(M2) Lecture 10 - Acidification

Question 1

Definition of acid deposition: wet (eg acid rain) and dry (eg particulates)

Answer 1

Acid deposition: The settling, or depositions, of acidic or acidic forming pollutants from the atmosphere onto Earth’s surface.

Includes:
- Acidic precipitation: acidic rain, snow, sleet, hail
- Acidic fog
- Acidic gases
- Acidic dry particles

*pH <5.6

Wet Deposition: Acids removed from the atmosphere in the form of water (rain, snow, sleet, hail)

Dry Deposition: Acids removed from the atmosphere in the form of particulates or gases (=no water). Often in the form of fly ash, sulphates, nitrates, and SO2 and NOx gas.

Question 2

Emissions that cause acidifications: SO2 and NOx (terrestrial and freshwater); CO2 (ocean/marine)

Answer 2

Sulfur dioxide (SO2)
- In Canada, largest source now is the oil and gas industry
- In the US, largest source is electricity generation

Nitrogen oxides (NOx)
- In Canada, largest source now is the oil and gas industry
- In Canada, NOx emissions have not decreased as much as SO2 has
- In the US it is still transportation
- Other sources: electricity generation, off-road vehicles

Carbon dioxide (CO2)
- CO2 from the atmosphere to the ocean
- 1/4 of CO2 released by burning coal, oil and gas dissolves into ocean; since the beginning of the industrial era
- In the pas 200 years, ocean water has become 30% more acidic
- Increase in emissions, mostly from oil and gas, and transport

Question 3

How pollutants transform into acid depositions (know all the steps of the chemical rxns)

Answer 3

The pollutants are transformed into acid particles that can be transported long distances.

2SO2 + O2 —> 2SO3
SO3 + H2O —> H2SO4

3NO2 + H2O —> 2HNO3 + NO

CO2 + H2O <—> H2CO3
H2CO3 <—> HCO3- + H+
HCO3- <—> CO32- + H+

Question 4

Acidification on landscapes: causes and impacts on soils, forests, streams lakes - including effects on organisms

Answer 4

Damages to soil
- depletes calcium and other base cations
- mobilizes aluminum, heavy metals from soil to water; toxic
- accumulate sulfur, nitrogen in soils; can lead to eutrophication

Damages to forests
- direct effect: leaches calcium out of needles; lose calcium in cell membranes, more susceptible to cold and freezing
- indirect effect: alters soil chemistry; even less calcium to uptake, more toxic aluminum

Damages to steams and lakes
- increased leaching of aluminum into surface waters as runoff from soils
- if pH too low, can be lethal for fish and aquatic organisms
- combined with low pH, can disrupt osmotic balance in fish, eventually leading to heart attacks
- zooplankton: dissolution of the calcium shells that prevent them from growing strong shells

Question 5

Acidification of oceans: cause and impacts = including effects on organisms

Answer 5

• Chemical changes in the ocean as a result of CO2 emissions in the atmosphere
• 1/4 of CO2 released by burning coal, oil and gas doesn’t stay in the air, but dissolves into the ocean
• pH of our oceans is dropping
• many organisms with calcium carbonate shell; if pH of the water changes the marine water starts to take calcium carbonate from shell
• coral bleaching = when the pH drops of if the temp changes, coral will expel its food source and lose colour

Question 6

Important legislation dealing with acid deposition in Canada

Answer 6

1985 Eastern Canada Acid Rain Program:
- Cap SO2 emissions in 7 easternmost provinces
- Establish monitoring
- Updated in 2000 with additional national cap

1991 Canada-United States Air Quality Agreement:
- Cut SO2 and NOx emissions
- Increase monitoring

Canada-Wide Acid Rain Strategy Post-2000
- Signed in 1998
- Continued reductions in SO2 emissions
- More monitoring
- Regulate reports to the public
- Prevent clean/undamaged areas from being degraded

2004 Acid Rain Science Assessment
- Need to reduce emissions even further
- Need to address acidification in the West and North

*Effect of legislation overtime: things are slowly getting better. Regulating emissions are having a positive effect. Reduction in acidic deposition and how pH is being impacted for fresh water.

Question 7

Definitions: Chemical and biological recovery of ecosystems

Answer 7

Chemical Recovery: decrease in damaging chemical (e.g., sulfate, nitrate, and aluminum) concentrations in soils and waters. If the decrease is sufficient, will lead to increase in pH.

Biological Recovery: multi-step return, and/or increase in health of organisms (animals and vegetation) in previously acidified ecosystems (aquatic or terrestrial).

Question 8

Is Chemical Recovery Occurring?

Answer 8

Yes, rate dependent on the resistance and resilience of the ecosystem to acid precipitation; it’s mostly about the amount of calcium naturally found in soils and surface waters
- Lots of Calcium = more resistant and resilient
- Low Calcium = less resistant and resilient

The potential of soils and bedrock to reduce the acidity of atmospheric deposition depends on composition of bedrock. Calcium carbonate bedrock more resistant to acidification. Soils:
- further acidification is not occurring
- aluminum levels are decreasing
- pH is increased

Question 9

Is Biological Recovery Occurring?

Answer 9

Probably, but slowly. Data is still limited.
- quicker for short lived species
- follows chemical recovery
- can take 10+ yrs for zooplankton to recover, 10-20+ for fish populations, and >20 for trees
- given the times, plus the stresses of climate change… it is hard to tell if organisms are rebounding and ecosystem fxn returning

Question 10

Phytoplankton, Zooplankton, and Fish biomass in Lake 302S

Answer 10

Phytoplankton
- primary producers, base of food chain
- during lake recover, the biomass increased initially then a steep decrease back to normal levels
- big shift in species type of phytoplankton, still an overall decrease in biomass

Zooplankton
- feed directly on phytoplankton
- recovery follows similar trends to zooplankton

Fish
- only 1/7 species in the lake could tolerate the lower pH
- once lake recovered, bc of connection to other part of lake, all species previously present returned