Acid Rain and Alkalinity of the Lakes in Canada - Essay Example

Acid Rain and Alkalinity of the Lakes in Canada Surface and soil waters such as lakes and streams receive acid from a variety of natural sources. Natural sources of acids is obtained by decomposition of animals and plants, forest fires, volcanoes, which produce sulfur oxide/sulfuric acid. Carbonic acid is formed by carbon dioxide in the air, and the lightning bolts changes nitrogen molecules in air to nitrogen oxides and nitric acid. In the same way, surrounding vegetations also determines the acidity or alkalinity of the lake, such as types of trees, soil, and decaying leaves. Humus (layers of decaying leaves) has rich organic matter and they produce acids similar to vinegar. Another determinant of lakes is its location and natural bases, that is, answer lies in geology. If the lake has surrounding of rocks containing limestone contain bases, then acids will be reduced (neutralized) by the natural bases and the pH of the lake will remain nearly the same. Calcite (CaCO3) greatly mitigates the effects of acid rain. Calcite is the principal mineral that makes up the rock limestone. For example, the case of sulfuric acid falling on limestone can be understood by the following reaction: H2SO4 + CaCO3 --> CaSO4.H2O + CO2 The sulfuric acid is changed into mineral gypsum (CaSO4.H2O) and Carbon dioxide is released. Thus, lakes located on limestone terrains will not suffer the consequences of acid rain. On the other hand, rocks which contain granite contain has very little bases and is unable to neutralize the acidic ingredients. Eastern Canada is facing widespread acidification of lakes due to acid rain, and presence of granite rocks. In Ontario approximately 1200 lakes are dead. Acid rain refers to all types of precipitation - rain, sleet, fog, hail, snow that has a pH lower than the 5.6 average of rainwater. Note that the rain water is naturally slightly acidic due to equilibration with atmospheric carbon dioxide. The "pure" rain water's acidity is between pH 5.6-5.7, somewhat pH readings vary depending upon place to place and amount of other gases present in the air, such as nitrogen oxides and sulfur oxide. The pH scale refers to the free hydrogen ions (electrically charged atoms) in water and a number that ranges from 0 to 14. Seven is considered neutral, that is, neither acidic nor basic. Number less than seven are acidic and those higher it is basic or alkaline. The pH scale is logarithmic (base 10), and not linear. For example, pH 3 is 10 times more acidic than pH 4 and 100 times more than pH 5. The formation of acid in the acid rain is due to two kinds of air pollutants - sulfur dioxide (SO2) and nitrogen oxides (NOx). These pollutants react with gaseous water in the atmosphere to form sulfuric acid (H2SO4) and nitric acid (HNO3). The two-step process explains the formation of acid solutions by SO2. First the sulfur dioxide molecules react with water molecules and forms molecules of sulfurous acid: SO2(gas) + H2O(liquid) H2SO3(aq) Then the Sulfurous acid molecules reacts with water and produces an equilibrium with H+(aq) and hydrogen sulfite. Because the Sulfurous acid only partially ionizes into H+(aq) so it is considered as a weak acid: H2SO3(aq) + H2O(liquid) H+(aq) + HSO3(aq) Sulfur dioxide also reacts with oxygen or ozone and form sulfur trioxide: SO2(gas) + O2(gas) + 2SO3(gas) SO2(gas) + O3(gas) SO3(gas) + O2(gas) Then the sulfur trioxide reacts with the atmospheric moisture to form sulfuric acid: SO3(gas) + H2O(liquid) H2SO4(aq) The sulfuric acid which is a strong acid, completely ionizes in the atmospheric precipitation to release H+(aq) ions: H2SO4(aq) H+(aq) + HSO4-(aq) These aqueous hydrogen are responsible for the acidic effects in the acid rain. In Canada about 60% of pollution is caused by transportation emission. Car engines uses gasoline, which burn using air as a source of oxygen. Nitrogen is the primary component of air and under high temperature inside the car engine it forms the pollutant nitrogen monoxide (NO). Under sunlight a series of secondary reactions takes place and this produces nitrogen dioxide and ozone. Both of these actively participate in acid rain reactions. Nitrogen dioxide with atmospheric water produces little nitric acid (HNO3) on account of the low solubility of NO2 in water: 2NO2(gas) + 2H2O(liquid) HNO2(aq) + HNO3(aq) Acid rain having major amounts of nitric acid likely generates without water: NO2(gas) + O3(gas) NO3(gas) + O2(gas) The gaseous nitrogen trioxide then forms reaction with any other reactive hydrogen donor (X) in the atmosphere: NO3(gas) + XH(gas) HNO3(aq) Like sulfuric acid, nitric acid is also a strong acid and it totally ionizes into aqueous hydrogen and nitrate ions: HNO3(aq) H+(aq) + NO3-(aq) The above reaction mechanism makes it clear how sulfuric acid and nitric acid makes a series of reaction and contributes in acid rain formation. The same when precipitates in lakes it reduces the pH from alkaline to acidic. Effect of Acid Rain on Lakes Scientists have shown that with increased acid rain deposition