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 2 + 58 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 2CO 2 + 2H 2 S LIGHT Food + H 2 O + 2S + 2 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