reactions All chemical reactions consist of transferring electrons from a donor to an acceptor.

Bacterial Metabolism and Biogeochemical Cycles. Redox Reactions All chemical reactions consist of transferring electrons from a donor to an acceptor.
Redox Geochemistry. WHY? Redox gradients drive life processes! –The transfer of electrons between oxidants and reactants is harnessed as the battery,

Redox Geochemistry. WHY? Redox gradients drive life processes! –The transfer of electrons between oxidants and reactants is harnessed as the battery,
E NVIRONMENTAL CHEMISTRY E 12. water and soil. W ATER AND SOIL Solve problems relating to the removal of heavy- metal ions, phosphates and nitrates from.

E NVIRONMENTAL CHEMISTRY E 12. water and soil. W ATER AND SOIL Solve problems relating to the removal of heavy- metal ions, phosphates and nitrates from.
Figure 4-1. Diagram of a Zn-Cu electrochemical cell. Zn and Cu metal electrodes are immersed in a CuSO 4 solution. Electrons flow from left to right and.

Figure 4-1. Diagram of a Zn-Cu electrochemical cell. Zn and Cu metal electrodes are immersed in a CuSO 4 solution. Electrons flow from left to right and.
Oxidation-Reduction (Redox) Reactions

Oxidation-Reduction (Redox) Reactions
Lec 5: Gases (DO & CO2) and pH

Lec 5: Gases (DO & CO2) and pH
Aquatic Plants and the Environment (SWES, ECOL, WFSc 474/574) Nutrient Cycles in Wetlands Dr. Kevin Fitzsimmons Professor – University of Arizona.

Aquatic Plants and the Environment (SWES, ECOL, WFSc 474/574) Nutrient Cycles in Wetlands Dr. Kevin Fitzsimmons Professor – University of Arizona.
Microbial Metabolism Overview of metabolism (you should know about TCA cycle, Embden-Meyerhof pathway- glycolysis, Proton motive force etc.) Overview of.

Microbial Metabolism Overview of metabolism (you should know about TCA cycle, Embden-Meyerhof pathway- glycolysis, Proton motive force etc.) Overview of.
Lecture 15 The Redox Sequence Oxidation State Half-Reactions Balanced Oxidation-Reduction reactions Predicted Sequence of Redox Reactions Tracers for these.

Lecture 15 The Redox Sequence Oxidation State Half-Reactions Balanced Oxidation-Reduction reactions Predicted Sequence of Redox Reactions Tracers for these.
Electrochemical Phenomena Eh and pE Approaches Redox Reactions pE-pH Diagrams Flooded Soils.

Electrochemical Phenomena Eh and pE Approaches Redox Reactions pE-pH Diagrams Flooded Soils.
REDOX CLASSIFICATION OF NATURAL WATERS

REDOX CLASSIFICATION OF NATURAL WATERS
Redox Geochemistry.

Redox Geochemistry.
Soil Aeration.

Soil Aeration.

Similar presentations

Ads by Google