REDOX: IRON, SULFUR, & SILICA

Redox Potential

• pE = -log free electrons• When corrected to pH 7 (H+ = OH-), called Eh

• When Eh positive – oxidizing environment

• When Eh negative – reducing environment

Redox vs. pH

Redox (mv) of common liquids

Example of Redox data

pH and ORP in Lake Skiennungen

Fe & Mn in oligotrophic and eutrophic lakes

Iron and Manganese in a Productive Lake

Redox: Sulfur and Iron

Particulate Fe and Fe (II) through the year

Sulfur and Iron in Mud

Fe & Mn in Crooked lake

(mesotrophic)

Fe & Mn in Little Crooked

lake(eutrophic)

Transport of Fe in a lake

Iron Oxidizing Bacteria

• Gallionella (an iron-oxidizing bacterium)• 4Fe (HCO3)2 + O2 + 6H2O 4Fe (OH)3 + 4H2CO3 + 4CO2 + 58 kcal

Ferrobacillus iron bacteria

• 4FeCO3 + O2+ 6H2O Fe(OH)3 + 4CO2

Mn cycling relative to O2

REDOX and Sulfur

S in oligotrophic and eutrophic lakes

SO4 in a mesotrophic

hardwater lake

SO4 budget for Linsley Pond

ORP, pH, and Sulfur bacteria

Autotrophic Sulfur-Oxidizing Bacteria and Iron Transformations

• Thiobacillus• Some of the reactions that it can mediate• FeS2 + 3½O2+H2O FeSO4 + H2SO4

• 2FeSO4 + ½O2+ H2SO4 Fe2(SO4)3 + H2O

Bacterial Transformations of Sulfur

• Sulfate-Reducing Bacteria (heterotrophic and anaerobic)

• Sulfur-Oxidizing Bacteria– Chemosynthetic– Pigmented Autotrophic

Sulfate-Reducing Bacteria

• Ex: Desulfovibrio• Heterotrophic and anaerobic• H2SO4 + 2(CH2O) 2CO2 2H2O + H2S

• H2SO4 + 4H2 H2S + 4H2O

Chemosynthetic Sulfur-Oxidizing Bacteria

• Ex: Beggiatoa• Deposit elemental S inside cell• H2S + ½O2 S + H2O

• S + 1½O2 + H2O H2SO4

• Ex: Thiobacillus• Deposit elemental S outside• 2Na2S2O3 + O2 2S + 2Na2SO4

Green Sulfur Bacteria

• Ex: Chlorobium• Uses a pigment similar to chlorophyll• CO2 + 2H2S LIGHT Food + H2O + 2S

• 2CO2 + 2 H2O + H2S LIGHT Food + H2SO4

Purple Sulfur Bacteria• Ex: Chromatium• They deposit sulfur

intracellularly• Same reactions as Chlorobium

Purple Non-Sulfur Bacteria

• Ex: Rhodobacter• Na2S2O3+2CO2 +3H2O LIGHT Food + Na2SO4 +H2SO4

Microbial-mediated Sulfur cycle in a lake

Sulfate reduction in Lake Gek Gel and the Black Sea

Distribution of sulfur in

meromictic Lake Belovod

Abandoned Mine Drainage

Microbial Oxidation of Pyrite

AMD Discharges

Acid Precipitation

Si in lakes

Some Common Diatoms

Si in oligotrophic Lawrence Lake

Si and diatom population dynamics in Lake Windermere

Dynamics of diatom periphyton and plankton

Green Algae and Diatoms