lec 17

Question 1

how can u measure salinity?

Answer 1

conductivity (measure using conductivity)

Question 2

what is the main source of ions in terms of carbon?

Answer 2

weathering, mainly resulting in carbonic acid

CO2 + H2O <–> H2CO3 (carbonic acid)

Question 3

what are sedimentary rocks rich in?

Answer 3

carbonates, Ca, Mg, HCO3-, and other minerals/ions
also sedimentary rocks weather quicker than

igneous or metamorphic rocks, making them a bigger source of inorganic carbon

Question 4

if we look at arid to temperate to tropical regions, what does ion concentration look like?

Answer 4

we start w temperate region! mostly our rocks are sedimentary and so are high in Ca and HCO3

as we move towards more arid regions, evaporation begins to dominate. when this happens, the salts that are leftover become more concentrated. these areas tend to have less weathering, and so the salts in the water are Na and Cl.

as we move towards more tropical regions, precipitation begins to dominate. in these regions, so much precipitation has occurred that weathering has long since finished, and the only salts that remain are those that get cycled ie Na and Cl

Question 5

what is aquatic systems’ natural mechanism against acidification? how were these effects demonstrated?

Answer 5

in cases of acid rain, acidification of water causes Ca bound in clay to bind to H+

because of continuous acidification over long periods of time, Ca gradually decreases. in these areas, a notable decline in Daphnia populations were observed, since Daphnia require Ca for their carapace and were outcompeted

Question 6

CO2 in water! pH? equation?

Answer 6

dissolution of CO2 in water results in natural acidity, as H+ is generated (OH- is prod but net production of H+ is higher)

CO2- + H2O <–> HCO3- + OH-
HCO3- + H2O <–> H2CO3 + OH-

in order of acidity (highest to lowest) it goes H2CO3, HCO3-, CO32-

Question 7

how does carbon act as a buffer - in other words, what happens when u add a acid to carbon?

Answer 7

u can think of it as a mini titration curve

initially, CO2 will buffer the added acids. its concentration will gradually decrease along with an increase in bicarbonate, and when CO2 is used up there will be a big spike in pH towards basicity.

the same process will occur with bicarbonate and carbonate, where bicarbonate decr and carbonate incr. when bicarbonate is used up, there is another spike towards basicity

[why does the spike occur?]

Question 8

in most conditions, what form of DIC do we find?

Answer 8

carbonic acid (H2CO3)
if u move to the left u become more acidic - if u move to the right (towards bicarbonate and carbonate) u become more basic

Question 9

what is the mechanism by which buffering occurs?

Answer 9

free protons (H+ ie what makes an acid an acid) gets bound up by bicarbonate and carbonate –> tends towards carbonic acid
(eventually if theres enough acid, it coverts to CO2 and then the acidity spikes)

conversely, when OH- is added, protons from carbonic acid are freed up –> tends towards bicarbonate

Question 10

what is calcite? why is it important?

Answer 10

calcite is CaCO3, a precipitate that forms when CO2 is removed from a system (indicator for removal of CO2)

Question 11

how do saline lakes come about?

Answer 11

closed basins where water primarily leaves through evaporation instead of outflow, with salts weathering into watershed

Question 12

what are tufa?

Answer 12

cool salt tower looking things that occur due to capillary action drawing salt water up, w the water eventually evaporating

Question 13

in terms of cations and anions, which ones dominate saline lakes?

Answer 13

cations: sodium, magnesium, some calcium

anions: chloride, sulfate, carbonate

Question 14

what are the long term effects of acidity?

Answer 14

incr alkalinity (become more basic) bc bedrock weathers faster

Question 15

what is the main source of acid precipitation? what is a natural buffer?

Answer 15

sulfuric and nitric acids in precipitation caused by combusting coal and petroleum.
natural buffer is limestone, which contains bicarbonate

Question 16

what are some effects of acidification on:
- general microbes
- algae
- animals that require bicarbonate (ex. molluscs)
- fish

Answer 16

1. in general, microbes decrease their activity at more acidic pH. the textbook specifically points to decomposers
2. green algae populations typically live in surface waters where they can get sunlight. this is the area most susceptible to acidification. if green algae are the prim prod of the area, collapse can result in anoxia
3. when acidification occurs, bicarbonate is used up to buffer it. animals that would use this bicarbonate (ex. molluscs, for their shell) are directly affected by the lack of available bicarbonate.
4. in lower pH environments, the conc of aluminum incr which is toxic to fish

Question 17

what are some treatments of acidification? (3)

Answer 17

• short term: adding limestone, which contains bicarbonate (problem: relatively weak)
• long term: adding calcium carbonate (problem: expensive)
• preemptive: legislation that reduces coal combustion (problem: u have to rally politicians)