Diatom and geochemical indicators of acidification in a tropical forest stream, singapore 4

Chapter Four BACKGROUND OF STUDY AREA 4.1 Overview 59 4.2 General Description of Singapore 59 4.3 The Pollution History of Singapore 61 4.4 Location and Description of Bukit Timah Nature Reserve 67 4.5 Location and Description of Jungle Falls Catchment 72 58 4.1 Overview Chapter four applies the wider issues examined in chapter two and three – the problem of acidification and how it is studied – to a Singaporean context. It begins by looking at Singapore and it’s location within the region, focussing on how the Asian monsoon, coupled with transboundary pollution from as far afield as Kalimantan, Indonesia, could exacerbate acidic pollution and deposition on the island and more specifically, the study site of Jungle Falls stream in BTNR. The chapter then examines the pollution history within Singapore and the levels of atmospheric pollution that the country has experienced. This would be an important source of information when examining a sedimentary record of atmospheric contamination within Jungle Falls stream in Singapore. A brief history of BTNR, where Jungle Falls stream is located, is provided. This history shows that the Jungle Falls stream has not been significantly affected by anthropogenic factors, such as the construction of a major road or industrial activities that directly pollute the stream. As such, any pollution that the Jungle Falls stream undergoes, is likely due to atmospheric contamination rather than land-use change. Furthermore, the value of the reserve is emphasised to demonstrate the importance of monitoring the potential acidification problem within. The chapter ends with a description of the study site at Jungle Falls stream. It explain how a unique sedimentary record has collected at this location, particularly since such a limnological sedimentary record is rare in Singapore and the region in general. 4.2 General Description of Singapore Located at the tip of peninsular Malaysia, Singapore is close to the equator and experiences a humid tropical climate with a maritime influence. The temperature ranges from a minimum of between 23oC to 26oC and a maximum of between 31oC to 34oC (NEA, 2002a) with almost no seasonal variation (Corlett, 59 1988). Singapore averages approximately 2200mm to 2400mm of rainfall annually with all months having greater than 100mm of rainfall on average (Turner et al, 1996). While Singapore does not have any distinct wet or dry seasons, it is affected by the Asian monsoon. Thus, Singapore experiences the northeast monsoon from December to early March and the southwest monsoon from June to September (figure 4-1, NEA, 2002a). Because the northeast monsoon blows over the South China Sea before reaching Singapore, it is able to collect more moisture than the southwest monsoon that travels over the Straits of Malacca, a smaller water body. (NEA, 2002a). Figure 4-1: Northeast Monsoon (left) and Southwest Monsoon (right) moving over Singapore (from NEA, 2002b) Aside from precipitation per se, the monsoon winds would also transport atmospheric pollution into Singapore from neighbouring countries. Thus, In a study of rainfall chemistry collected at an atmospheric monitoring station in the National University of Singapore (NUS) from November 1999 to October 2000, Hu et al (2003) found that there were large variations in the monthly pH levels of rainfall, with values ranging from 4.01 to 4.67. The highest concentrations of sulphate and nitrate in rainwater was in April 2000, and pH levels of rainwater was also lowest in this month, at 4.01. 60 In May, when the highest concentrations of Ca2+, Na+, Mg2+, NH4+, and Clwere recorded, rainwater pH rose to 4.20. Hu et al (2003) believe that as the prevailing wind direction in May was from the south and southeast, and because there were forest fires in Kalimantan, Indonesia, the fly ash from this biomass burning raised the concentrations of Ca2+ and NH4+ in Singapore. These cations neutralised the acidity in rainwater, leading to higher pH levels in rainwater. It is interesting to note that acid pollution into Singapore can have a monthly component, even though this study is looking at acidification of a tropical stream in Singapore over the course of decades. While Hu et al (2003) did not look at the transport of sulphur dioxide and nitrogen oxides into Singapore from neighbouring countries, focussing instead on biomass burning, they showed that atmospheric contaminants released by surrounding countries can be transported to and affect the rainwater in Singapore. While the transport distance of acid pollution varies greatly, depending on factors such as air speed and smokestack heights, SO2 and NOx are estimated to have transport distances of between 400km to 1200km (Schwartz, 1989; Downing et al, 1997). As Singapore is around 300km from Kuala Lumpur and has received fly ash particles from Kalimantan, around 800km away, the potential for trans-boundary acid pollution into Singapore is great. Besides pollution from foreign sources (see section 2.5), domestic pollution has also contributed to acid deposition in Singapore and the following section will look at the pollution history of Singapore. 