Specific chemical processes in estuaries Flashcards
(13 cards)
What does fluorine show in estuarine mixing diagrams?
Conservative, and higher concentration in sea water.
What does iron show in estuarine mixing diagrams?
Non-conservative
Why does iron concentration decrease with increasing salinity?
Ligands lost by flocculation and/or the effects of increased ionic strength.
What does silicon show in estuarine mixing diagrams?
Both conservative and non-conservative behaviour across the year.
What are the sources of dissolved silicon?
Salt marshes and desorption from resuspended sediments.
What do silicon isotope analyses provide evidence for?
Removal of light Si at salinities >20, especially in July.
Why does manganese experience intensive cycling in estuaries?
Chemistry linked to changes in redox conditions.
What happens to manganese in anoxic sediments?
Mn IV is reduced to Mn II which is soluble so it can diffuse out the sediments.
Where are maximum concentrations of dissolved manganese found?
Intermediate salinities ~10 due to input of dissolved Mn II from reducing sediments.
Why is silicon both conservative and non conservative
Conservative = Simple mixing of river and seawater - Low biological activity, clear water
Non-Conservative = Biological uptake, adsorption, desorption, sediment input - Productive estuaries, muddy waters, SGD zones
How do reducing sediments affect dissolved Mn?
Low salinity: High Mn²⁺ (released from sediments).
Mid-salinity: Mn oxidizes → particles (removal).
High salinity: Low Mn (scavenged).
Why is silicate non-conservative in summer?
Diatom uptake (blooms).
Measure: Diatom counts, nutrients (NO₃⁻, PO₄³⁻), light/temperature.
How does increasing temperature affect silicate weathering, and what is its impact on global climate?
Higher temperatures speed up silicate weathering, which removes CO₂ from the atmosphere.
This leads to long-term climate cooling, forming a negative feedback loop that helps stabilize Earth’s temperature over geological timescales.
