'Acid rain' and forest mass: Another perspective

A few years ago the study of the effects of atmospheric deposition on forest ecosystems reached beyond the scientific sphere and the term "acid rain" was coined. This problem, which ignores frontiers, happens because, due to the burning of fossil fuels, the amount of sulphur and nitrogen oxides in the atmosphere is greater than that derived from natural processes.

These oxides, in the presence of water vapour and under the oxido-reduction conditions present in the atmosphere, produce acids that are deposited, amongst other places, on the forest biomass. Also, intensification in the cattle sector, together with stabling and grouping together of herds, have given rise to the concentration of ammonia emissions in certain zones. This compound, deposited close to the sources of emission, is able to react with the acidic ions deposited at the same time. Subsequently, certain bacteria are capable of oxidising the compound, thus forming nitrate and liberating protons that acidify the soil. Amongst the effects of the deposition of these compounds on the forest mass are the well-known nutrition disorders of the same. One classic effect is that of cation deficit (particularly magnesium) due to the washing both of the forest canopy and the soil produced by these together with anions (sulphates and nitrates). This problem is not very common in forest ecosystems close to the sea given that, in these conditions, the uptake of magnesium with precipitation is high. Another consequence is what is known as the eutrofization of terrestrial ecosystems due to the increase in nitrogen availability (saturation) in systems where historically this element has been the limiting factor in productivity.

In this research, the recycling of nutrients was studied in two, five-year period stages and in two young radiata pine forests (the first stage) and in two oak woods (the second). To this end, weekly samples of rain, transcolation (fraction of the precipitation that passes through the forest canopy), and litterfall (vegetable material fallen from trees: leaves, twigs, fruit, and so on), the first 25 cm of mineral soil and green foliage were taken and analysed chemically, according to standard protocols. The location of parcels was carried out as a function of their distance from different foci of emission of contaminants. A flow equilibrium model for the canopy was drawn up together with a generalised micrometeorological model in order to estimate the total deposition of atmospheric constituents. Also, a model for foliar growth and abscision was designed using proportions of the various cohorts of the samples of green branches and litterfall.

The total nitrogen deposition was greater that that deemed to be the admissible critical load in European forest ecosystems so that the nitrogen saturation of the ecosystems studied is, or shortly will be, a fact. The canopy of the forests was able to neutralise the atmospheric deposition in an effective manner although the potential acidity was greater in those areas near emission foci. The uptake of acidifying ions and nitrogen caused an acceleration of the return of nutrients (amount of nutrients that the vegetation gives back to the soil together with the litterfall and foliar excretion) and a drop in their retranslocation (reabsorption of nutritive elements). Thus, the efficiency in the use of cations was affected by the atmospheric deposition of contaminants. Magnesium deficiency was observed in all the adult formations studied. The acceleration of the return of nutrients and the drop in the efficiency of their use is proposed as an explanation of this disorder.

Important facts on the Formation of Acid Rain

In the atmosphere, the sulphur and nitrogen oxides undergo complex chemical processes that transform them into their respective acids such as sulphuric acid and nitric acid.

The formation of acid rain involves the types of phases. These are:

(I) Gas Phase Reactions:

Gas phase reactions predominate in the ninety of emission sources. The oxides can be converted into acids in several ways in the pressure of catalyst such as photo chemically generated free radicals. These free radicals are formed under the influence of sunlight. Sunny weather accelerates the rate of conversion to the formation of acid. After sunset, the rate of conversion falls off rapidly.

(II) Liquid Phase Reactions:

Liquid phase reaction predominates of great distance from the source of emission. However, there is a great deal of controversy regarding the mechanism involved in such reactions. In case of formation of sulphuric acid rain, it is considered essential that the presence of strong oxidizing agents such as metal catalysts are important in the polluted areas.

Acid rain causing decline in sugar maples, say researchers

Acid rain, the environmental consequence of burning fossil fuels, running factories and driving cars, has altered soils and reduced the number of sugar maple trees growing in the Northeast, according to a new study led by Cornell University researchers.

The sugar maple is the most economically valuable tree species in the eastern United States because of its high-priced lumber, syrup and tourist-attracting fall colors.

The study, whose lead author, Stephanie Juice '04, was an undergraduate when the research was conducted, suggests that because acid rain makes the soil more acidic, unfavorable conditions are created for sugar maples. In acidic soils, sugar maples produce fewer seedlings that survive and mature, and more adult trees die, the researchers found. They drew these conclusions after adding nutrients to soil in a test plot and reproducing the favorable soil conditions that existed prior to 20th century industrial pollution. The result: Sugar maples on the plot rebounded dramatically.