4.3 The Pollution History of Singapore Singapore currently has the fourth largest port in the world, is the third largest oil refining centre globally, having a capacity of over one million barrels per day, and also houses industries such as petroleum products, petrol-chemical and chemical products and refined petroleum products (Koh, 2002). Yet, a brief 61 50 years ago, during the 1960s, Singapore was a third world country whose Gross National Product (GNP) per capita was less that US$320 (EDB, 2009). There was high unemployment, with only a few industries present, and high civil unrest and uncertainty due in part to the withdrawal of Britain along with Singapore’s separation from Malaya in 1965 (EDB, 2009). There was therefore a major push for rapid industrialisation and urbanisation for economic and political survival and to better the standard of living in Singapore, as evidenced in the Republic’s first Economic Plan from 1961-64 (Chin, 1978; Koh, 2002). Unfortunately, industrialisation is a major cause of environmental degradation and results in significant air pollution. This, along with the significant increase in the number of motor vehicles in Singapore, caused the issue of air pollution to arise in Singapore (Chin, 1978; Soon, 1982). SO2 and particulate matter are by products from the combustion of petroleum fuels in power stations and oil refineries and carbon monoxide, lead and the NOx are emitted from the combustion of gasoline in vehicles (Soon, 1982). Other pollutants include hydrocarbons, ozone and toxic substances (Chin, 1996). Thus, air pollution originates from sources that can be stationary or mobile, making prevention and control of air pollution and its effects complex and focused on technology to set minimum acceptable standards (Soon, 1982). While Singapore could have adopted a ‘pollute now, clean later’ approach, as numerous other developing countries have done and are doing, it chose instead to address these pollution problems immediately as future economic and health costs could end up higher in the long run (Koh, 2002). Singapore’s rapid industrialisation and urbanisation in the late 1960s and early 70s was also timely as it coincided with growing international concern over environmental conservation. For instance, in 1970, the WHO began to compile data on air pollution in industrialised areas worldwide in order to “awaken the 62 developing countries to the need to take precautions against pollution before they go any further with their industrialisation programmes” (The Straits Times, 1970: 3). In 1967, the WHO director for the Western Pacific highlighted to Singapore Health Ministry officials that the fast pace of industrialisation in Singapore would lead to environmental problems, including air pollution, and that the government needed to monitor these issues and arrest them before they got out of control (The Straits Times, 1967). Thus, in 1970, at the request of the Government of Singapore, Dr. Graham J. Cleary, the WHO Consultant on Air Pollution Control, arrived in Singapore to assess the air pollution situation and to recommend management solutions (Cleary, 1970). Cleary’s recommendations led directly to the setting up of the Anti Pollution Unit (APU) in 1971 (Chin, 1978), which then led to the passing of the Clean Air Act at the start of 1972. This Act enforced air pollution control in Singapore (The Straits Times, 1972; Chin, 1996). The effectiveness of the pollution management policies within Singapore can be seen in figures 4-2 to 4-4. The emissions of SO2 were controlled by limiting the sulphur content of industrial fuel oil and automotive diesel, with the maximum permitted sulphur content of automotive diesel reduced from 0.5% to 0.3% (Chin, 1996; Bashkin and Radojevic, 2003). Sulphur in fuel oil for power stations and oil refineries, on the other hand, was lowered to average about 3% by weight (Chin, 1978). The control of emissions from power stations and refineries was crucial as “at its peak, it has been estimated that the sulphur dioxide emission from this source contributed about 40% of total emission in the Republic” (Chin, 1978: 6). Figure 4-2 shows the SO2 levels in Singapore. It can be seen that following the enforcement of the Clean Air Act in 1972, SO2 levels began to drop significantly since 1976. However, it is important to note that SO2 levels appear to be increasing once again post-1985. 