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Acid Deposition

1) What are the major causes of acid deposition?

2) How are lakes impacted by acid deposition?

3) Why are some lakes more sensitive to acid depositionthan others?

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Acid rain is thecommonly usedterm todescribe the

many ways thatacid falls out ofthe atmosphere

Better term is acid deposition because it is not just

rain (also snow, hail, fog and dry deposition)

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pH ranges from0 to 14

7 = neutral< 7 = acidic> 7 = alkaline

Measure acidity as concentration of H+

pH = - log [H+

]pH = log [1/H+]

http://www.epa.gov/acidrain/site_students/images/phscale.gif

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Acid Rain linked to coal burning in England in 1852

US and Canadian governments officially recognized

effects in 1986

Acid rain (pH as low as 4.2) comes from the

combustion of fossil fuels

Normal rainwater is pH 5.5-6

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Primarily caused by airborne pollutants

sulfur dioxide (SO2) sulfuric acid (H2SO4)

nitrogen oxides(NO and NO2) Nitric Acid (HNO3)

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Once produced, the SO42- and the NOx have anatmospheric residence time of ~1-3 days

In that time, they can travel 400-1,200 km

In North America and Europe, sulfur emissions morethan doubled between 1900 and 1980

Nitrogen emission are harder to quantify, but may be

as high as 20x the 1900 level

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Prevailing winds in both North America and Europetend to be from the southwest

Lakes in Canada, New England and Scandinavia arehighly impacted

Estimates:Canada >14,000Sweden 20,000

Adirondack Region (NY) 500

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annual meandeposition

pH1980

http://www.utoronto.ca/imap/collections/air_quality/maps/ph_1980.jpg

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Annualmeandeposition

pH1996

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What are the effects

of acid deposition on

aquatic habitats?

Why are some lakes more sensitive to acid deposition

than others?

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Ability to resist changes in pH with respect to theaddition of acid is called AlkalinityorAcid neutralizing capacity-ANC

The Bicarbonate Buffer System

Lakes that have a lot of carbonate can resist changesin pH with the addition of acids

How much DIC is available in the lake?

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ANC is measured by titrating with acid until the pHchanges to 4.5

The more acid needed to reach 4.5, the morebuffered a lake is against changes in pH

Recall equations from lecture on DIC

CO2 + H2O H2CO3 HCO3- + H+ CO3

2- +2 H+

Carbonic Acid

Bicarbonate

Carbonate

Some lakes get a lot of DIC from the watershed

(limestone (CaCO3), Calcium bicarbonate (Ca(HCO3)2)

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Lakes in limestone regions have high ANC and aretherefore not as impacted by acid deposition. Lakeson granite are highly impacted.

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Experimental Lakes AreaDavid SchindlerWhole-lake acidification of Lake 223

How does Acid Rain impact lakes?

(http://www.umanitoba.ca/institutes/fisheries/)

In 2 years, added enough concentrated sulfuric acidto equal 18 years of acid deposition in eastern

Ontario

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Mysisrelicta(7 million to 0)Fathead minnows did not reproduceMore phytoplankton change1 zooplankton species lost (copepod)

Started experiment in 1976, with a pH of 6.8

6.13 (1977) shift in phytoplankton assemblage

5.93 (1978)

Schindler et al. 1985

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5.02 (1981) More zooplankton changes

5.64 (1979) Increase in filamentous algaeSofter shells on crayfishMinnow and sculpin decline

5.59 (1980) Increase in pearl daceCrayfish having problemsMore zooplankton losses

Most fish not reproducing

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Stop adding acid in 1982

No reproduction of fish,no crayfish.

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These metals are toxic to aquatic organisms

Low pH causes some of these impacts directly

Also liberates metals such as aluminum, cadmium,mercury, lead

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1983-1984 studiedboth basins

Acidification of Little Rock Lake, WI

Divided one lake with a curtain

Added sulfuric aciduntil 1990 to drop pHto ~4.7

www.civil.mtu.edu/~nurban/ classes/ce453/proj1.htm

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At least two solutions to the problems of aciddeposition:

Liming addition ofcalcium carbonate.

Works, but is expensive

and only a short termsolution

Long-term solution reduce emissions and letlakes recover naturally

Chemical recovery much

faster than biological

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Concepts to know Why are lakes in the northeastern United

States, much of Canada and Scandinavia soimpacted by acid deposition?

What is ANC? What is the bicarbonatebuffer cycle?

What are the direct and indirect effects of

acid deposition on aquatic habitats? What are the solutions counteracting the

effects of acid deposition?