Diatom and geochemical indicators of acidification in a tropical forest stream, singapore 2

Chapter Two ACID DEPOSITION AND THE ACIDIFICATION OF FRESHWATER ECOSYSTEMS 2.1 Overview 7 2.2 Acid Deposition 8 2.3 Causes 11 2.4 Impacts 18 2.5 Acid Deposition in Asia 23 6 2.1 Overview Chapter two focuses on acid deposition. It begins by explaining what acid deposition is and provides a brief history of the phenomenon. It then goes on to examine why acid deposition is such a pertinent issue by looking at its causes and impacts. There is an emphasis on the impacts of acid deposition on freshwater ecosystems as it is directly relevant to this study of the acidification of a tropical forest stream. As the problem of acid deposition was first observed in North America and Europe, much of this initial research is based in these regions during the 1970s to 1990s. Following the 1980s and 90s, with effective pollution control legislation, acid deposition was alleviated in Europe and North America. However, researchers realised that Asia, a region that was beginning to industrialise rapidly, was in danger of the same acidification problems North America and Europe once faced. This lead to a boom in research on acidification in Asia during the 1990s. Unfortunately, by the end of the 1990s, the amount of research on acid deposition in Asia declined sharply. However, this is not because acid deposition is no longer occurring in the region. Rather, as the effects of acid deposition have not yet manifested themselves and caused widespread environmental degradation, it is possible that countries are choosing to focus on economic development at the price of environmental health. This is compounded by the fact that the large-scale research projects in Europe and North America were also completed by the early 1990s, and studies on acidification in general declined. As atmospheric contaminants can be transported over long distances before being deposited, atmospheric pollution and acidification in Asia is a cause for concern to the Singapore environment. 7 2.2 Acid deposition The phenomenon of acid precipitation was first observed in the early 1850s by Robert Angus Smith while he was studying the effect of coal combustion on air and rain in England (Gorham, 1989; Mannion, 1999). He coined the term “acid rain” to describe precipitation that had unusually low pH due to atmospheric pollution. While the term “acid rain” is widely used in both scientific literature and the popular press, it is somewhat misleading as this pollution also occurs as snow, hail, gas clouds, fog, mist and dry dust (Bell and Walker, 1992). Furthermore, uncontaminated rain already has a pH below 7 and is, therefore, acidic. “Pure” water generally has a pH of between 5.6 and 5.7 because water molecules combine with carbon dioxide present in the atmosphere to form carbonic acid (Boyle and Boyle, 1983). In addition, sulphur compounds from volcanic eruptions and nitrogen oxides from events such as lightning strikes are converted to sulphuric acid and nitric acid in the atmosphere, which then contributes to the acidity of precipitation (Jones, 2000; Galloway, 1995). Thus, this form of atmospheric pollution is more accurately referred to as “acid deposition” (Bell and Walker, 1992). Unfortunately, while Smith recognized the environmental damage caused by acid rain, his research was largely forgotten until a century later when the continental scale of acid rain effects was discovered (Schindler, 1988). Depending on prevailing wind directions, acid deposition can be carried hundreds of kilometres from the source area (Mannion, 1992). Acidification is so extensive that its presence at the hemispheric scale can be found in polar ice core records. These show an increase in N2O from the 1800s with current high levels unprecedented for the last 200,000 years (Raynaud et al, 1993). Furthermore, in 8 the Northern Hemisphere, many lakes have become acidified by at least one pH unit (table 2-1, Mannion, 1999). Site Location pH change Loch Enoch Loch Grannoch Loch Dee Round Loch Glenhead Loch Laidon Grosser Arbersee Kleiner Arbersee Gårdsjön Hovvatn Holmvatn Malalajärvi Hirvilampi Big Moose Lake Woods Lake Ledge Pond Beaver Lake Lake B Lake CS SW Scotland SW Scotland SW Scotland SW Scotland SW Scotland W Germany W Germany Sweden Norway Norway Finland Finland USA USA USA Canada Canada Canada 0.9 1.2 0.5 1.0 0.7 0.8 0.8 1.5 0.8 0.5 1.0 0.7 1.0 0.4 0.6 0.6 1.6 1.0 Approx. date of initial pH change 1840 1925 1890 1950 1850 1965 1950 1960 1918 1927 1950 1950 1950-1960 1930s 1880s 1950s 1955 1955 Table 2-1: Examples of changes in pH of lake waters that have occurred since 1840 in the UK, Europe and North America (data from Mannion, 1999) Thus, during the late 1970s and early 1980s, acidification gained widespread public attention due to environmental concerns – studies were emerging that linked the acidification of lakes due to industrial pollution to declining fish population (Antoniades, 2007). Acidification became an a source of hostility between acid-producing and acid-receiving nations (Mannion, 1992). Table 2-2 shows the annual sulphur dioxide (SO2) emissions and deposition during the 1980s in some countries within Europe, Russia and North America. The major producers of SO2 were Russia and the United States of America (USA), both producing over 20x106 tonnes annually. Of the sulphur deposition within