63 Sulphur*dioxide*levels,*Singapore* 70" Micrograms*per*cubic*metre* 160" 60" 140" 50" 120" 100" 40" 80" 30" 60" 20" 40" 10" 20" 0" 1974" Micrograms*per*cubic*metre* 180" 0" 1976" 1978" 1980" 1982" 1984" 1986" 1988" 1990" 1992" 1994" Year* Total"emissions" Industrial"emissions" Figure 4-2: SO2 levels in Singapore from 1974 to 1993 (data from Chin, 1996) With regard to lead pollution, the lead concentration in petrol was progressively lowered since 1980; going from 0.6-0.8g/l of petrol in 1981 to 0.15g/l in 1983 (Chin, 1996). Unleaded petrol was introduced in January 1991 and by July, all petrol-driven motor vehicles to be registered for the first time had to be able to run on unleaded petrol (Chin, 1996; Koh, 2002). Differential pricing introduced in February made regular petrol more expensive than unleaded petrol (Chin, 1996). This had led to a decrease in lead concentration in the air from 0.3 units in 1991 to 0.1-0.2 units in 1993 (Chin, 1996). From July 1994 onwards, all new vehicles also have catalytic converters to meet stricter vehicular emission standards (Chin, 1996; Bashkin and Radojevic, 2003). Vehicular emissions have also been controlled indirectly through traffic management solutions like encouraging the use of public transport, restricting car ownership and improving road infrastructure (Koh, 2002). The effect of the lowering of lead levels in petrol can be seen in Figure 4-3 that shows the lead levels in Singapore following 1980 and up to 1992. Unlike the figure for sulphur dioxide levels, the lead graph does not have a post-1985 increase. 64 Lead*levels,*Singapore* 4" Micrograms*per*cubic*meter* 3.5" 3" 2.5" 2" 1.5" 1" 0.5" 0" 1980" 1982" 1984" 1986" 1988" 1990" 1992" Year* Figure 4-3: Lead levels in Singapore from 1980 to 1992 (data from Chin, 1996) Nitrogen oxides were similarly controlled, with the release of nitric acid or oxides of nitrogen from the manufacture of nitric acid limited to a maximum of 4.0g/nm3 in 1972, and nitric acid or oxides of nitrogen from the manufacture of nitric acid and other processes limited to a maximum of 0.20g/nm3 and 2.0g/nm3 respectively from 1978 (Chin, 1978). The effect of these NOx controls can be seen in figure 4-3. Similar to levels of SO2 levels, NOx levels begin to decrease from 1976 onwards, aside from that of urban emissions, which begin to decrease from 1979 onwards, similar to that of lead levels. This is because the urban emissions of NOx would be linked to vehicular exhaust emissions. It is important to note the contrast in figure 4-2 and 4-4 compared to figure 2-7 and 2-8. While SO2 and NOx levels are generally decreasing in Singapore, they are increasing significantly in the region, which would be a cause for concern in Singapore. 65 Nitrogen*oxide*levels,*Singapore* Micrograms*per*cubic*metre* 100# 90# 80# 70# 60# 50# 40# 30# 20# 1974# 1976# 1978# 1980# 1982# 1984# 1986# 1988# 1990# 1992# 1994# Year* Urban#emissions# Industrial#emissions# Rural#emissions# Figure 4-4: NOx levels in Singapore from 1974 to 1993 (data from Chin, 1996) In 1997 and 1999, studies were carried out by the Department of Chemical and Environmental Engineering of NUS to examine the chemistry of precipitation in Singapore. Balasubramanian et al (2001) and Hu et al (2003) collected rainwater at the Atmosphere Research Station within the University. These samples were taken over the course of a year, from August 1997 to July 1998 and from November 1999 to 2000 respectively. Hu et al (2003) found that sulphate in rainwater had an average concentration of 83.47µeq/l. As marine and crustal sources accounted for only 5% of this sulphate, anthropogenic sources comprised most of this deposition. The combined concentration of sulphate and nitrate in precipitation was 101.84µeq/l which is “a high concentration compared to the other areas where acid rain exists” (Hu et al, 2003: 749). 20% of the precipitation collected had a pH of less than 4.0, 75% of the precipitation had a pH of less than 4.4 and all the precipitation collected was below pH 5.6 (Hu et al, 2003). Rainwater with a pH of less than 4.8 imply an influence of anthropogenic sources and as rainwater collected from 1999 to 2000 had a mean of pH 4.2, Hu et al (2003: 751) concluded that there is a “strong 66 impact of anthropogenically derived pollutants on rainwater quality in Singapore”. The study conducted by Balasubramanian et al (2001) had similar results. Their rainwater samples had a mean of pH 4.5 and approximately 88% of their samples had a pH value less than 5.0, showing the effect of anthropogenic emission on air quality in Singapore. Thus, while the Singapore Government has been effective in controlling and managing pollution in Singapore, air pollution and acid precipitation is still a significant issue in Singapore. Based on the history of acid pollution from within Singapore and the region, it is believed that acidification issues in the 1960s to 80s were largely due to domestic emissions. However, recent acidification trends observed in Singapore could originate from transboundary pollution. With pollution from the region set to increase, and transport from the monsoonal winds bringing pollution to Singapore, the Government will need to keep an eye on Singapore’s air quality in the years to follow. 