the acidity of some lakes have touched danger level which is threatening the aquatic life. As claimed by some environmentalist groups that about 14000 Canadian lakes have suffered huge damage due to acid rain. Those lakes which are naturally poorly buffered are the most affected. Limestone is a natural alkaline buffer and it has the capacity to neutralize excessive acidic compounds accumulated from acidic rain. But granite (bedrock) has least capacity to provide buffer protection. This is the reason that acidic precipitations have been recognized as a problem in South Central and Eastern Canada, which has granite rocks. The lakes are becoming progressively acidified and forests are under assault. Some lakes in this areas have recorded pH levels even lower than 5.0, however, natural pH levels should range from 6.5-7. This has adversely affected aquatic organisms. Death of snails, crustaceans and other zooplanktons has been noticed Effect on Aquatic Plants and Animals For all life forms the amount of acid or pH is extremely critical whether it be inside of individual cells or outside of the body. Higher animals are normally well protected by skin from the changes in acid levels; however inner organs such as lungs, digestive system, and reproduction may be affected by changes in pH. Sperms, eggs, insects, bugs, developing young may be fairly sensitive to small changes in pH. With the loss of natural bases or alkalinity in the lake changes also begins to occur. As the acid level increases there is a huge reduction in the number of phytoplankton, zooplankton, crustaceans, and mollusks. This leads to slowdown in the rate of decomposition of dead animals and plants. Fishes bear direct effect on their reproductive cycles, malformation of bone takes place due to calcium deficiency. Other to it, aluminum hydroxide gets clogged in their gills leading to suffocation of the fish. Even the songbirds get affected due to consumption of insects contaminated with toxic metals. The increasing acidic levels of lake water are proving detrimental for aquatic plants and animals. Given below is the table that indicates that if the pH level of a lake decreases than the specified level it becomes very harmful for aquatic life. pH Limits for Life in Aquatic Plants and Animals Animal pH Mussel 6.5-6.0 Small mouth Bass 6.0-5.5 May Fly 6.0-5.5 Brown Trout 5.5-5.0 Salamander 5.5-5.0 Yellow Perch 5.0-4.5 Lake Trout 5.0-4.5 Zooplankton 5.0-4.0 Frogs 4.5-4.0 As you can see the pH range for different aquatic life varies and for healthy function it should not be below the specified level. Because the pH scale is logarithmic and so even a slight decrease, such as pH 6.5 to 5.5 represents a 10 times increase in acidity, and could put a question mark on the survivability of the aquatic life. Contrary View The benchmark of "rain water" is pH 5.6. It is naturally slightly acidic due to equilibration with atmospheric carbon dioxide. Acid precipitation in the range of 5.0-4.2 has been recorded in Eastern Canada and United States. Electric Power Research Institute (EPRI) has tried to compare the pH values with some familiar objects, which we use in day-to-day life and gives impression that these pH values are not harmful. For example, Carrot has pH 5.0, Bananas 4.6, Tomatoes 4.2, Soft drinks and Apples 3.0 and Lemon juice 2.0. From these examples EPRI explains that pH 5.6 should not be a valid reference to consider the natural acidity of precipitation. Since the "natural background" condition is unknown, it is difficult to quantify man-made influences to the natural conditions. Even without man's contribution, there are various other natural sources that determine the precipitation of acidity, such as sulfur oxide, nitrogen oxides and other species. It has been noted that in 1960s in the forest areas of Brazil beside Amazon river, which is far remote from civilization had monthly average of 100 rains events the pH ranged from 4.3 to 5.2, while median value was pH 4.6 and one reading was as low as 3.6. Even in Hawaii, which is remote form industrial activities had average rain fall over a 4 year of pH 5.3, with minimum value of 3.8. Acid Rain in Provinces of Canada It is estimated that about half of the 700,000 lakes in the six eastern provinces and south of 520 N in Canada have alkalinity below m eq/liter, which indicates that they are acid sensitive. Those provinces which are part of the Canadian Precambrian Shield, such as Quebec, Ontario, Nova Scotia and New Brunswick are the hardest hit areas, because their water lack natural alkalinity - like lime base. The western provinces are relatively less acid sensitive due to lower level of industrialization, combined with natural factors - like eastward moving weather patterns and abundance of limestone rocks. However, natural protection is not available to all areas in western Canada. Such as, the Canadian Shield in northeastern Alberta, northern Manitoba and Saskatchewan, Nunavut, parts of western British Columbia and the Northwest Territories are resting on granite bedrocks which are very poor neutralizer. Lakes in