Acid Rain

In this Section      Forests      Acid Rain: Causes      Acid Deposition

Fish mortalities tend to occur due to springtime melting of acidic snow, which drains into common waterways. Some fish that are highly susceptible to of acidity are smallmouth bass, walleye, brook trout and salmon. Signs of acid stress in fish include the failure of females to spawn, or the failure of hatchlings or fry are to thrive. This would explain why some acidic lakes contain only older fish. Other impacts of acid rain on lake fish include decreased growth, the inability to regulate body chemistry, deformities in the young and increased susceptibility to naturally occurring diseases. Acid rain can have devastating effects on lakes, rivers and streams. Lakes that once supported a variety of life can no longer because of the acid level present. The entire food chain from plankton, to photosynthetic basis of the food chain, clear through to invertebrates to small and large fish are affected.

As fish supplies decrease so do fish catching birds and mammals. Increased acidity in rivers and lakes results in an imbalance in the ecosystem. Not only are several species depleted, but some thrive on acidic conditions for instance, bottom dwelling plants such as mosses, and certain insects such as black fly larvae.

Forests:

Acid rain can have minimal to severe impacts on forests depending on the acidity of the rain, as well as regional geological and biological features. Acid rain can deplete certain minerals in the soil, altering the nutrients available to sustain vegetation. Acid rain also damages the surface of leaves and needles, thus affecting the photosynthetic process. Acidic conditions inhibit germination and the reproductive process and make trees more vulnerable to pathogens and pests. Disease ridden trees are more likely to die and have a lower economic value.

Acid Rain: Causes

There are two chemicals that contribute to acid rain. These two chemicals are sulphur dioxide (SO2) and nitrogen oxides (NOx). Both occur naturally in the environment. SO2 is naturally released from volcanoes, oceans, biological decay and forest fires. Worldwide SO2 emissions are estimated to be around 79 million tons annually. Canada contributes 2.7 million tons of SO2 to this problem. NOx is naturally emitted from volcanoes and biological decay. Scientists estimate that between 20 million and 90 million tons of NOx are released annually from natural sources. In addition, around 22 million tons are produced and released into the atmosphere from human activities. Human activities that produce SO2 and NOx include the burning of fossil fuels by coal-fired power generators, industrial operations, vehicle use, and home furnaces.

Acid Rain: Acid Deposition

Acid rain is a term used to describe acidic precipitation in any form, including snow, fog, mist, and hail. Acid rain is created when SO2 and NOx combine with water vapour in the atmosphere to create sulphuric acid and nitric acid. These acids can be carried long distances with the wind, combine with water vapour and fall to earth as precipitation. Where 'pure' water has a neutral pH value of 7, normal rain has an acidity level of about pH 5.6. Acid rain may be as acidic as pH 3 or 4. The lower the pH value, the more acidic the substance is. Remember- acid rain is measured on a log scale. For example, a pH of 6 is 10 times more acidic than a pH of 7. Therefore, a pH value of 5 is 100 times more acidic than a pH 7!

On land, acid rain becomes a problem when natural environmental processes cannot neutralize the acid. For example, eastern Canada's freshwater lacks a natural alkalinity - such as a lime base - and consequently these waterways cannot neutralize acid naturally. Acid rain poses the most threat to Ontario, Quebec, New Brunswick, and Nova Scotia because these regions lack natural neutralizers. Acid rain has many far-reaching effects on vegetation, wildlife, and human health, including damage to tree leaves, alteration in soil, chemistry and nutrient availability to plants, alteration of the chemical make up of lakes, rivers and streams and subsequent damage to aquatic organisms.