Russia, at least 50% was produced domestically and 32% from foreign sources. On the other hand, Sweden and Norway only produced 483x103 and 141x103 tonnes of SO2 respectively, and foreign sources account for at least 58% and 63% of sulphur deposition respectively, twice that of Russia. In a similar vein, much of the sulphur deposition Canada received originated from the USA. Thus, 9 the acid-producing nations are not always the ones that suffer the greatest damage (Mannion, 1992). Sulphur dioxide emissions Sulphur deposition (%) (10 3 tonnes) 1980 1983-1986 Foreign Domestic Unknown USSR 25000 24000 32 53 15 USA 23200 20800 ? ? ? Poland 4100 4300 52 42 6 East Germany 4000 4000 32 65 3 Canada 4650 3727 50 50 United Kingdom 4670 3540 12 79 9 Czechoslovakia 3100 3050 56 37 7 West Germany 3200 2400 45 48 7 France 3558 1845 32 54 14 Finland 584 370 55 26 19 Sweden 483 272 58 18 24 Norway 141 100 63 8 29 Table 2-2: Annual SO2 emissions and deposition in selected countries (data from Mannion, 1992) Country This made acidic pollution and acid deposition an issue of huge economic and international political importance, studied by thousands of scientists utilising many hundreds of millions of dollars of research funds (Schindler, 1988). Boyle and Boyle (1983: 12) called it “the single most important threat to the United States and Canada”. In 1979, a convention on Long-range Transboundary Air Pollution was signed in Geneva by 35 countries. While it was merely a token treaty, it provided important recognition among industralised nations that tackling the problem of acidification required collective action (Mannion, 1992). In 1983, the “30% Club” was established and implemented a protocol which required signatory countries to reduce sulphurous emissions by at least 30% of 1980s levels by 1993. The United Kingdom (UK) and the USA did not sign this protocol. In 1989, a second protocol, which included the UK and the USA, was signed that included an agreement to also reduce the emissions of nitrogen gases. The result was a significant reduction in the output of SO2 and nitrogen oxides (NOx) from most industralised nations (Mannion, 1992). 10 2.3 Causes Sulphur dioxide and the two nitrogen oxides – nitric oxide (NO) and nitrogen dioxide (NO2) – are the basic elements involved in acid deposition (Bell and Walker, 1992). These pollutants originate from the burning of fossil fuels and petroleum products, the smelting of metallic ores, the petrochemical and associated industries and from vehicular exhausts (Bell and Walker, 1992). In other words, acid deposition is the product of a fuel-powered urban-industrial system (Figure 2-1, Manion, 1992). Figure 2-1: The formation and deposition of acid pollution (modified from Mannion, 1992) These oxides of sulphur and nitrogen combine with water in the atmosphere, creating sulphurous and sulphuric acids and nitrous and nitric acids (Mannion, 1999). With regard to SO2, it dissolves in cloud water, producing sulphurous acid: SO2 + H2O → H2SO3 ⇌ H+ + HSO3- Sulphurous acid can also be oxidized in the gaseous or aqueous phase by various oxidants: SO2 oxidant → SO3 Aqueous sulphur trioxide forms sulphuric acid: 11 SO3 + H2O → H2SO4 ⇌ H+ + SO4- ⇌ 2H+ + SO42With regard to NOx, they are involved in numerous chemical processes in the atmosphere, some of which damage the ozone layer in the stratosphere (Mannion, 1999). Nitric oxide can be converted to nitrogen dioxide through a reaction with ozone: O3 + NO ⇌ NO2 + O2 On the other hand, nitrogen dioxide can also be converted back to nitric oxide through a reaction with light. The oxygen atom released then reacts to form ozone: NO2 light → NO + O O + O2 → O3 Nitrogen dioxide may dissolve in cloud water to produce nitric and nitrous acids: 2NO2 + H2O → HNO3 + HNO2 The above equations are based on Mannion (1999). It should be noted that both SO2 and NOx also have natural sources. For example, SO2 can originate from gases released during volcano eruptions (Jones, 2000) and NOx from lightning and microbial processes (Galloway, 1995). However, while there is significant uncertainty in the magnitude of these natural fluxes, there is a general agreement that anthropogenic fluxes are larger than natural ones (Galloway, 1995). According to Galloway (1995), in 1990, anthropogenic SO2 emissions exceeded natural emissions of sulphur dioxide by approximately three times (≈75 Tg S/yr compared to ≈25 Tg S/yr) and emissions of nitrogen oxides followed a similar pattern with contribution from fossil-fuel combustion totalling ≈20 Tg N/yr, 12 over twice that of natural emissions which were ≈8 Tg N/yr. While this study is dated, anthropogenic emissions have increased rather than dropped, making their magnitude over natural fluxes greater, not smaller (figure 2-2). Figure 2-2 shows the global emissions of sulphur and nitrogen since the mid-1800s along with the acidification potential of these emissions. Global*sulphur*dioxide*emission* 4500" 4000" 120000" 3500" Emission*(Tg)* 100000" 3000" 80000" 2500" 60000" 2000" 1500" 40000" 1000" 20000" 500" 0" 1850" Acidifica'on*poten'al*(Tg*equivalents)* 140000" 0" 1870" 1890" 1910" 1930" 1950" 1970" 1990" 2010" Year* Sulphur"dioxide"emissions" Acidifica>on"poten>al" Global*nitrogen*oxide*emission* 3000" 45000" 2500" 40000" Emission*(Tg)* 35000" 2000" 30000" 25000" 1500" 20000" 1000" 15000" 10000" 500" 5000" 0" 1850" Acidifica'on*poten'al*(Tg*equivalents)* 