Acidification Flashcards
Which parameters are used to assess acidification?
pH, alkalinity, ANC (base caions, strong acidic anions), inorganic aluminium,
Describe the mobile anion hypothesis
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+.
Describe the critical load cocept
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).
What does the ion balance equation mean?
That postive and negative charges need to balance each other out in a solution
Describe wheatering in the context of acidification
The wheatering of minerals in the ground provides buffering capacity for the water. Carbonic acid drives this process. The process also results in BC.
Describe ANC
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.
Which factors affect the pH?
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.
Which factors are needed to assess pH?
ANC, DOC, CO2 pressure, aluminium
Which factors of ANC, DOC, CO2 pressure, aluminium are the most sensitive in the pH range 5-7?
ANC and DOC
Describe why the deposition of nitrate for the time being is not a problem.
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.
What are reasons for natural acidic waters?
• 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
What can be reasons for antrphogenic acidification besides deposition?
Ditiching, straightning of streams for log transports
What is episodic acidification?
Describes a short-time and reversible pH-drop
What can be reasons for acidic epsiodes during the spring flood?
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.
What can be reasons for acidic episodes?
• 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
Why can sea salt deposition lead to acidification?
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.
Why do we today see more brownification?
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.
What does the water frame work directive say?
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.
Why do you seldom measure the minium value when assesing acididty?
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.
How do you find reference values accoriding to WFD?
- Find a comperable unimpaired water of the same type
- Histroic measurments
- Modelling
- Expert opinion
Describe the MAGIC model
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.
Describe the FAB model
Is a static model which puts more focus on the processes in the denitrification and N uptake. Used to obatin critical load.
How do you assess a limed water?
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.