The study provides "the most conclusive evidence to date" that the decline of sugar maples is linked to the effects of acid rain produced by human activity, said Timothy Fahey, professor of forest ecology at Cornell and co-author of the study, which is published in the May issue of Ecology. Juice wrote the main part of the paper as part of her senior thesis.

"The research addresses how a long-term, human-caused change in the environment is affecting sugar maples, which are valuable both ecologically and economically as one of the dominant species in our region," said Juice, who now works for the Institute of Ecosystem Studies in Milbrook, N.Y., as a project assistant and is applying to the Peace Corps for next year.

The research was conducted at Hubbard Brook Experimental Forest (HBEF), a 3,160-hectare reserve near North Woodstock, N.H., where scientists have measured soil composition for the past 50 years. The scientists added nutrients in a test plot to replicate soil conditions that existed prior to the loss of sugar maples over the past 25 years.

Nitric and sulphuric acid in acid rain leaches calcium from the soil. Calcium is the second most abundant plant nutrient (after nitrogen). In addition, the loss of calcium leads directly to more acidic soils. When soils become too acidic, such trees as sugar maples become stressed and have a harder time growing or producing seeds and seedlings.

"Because of the detailed measurements for the last 50 years, we know almost exactly how much calcium was removed by acid rain," said Fahey. "Our treatment was designed to replace just that amount of calcium to bring the system to what it was like prior to the acid rain era."

The study used two 10-hectare (25-acre) watersheds. On one 25-acre site, a calcium-rich mineral called wollastonite was spread in pellet form by helicopter in October 1999. The other site served as a control.

While the pellets dissolve slowly over five to 10 years, the researchers were surprised to find that by summer 2002, the soil acidity in both the top and lower layers of the test plot neutralized from being highly acidic to more acceptable levels for sugar maples. The researchers also found that by the second year, calcium levels in the maples' leaves had risen.

Acid rain also increases levels of the trace nutrient manganese in the soil, which can be toxic to trees in higher doses. By year four and five, manganese in the leaves had declined to healthier levels. In addition, seed production and the density and size of sugar maple seedlings all increased in the few years following treatment, compared with the untreated neighboring plot.

The researchers also found that the communities of mycorrhizae -- soil fungi that help provide more nutrients to plant roots -- were substantially greater around the roots of both seedlings and mature sugar maples in the treated plot. Future research will explore the relationship between mycorrhizae and acid rain.

Though pollution-control legislation has helped reduce sulphuric acid by one-third since its high point in the 1960s, nitric acid from automobiles has not significantly declined.

How to Avoid Acid Rain

Acid rain is a popular phrase used to describe rain, snow, fog, or other precipitation that is full of acids that collect in the atmosphere due to the burning of fuels such as coal, petroleum, and gasoline. Acid rain was first recognized in Europe in the late 1800s but did not come to widespread public attention until about 1970, when its harmful effects on the environment were publicized. Research has shown that in many parts of the world, lakes, streams, and soils have become increasingly acidic, prompting a corresponding decline in fish populations. Acid rain occurs when polluted gases become trapped in clouds that drift for hundreds, even thousands, of miles and are finally released as acidic precipitation. Trees, lakes, animals, and even buildings are vulnerable to the slow, corrosive effects of acid rain.



Acidification, the process of making acid, is not just caused by deposits of acidic rain but also by chemicals in snow and fog and by gases and particulates when precipitation is not occurring. The major human-made causes of acid deposition are (1) emissions of sulfur dioxide from power plants that burn coal and oil and (2) emissions of nitrogen oxides from automobiles. These emissions are transformed into sulfuric acid and nitric acid in the atmosphere, where they accumulate in cloud droplets and fall to Earth in rain and snow, wet deposition. Other sources of acid deposition are gases like sulfur dioxide and nitrogen oxides, as well as very small particulates. These gases and particulates are usually deposited when it is not raining or snowing which is called dry deposition.



 While large areas of Europe and North America are exposed to acidifying depositions, only certain types of ecosystems are affected by these depositions. The most vulnerable ecosystems usually have a thin cover of soil, containing little calcium and sitting upon solid rock made up of hard minerals such as granite or quartz. Many freshwater lakes, streams, and rivers have become acidic, resulting in the decline or local destruction of some plant and animal populations. It is not yet certain that land-based ecosystems have been affected by acidic deposition. After acid rain was discovered in Europe, scientists began measuring the acidity of rain in North America. Initially, they found that the problem was concentrated in the northeastern states of New York and Pennsylvania because the type of coal burned there was more sulfur containing.

