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ACID DEPOSITION & ITS IMPACTS ON TERRESRIAL

& AQUATIC ECOSYSTEMS

Why this topic? • Nonpoint source – atmosphere; widespread dispersal • Great example of how pollution problems created far away

(distal source) can effect local ecosystems; global extent • Cascading effects of pollution; connection and feedbacks

between pollutants mechanisms • A success story for environmental science, management

and regulation.

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NOTES from: • Acid Rain Revisited – Hubbard Brook Ecosystem Forest,

NH. • Driscoll et al. 2001 – Acidic deposition in the Northeastern

US. BioScience 51(3): 180-198. • Acid Rain in the Adirondacks: An Environmental History.

J. Jenkins, K. Roy, C. Driscoll, and C. Buerkett. Cornell University Press. 2007.

• NAPAP 2011 Report (updated trends and results)

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Organization of lecture:

1. Background, what is acid rain or deposition? 2. Sources of acid deposition

3. History of acid rain

4. Spatial pattern of acid deposition across US

5. Trends in deposition

6. Consequences of Acid Rain

a. Soils b. Forests c. Streams & lakes

7. Recovery

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1. BACKGROUND; WHAT IS ACID DEPOSITION? pH definition - pH measure of acidity = - log10 [H+] neutral pH = 7.0 (H+ = 10-7) less than 7.0 – acidic greater than 7.0 – basic when H+ ion increases pH decreases; 1 unit of pH change = an order of magnitude change in H+ concentration

Natural rain water is NOT Neutral (pH not equal to 7) Why?

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Because rainwater dissolves CO2 and thus forms Carbonic acid – which is a weak acid H2O + CO2 = H2CO3 H2CO3 = HCO-

3 + H+ HCO- = CO3

2- + H+ Thus because of these H+ ions, natural rainwater will typically be around pH = 5.6 to 5.7 ****Thus Acid Rain is when pH < 5.6 Acid deposition - Transfer of strong acids and acid forming substances from the atmosphere to the surface of the earth Agents of transfer: • Wet deposition (with rainfall) • Dry deposition (with particulate matter) 3 main Chemicals involved: • Sulfur oxides – SOx • Nitrogen oxides - NOx • Ammonia – NH3

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An excess of these chemicals has been created in the air because of anthropogenic activities – power plants, waste incinerators, vehicle emissions, etc. Acids generated by these oxides are MUCH STRONGER than Carbonic acid, and thus small amounts of the acids can depress the rain pH significantly

3SO2 + 3H2O + O3 2H2SO4

SO2 + 2OH- H2SO4

2NO + H2O + O3 2HNO3

NO + O3 NO2 + O2

NO2 + OH- HNO3

Sulfuric acid and Nitric acids Note – Ozone (O3) is involved in the oxidation process Pictorially –

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For Sulfur (S) only - the reactions proceed faster in humid temperatures with high sunlight Thus acid rain is typically more elevated during summer

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Spatial pattern of pH in 1999. So where are the inputs of SOx and NOx coming from??????

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2. SOURCES OF ACID RAIN • SO2 are derived from burning of S in coal; higher the S

content – the greater the emissions. Eastern US coal is typically higher in S content.

Sulfur content of Midwestern coal = 2 to 4%

o Sulfur dioxides – electric utilities account for the largest proportion [60-70%] (point sources)

• NOx is generated during the combustion process –

oxidation of N2 in the atmosphere (78% by content in the atmosphere) o Nitrogen oxides – transportation/auto emissions

• Ammonia – land application of animal wastes; feedlots; agricultural operations o significant source now in the Rocky Mountains –

Colorado!

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• Seven states in the Ohio River Valley – contributed

towards 41% of the total national emissions – the regional nature of the problem!

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• Easier to control SOx emissions – by switching fuel type

or scrubbers – limited choice for NOx!!!

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3. BREIF HISTORY OF ACID RAIN • Term coined by Roger Angus Smith in England in 1872 (to

describe the problem in Manchester, England) • First emerged as an issue of concern in the late 1960s and

early 1970s – with reports of surface water acidification in Sweden and around Scandinavia. .