50000" 0" 1870" 1890" 1910" 1930" 1950" 1970" 1990" 2010" Year* Nitrogen"oxide"emissions" Acidifica>on"poten>al" Figure 2-2: SO2 and NOx emissions along with their acidification potential (data from Galloway, 1995; Galloway, 2001 and Smith et al, 2011) Acid deposition has the greatest impact on freshwater ecosystems that experience high precipitation rates and have an acid bedrock (such as granite) as acid bedrocks provide little buffering capacity. Conversely, alkaline bedrocks 13 have a neutralising effect on acid deposition (Mannion, 1992). Freshwater systems are also already naturally acidic though processes such as the dissociation of carbonic and humic acids (Ho and Todd, 2010). Aside from acid deposition, there are two other possible causes of acidification in a freshwater ecosystem that need to be taken into account in any acidification study – long-term acidification and land use change (Renberg and Battarbee, 1990). It was found in the 1920s that lakes in catchments which had base-poor or slow-weathering bedrock had a gradual tendency to become more acidic during the post-glacial time period (Renberg and Battarbee, 1990). This was because, as soils became stabilised by forest cover, the mineral elements within, namely calcium, magnesium, sodium and potassium, were leached out, causing the brown forest soils to become acid brown earths and podsolic soils. As some areas underwent paludification, which is “the expansion of a bog caused by the gradual rising of the water table as accumulation of peat impedes water drainage” (Goudie, 2000: 356), the accumulation of acidic organic matter significantly increased the acidity of the water moving through it, causing the subsequent acidification of freshwater ecosystems (Pennington, 1984). Landscape stabilisation and paludification as a cause of long-term acidification is a process that has thus far only been observed in post-glacial temperate landscapes, particularly with the formation of upland peat bogs. However, such a process could occur in the tropics. This is because mainland east Asia, the Caribbean, southern Africa, Central and South America and Southeast Asia contain extensive peatland (Page et al, 2006). Most tropical peatlands occur in low altitude, coastal and sub-coastal (between 0m to 50m above sea-level) areas. They are ombrogenous and convex in shape, “analogous to raised bogs of the Northern Hemisphere” (Dommain et al, 2011: 999). There are also peatlands in mountainous regions. For instance, in Central Kalimantan, 14 peatlands “extend up to 200km or more inland from the coast and occupy thousands of square kilometres, covering the gently sloping landscape in a manner analogous to temperate zone blanket peat” (Page et al, 2006: 151). The majority of these peatlands formed during the mid-Holocene as a response to post-glacial sea-level changes, coupled with an intensification of the Asian monsoon (Dommain et al, 2011). The difference is that while paludification is a common process of peatland formation in the tropics, in temperate regions, it is terrestrialisation that is the primary mechanism of peatland initiation, which is then followed by paludification (Kamal and Varma, 2008). This would mean that in the tropics, which did not experience the widespread glaciation that temperate environments undergo, the weathering system may be in quasi-equilibrium, and would not experience the dramatic geochemical changes temperate environments undergo. It is therefore uncertain whether tropical peatland environmental dynamics would cause similar long-term acidification as seen in temperate environments. In any case, long-term acidification is usually a very slow process, implying that a quasi-equilibrium exits in most catchment soils between cation generation from weathering and cation loss from leaching (Renberg and Battarbee, 1990). For example, based on data from acidification studies in Europe, at sites that exhibited signs of long-term post-glacial acidification, prior to the 1800s, acidification was 0 or less than 0.1 pH units per 1000 years (Renberg and Battarbee, 1990). Recent (post-1850) acidification, on the other hand, is a significantly more rapid process (Renberg and Battarbee, 1990). Furthermore, according to Smol (2008), natural changes cannot account for the current highly acidic state of various lakes in Europe, though it can make lakes more vulnerable to anthropogenic acidification. That being said, as Jungle Falls stream is not in, 15 surrounded or affected by peatlands, this factor will not be considered further in this study. Other opponents of the severity of acid deposition often ascribe present day acidification of freshwater ecosystems to land use change. For instance, Rosenqvist (1978) concluded that the cause of acidification in Norway was a response to an increase in timber production and export along with changing agricultural practices from semi-nomadic cattle farming to sedentary farming. According to Rosenqvist (1978), the growing trees, as vegetation changed from grassland to forests, extracted bases from the ground and increased the amounts of humic acids, thus causing the acidification of river waters. Debates regarding the relative importance of land use and acid deposition in causing recent lake acidification has since been highly contentious (Sullivan et al, 1996). Another study area where land-use change was discovered to