Chemical processes Flashcards
(19 cards)
Why are estuaries significant?
Estuaries are important transition zones for continentally derived material, influencing flux entering the ocean and chemical distributions, which may affect biological processes and anthropogenic inputs.
What characterizes estuarine mixing: highly stratified?
In highly stratified estuaries, a salt wedge forms due to large river input and weak tidal input, with isohalines almost horizontal and close together. The position of the salt wedge depends on river flow.
What characterizes estuarine mixing: partially mixed?
In partially mixed estuaries, small river input and large tidal input lead to inflow of salt water dominating, causing turbulence that shears the halocline, with salinity contours dipping steeply near the seabed and surface.
What characterizes estuarine mixing: well mixed?
In well mixed estuaries, small river input and very large tidal input occur. If the estuary is wide, the Coriolis force may segregate river and sea water horizontally, resulting in nearly vertical isohalines.
What characterizes estuarine mixing: inverse estuary?
Inverse estuaries exhibit negative circulation, with salinity increasing towards the river mouth, typically found in hot arid climates where evaporation exceeds freshwater input.
At what salinities do the greatest changes in proportion of major ions occur?
The greatest changes in proportion of major ions occur at salinities less than ~5 pH.
How are ions in seawater diluted in estuaries?
Ions in seawater are diluted by mixing with freshwater in the estuary.
What do estuarine mixing diagrams reveal about the behaviour of a solute in an estuary?
If the concentration of the solute falls on a mixing line between the freshwater and seawater endmembers, it behaves conservatively. If it lies above or below the TDL, it behaves non-conservatively.
What processes affect the distribution of minor and trace constituents?
Processes include mixing, biological processes, absorption and desorption on particle surfaces, coagulation, flocculation, precipitation, and redox processes.
What is absorption?
Absorption is the binding of dissolved chemical species to a mineral surface by formation of surface complexes, incorporating the solute into the mineral structure.
What does the ability of minerals to absorb solutes depend on?
It depends on the mineral and pH: At the pHpzc, surface charge is zero; above it, the surface is negatively charged and sorbs cations; below it, the surface is positively charged and sorbs anions.
What are colloids?
Colloids are very small particles or nanoparticles that remain suspended in aqueous solutions.
What are the main colloidal phases in rivers?
Main colloidal phases include clay minerals (kaolinite, montmorillonite), iron (hydr)oxides (goethite, hematite, ferrihydrite), and humic/fulvic acids associated with FeOOH.
When will colloids flocculate?
Colloids will flocculate when their surface charge equals 0, such as when river water encounters seawater or at salinities around 5.
What happens in estuaries in terms of redox processes?
Estuarine sediments are usually reducing, leading to varying concentrations of dissolved species in sediment pore waters compared to overlying estuarine water, causing diffusion into/out of sediments.
How do processes affecting the distribution of constituents affect estuarine mixing diagrams?
These processes may add or remove solutes, causing positive or negative deviations from the TDL, indicating non-conservative behavior.
What are the assumptions of mixing diagrams?
Assumptions include that the estuary is in steady state, concentration of endmembers is constant over time, there is only one river endmember and one seawater endmember, and no additional sources of material.
What are the limitations of mixing diagrams?
Limitations include inability to detect non-conservative behavior if residence time is short, and potential misinterpretation of non-conservative behavior due to temporal variability or multiple sources of material.
Describe an Experiment to Demonstrate Flocculation
Method:
Prepare a jar of clay-rich turbid water (e.g., mix soil + water).
Add a flocculant (e.g., alum or saltwater).
Stir gently and observe over time.
Expected Result:
Particles clump (flocs form) and settle faster than in the control (no flocculant).
Key Principle:
Flocculation neutralizes particle charges, promoting aggregation