• First reports – Sweden – pH of lakes dropped 2 units from

1930s to 1960s. By 1960s – 50% of the lakes < pH 6.0. fish populations were affected.

• First reports of impacts of acid rain in the US: 1960-70

studies of high elevation (greater than 600 m) Adirondack Lakes - pH of less than 5 and 90% of the lakes had no fish at all!

• Mean pH of Adirondack lakes during 1930-38 = 6.5; but

the mean pH between 1969 and 75 dropped to 4.8!

• Likens visited Sweden in 1969. 1974 Science paper by Likens and Bormann - http://science.sciencemag.org/content/184/4142/1176

• 2 factors accelerated the problem of acid rain –

increased use of fossil fuels & increased height of smoke stacks!

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• Acid Rain became a regional problem (from a local one) – when smoke stack heights were increased!

• Fish affected by acid rain – smallmouth bass, walleye, northern pike, lake trout, lake herring, perch and rock bass.

• Controls on sulfate emissions were first implemented

through amendments to the 1970 Clean Air Act (CAA) – Acid Rain Program (ARP).

• In 1980, the U.S. Congress passed an Acid Deposition Act.

-- established a 10-year research program under the direction of the National Acidic Precipitation Assessment Program (NAPAP). NAPAP looked at the entire problem.

• In 1991, NAPAP provided its first assessment of acid rain

in the United States: o 5% of New England Lakes were acidic, with sulfates

being the most common problem. o 2% of the lakes could no longer support Brook Trout o 6% of the lakes were unsuitable for the survival of

many species of minnow. • In 1990 via Title IV of the Acid deposition control program

US Congress implemented further controls http://www.epa.gov/oar/oaqps/peg_caa/pegcaain.html

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• Phase I began in 1995, and limited sulfur dioxide emissions from 263 of the largest (> 100 MW) power plants to a combined total of 8.7 million tons of sulfur dioxide: about 10 million tons less than those plants had emitted annually during 1985-1987.

• Phase II began in 2000, and included all power plants in

the country > 25 MW and all new fossil-fuel plants.

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4. SPATIAL PATTERN OF ACID DEPOSITION Total deposition = Wet + Dry Wet deposition = concentration x amount of rainfall Wet deposition - easy to measure and quantify Dry deposition – greater variability and considerable uncertainty Lovett (1994) estimated - • Dry deposition of S = 9 – 59% of total S deposition

• Dry deposition of NO3

- = 25 to 70 % of total NO3-

deposition • Dry position of NH4

+ = 2 - 33% of total NH4+

Wet deposition is being monitored via National Atmospheric Deposition Program (NADP) sites – http://nadp.sws.uiuc.edu/ 250 sites in the US

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Dry deposition is being monitored by: EPA –CASTNET http://www.epa.gov/castnet/index.html NOAA-AirMON http://www.arl.noaa.gov/research/programs/airmon.html

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5. TRENDS – EMISSIONS AND DEPOSITION THROUGH TIME

SO2 emissions • 1970 and 1990 Clean Air Act Amendments (CAAA) made

an impact on the Sulfur emissions. Required reductions in SO2 emissions from electric utilities.

• SO2 emissions were 5.7 million tons in 2009 - 64% lower

than 1990 emissions and 67% lower than 1980 emissions.

• Below the 2010 Title IV statutory cap of 8.95 million tons of SO2 emissions.

• SO2 emissions from all sources including those sources not covered by the ARP, have decreased by 59% since 1990,

How were the reductions achieved? • Low-sulfur coal • Scrubbers on smoke stacks • Increased combustion efficiencies and new technology • Cap and trade policies

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NOx emissions: • Lesser changes than SO2 • NOx emissions were 2 million Tons in 2009, 67% lower

than 1995 emissions, exceeding the Title IV goal of a 2-million-ton reduction in NOx emissions from projected 2000 levels without the ARP, as required by the 1990 CAAA.

• Emissions of NOx from all sources have decreased by 40%

since 1990. • NH3 – contribute to 30% of the total N – trends suggest no

significant decreases? • Ammonia – increasing opportunities sought for land

application of animal wastes; increasing number of hog farms in the Southeast – long term region-wide implications?