have caused surface water acidification, is at the Trossachs region of Scotland. By comparing afforested (Loch Chon) and non-afforested (Loch Tinker) sites, Kreiser et al (1990) found that the main acidification of Loch Chon occurred after conifer afforestation while the pH at Loch Tinker, an adjacent moorland “control” site remained largely unchanged. Kreiser et al (1990) concluded that the afforestation of sensitive catchments can cause freshwater ecosystems to acidify, but only in regions that receive high levels of sulphur deposition. A similar research project was conducted in 1983 at the Llyn Brianne catchment in Wales. Researchers found that not only did afforestation of Sitka Spruce enhance stream water acidification in the area (Whitehead et al, 1988), but that forest age also had an impact on acidification levels (Waters and Jenkins, 1992). Differences in stream chemistry between afforested young forests and moorlands were due to disturbances caused during site preparation, 16 such as ploughing, planting and fertilisation, which alters soil drainage, increasing sulphate and nitrate mineralisation, consequently causing stream acidity to rise (Waters and Jenkins, 1992). As a forest aged, and a canopy developed, not only did uptake and retention of base metals and inorganic nitrogen occur, along with the accumulation of biomass, scavenging of dry and occult deposition of sulphur and nitrogen also exacerbated acidification (Waters and Jenkins, 1992). In order to investigate the significance of land use change to freshwater acidification, several studies in Norway, the UK and Sweden, as part of the Royal Society Surface Waters Acidification Programme (SWAP), were designed to either eliminate or independently vary the influence of one or the other factor. This included choosing sites with no decrease in grazing intensity, sites that were above the treeline and sites that had minimal catchments (Renberg and Battarbee, 1990). It was found that “all paleolimnological tests designed to disprove the land-use hypothesis for surface waters acidification have succeeded while those designed to disprove the acid deposition hypothesis have consistently failed, both in Europe and North America” (Renberg and Battarbee, 1990: 296). In other words, while long-term acidification has increased the sensitivity of numerous lakes to acid deposition and it is also possible that afforestation in areas of high acid deposition has affected the timing and intensity of acidification, these factors have not been a direct cause of the recent acidification of freshwater ecosystems (Renberg and Battarbee, 1990). This recent acceleration in acidification of numerous freshwater ecosystems is mainly due to anthropogenic causes (Mannion, 1992). However, it is vital to recognise that “the importance of acidic deposition as an agent of acidification does not preclude the fact that land use and landscape changes may also be important, and in some cases more important than acidic deposition” (Sullivan et al, 1996: 233). 17 2.4 Impacts Acid deposition has adverse impacts on both anthropogenic and natural environments (figure 2-3). Due to the myriad of impacts of acid deposition, this section will only focus on the impacts of acidification in terrestrial and freshwater ecosystems. In these ecosystems, upon reaching the ground, acid deposition causes chemical reactions to occur. In areas of acidic soils and peatlands, pH declines as hydrogen ions (H+) accumulate in the system. Sulphate and nitrate anions (SO42- and NO3-) present will also combine with nutrients in the soil, such as sodium and potassium, and the resulting compounds wash out of the substrate easily, leaving it nutrient poor, limiting vegetation growth which will then lead to greater erosion (Mannion, 1992). Corrosion of buildings in urban areas, reduced visibility Acidification of clouds and provision of cloud condensation nuclei Emissions of SO2 and NOx Acidification of lakes and rivers Forest damage from occult precipitation Groundwater acidification Acidification of soil due to wet and dry deposition Decline in fish population Forest and terrestrial ecosystem damage Changes in soil flora and fauna Figure 2-3: The environmental impacts of acidification (data from Mannion, 1992) 18 For example, in southern Sweden, over the past 35 years, data indicates that soil pH has dropped by as much as 1.5 units, leading to a long term decline in tree growth (Bell and Walker, 1992). In Germany, by the mid-1980s, over half of the forests there were showing some effects of air pollution (Downing et al, 1997). This was also observed in Canada where, during the early 1980s, there was widespread damage to forested areas and the acidification of freshwater ecosystems resulting from increasing sulphur emissions originating from tall smokestacks in northeastern USA (Downing et al, 1997). The impact of acid deposition is, therefore, not just a lowering of pH through the accumulation of hydrogen ions but it also induces a series of positive feedbacks by changing the biogeochemical cycles of the major nutrients essential to plant growth. It causes some nutrients to be limited in supply, while other nutrients begin to accumulate to concentrations that are detrimental to the health of the ecosystem (Mannion, 1992). This change in biogeochemical cycling in terrestrial and forest ecosystems also indirectly affects freshwater