Biogeochem - Chapter 1: Water (Henrik)

Question 1

What temp is waters highest density?

Answer 1

4ºC

Question 2

What causes stratified bodies of water?

Answer 2

If the temperature difference and density gradient are big enough

Question 3

When are temperate lakes stratified

Answer 3

In the summer (warm surface water) and in the winter (cooler surface water)

Question 4

When do temperate lakes mix and what does this enable?

Answer 4

In autumn and spring
the water column has no
temperature gradients and can mix.
This allows oxygenated water to
get to the bottom of the water body.

Question 5

What does a Amictic lake mean?

Answer 5

Bodies of water that never turn over. They are permanently covered in ice. These are usually found in Antarctica or at high altitudes in mountains

Question 6

What is a cold monomictic lake?

Answer 6

A body of water that contains waters never exceeding 4ºC. They turn over one a year in the summer and are thermally stratified the rest of the year

Question 7

Meaning of a dimitic lake?

Answer 7

A lake that turns over twice a year, in the spring and autumn. They are thermally stratified at other times in the year.

Question 8

Where do you find dimitic lakes?

Answer 8

They are typically found in temperate climates and at high altitudes in the subtropics

Question 9

What are warm monomictic lakes and when do they turn over?

Answer 9

A body of water that water temp is NEVER BELOW 4ºC. They turn over once a year in the winter and are thermally stratified the rest of the year.

Question 10

What is a oligomictic lake and where do you find them?

Answer 10

they contain water that is significantly warmer than 4ºC. They turn over irregularly and are mostly found in tropical zones

Question 11

What is a polymictic lake and where do you find them?

Answer 11

a lake that has water just over 4ºC and can turn over continually. These occur at high altitudes in equatorial regions.

Question 12

What is a meromictic lake?

Answer 12

They are deep, narrow lakes with bottom waters that never mix with the waters above.

Question 13

What are the properties of meromictic lakes?

Answer 13

Bottom waters generally have high dissolved salt concentrations which makes them dense and separates them from overlying waters by a chemocline. The upper waters in temperature climates may be thermally stratified in the summer and winter and undergo turnover in the spring and fall

Question 14

Are tropical lakes usually thermally stratified

Answer 14

tropical lakes are not usually thermally stratified due to the lack of seasons with strong temperature differences

Question 15

What does epilimnion refer to?

Answer 15

Epilimnion refers to the upper body of water

even during the stratification period, the epilimnion is usually fully mixed

Question 16

What does hypolimnion refer to?

Answer 16

Hypolimnion refers to the deeper body of water

Question 17

what is the thermocline?

Answer 17

the water layer where a steep temperature gradient is found

the larger the lake, the bigger the waves and the deeper the thermocline

Question 18

Is salinity a volatile or stable stratification?

Answer 18

Salinity (haline) stratification is usually stable and permanent, in contrast to temperature

Question 19

what does littoral mean/describe?

Answer 19

it describes zones close to the shore of the lake where light penetrates to the ground and the entire water column is above compensation depth (where photosynthesis > respiration)

Question 20

What sediment form the benthic zones (nb: sediment from which shore zones)

Answer 20

The littoral and profundal (permanently dark) sediment together form the benthic zone

Question 21

where do you find pelagic waters?

Answer 21

They are found above the compensation depth and above/on top of profundal waters

(this differs to littoral which is underlain by sediment!)

Question 22

What determines the epilimnion?

Answer 22

the lake size and energy input (wind)

Question 23

what determines the compensation depth?

Answer 23

(this separates the pelagic and profundal zones)

it is determined by the turbidity of the water in the lake

Question 24

What does stratification inhibit?

Answer 24

It inhibits the exchange of dissolved compounds (eg oxygen) between the different bodies of water

Question 25

how do the narrow veins of liquid water form in ice?

Answer 25

When ice crystals form, dissolved solids (salts and other compounds) are excluded from the ice crystals and become highly concentrated in the remaining liquid water which turns into brine.

the high salinity of brine lowers the freezing point, so tiny veins of liquid water are still present within the ice.

these liquid veins harbour complex microbial communities

Question 26

Properties of water due to hydrogen bonding

Answer 26

high boiling point (temp at which it goes from liquid to gas)

strong cohesion between molecules

large heat of evaporation (energy required to evaporate water)

capillary forces

Question 27

how high can water travel through capillary action?

Answer 27

120-130m high…. hence the height limit for trees is 120-130m tall

Question 28

How does H2S behave differently to H2O

(Hint: molecule weight and boiling point…)

Answer 28

H2S should behave similar to water… but as it is heavier it should have a higher evaporation energy and higher boiling point… this doesnt happen because it cant form efficient hydrogen bonds

Question 29

Difference between soil and sediment

Answer 29

Soil
- usually used for terrestrial habitats
- has 3 fractions: air, water and particles

Sediment
- usually used for deposits underlying a water body
- has 2 fractions: particles and water

Question 30

similarities between soil and sediments

Answer 30

both have a component of weathered rock materials
- soild mostly derived from underlying base rock
- sediments contain material that has often been transported over large distances

Question 31

Porosity definition

Answer 31

symbol = φ

describes the water content of a sediment (not usually used for soils)

the volume of pore water per volume of sediment

Question 32

porosity equation

Answer 32

φ = volume of pore space / total sample volume

Question 33

Porosity of surface sediments and water

Answer 33

Surface sediment porosity of between 0.4 - 0.8

pure water has a porosity of 1

Question 34

definition of tortuosity

Answer 34

described the effect of the shape and size of sediment particles on sediment diffusive fluxes

symbol = ϴ

Question 35

difference between sandy soils and peat

Answer 35

Sand
- usually have very little organic matter

Peat
- are usually/almost exclusively organic matter and contain very little mineral material

Question 36

Why can’t macropores retain water and what does this mean?

Answer 36

the diameter of the pores are too large for capillary action

this means water can drain freely as long as the soil is above the water table.

macropores are important for soil aeration

Question 37

why can micropores retain water?

Answer 37

they are small enough in diameter to retain water

(the smaller the diameter the stronger the capillary force keeping water inside)

Question 38

what is hygroscopic water

Answer 38

it is water that is not available to plants because it is held by strong intermolecular forces between soil particles (eg clays)

Question 39

whats the difference between soil saturation, field capacity and wilting point?

Answer 39

Soil saturation
- all pores filled with water
- gravitational water about to drain

Field capacity
- micropores filled with water
- macropores filled with air
- ‘suction’ forces in soil resist gravity flow of water

Wilting point
- most pores filled with air
- water present in small, unavailable quantities

Question 40

what does the term cyclic salt describe?

Answer 40

it describes salt that is transported by air currents (wind)