Acid rain is measured through pH tests that determine the concentration of hydrogen ions in a liter of fluid. The pH scale is used to measure acidity or alkalinity. It runs from 0 to 14. Water has a neutral pH of 7. The greater the concentration of hydrogen ions and the lower the pH number, the more acidic a substance is and the lower the concentration of hydrogen ions and the higher the pH number, the more alkaline or basic a substance is. So a pH greater than 7 indicates an alkaline substance while a pH less than 7 indicates an acidic substance. It is important to note that a change of only one unit in pH equals a tenfold change in the concentration of hydrogen ions. For example, a solution of pH 3 is 10 times more acidic than a solution of pH 4. Normal rain and snow measure about pH 5.60. In environmental science, the definition of acid precipitation refers to a pH less than 5.65.



Measured values of acid rain vary according to geographical area. When pH levels are drastically upset in soil and water, entire lakes and forests are endangered. Evergreen trees in high elevations are especially vulnerable. Although the acid rain itself does not kill the trees, it makes them more susceptible to disease. Also, high acid levels in soil cause leaching of other valuable minerals such as calcium, magnesium, and potassium. Small marine organisms cannot survive in acidic lakes and rivers, and their depletion affects the larger fish who usually feed on them, and, ultimately, the entire marine-life food chain. Snow from acid rain is also damaging; snowmelt has been known to cause massive, instant death for many kinds of fish. Some lakes in Scandinavia and New York's Adirondack Mountains are completely devoid of fish life. Acid rain also eats away at buildings and metal structures. From the Acropolis in Greece to Renaissance buildings in Italy, ancient structures are showing signs of corrosion from acid rain. In some industrialized parts of Poland, trains cannot exceed 40 miles (65 kilometers) per hour because the iron railway tracks have been weakened from acidic air pollution. Usually, waters affected by acid rain are treated by adding limestone or lime, an alkaline substance (base) that reduces acidity. Fishery biologists especially are interested in liming acidic lakes to make them more habitable for sport fish. In some parts of Scandinavia, for instance, liming is used extensively to make the biological damage of acidification less severe.



While neutralizing ecosystems that have become acidic, treats the symptoms but not the sources of acidification. Although exact sources of acid rain are difficult to pinpoint and the actual amount of damage caused by acid deposition is uncertain, it is agreed that acid rain levels need to be reduced. Scientific evidence supports the notion that what goes up must come down, and because of public awareness and concerns about acid rain in many countries, politicians have begun to act decisively in controlling or eliminating human causes of such pollution. Emissions of sulfur dioxide and nitrogen oxides are being reduced, especially in Western Europe and North America. For example, in 1992 the governments of the United States and Canada signed an air-quality agreement aimed at reducing acidifying depositions in both countries. While countries in Western Europe and North American have actively carried out actions to reduce emissions of gases leading to acid deposition for a number of years, countries in other parts of the world have only recently addressed the issue. In Eastern Europe, Russia, China, India, Southeast Asia, Mexico, and various developing nations, acid rain and other pollution problems are finally gaining notice. For example, in 1999, scientists identified a haze of air pollution that hovers over the Indian Ocean near Asia during the winter. The 3.8 million-square-mile haze (about the size of the combined area of all fifty American states) is made up of small by-products from the burning of fossil fuels. Such a cloud has the potential to cool Earth, harming both marine and terrestrial life.

Acid rain limits global warming

Acid rain restricts global warming by reducing methane emissions from natural wetland areas, suggests a global climate study.

Acid rain is the result of industrial pollution, which causes rainwater to carry small quantities of acidic compounds such as sulphuric and nitric acid. Contaminated rainwater can upset the chemical balance rivers and lakes, killing fish and other organisms and also damage plants, trees and buildings.

But the new study shows that sulphur in acid rain may have benefits, limiting global warming by counteracting the natural production of methane gases by microbes in wetland areas.

Methane is thought to account for 22 percent of the human-enhanced greenhouse effect. And microbes in wetland areas are its biggest producers. They feed off substrates such as hydrogen and acetate in peat and emit methane into the atmosphere.

Global warming itself will only fuel the production of methane as heating up the microbes causes them to produce even more methane. But the new model suggests that sulphur pollution from industry mitigates this.

This is because sulphur-eating bacteria also found in wetland regions outcompete the methane-emitting microbes for substrates. Experiments have shown that sulphur deposits can reduce methane production in small regions by up to 30 per cent by activating the sulphur-eating bacteria.