ecosystems. Numerous metals in soils, particularly aluminium, are more soluble at low pH and will be removed from soils or peats into lakes and rivers. These metals are toxic to many forms of aquatic life (Bell and Walker, 1992) and, along with the lowering of pH, has a negative impact on lake biota, particularly fish (Antoniades, 2007). For instance, with regard to aluminium in lake water, “at concentrations of less that 100µg/l the ability of fish to regulate their salt and water content is impaired, and at concentrations above 100µg/l aluminium hydroxide [Al(OH3)] is formed as a gelatinous precipitate on fish gills. Eventually, this causes death through the impairment of respiration” (Mannion, 1999: 39). Aluminium also combines with phosphorus in lakewater to form chemical complexes, removing phosphorus from active circulation, leading to a decline in primary productivity (Mannion, 1992). Aside from the phosphorus cycle, 19 acidification also affects the nitrogen cycle as once the pH of a lake drops to 5.45.7, the activity of nitrifying bacteria is restricted and ammonia (usually oxidised to nitrate by these bacteria) will accumulate in the system. This accumulated ammonia is used by some algae in a complex process which eventually leads to a greater accumulation of hydrogen ions, compounding acidification (Mannion, 1992). Lastly, acidification may also reduce dissolved organic carbon (DOC) concentrations in freshwater ecosystems (Antoniades, 2007). As DOC acts as a natural sunscreen, absorbing UV radiation in wavelengths most harmful to fish, this reduction in DOC will cause biotic damage (Antoniades, 2007). In order to monitor the effects of acidification in freshwater ecosystems, an entire lake – Lake 233 – in the Experimental Lakes Area (ELA), northwestern Ontario, was deliberately acidified in the late 1970s by Schindler et al (1985). This lake was chosen as it was representative of “thousands of poorly buffered softwater lakes that were being threatened by acidification” (Smol, 2008: 89). Furthermore, as the ELA was surrounded by virgin boreal forest (Schindler et al, 1985) and not affected by high acid deposition rates, pre-acidification baseline conditions could be established (Smol, 2008). Prior to manipulation, Lake 233 had a pH of roughly 6.8. In 1976, sulphuric acid was added to the lake to mimic the acidification process and from the start of the manipulation process to the end, in 1983, Schindler et al (1985: 1395) observed striking alterations in the lake, “ranging from direct toxicity of hydrogen ion to disruption of normal food-chain relations, behavioural patterns of animals and biogeochemical cycles in the lake”. By 1983, the pH of the lake had reached 5.1 (Smol, 2008). Among the changes in Lake 233 was a considerable increase in the population of Mougeotia, a green algae, which then affected fish spawning 20 grounds. Fish reproduction was first disrupted, and ceased altogether when the pH of the lake reached 5.4. Invertebrate communities were also affected. For instance, crayfish became infested with the microsporozoan parasite, Thelohania, and opossum shrimp stopped reproducing. As the species at the bottom of the food web were affected and their numbers reduced, top predators in the lake, such as the trout, began to starve (plate 2-1). By the end of the lake manipulation, the number of species within had dropped by 30% (Smol, 2008). This may potentially result in a major loss of biodiversity in the area (Ho and Todd, 2010). ! A! B! Plate 2-1: Lake trout taken from Lake 223 in 1979 when the pH was 5.6 (A), and one taken in 1982 when the pH was 5.1 (B) (from Schindler et al, 1985) Moving out from the ELA, a decline of fish stocks in freshwater ecosystems was also observed throughout northwest Europe and North America 21 (Bell and Walker, 1992). In New York, acid deposition made 212 lakes in the Adirondacks unsuitable for fish (Boyle and Boyle, 1983). In fact, “only at a pH above 5 are there no adverse impacts on fish populations” (Mannion, 1999: 39). While the impact of acidification on lakes and rivers are severe, when acid inputs stop, ecosystems can recover – Lake 233 began returning to preacidification conditions once researchers ceased adding acid to it (Smol, 2008). Mitigation measures, namely the liming of lakes, have also proved successful and rapid improvements in pH can occur, though only on a short-term basis, “a product of treating symptoms rather than the underpinning causes” (Mannion, 1999: 41). Regions that have experienced the most severe acidification problems to date include Scandinavia, northern Europe, northern Russia, north-east USA and eastern Canada (Mannion, 1999). However, following much research on the causes and impacts of acidification in Europe and North America during the 1970s and 80s, and with the implementation of environmental pollution control legislation by the 1990s, industralised nations have enjoyed a measure of success in combating acid deposition (Mannion, 1999; figure 2-4). Thus, research on acid deposition has been decreasing since the 1980s (Smol, 2008). However, as developing countries become more industralised, and their fossil fuel consumption increases, acid deposition is emerging as a problem in the tropical regions and the Southern Hemisphere (Mannion, 1999). 