Biogeochem - Redox Sensitive Metals Flashcards
What is the product if Fe(II) is oxidised
Fe(III)
What is the product if Fe(III) is reduced?
Fe(II)
What are some redox sensitive elements?
Iron, Manganese and nickel
What is a redox reaction?
A chemical reaction involving the transfer of electrons between two chemical species
List examples of redox reactions
Photosynthesis, Respiration, combustion, corrosion, biofouling, rusting
What is the relationship between Redox reactions and gibbs free energy?
Redox reactions produce and consume gibbs free energy
List some examples of environmental redox reactions in anoxic environments
- Anaerobic methane oxidation
- Methanogenesis
- nitrate reduction
- sulphate reduction
- nitrogen fixation
List some examples of environmental redox reactions in oxic environments
- Aerobic methane oxidation
- Ammonia oxidation
- Aerobic sulphur oxidation
what are some major forms of iron in the environment?
Hematite ((Fe3+)2O3)
Ferrihydrite
Magnetite
What are the main oxidation states you can find iron in?
Pure Iron = Fe –> neutral atom
Ferric iron = Fe3+
Ferrous Iron = Fe2+
characteristics of ferric iron
(Fe3+)
- Electron acceptor for anaerobic respiration
- poorly soluble at neutral pH
examples of ferric iron
Hematite, Ferrihydrite
examples of ferrous iron
magnetite
characteristics of ferrous iron
Electron donor for lithotrophic bacteria
oxidises spontaneously at neutral pH
Main forms of Manganese in the environment
Pure Mn
Mn (IV) oxide (Mn4+ or MnO2)
Mn (III) oxide-hydroxide
Oxyhydroxide
Mn (III) oxide
Mn (II) oxide
give an example of an Oxyhydroxide
(hint: Mn)
Magnatite
Reasons why life might be limited by iron
in oceans, due to oxygen levels, iron is usually in its most oxidised state, Fe(III). This is not bioavailable to organisms due to its low solubility
Oceans main iron input is from aeolian dust from continent meaning that central open oceans which are further away from iron inputs have less iron available
- Moore and Braucher 2008
iron is needed for photosynthetic activity so a scarcity of it significantly impacts primary production and phytoplankton growth
- Schoffman 2016
Why might weaker oxygen minimum zones (OMZ) increase the iron supply?
OMZ is a region in the ocean where the dissolved concentration of oxygen is at its lowest.
Low oxygen environments favour iron reduction, forming Fe(II) which is more soluble in seawater than ferric iron, increasing the concentration of Fe(II) in the water. This is more bioavailable for phytoplankton to use
- Scholz 2014
what type of bacteria are iron-oxidising bacteria?
chemolithoautotrophs
What reaction does iron have with oxygen at differing pH levels?
spontaneous reaction at neutral pH
stable raction at an acidic pH
what is the term used to describe iron oxidising bacteria that favour acidic conditions
acidophilic iron oxidisers
what is the term used to describe iron oxidisers that favour neutral environments
Neutrophilic iron oxidisers
Example of stalk-forming iron oxidising bacteria in freshwater and marine environment
Freshwater Betaproteobactera
- Gallionella furreginea (neutrophillic)
- Ferriphaselus
Marine Zetaproteobacteria
- Mariprofundus ferroxydans
what forms of iron oxidising bacteria can you have?
- sheath-formers
- stalk-formers