Industrial emissions have been blamed as the major cause of acid rain

Acid rain, which is a form of air pollution, currently becomes a subject of great debate because of widespread environmental damage for which it has been blamed. It forms when oxides of sulfur ($L) and nitrogen ( M,) combine with atmospheric moisture to yield sulfuric and nitric acids, which may then be carried long distances from their source before they drop in the form of rain. The pollution may also take the form of snow or fog or fall down in dry forms. In fact, although the term "acid rain" has been in use for more than a century — it is derived from atmospheric studies that were made in the region of Manchester, England — the more accurate scientific term would be "acid deposition " . The dry form of such deposition is just as damaging to the environment as the liquid form.

The problem of acid rain originated with the Industrial Revolution, and it has been growing ever since. The severity of its effects has long been recognized in local settings, as exemplified by the spells of acid smog in heavily industrialized areas. The widespread destructiveness of acid rain, however, has become evident only in recent decades. One large area that has been studied extensively is northern Europe, where acid rain has eroded structures, injured crops and forests, and threatened life in freshwater lakes. In 1984, for example, environmental reports indicated that almost half of the trees in Germany's Black Forest had been damaged by acid rain. The northeastern United States and eastern Canada have also been particularly affected by this form of pollution; damage has also been detected in other areas of these countries and other regions of the world.

Industrial emissions have been blamed as the major cause of acid rain. Because the chemical reactions involved in the production of acid rain in the atmosphere are complex and as yet little understood, industries have tended to challenge such assessments and to stress the need for further studies; and because of the cost of pollution reduction, governments have tended to support this attitude. Studies released by the US government in the early 1980s, however, strongly indicated industries as the main source of acid rain, in the eastern US and Canada.

Green Energy Wake-Up Calls: Global Warming, Acid Rain, and Smog

Smog

The particles and gases from auto exhaust pipes can create photochemical smog. This form of smog is very often found in hot, dry and bright cities like Athens in Greece, Cairo in Egypt and Mexico City. The automobile exhaust pipes pump out gases like nitrous oxide, carbon monoxide and ozone that react together in the sunlight. The result is a smoggy haze over the city.

LA in California, USA, has suffered badly during the past from smog. The smog was due partly to the exhaust fumes from millions of cars, but also from the local geography. The town lies by the coast and is encircled by mountains. In certain climatic conditions, the smoggy air would be encircled over the city, and air quality would fall steadily until atmospheric conditions changed and the smoggy air was replaced by cleaner air. A hazy layer can still be seen over Los Angeles, but the level of pollutants has fallen dramatically due to new legislation and improved pollution control on vehicles.

Acid rain

Coal-fired power stations release sulphur dioxide, particularly those burning lignite coal. This gas, together with nitrous oxides from car exhausts, reacts with water in the air to form puny acids. These acids create acid rain — rain that has a lower pH than ordinary. Acid rain erodes and damages the exterior of buildings and statues, especially than made of limestone.

Acid rain falling on conifer forests in mountainous areas of Scandinavia, North America and central Europe has caused long—term damage to the trees. The soils get more acid and this causes noxious compounds, such as aluminum, to be released. The 1st appearances of damage are a tree\’s needles turning brown and whole branches dying. Increased acidity in the soil damages trees \’ roots, and this reduces their capability to take up water and nutriments. The trees become even more exposed to frost and disease. Ultimately, they die.

Lakes are also exposed. The acidic rainwater drains off soils into the lake, making it become even more acid. Aluminum in the water causes the gills of fish to supply more mucus, and this prohibits them from getting sufficient oxygen from the water. In extreme cases, all life in the water may die.

Global warming

Burning fossil fuels releases carbon dioxide. Carbon dioxide is described as a \’greenhouse \’ gas, because it traps heat in the atmosphere. The presence of some greenhouse gases keeps the Earth at a temperature of approximately 15C, which permits life to survive. A recent increase in the usage of fossil fuels has caused the levels of carbon dioxide in the atmosphere to extend, too. More carbon dioxide implies that more heat is surrounded, and this has caused the average world temperature to rise. This is named global warming.

The exposed solar power effects of global warming are uncertain, but it\’s probable that the skyrocketing temperatures will disrupt climates around the globe, causing some regions to have lower rainfall and other regions to have more. The hotter temperatures will cause ice caps and glaciers to melt, which, mixed with the growth of water in oceans, will cause sea levels to rise, flooding low lying areas which are heavily populated. Acute weather events such as droughts and storms could also become more common.