22 Sulphur'dioxide'emissions' 45000" 40000" Emissions'(Tg)' 35000" 30000" 25000" 20000" 15000" 10000" 5000" 0" 1850" 1870" 1890" 1910" 1930" 1950" 1970" 1990" 2010" Year' North"America" Europe" Figure 2-4: SO2 emissions in North America and Europe (data from Smith et al, 2011) 2.5 Acid Deposition in Asia The majority of acidification research has thus far been focussed on Europe and North America, with less attention paid to the potential and impacts of acidification in tropical regions (Galloway, 1995). That being said, by the 1990s, acid deposition was already recognised as an important environmental issue in Asia. This is because, in addition to emission levels in the region being large already (Galloway, 1995), as developing countries, particularly China and SEA, continue to industralise, emission levels will keep rising in the near future, bringing with it the problem of acid pollution (Mannion, 1999). Therefore, by the early 1990s, Bhatti et al (1992: 560) wrote that the “potential for the formation of, and damage from, acid deposition in these developing countries is very high”. Unfortunately, in the course of their pursuit for industralisation to reach a level of development comparable to the developed world, many Asian nations implement strategies that involve a significant expansion of their energy consumption (Bhatti et al, 1992). This emphasis on economic and agricultural 23 development, coupled with the high rate of population growth stemming from an already large population base, virtually guarantees that SO2 and NOx emissions will increase significantly (Ayers, 1991). Such was the concern that in the mid1990s, The World Bank, along with the Asian Development Bank, funded a programme to devise a model assessing the future and impacts of acid deposition in Asia. The Regional Air Pollution Information and Simulation Model for Asia (RAINS-ASIA) was created. In a report of the project by Downing et al (1997), they found that the average level of economic growth in Asia is higher than any other region and the total energy demand in Asia doubles ever 12 years, as opposed to a world average of 28 years. Approximately 80% of this energy demand is met through the burning of fossil fuels, with biomass constituting another 15% (Downing et al, 1997). Within this 80% reliance on fossil fuel, 60% is in the form and coal and the majority of the remainder is from fuel oil, both high emitters of pollutants (Bhatti et al, 1992). Should this trend continue, emissions of SO2 will more than triple over the next thirty year, increasing from 33.6 million tons in 1990 to more than 110 million tons by 2020, a 230% increase (Downing et al, 1997). This predicted increase in pollution is high enough that many ecosystems will not be able to absorb it, creating a danger of irreversible environmental damage (Downing et al, 1997). By the late 1990s, the effects of acid deposition in Asia could already be observed. Measurements of rainfall in China, Japan and Thailand were as much as ten times more acidic than unpolluted rain (Downing et al, 1997). The National Environmental Protection Agency in China found that about 40% of China’s agricultural lands show damage by acid deposition (Downing et al, 1997). Acid deposition had also been recorded in India, Korea and Bangladesh (Bhatti et al, 1992). In Hong Kong, while data revealed a significant contribution of 24 anthropogenic emissions to rainwater sulphate and nitrate concentrations, the levels recorded were lower than those that caused concern in Europe and North America (Ayers, 1991). In Malaysia, rainfall pH values range from 4.4 to 4.8 in and around Kuala Lumpur to 4.9 to 5.5 in Perak (Bhatti et al, 1992). An estimation of the most polluted cities in the world by the United Nations Environment Programme (UNEP) found that 12 of the 15 cities are in Asia, with pollution levels regularly surpassing World Health Organisation (WHO) guidelines by several times (Downing et al, 1997). Downing et al (1997) attempted to map out the vulnerability of the different countries in Asia to acid deposition by employing the concept of a critical load. This critical load is “the level of a substance – acid deposition, for example – that does not cause long-term damage to an ecosystem” (Downing et al, 1997: 33). Thus, areas with a low buffering capacity to neutralise acid deposition will have a low critical load. Three factors were taken into consideration when determining the critical loads for each country – climatic factors (annual rainfall and temperature), soil chemistry and mineralogy (soil pH, texture and geology) and the vegetation cover and land use of the area (Downing et al, 1997). As seen in figure 2-5, SEA soils are particularly vulnerable to acid deposition. This is because much of the geology of SEA is underlain by granite or gneiss which have a low buffering capacity. Furthermore, precipitation is high in the area, resulting in strong leaching, lowering the buffering capacity of surface soils even more. The soils in the area also have a high organic matter content. Lastly, much of SEA is undergoing rapid deforestation and the intensification of agriculture (Bhatti et al, 1992). 