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Trend of emissions from Power plants affected by ARP

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Deposition trends – • Wet sulfate deposition has decreased since 1990.

• Average annual sulfate deposition in the Northeast and

Southeast in 2007–2009 was 43% lower than in 1989–1991, deposition in the Mid-Atlantic was 42% lower, and the Midwest was 44% lower.

• Wet inorganic nitrogen deposition has decreased regionally. Decreases were less than those of wet sulfate deposition - continuing large contribution from other sources of NOx such as on-road vehicles and non-road vehicles.

• Average annual wet inorganic nitrogen deposition in 2007–2009 was 16% to 27% lower than in 1989–1991 in the Midwest and eastern United States.

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While Emissions and deposition of S and N may be on the decline, recovery of surface waters may not be immediate! Figure 7: Trends in Lake and Stream Water Chemistry at LTM Sites, 1990–2008, Sulfate Ion Concentration (μeq/L/yr)

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Figure 8: Trends in Lake and Stream Water Chemistry at LTM Sites, 1990–2008, ANC Levels (μeq/L/yr)

Source: EPA, 2010

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6. CONSEQUENCES OF ACID RAIN

Impact on soils • Depletion of base cations • Mobilization of Aluminum • Increase in S and N

Leached soil profile from the Adirondacks, NY

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(Ca2+, Mg2+, K+, Na+) – referred to as base cations – increase pH H+ and Al3+ - acid cations – decrease pH SO4

2- and NO3- anions associated with acid rain displace base

cations off exchange sites -- Removal of cations faster than replenishment from weathering of rocks and minerals

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Sorption strength dictated by charge and concentration • If the soil has a large store of base cations (Ca2+, Mg2+, K+,

Na+) – it will neutralize the acidity greater buffering capacity

• Landscapes with thicker soils, greater amount of clays,

large amounts of adsorbed cations will be more resistant to acid rain.

• This ability to neutralize acidity is measured by ANC –

acid neutralizing capacity • The greater the amount of base cations – the greater will be

the ANC. ANC can be estimated by (when expressed in moles) = (Σ strong base cations - Σ strong acid anions) Strong base cations = Ca2+, Mg2+, K+, Na+ Strong acid anions = SO4

2-, Cl-, NO3-,

Where the soil and bedrock have low base cations to start with – the soil and water can become deficient in base cations quickly. Or if

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Acid deposition > rate of base cation supply by weathering This can lead to Alteration of cycles of Ca2+, Mg2+….

Calcium cycle in the Northeast watersheds Mobilization of Aluminum: Base saturation - % of cation exchange sites occupied by base cations

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• If base saturation is below 20% - mobilization and

leaching of Al3+ will occur

• Release of inorganic Al3+ is extremely toxic to terrestrial

and aquatic biota (organic Al is not!) • Al3+ is also tied up with organic complexes – but removal

of base cations and the addition of anions leads to the removal of Al3+ from these organic complexes – and its eventual release into stream waters

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Accumulation of Sulfur and Nitrogen in the soils • Current exports of sulfate from the watershed exceed the

inputs from precipitation – this pattern suggests that S has accumulated over decades and is now being released?

• Similar trends for N – N saturation hypotheses. Question - What are the long-term implications of S & N accumulation in soils?

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Impacts on vegetation Two species that have especially been impacted in northeastern US and Scandinavian forests – • Red Spruce • Sugar Maple

• Mortality of high elevation spruce observed since the

1960’s • Dieback of sugar maple stands in the 1980s

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Red spruce – impacted at high elevations – 50% of the canopy trees in the Adirondacks and the Green Mountains died during the 1970s and 1980s Direct & Indirect effects

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• Acidic water reduces the cold tolerance of current year Red Spruce needles by 3-10 deg C – because of leaching of calcium from the needles – susceptibility to freezing

• Mobile Al in the soils can block the plant uptake of Ca. Ca

is an important macro-nutrient for the trees. • Cronan & Grigal (1995) found that Ca:Al ratio of less

than 1.0 in soil waters indicated a greater than 50% probability of impaired growth in Red Spruce.