4.4 Location and Description of Bukit Timah Nature Reserve Bukit Timah Nature Reserve, located at 1o21’N and 103o47’E, is likely to be the oldest rainforest reserve in the region, if not the world (Corlett, 1995b). It currently covers an area of 163 hectares (NParks, 2011), though its size was as little as 66 hectares during the 1930s (Lum and Sharp, 1996). Topographically, it is a ridge that also includes Singapore’s highest hill, Bukit Timah Hill, which stands at 162.5m above sea-level (figure 4-5; Corlett, 1995b). The Singapore Government has ranked the reserve “foremost” among the areas of natural landscape in Singapore to be conserved (Waller, 2001: 133). BTNR has the sole remaining patch of primary (undisturbed) rainforest in Singapore (plate 4-1; Sharp, 1985). However, much of the forest in this reserve is secondary, having previously been occupied by Chinese gambier farmers, present by the 1830s, used for recreational purposes during colonial times, as 67 well as suffering damage during World War II (Lum and Sharp, 1996). It is estimated that only around 65 hectares of the reserve is under primary forest (Waller, 2001). The underlying geology of the reserve is Bukit Timah Granite with a high quartz content, formed during the Triassic from an intrusion of igneous rocks (Waller, 2001; Lu et al, 2005). Figure 4-5: BTNR with an arrow indicating the location of Jungle Fall Valley where the study site is situated (modified from NParks, 2011 and Sherlock et al, 1995) 68 Plate 4-1: ‘Original’ Lowland Evergreen Tropical Rainforest in BTNR. Except for the tops of exotic trees in the foreground, rooted outside the Reserve, no signs of human interference are visible. Photo: Dr Ivan Polunin, 1984 (from Corlett, 1988) The preservation of BTNR stretches as far back as the 1840s when the colonial government banned forest clearance on the hill due to fears of its effect on the climate of the area (Corlett, 1995c). By 1860, the forests on Bukit Timah hill were isolated (Corlett, 1995b) and by 1882, only seven per cent of the island remained forested. Nathanial Cantly, the Superintendant of the Singapore Botanic Gardens, established Bukit Timah as a forest reserve in 1884 (Tan, 1985). Unfortunately, the hill was seen more as a resource than a reserve and plantations were established and quarrying of the Bukit Timah Granite occurred. By 1936, only a section (approximately 66 hectares) of the original 343 hectare area was preserved for scenic purposes and other amenities (Lum and Sharp, 1996). While the nature reserve was at the front line of the battle for Singapore during World War II, and must have endured significant damage, apart from felling some trees and carrying out some excavations for defensive 69 purposes, on the whole the Japanese kept the reserve protected (Corlett, 1988). Finally, in 1951, the forest was granted official protection as a Nature Reserve under the Nature Reserves Ordinance (Tan, 1985). By 1995, there were approximately 140,000 annual visitors to the reserve (Lum and Sharp, 1996). BTNR contains a huge diversity of wildlife, with more than 840 different flowering plants and over 500 species of animals (NParks, 2011). This is because tropical rainforests have the greatest structural complexity, species diversity and biomass per unit area among the various natural communities on earth (Wee and Corlett, 1986). BTNR houses more than 40% of Singapore’s native flora, most of which is not found anywhere else on the island (Corlett, 1988). Incredibly, there are more plant species in this reserve than in the whole of North America (Lum and Sharp, 1996). Unfortunately, many groups of organisms within the reserve, including most of the invertebrates, are unstudied (Corlett, 1995b). Although many bird and mammal species in the reserve have been lost (Corlett, 1988), there is much valuable fauna within the reserve that remains. This includes a sighting, in the 1980s, of a Yellow-banded Caecilian, “a rare snake-like amphibian, only the third ever recorded at Bukit Timah” (Lum and Sharp, 1996: 30). In 1986, a new species of freshwater crab (Johora singaporensis) that is endemic to Singapore was also discovered (Lum and Sharp, 1996). It is this richness and variety of species within BTNR that makes the issue of acidification within it such a