25 Figure 2-5: Critical Loads for Acidity in Asia (from Downing et al, 1997) In the RAINS-ASIA model, Downing et al (1997) took the analysis one step further, predicting the level of SO2 each area in Asia would experience in 2020 if no steps were taken to control pollution. By comparing the predicted level of sulphur deposition in Asia in 2020 to the critical loads of each area, Downing et al (1997) were able to predict which countries in Asia were most vulnerable to the effects of acid deposition (figure 2-6). It can be seen that a large area of southern and eastern China, northern and eastern India, the Korean peninsular, Northern and central Thailand and Singapore are particularly vulnerable and receive levels of acid deposition exceeding the carry capacity of their ecosystems. Rodhe et al (1992) ran their own simulation of acid deposition in Asia, which also found SEA particularly vulnerable to acid deposition. 26 Figure 2-6: Excess sulphur deposition above critical loads in 2020 (from Amann and Cofala, 1995, found in Downing et al, 1997) There are several factors which intensify the acid deposition problem in Asia, making it unique when compared with Europe and North America. Firstly, the higher temperatures and sunlight intensity in most Asian countries will increase the efficiency of the atmospheric chemical reactions that transform SO2 and NOx to acidic sulphates and nitrates (Bhatti et al, 1992). Secondly, rainfall rates in many Asian countries are high, which would lead to a larger total H+ deposition than that predicted on the pH of precipitation alone (Bhatti et al, 1992). Thirdly, the strong vertical mixing of the lower portion of the atmosphere in the tropics and subtropics would transport pollutants to a higher altitude, leading not only to longer residence times, meaning greater opportunity for the conversion of SO2 and NOx to acid deposition, but also the transport of pollutants further afield (Bhatti et al, 1992). Fourthly, there are negligible industrial emission regulations in many countries in Asia, and any regulations that are in place are rarely enforced. This lack of industrial regulation is compounded by the shift of polluting industries from the developed world (with more stringent pollution laws) to the 27 developing world (Bhatti et al, 1992). Lastly, the close proximity of many of the urban and industrial centres in Asia, such as Tokyo, Seoul, Hong Kong, Bangkok, Kuala Lumpur, Singapore and Jakarta, heightens the potential for air pollution problems (Hu et al, 2003). The Asian monsoon will further aid in transporting this air pollution around the region. Thus, in Japan, “it has been observed that concentrations of sulphur and nitrogen oxides in precipitation on the west coast (facing the Japan Sea) are higher in the winter when the prevailing winds are from the Asian mainland” (Bhatti et al, 1992: 551). Unfortunately, by the end of the 1990s, the concern regarding acid deposition in Asia appears to have diminished. For example, the RAINS-ASIA project was supposed to lead the way for pollution control policies in the region. It involved a collaboration between researchers and policymakers from Thailand, Bangladesh, China, India, Indonesia, the Republic of Korea, Japan, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Thailand and Vietnam along with involvement from Australia, Austria, the Netherlands, Norway, Sweden and the United States (Downing et al, 1997). However, the last update on the RAINSASIA website is from 1999 and the project report discussed in this study, compiled by Downing et al (1997), is still classified under “new” on the website (RAINS-ASIA, 1999). Information on ongoing related activities and research projects all contain dead links and, while there is mention of a “RAINS-ASIA 2”, the last report of it is a presentation of the model in a conference in December 2000 (RAINS-ASIA, 1999). It is difficult to find any literature on acid deposition in Asia past the year 2000, and any available is focussed on acid deposition issues in China (Larssen et al, 2006; Huang et al, 2008; Lu et al, 2010; Smith et al, 2011). However, this lack of information on acid deposition in Asia does not imply that the issue no longer exists. Rather, it is likely that economic development in the region has 28 taken precedence over environmental issues and, until the effects of acid deposition are felt as strongly as it once was in Europe and North America, no action will be taken. The reason why Asia still faces acid deposition issues is because anthropogenic pollution data available for the region show that SO2 and NOx levels are still rising (figure 2-7 and figure 2-8). It can be seen from figure 2-7 that SO2 emissions in China are increasing particularly rapidly, and is increasing in India and other parts of South and East Asia, with the exception of Japan. The decrease in sulphur dioxide emissions in Japan reflects the beginning of pollution control agreements from the mid 1960s onwards (Tsutsumi, 2001). Figure 2-8 similarly shows increasing nitrogen oxide levels in Asia, with the pace of this increase accelerating in recent years. Sulphur'dioxide'emissions'in'Asia' 50000" 45000" 40000" Emissions'(Tg)' 35000" 30000" 25000" 20000" 15000" 10000" 5000" 0" 1850" 1870" 1890" 1910" 1930" 1950" 1970" 1990" 2010" Year' China" Japan" India" Other"South"&"East"Asia" Total" Figure 2-7: SO2 emissions in Asia (data from Smith et al, 2011) 29 Nitrogen)oxide)emissions)in)Asia) 30# Nitrogen)Oxide)Emission)(Tg)) 28# 26# 24# 22# 20# 18# 16# 14# 12# 10# 1980# 1985# 1990# 1995# 2000# 2005# Year) Figure 2-8: NOx emissions in Asia (data from Monks et al, 2009) It is thus clear that acid deposition is increasingly emerging as a significant issue in Asia. Unfortunately, “the state of knowledge of factors such as emission source strengths for acidic and alkaline substances, and sensitivities of plants, soils and groundwater systems to acidic deposition throughout the region is insufficient for an adequate assessment to be made” (Ayers, 1991: 232). More data is required for the region and monitoring programmes need to be set-up in Asia. Ultimately, as the future emissions of SO2 and NOx from industrialising nations will significantly exceed current emissions into the global atmosphere, acid deposition is going to continue be a major threat to the global environment in the years to come. 30 [...]