Biogeochem - Chapter 1: Water (Henrik) Flashcards
What temp is waters highest density?
4ºC
What causes stratified bodies of water?
If the temperature difference and density gradient are big enough
When are temperate lakes stratified
In the summer (warm surface water) and in the winter (cooler surface water)
When do temperate lakes mix and what does this enable?
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.
What does a Amictic lake mean?
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
What is a cold monomictic lake?
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
Meaning of a dimitic lake?
A lake that turns over twice a year, in the spring and autumn. They are thermally stratified at other times in the year.
Where do you find dimitic lakes?
They are typically found in temperate climates and at high altitudes in the subtropics
What are warm monomictic lakes and when do they turn over?
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.
What is a oligomictic lake and where do you find them?
(irregular)
they contain water that is significantly warmer than 4ºC. They turn over irregularly and are mostly found in tropical zones
What is a polymictic lake and where do you find them?
a lake that has water just over 4ºC and can turn over continually. These occur at high altitudes in equatorial regions.
What is a meromictic lake?
think mero.. think mermaind… think deeeep…..
They are deep, narrow lakes with bottom waters that never mix with the waters above.
What are the properties of meromictic lakes?
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
Are tropical lakes usually thermally stratified
tropical lakes are not usually thermally stratified due to the lack of seasons with strong temperature differences
What does epilimnion refer to?
Epilimnion refers to the upper body of water
even during the stratification period, the epilimnion is usually fully mixed
What does hypolimnion refer to?
Hypolimnion refers to the deeper body of water
what is the thermocline?
the water layer where a steep temperature gradient is found
the larger the lake, the bigger the waves and the deeper the thermocline
Is salinity a volatile or stable stratification?
Salinity (haline) stratification is usually stable and permanent, in contrast to temperature
what does littoral mean/describe?
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)
What sediment form the benthic zones (nb: sediment from which shore zones)
The littoral and profundal (permanently dark) sediment together form the benthic zone
where do you find pelagic waters?
They are found above the compensation depth and above/on top of profundal waters
(this differs to littoral which is underlain by sediment!)
What determines the epilimnion?
the lake size and energy input (wind)
what determines the compensation depth?
(this separates the pelagic and profundal zones)
it is determined by the turbidity of the water in the lake
What does stratification inhibit?
It inhibits the exchange of dissolved compounds (eg oxygen) between the different bodies of water
how do the narrow veins of liquid water form in ice?
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
Properties of water due to hydrogen bonding
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
how high can water travel through capillary action?
120-130m high…. hence the height limit for trees is 120-130m tall
How does H2S behave differently to H2O
(Hint: molecule weight and boiling point due to hydrogen bonding)
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
Difference between soil and sediment
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
similarities between soil and sediments
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
Porosity definition
symbol = φ
describes the water content of a sediment (not usually used for soils)
the volume of pore water per volume of sediment
porosity equation
φ = volume of pore space / total sample volume
Porosity of surface sediments and water
Surface sediment porosity of between 0.4 - 0.8
pure water has a porosity of 1
definition of tortuosity
think contortionism… shape…
described the effect of the shape and size of sediment particles on sediment diffusive fluxes
symbol = ϴ
difference between sandy soils and peat
in terms of organic matter levles
Sand
- usually have very little organic matter
Peat
- are usually/almost exclusively organic matter and contain very little mineral material
Why can’t macropores retain water and what does this mean?
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
why can micropores retain water?
they are small enough in diameter to retain water
(the smaller the diameter the stronger the capillary force keeping water inside)
what is hygroscopic water
(hygro… ‘bye-gro’)
it is water that is not available to plants because it is held by strong intermolecular forces between soil particles (eg clays)
whats the difference between soil saturation, field capacity and wilting point?
(in terms of pore space)
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
what does the term cyclic salt describe?
it describes salt that is transported by air currents (wind)
