Lakes and their sediments

Question 1

What do all lakes have in common?

Answer 1

• A closed depression
  This distinguishes a lake from a river
  Depressions slow down the water
  This fundamentally alters the physical and chemical properties of the water body

Question 2

What does low flow velocity mean?

Answer 2

Low capacity for sediment erosion or transport

Question 3

What is the average stream flow?

Answer 3

Commonly in the order 1m/s

Question 4

What are the average flow velocities in lakes?

Answer 4

<0.01m/s

Question 5

What part of a river are lakes?

Answer 5

Slow-moving parts of the river system, in which river-carried sediments accumulate

Question 6

What sediment accumulates at lakes?

Answer 6

Eroded soil
Soil humic matter
Biogenic particles
Fe and Mn oxyhydroxides

Question 7

What happens after the sediment has accumulated?

Answer 7

The coarse particles settle quickly, thus near the inflow or shoreline
The fine particles mix throughout the lake, and settle slowly

Question 8

Where do the different kinds of sediment settle?

Answer 8

• Edge has coarse sediment
• The centre is fine

Question 9

What does the lake edge have?

Answer 9

Complicated, relatively disturbed, sediment

Question 10

What does the lake centre have?

Answer 10

Provided away from slumps and debris flows, has fine steadily accumulating material
This provides a time sequence with progressively younger ages up through the sediment layers

Question 11

What do the layers of sediment provide?

Answer 11

A time sequence with progressively younger ages up through the sediment layers
Record progressive changes in the lake-catchment system