concern. For example, the aforementioned endemic freshwater crab species, Johora singaporeansis, is now listed on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species as critically endangered and has not been spotted in BTNR in recent times despite intensive surveys (Esser et al, 2008). It is believed that this crab 70 could already be extinct in the reserve (Tan et al, 2010). The suspected reason for this decline is the acidification of water along with the loss of forest cover, aquatic pollution and the lowering of the water table (Tan et al, 2010; Esser et al, 2008). It is possible that streams within BTNR could be becoming more acidic, which may cause the wildlife within to be under stress. Streams in the reserve currently have a pH value of 4.4 to 4.7 and acidity levels appear to drop after a precipitation event. Such is the concern for the reserve that the main Singapore newspaper – The Straits Times – has reported on this issue, particularly focussing on the effects that acidification would have on wildlife (Gunasingham, 2009). However, this issue is controversial as long-term data on the pH of the streams within the reserve are unavailable. As such, Sharon Chan, the Assistant Director of Central Nature Reserve at NParks, was quick to point out that while acidification is a concern, the data available is currently insufficient to draw any definite conclusions, with rainfall monitoring conducted by the National Environmental Agency (NEA) not showing increasing trends in rainfall acidity (Chan, 2009). The issue is complicated as streams in BTNR are also naturally acidic as the bedrock of the reserve is granite (Mannion, 1999). Furthermore, “the microbiological formation of humic substances releases humic, fulvic and other organic acids into the waters, contributing to a further decrease in pH” (Ho and Todd, 2010: 4). Thus, it is vital to pinpoint the cause of acidification within BTNR in order to aid management of the freshwater habitats within (Chan, 2009). Should the cause of acidification in the reserve be anthropogenic in origin, the acidic bedrock of BTNR would also makes it more susceptible to further acidification, as there is little or no buffering capacity for the addition of hydrogen ions (Mannion, 1999). 71 In order to investigate the potential acidification at BTNR, a stream-water chemistry monitoring programme was established at Jungle Falls in 2005. Data collected thus far indicate that stream-water pH can decrease by 0.2 to 0.3 pH units following storm events. As part of this monitoring programme, because anthropogenically induced acidification is suspected at Jungle Fall stream, and the health of this freshwater ecosystem is of concern, yet long term data on water chemistry is unavailable, this paleolimnological study of sediments from Jungle Fall stream was initiated to investigate the issue. 4.5 Location and Description of Jungle Falls Catchment Jungle Falls catchment, within Jungle Falls Valley, is approximately 0.05km2 in size and is located in the north-western side of BTNR (Figure 4-5, Sherlock et al, 1995). It is part of the original primary rainforest in the reserve (Lim and Ng, 1990) and is named after the Jungle Falls, “a man-made waterfall which cascades down an exposed granite cliff” (Lum and Sharp, 1996: 108). The source of the Jungle Fall stream is “a freshwater spring encased by an old well in the middle of the jungle” (Rajathurai, 1996: 100). Within the Jungle Falls stream is a series of man-made brick dams, one of which is shown in plate 4-2. Sediment has accumulated behind this dam, forming a section with a water depth of approximately 15cm (plate 4-3). It is rare to find such a sedimentary record in Singapore (see section 3.2), particularly because of Singapore’s high urbanisation, and this sequence is at an opportune location to study potential acidification of the Jungle Falls stream. However, it is unclear when this dam was actually built, with the dams rarely mentioned in any literature, and NParks unsure of any dates either. 72 Plate 4-2: Man-made dam at Jungle Falls Valley Core C Core B Core A Plate 4-3: Artificial impoundment at Jungle Falls Valley with arrows pointing to the core collection sites – Core A, Core B and Core C According to Lum and Sharp (1996) the dams were constructed in the late 1930s when the nature reserve was used for recreational activities. During this da sssssssssssdsdsdadadadadaaaaaaaaaadasdsadsadasda 73 time, in addition to signposting trails, labelling trees, building shelters and positioning maps, “the Health Department constructed an artificial pool on the western side of the Reserve, in Jungle Fall Valley, ostensibly to ‘flush’ the valley as an anti-malaria measure” (Lum and Sharp, 1996: 26). This dam had accumulate sediments to a depth of approximately 25cm and sediment cores for this study were retrieved from this accumulation (plate 4-3). 