these areas are prone to acid rain same as those in northern Ontario. If the rate of sulfur dioxide and nitrogen oxide emissions are not contained the western Canada could witness the same harmful impacts that have happened in eastern Canada. Methods for Control Steps are been take by governmental agencies as well as corporate sectors to reduce emission of sulfur and nitrogen oxides. This has helped reduction of harmful content in the air, but to actually reverse the trend of acid rain still more efforts are needed. Some steps are using low Sulfur coal, scrubbers and fluidized bed combustions. About 80-90 per cent of sulfur oxides are removed by using scrubbers, though they are costly to retrofit to existing power plants. Scrubbers are like "liquid" filters containing calcium hydroxide (lime). When the exhaust gases passes through it, the sulfur dioxide gas reacts with the calcium hydroxide and produce solid calcium sulfate, which is then pumped into a temporary storage. Another technique to reduce nitrogen and sulfur oxides is fluidized-bed combustion. This has capacity to remove 15-35 per cent of the nitrogen oxides and 90 per cent of the sulfur oxides. Limestone injection multiple burning technique is still under testing and development stage, but its efficiency level is manifold more than any other method. It can remove 70 per cent both nitrogen and sulfur oxides. Governmental Effort The Canada-Wide Acid Rain Strategy for Post-2000 is a long term program for Acid Rain Management in Canada. In 1998, provincial, federal, territorial and environment ministers signed on this sulfur dioxide emission reduction target. The strategy was formulated after consultation from multi-stakeholder task group. This program is design after the success implementation of the 1985 Eastern Acid Rain Program. In 1997, emissions in Quebec, Ontario, Nova Scotia and New Brunswick were below their provincial caps. Emission is currently 30 per cent below the cap in the southeast Canada Sulfur Oxide Management Area (SOMA), thus Canada is presently meeting more than targeted international commitments on SO2 emissions. On the other hand United States is expected to reach its 40 per cent emission reduction of SO2 (from 1980 level) no sooner than 2010. To achieve the target of "The Strategy" the Ontario government has introduced stringent emissions caps for those power stations that burn fossil fuel, effective from January 1, 2002. Despite difficult economic conditions in Quebec, Noranda Inc. remains committed to reduce 90 per cent of its SO2 emissions and has closed the smelter in Murdochville Quebec in April 2002. In western Canada Alberta has initiated various plans to bring SO2 emission level down. Numerous government and corporate policies have helped to reduce the levels of SO2 and NOX. Trend The analysis the trend of acid depositions it show brighter face, that is, considerable reduction in sulfur and nitrogen dioxide is taking place. During 2000, Canada's sulfur dioxide emissions had come down by 45 per cent, lesser than the 1980 level and 20 per cent lower to the national target which was fixed for 2000 onwards. Similarly, emission of sulfur dioxide was 30 per cent below the cap as set for eastern Canadian states. However, Canadian nitrogen oxide emissions remained slightly above the 1980 level. Since early 1980s about152 lakes were monitored for the acid rain effects in Quebec, Ontario and the Atlantic Region, in which 41 per cent showed improvement from acidity level, 50 per cent showed no improvement and 9 per cent had worsen up. This improvement in acidity level indicates reductions in sulfur dioxide emission. Anyway, it will take time, may be many years for the improvement in lake's alkalinity and reduction of acidity. Overview The effects of acid rain on aquatic life are yet undiscovered and needs more detailed scientific studies. Lakes acid-sensitivity is becoming greater that earlier though to be. An area of estimated 800,000 sq/km, which extends from central Ontario via southern Quebec up to Atlantic Canada; is expected to receive sulfur deposition for a long time, even after full implementation of Canadian and U.S. control programs. This will adversely affect the aquatic ecosystem. Scientists suggest a further 75 per cent reduction in sulfur dioxide emissions is necessary to maintain improvement in aquatic ecosystem. Other to it, least studies has been done to understand nitrogen oxide deposition. This may eventually blunt the benefits of sulfur dioxide emission reduction. Last but not least, a holistic approach to emission reduction strategy is the necessity of the time. Measures taken for protection of aquatic life may not unduly punish economic growth or vice versa. Works Cited Jeffries, D.S., et al. Monitoring the Results of Canada/U.S.A. Acid Rain Control proms: some Lake Responses Jeffries, Dean S., et al. Assessing the Recovery of Lakes in Southeastern Canada from the Effects of Acidic Depositions McNicol, Donald K., et al. Recent Temporal patterns in the Chemistry of Small, Acid-sensitive Lakes in Central Ontario, Canada Read More