Acidification

Question 1

Which parameters are used to assess acidification?

Answer 1

pH, alkalinity, ANC (base caions, strong acidic anions), inorganic aluminium,

Question 2

Describe the mobile anion hypothesis

Answer 2

The mobile anion hypothesis says that by the acid deposition on the soil the base cations will be exchanged for H+ which will (in the beginning) bind to the soil. The SO4- anion will attract the cation ad drag it out to the lake/stream. This willl cause acidification of the soil. When all the BC have been exchanged SO4- will start to drag with itself H+.

Question 3

Describe the critical load cocept

Answer 3

The critical load concept is based on a steady state model. Often used to describe the combination of nitrate and sulphate deposition where both have a maxiumum. Maximum levels of deposition are given which say below which levels no harmful effects are expected. You firstly define this level and then make a steady state model from the the effects of acid rain and lastly calculate the critical load (how much does the ecosystem tolerate).

Question 4

What does the ion balance equation mean?

Answer 4

That postive and negative charges need to balance each other out in a solution

Question 5

Describe wheatering in the context of acidification

Answer 5

The wheatering of minerals in the ground provides buffering capacity for the water. Carbonic acid drives this process. The process also results in BC.

Question 6

Describe ANC

Answer 6

All the protolyes
HCO3- + CO32- + RCOO- + OH - - Al n+ - H +
=
Base cations (BC) and Strong acid anions (SAA)
Ca 2+ + Mg2+ + Na+ + K + - SO42- - NO3- - Cl -
=
ANC (mekv/l)

Is derived from the ion balance eq. BC and SAA are often easier to assess even if they do not affect the acidification directly.

Question 7

Which factors affect the pH?

Answer 7

The carbonate buffer system, organic acid buffer system and the aluminium buffer system, mount of OH- and H+, all of these factors play in to the ANC.

Question 8

Which factors are needed to assess pH?

Answer 8

ANC, DOC, CO2 pressure, aluminium

Question 9

Which factors of ANC, DOC, CO2 pressure, aluminium are the most sensitive in the pH range 5-7?

Answer 9

ANC and DOC

Question 10

Describe why the deposition of nitrate for the time being is not a problem.

Answer 10

Right now the ecosystem still take up all the nitrogen and we have a balance between ammonium and nitrate. But though nitrogen leaching nitrate could also become a mobile anion.

Question 11

What are reasons for natural acidic waters?

Answer 11

• Most soils are of granitoide origin – feldspars and quartz minerals
– Low weathering rates giving low buffering capacity
– low BC and HCO32-
• Natural high concentrations of organic acids
– Humic substances from mires – especially narrow riparian soils

Question 12

What can be reasons for antrphogenic acidification besides deposition?

Answer 12

Ditiching, straightning of streams for log transports

Question 13

What is episodic acidification?

Answer 13

Describes a short-time and reversible pH-drop

Question 14

What can be reasons for acidic epsiodes during the spring flood?

Answer 14

Due to the higher flow the factors contributing to the ANC are diluted which leads to a lower buffering capacity, organic acids increase with higher discharge, meaning that the DOC increases. From antrophogenic deposition that has fallen on the snow and that is now released.

Question 15

What can be reasons for acidic episodes?

Answer 15

• Dilution of ANC (buffering capacity) during periods of high
discharge
• Temporary increase of organic acids
• Temporary increase of sulphate (snow melt at high deposition or
after drought through oxidation)
• Temporary increase of nitrate
• Deposition of sea salt

Question 16

Why can sea salt deposition lead to acidification?

Answer 16

NaCl does in itself not have any effect on the acidification, But Na+ can be exchanged for H+ in the soil though cation exchange. Cl- will act as the mobile anion and drag the H+ into the water and thereby cause acidification.

Question 17

Why do we today see more brownification?

Answer 17

Possible reasons:

Climate change - More periciptation and higher temperature

Change in land use - Reforeststation

Recovery from acidification - Higher pH and lower ionic strength causes higher solubility of DOC.

Question 18

What does the water frame work directive say?

Answer 18

Has ecological integretity in focus and sees ecological deviation as the deviation from a reference value (represents undisturbed state). It also puts a price on water, transparancy and public participtation and administration whitin water basins. The philodophy behind is that human impact should not change the biological community too much and that ecological integretity rather than human intresets should be protected.

Question 19

Why do you seldom measure the minium value when assesing acididty?

Answer 19

As you usually only make a number of recording each year there is a large risk taht you miss the “real” minimum. Therefore the median is used insteas which is correlated to the minima. It also shows the risk of having a toxic effect.

Question 20

How do you find reference values accoriding to WFD?

Answer 20

• Find a comperable unimpaired water of the same type
• Histroic measurments
• Modelling
• Expert opinion

Question 21

Describe the MAGIC model

Answer 21

Is a dynamic model that is based on the present lake chemistry. It can reconstruct deposition sceanrios and both be used to calculate back and “forsee” the future. It uses the following simplification:

• Constant TOC
• All soil as one mixing tank
• No short time variation

MAGIC primalry gives ANC from which pH can be caluclated.

Question 22

Describe the FAB model

Answer 22

Is a static model which puts more focus on the processes in the denitrification and N uptake. Used to obatin critical load.

Question 23

How do you assess a limed water?

Answer 23

As liming adds calcium the unlimed concentration of ca can be obtained by using the ratio between Ca/Mg. Here you use the amount of Mg from the limed lake and the Ca/Mg from a unlimed reference. Thereby the ANC without liming can be obtained. Large errors for individual waters but good enough on a regional scale.