74 [...]... da sssssssssssdsdsdadadadadaaaaaaaaaadasdsadsadasda 73 time, in addition to signposting trails, labelling trees, building shelters and positioning maps, “the Health Department constructed an artificial pool on the western side of the Reserve, in Jungle Fall Valley, ostensibly to ‘flush’ the valley as an anti-malaria measure” (Lum and Sharp, 1996: 26) This dam had accumulate sediments to a depth of approximately... valuable fauna within the reserve that remains This includes a sighting, in the 1980s, of a Yellow-banded Caecilian, a rare snake-like amphibian, only the third ever recorded at Bukit Timah” (Lum and Sharp, 1996: 30) In 1986, a new species of freshwater crab (Johora singaporensis) that is endemic to Singapore was also discovered (Lum and Sharp, 1996) It is this richness and variety of species within... are unavailable As such, Sharon Chan, the Assistant Director of Central Nature Reserve at NParks, was quick to point out that while acidification is a concern, the data available is currently insufficient to draw any definite conclusions, with rainfall monitoring conducted by the National Environmental Agency (NEA) not showing increasing trends in rainfall acidity (Chan, 2009) The issue is complicated... forming a section with a water depth of approximately 15cm (plate 4- 3) It is rare to find such a sedimentary record in Singapore (see section 3.2), particularly because of Singapore s high urbanisation, and this sequence is at an opportune location to study potential acidification of the Jungle Falls stream However, it is unclear when this dam was actually built, with the dams rarely mentioned in any... (Tan, 1985) Unfortunately, the hill was seen more as a resource than a reserve and plantations were established and quarrying of the Bukit Timah Granite occurred By 1936, only a section (approximately 66 hectares) of the original 343 hectare area was preserved for scenic purposes and other amenities (Lum and Sharp, 1996) While the nature reserve was at the front line of the battle for Singapore during... (Lum and Sharp, 1996) BTNR contains a huge diversity of wildlife, with more than 840 different flowering plants and over 500 species of animals (NParks, 2011) This is because tropical rainforests have the greatest structural complexity, species diversity and biomass per unit area among the various natural communities on earth (Wee and Corlett, 1986) BTNR houses more than 40 % of Singapore s native flora,... programme was established at Jungle Falls in 2005 Data collected thus far indicate that stream-water pH can decrease by 0.2 to 0.3 pH units following storm events As part of this monitoring programme, because anthropogenically induced acidification is suspected at Jungle Fall stream, and the health of this freshwater ecosystem is of concern, yet long term data on water chemistry is unavailable, this paleolimnological... paleolimnological study of sediments from Jungle Fall stream was initiated to investigate the issue 4. 5 Location and Description of Jungle Falls Catchment Jungle Falls catchment, within Jungle Falls Valley, is approximately 0.05km2 in size and is located in the north-western side of BTNR (Figure 4- 5, Sherlock et al, 1995) It is part of the original primary rainforest in the reserve (Lim and Ng, 1990) and is named... complicated as streams in BTNR are also naturally acidic as the bedrock of the reserve is granite (Mannion, 1999) Furthermore, “the microbiological formation of humic substances releases humic, fulvic and other organic acids into the waters, contributing to a further decrease in pH” (Ho and Todd, 2010: 4) Thus, it is vital to pinpoint the cause of acidification within BTNR in order to aid management of the... named after the Jungle Falls, a man-made waterfall which cascades down an exposed granite cliff” (Lum and Sharp, 1996: 108) The source of the Jungle Fall stream is a freshwater spring encased by an old well in the middle of the jungle” (Rajathurai, 1996: 100) Within the Jungle Falls stream is a series of man-made brick dams, one of which is shown in plate 4- 2 Sediment has accumulated behind this dam, ... recreational activities During this da sssssssssssdsdsdadadadadaaaaaaaaaadasdsadsadasda 73 time, in addition to signposting trails, labelling trees, building shelters and positioning maps, “the Health... biomass burning raised the concentrations of Ca2+ and NH4+ in Singapore These cations neutralised the acidity in rainwater, leading to higher pH levels in rainwater It is interesting to note that... region in general 4. 2 General Description of Singapore Located at the tip of peninsular Malaysia, Singapore is close to the equator and experiences a humid tropical climate with a maritime influence