Sediments

Question 1

Under what conditions are acid sulphate soils (ASS) forming (mention also the chemical components that are required for the formation of ASS)

Answer 1

waterlogged/oxygen-free conditions, sulphate from seawater or saline groundwater as well as organic matter and metals (Fe etc) are needed. Carbonates are needed.

Question 2

(2) Lake sediments are composed of different types of solid material that can be classified as detrital or non-detrital material. Give three examples of materials that can be found in sediments and indicate whether these materials tend to be more stable under oxic or anoxic conditions in the sediment (your three examples should contain both detrital and nondetrital materials).

Answer 2

Silicate minerals (detrital – primary minerogenic material) – don’t care about oxygen.
Carbonate minerals (detrital) – don’t care about oxygen, pH is important.
Dead plankton (non-detrital) – more stable in oxic environments.
Organic matter (non-detrital) – more stable in oxic environments.

Question 3

What does the components of FIck’s law mean? J = -Ø D ∆C/∆Z.

Answer 3

J – diffusion flux, Ø – sediment porosity, D – diffusion coefficient, ∆C/∆Z – concentration gradient in pore water (concentration difference/depth difference)

Question 4

What is deposition rate and sedimentation rate?

Answer 4

Sedimentation rate (S) translates the depth into a timescale. mg accumulated sediment /cm2 /year or mm accumulated sediment /year

Deposition rate D= SC if S is mg/cm2/year. D= (1-porosity)density*C if S is mm/year.

Question 5

What is pore water?

Answer 5

Pore water fills pore spaces between the
solid mineral grains in the
sediment.

Question 6

When do we have potential ASS and active ASS?

Answer 6

Potential: field pH > 4. Waterlogged. Water pH nearly neutral.

Active: field pH < 4. Water pH < 5.5. Iron stains.
Three different zones in active soils:
Oxidation zone: pH <4 in field.
Transition zone: pH between 4 and 6 in field.
Reduction zone: pH > 6.