Ca:Al – thus a useful indicator for ecosystem recovery from acidic deposition

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Sugar Maple – impaired health due to lack of Ca and Mg – makes them susceptible to other stresses such as insect defoliations – Multiple stress syndrome

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Question - Sugar Maple trees on ridgetops and on upper slopes are especially vulnerable. Why?

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Effects on surface waters (streams, lakes)

Depression of pH Decrease in ANC Increase in solubility of inorganic Al • the ANC value is an indicator of the likely health of the

aquatic ecosystem ANC thresholds: • < 0 μeq/L – chronically acidic (throughout the year)

• 0-50 μeq/L – suffer from episodic acidification (seasonal

or for short periods) • 50 μeq/L – relatively insensitive to acidic deposition

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What is Episodic Acidification? Associated with: • Spring snowmelts – high nitrate release! • large storms in summer and the fall • winter snowmelts

Why these periods?

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Spatial watershed-scale patterns in episodic acidification – interest in identifying streams that are acidic and the likely influences of – • Topography • geology • Soils • Hydrologic flow paths

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Deeper flow paths,Greater contact timeMore cationsHigher pH

Shallow flow pathsLess contact timeLow cationsLow pH – closer to rainfall

Hydrologic flow paths and chemistry

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Question - Acidification has a greater impact on streams than lakes. Why?

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Effects on aquatic biota

Brook Trout Fishes that are affected by acidity – smallmouth bass, walleye, northern pike, lake trout, lake herring, perch and rock bass. Aquatic biota can be affected by – • Acidity – affects the fish reproductive cycle

• Ca levels in fish may be lowered –

o eggs fail to pass from ovaries o if fertilized, the eggs or larvae develop abnormally

• failure of fish to osmoregulate – imbalance of salts in the

body – Ca, Na. – leads to heart attack!

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• mobilization of metals like Al that are toxic to the fish

o solubility of Al increases when pH is lowered from 7 to 5

o Acutely toxic results – severe necrosis of the fish’s gill epithelium

• Acidity may affect frogs and salamanders – acids in the

meltwater pools may prevent hatching of 80% of the eggs • Lake acidification – leads to declines in algal species –

survival of the acid tolerant species only -- also impacts macroinvertebrate and zooplankton communities

• Decrease in decomposer organisms like bacteria and fungi –

buildup of water products and organic matter – reduction in cycling of N and P.

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• Adirondack lake survey performed in 1984 and 87 of 1469

lakes – showed that 346 lakes (24%) did not support any fish

• Radio-tagged brook trout emigrated downstream during

acidic episodes in streams • Lakes experiencing high concentrations of Al – display

a crystal-clear appearance (suggesting clean water suitable for habitat) – the clarity is due to the flocculating impact of the Al ions!

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Susceptibility of lakes/landscapes to Acid Deposition Resistant areas: • With thick soils • With sedimentary rocks (limestone) – rocks that contain

large amounts of base cations and that leach these ions Sensitive areas: • Lie downwind of SOx and NOx sources • Watersheds are underlain by chemically unreactive bedrock

(granite and basalt) and which have thin soils • Headwater watersheds – small streams

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7. ECOSYSTEM RECOVERY FROM ACID DEPOSITION

So, what are the stages of recovery???? Characterized by –

1. Chemical recovery

2. Biological recovery Chemical recovery thresholds:

1. Ca:Al > 1.0

2. Base saturation > 20%

3. pH > 6.0

4. ANC > 50 μeq/L

5. Al < 2.0 μmol/L Chemical recovery will depend:

1. Magnitude of decreases in deposition 2. Depletion of base cations from the soil 3. Local rate of weathering and inputs of base cations 4. Accumulated S and N and its release

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Acidic sites with low base saturation will recover slowly. At most sites it appears that recovery will require DECADES Biological recovery • Sustained biological recovery will occur only after

chemical soil water conditions have improved. • Considerable uncertainty

• Stream populations of macroinvertebrates ~ 3 years

• Lake populations of zooplankton ~ 10 yrs

• Fish populations ~ 5-10 yrs after zooplankton recovery

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