... consequently causing stream acidity to rise (Waters and Jenkins, 19 92) As a forest aged, and a canopy developed, not only did uptake and retention of base metals and inorganic nitrogen occur, along with the accumulation of biomass, scavenging of dry and occult deposition of sulphur and nitrogen also exacerbated acidification (Waters and Jenkins, 19 92) In order to investigate the significance of land use change... The reason why Asia still faces acid deposition issues is because anthropogenic pollution data available for the region show that SO2 and NOx levels are still rising (figure 2- 7 and figure 2- 8) It can be seen from figure 2- 7 that SO2 emissions in China are increasing particularly rapidly, and is increasing in India and other parts of South and East Asia, with the exception of Japan The decrease in sulphur... ongoing related activities and research projects all contain dead links and, while there is mention of a “RAINS-ASIA 2 , the last report of it is a presentation of the model in a conference in December 20 00 (RAINS-ASIA, 1999) It is difficult to find any literature on acid deposition in Asia past the year 20 00, and any available is focussed on acid deposition issues in China (Larssen et al, 20 06; Huang... acidification in the area (Whitehead et al, 1988), but that forest age also had an impact on acidification levels (Waters and Jenkins, 19 92) Differences in stream chemistry between afforested young forests and moorlands were due to disturbances caused during site preparation, 16 such as ploughing, planting and fertilisation, which alters soil drainage, increasing sulphate and nitrate mineralisation, consequently... America and Europe (data from Smith et al, 20 11) 2. 5 Acid Deposition in Asia The majority of acidification research has thus far been focussed on Europe and North America, with less attention paid to the potential and impacts of acidification in tropical regions (Galloway, 1995) That being said, by the 1990s, acid deposition was already recognised as an important environmental issue in Asia This is because,... area, Downing et al (1997) were able to predict which countries in Asia were most vulnerable to the effects of acid deposition (figure 2- 6) It can be seen that a large area of southern and eastern China, northern and eastern India, the Korean peninsular, Northern and central Thailand and Singapore are particularly vulnerable and receive levels of acid deposition exceeding the carry capacity of their ecosystems... (Bell and Walker, 19 92) and, along with the lowering of pH, has a negative impact on lake biota, particularly fish (Antoniades, 20 07) For instance, with regard to aluminium in lake water, “at concentrations of less that 100µg/l the ability of fish to regulate their salt and water content is impaired, and at concentrations above 100µg/l aluminium hydroxide [Al(OH3)] is formed as a gelatinous precipitate... from semi-nomadic cattle farming to sedentary farming According to Rosenqvist (1978), the growing trees, as vegetation changed from grassland to forests, extracted bases from the ground and increased the amounts of humic acids, thus causing the acidification of river waters Debates regarding the relative importance of land use and acid deposition in causing recent lake acidification has since been highly... neutralise acid deposition will have a low critical load Three factors were taken into consideration when determining the critical loads for each country – climatic factors (annual rainfall and temperature), soil chemistry and mineralogy (soil pH, texture and geology) and the vegetation cover and land use of the area (Downing et al, 1997) As seen in figure 2- 5, SEA soils are particularly vulnerable to acid... Forest damage from occult precipitation Groundwater acidification Acidification of soil due to wet and dry deposition Decline in fish population Forest and terrestrial ecosystem damage Changes in soil flora and fauna Figure 2- 3: The environmental impacts of acidification (data from Mannion, 19 92) 18 For example, in southern Sweden, over the past 35 years, data indicates that soil pH has dropped by as much ... because mainland east Asia, the Caribbean, southern Africa, Central and South America and Southeast Asia contain extensive peatland (Page et al, 20 06) Most tropical peatlands occur in low altitude,... that a large area of southern and eastern China, northern and eastern India, the Korean peninsular, Northern and central Thailand and Singapore are particularly vulnerable and receive levels of. .. researchers and policymakers from Thailand, Bangladesh, China, India, Indonesia, the Republic of Korea, Japan, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Thailand and Vietnam along with involvement