REDOX: IRON, SULFUR, & SILICA

Redox Potential pE = -log free electrons When corrected to pH 7 (H + = OH - ), called E h When E h positive – oxidizing environment When E h 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 (HCO 3 ) 2 + O 2 + 6H 2 O 4Fe (OH) 3 + 4H 2 CO 3 + 4CO kcal

Ferrobacillus iron bacteria 4FeCO 3 + O 2 + 6H 2 O Fe(OH) 3 + 4CO 2

Mn cycling relative to O 2

REDOX and Sulfur

S in oligotrophic and eutrophic lakes

SO 4 in a mesotrophic hardwater lake

SO 4 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 FeS 2 + 3½O 2 +H 2 O FeSO 4 + H 2 SO 4 2FeSO 4 + ½O 2 + H 2 SO 4 Fe 2 (SO 4 ) 3 + H 2 O

Bacterial Transformations of Sulfur Sulfate-Reducing Bacteria (heterotrophic and anaerobic) Sulfur-Oxidizing Bacteria – Chemosynthetic – Pigmented Autotrophic

Sulfate-Reducing Bacteria Ex: Desulfovibrio Heterotrophic and anaerobic H 2 SO 4 + 2(CH 2 O) 2CO 2 2H 2 O + H 2 S H 2 SO 4 + 4H 2 H 2 S + 4H 2 O

Chemosynthetic Sulfur-Oxidizing Bacteria Ex: Beggiatoa Deposit elemental S inside cell H 2 S + ½O 2 S + H 2 O S + 1½O 2 + H 2 O H 2 SO 4 Ex: Thiobacillus Deposit elemental S outside 2Na 2 S 2 O 3 + O 2 2S + 2Na 2 SO 4

Green Sulfur Bacteria Ex: Chlorobium Uses a pigment similar to chlorophyll CO 2 + 2H 2 S LIGHT Food + H 2 O + 2S 2CO H 2 O + H 2 S LIGHT Food + H 2 SO 4

Purple Sulfur Bacteria Ex: Chromatium They deposit sulfur intracellularly Same reactions as Chlorobium

Purple Non-Sulfur Bacteria Ex: Rhodobacter Na 2 S 2 O 3 +2CO 2 +3H 2 O LIGHT Food + Na 2 SO 4 +H 2 SO 4

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