Microbial mats

Question 1

why does geochemical zonation occur

Answer 1

microbial elemental cycling - microbial metabolic reactions in the environment change the chemistry of the environment

Question 2

what are the well-known zoned systems

Answer 2

-microbial mats
-marine sediments
-aquifers and polluted soils
-some lake waters

Question 3

Process of the formation of microbial mats

Answer 3

1. Mats begin with solid particles in water (surface for cell attachment)
2. Biofilms develop, usually single species
3. Left undisturbed, biofilms thicken and other species join
4. Vertically stratified species dependent on different metabolic needs and abilities

Question 4

what is the main component of microbial mats

Answer 4

EPS - extracellular polymeric substances - where the electrons donors and nutrients accumulate

Question 5

What species are dominant in the early stages and what comes next

Answer 5

1. Cyanobacteria, diatoms, microalgae
2. Fermentatie and heterotrophic bacteria colonise
3. Aerobic heterotrophs deplette O2, SRB produces H2S
4. Chemolithotrophs join the party

Question 6

what are the characteristics of a microbial mat

Answer 6

steep, micro-scale gradients in light, Eh, pH, redox-active elements

Question 7

examples of 2 types of mats

Answer 7

• photosynthetic mats
  -chemolithoautotrophic mats

Question 8

the biosedimentary structures of microbial mats

Answer 8

mature mats exhibit laminations

Question 9

what does lamination show

Answer 9

change in sedimentation, salinity, seasons

Question 10

what are stromatolites and where do we find them

Answer 10

lithified mats preserved in the rock record

Question 11

what is diagenesis

Answer 11

the processes between deposition and metamorphism (between deposition and weathering)

Question 12

what are the microbial processes that occur during diagenesis

Answer 12

-mineralogy
-porewater chemistry
-isotropic signatures

Question 13

three components of sediments that are deposited on the seafloor

Answer 13

-inorganic detritus
-organic matter (particulate organic carbon (POC))
-water with solutes

Question 14

What is POC (particulate organic matter)

Answer 14

organic matter that is deposited on the seafloor

Question 15

what happens to buried marine sediments

Answer 15

diagenesis:
- compaction
-mineral transformations
-organic matter degradation
-generation of hydrocarbons
-changes in pore water composition
-cementation of unconsolidated sediment

Question 16

What happens to POC (particulate organic carbon)

Answer 16

• most of the ocean is oxygenated so POC is degraded by aerobic chemoheterotrophs
• most deposited POC is respired (oxidized) by microbes at the sediment surface
• leftovers are buried and provide PED for subsurface microbes
• diagenesis forms rock