Biology 381 Pollution Biology Department of Biological Sciences University of Alberta Edmonton, Alberta

7.1 Required Reading and other announcements.

No required reading.

7.2 A multiplicity of effects. 

Photos taken approximately 60 years apart show evidence of rapid deterioration due to acid precipitation (and other pollutants).
http://btdqs.usgs.gov/jgordon/statfinl.gif

Documented effects of acid precipitation include:

Acidification of surface waters.

Alterations in plant growth and forest productivity.

Materials degradation.

reduced  visibility.

health effects (sulfate aerosols, NOx).

The mechanistic bases of these effects are not always clear. 

7.3 Does acid precipitation affect plant growth?

Many scientists now believe that the direct and indirect impacts of acid deposition on vegetation are substantive, whether these effects are measured in a biological or an economic context.

The growth rate of spruce trees in the Green Mountains of Vermont declined by 50% between 1963 and 1973.

Tree ring analysis suggests similar reductions in forest growth in Europe.

 

 

 

 

Declining annual growth-rings in damaged silver fir trees in the Alpirsbach region of Germany (1940-1983),  Figure 5.2, Park (1987).

Acid precipitation has been implicated in these declines, but unambiguous cause effect relationships are lacking. 

7.4 The relationship between acid deposition and phytotoxic effects is complex.

In addition to the extent of acid deposition (concentration or total deposition), the response of plants to acid deposition will depend on a number of factors including:

Plant species, ecotype or cultivar.

Plant age or stage of development.

Characteristics of exposure (frequency, duration, period, form of acidity, time between exposures, and others).

Other environmental factors that affect plant vigour.

Buffering capacity/sensitivity.

To address these challenges, many scientists have resorted to research in controlled environments such as greenhouses or growth chambers, using simulated acid precipitation.

Interestingly, plants grown in controlled environments show greater susceptibility to foliar injury, and a lower threshold for yield reductions than field grown plants.

A general observation is that most plants show only small growth effects due to simulated acid precipitation of the same acidity as ambient rainfall.

Where growth effects have been established, they are in the range of of 5-10%.

Acid deposition may affect vegetation through direct effects and indirectly through secondary stresses.  Not all secondary effects would be evident in laboratory studies or in short-term field studies.

7.5 The phytotoxic effects of acid precipitation.

 

 

 

 

 

A summary of the potential effects of acid precipitation on plants. 
Figure 5.4, Park (1987)

Direct effects of acid deposition

Damage to protective surfaces such as the cuticle.

Damage of the cuticle can lead to visible injury to foliage, fruits, or flowers, possibly leading to lower productivity, lower economic yield, and increased susceptibility to attack by insects, fungi, and other plant pathogens.

Damage to the cuticle may also increase the sensitivity of plants to drought.

Direct H⁺ toxicity on leaf metabolism after penetration through stomata or the cuticle.

Processes which may be affected include stomatal function, photosynthesis, membrane function, and hormone action.

Alteration of leaf and root exudation processes.

Acidity can modify normal patterns of exudation from leaves and roots. Such exudates may be essential for mediation of plant/microbe interactions.

Accelerated leaching of nutrients from leaves.

 

 

 

 

 

 

Figure 9.2, Smith (1981).

Sulphuric acid and nitric acid can serve as a source of essential mineral nutrients (N, S), possibly leading to improved growth.

 

 

 

 

 

 

Figure 5.3, Park (1987).

Indirect effects of acid deposition

Increased susceptibility to drought.

Water loss is accelerated by damage to the leaf cuticle. 

Water uptake is reduced by damage to fine roots and root hairs, which may be caused by mobilization of phytotoxic metals which accompany soil acidification.

Alteration of host/parasite interactions.

Damage to the plant cuticle and fine roots may allow more rapid penetration of pathogens into foliar tissue.

Alteration of symbiotic interactions.

Nitrogen fixation may be affected by alterations in root exudation processes, and is clearly inhibited by soil acidification.

Mineral deficiencies brought about by damage to fine roots and increased nutrient leaching from soils and leaves.

Acid precipitation greatly increases the rate of nutrient leaching from soils.

 

 

 

 

Figure 14-13, Nebel (1987)

 

 

 

 

 

Figure 9.3, Smith (1981).

Declining nutrient status of soils is accompanied by damage to fine roots caused by increasing soil acidity and aluminum toxicity.

Aluminum toxicity.

Aluminum is a highly toxic metal which is abundant in many soils. When pH is above 5.0, however, aluminum is largely insoluble.

If acid precipitation reduces the pH of soil below 4.8, mobilization of soil aluminum may occur, possibly leading to aluminum toxicity.

 

 

 

 

 

The relationship between concentrations of aluminum in surface waters and surface water pH in 151 Belgian lakes. Figure 4.8, Park (1987).

7.6 Is acid precipitation involved in forest decline?

7.7 Additional world wide web information.

Pollution Matrix.   Internationella Miljöinstitutet, Pollution Matrix has information about effects of acid rain on plant too. 

IGC: Acid Rain. A listing of extensive acid rain resources for those who need more information.

The U.S. EPA's Environmental Effects of Acid Rain Page. A broad array of information related to the impacts of acid precipitation.

Introduction to Physical Geography.  Acid precipitation is also taught at Okanagan University College.  See what they are learning.