Chapter Seven
CONCLUSION
7.1 Overview
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7.2 Summary of Study
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7.3 Contribution of Study to Wider Acidification Research
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7.4 Extensions of Research
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7.1 Overview
Chapter seven provides a summary of this study and begins by
discussing its primary aim, which was to look at the potential acidification of
Jungle Falls stream. Following this, an evaluation of the use of paleolimnological
indicators for acidification research in Asia is provided, which is the secondary
aim of this thesis. As this study is a first attempt at paleolimnological research on
acidification in Singapore and possibly the region, the chapter concludes by
looking at several extensions that would either expand or supplement the data
obtained.
7.2 Summary of Study
The primary aim of this study was to investigate the potential acidification
of Jungle Falls stream in BTNR. This reserve has much ecological value and
faces concerns of acidification, particularly being located in a region where
atmospheric pollution is increasing rapidly. While the Singapore government has
been successful in controlling domestic pollution, pollution levels, particularly
SO2, are increasing in recent years. It is therefore vital to examine whether
acidification is currently affecting streams within the nature reserve to aid
management of it.
While there is a lack of suitable study sites in Singapore, the damming of
Jungle Falls stream provides an excellent location for paleolimnological studies. It
is believed that this dam was constructed during late 1930s. In this study, diatom
along with geochemical analysis was adopted to investigate the potential
acidification of Jungle Falls stream.
Results indicate that the Jungle Falls stream sediments contain a record
of atmospheric contamination into the area. As there were no abrupt changes
within the data, such as sharp drops in %LOI or trace metal concentrations, this
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sedimentary record is likely to be continuous, with no hiatus in deposition or
significant erosion occurring. The stream was dammed at a time when
atmospheric pollution levels were also expected to being increasing and hence,
there is a need to separate one signal (changing hydrological conditions due to
the damming of the stream) from another (atmospheric contamination).
At the base of the record, trace metal concentrations are low. The diatom
assemblage at this depth points to an acidic environment, but with a higher
abundance of taxa present in less acidic waters (Eunotia vanheurckii, Eunotia
curvata and Fragilaria bicapitata), and a lower abundance of taxa present in more
acidic waters (Eunotia incisa and Eunotia flexuosa).
Trace metal concentration begin increasing up-core and peak at 15cm.
This could be due to changing catchment conditions caused by the impoundment
compounded by a rise in atmospheric pollution. This peak at 15cm likely
corresponds to the mid to late 1960s when Singapore was undergoing rapid
industrialisation and pollution controls were not yet in place, resulting in a high
level of atmospheric pollution and contamination. This interpretation is
complimented by the fact that the diatom assemblage also changes at this depth,
with levels of Eunotia vanheurckii, Eunotia curvata and Fragilaria bicapitata
dropping and levels of Eunotia incisa and Eunotia flexuosa rising. This implies
that the stream is becoming more acidic.
During the 1970s, with the implementation of the Clean Air Act and
effective management of industrialisation and urbanisation, pollution levels, and
thus, atmospheric contamination into the stream, began to drop. This is in line
with the sedimentary record whereby, moving up past 15cm, lead and zinc
concentrations once again begin to decrease even as sodium and potassium
levels appear to stabilise.
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At the top of the sedimentary record, while lead levels remain low, zinc
and sulphur levels appear to rise once again. This increase in sulphur
concentration can be linked to an increase in sulphur dioxide levels in Singapore
(figure 4-2) and an increase in acidity measured in Singapore (figure 6-9). Based
on comparing sulphur concentration levels within the core to acidity levels
measured in Singapore (figure 6-9), there is a possibility that sedimentation within
the impoundment may have ceased by the mid-1990s due to the dam reaching
full capacity.
This increase in atmospheric contamination within the core, implying an
increase in atmospheric pollution to the catchment, may be due to transboundary
pollution. While the diatom assemblage does not show a similar change as the
trace metal concentrations at the top of the core, this could be because the
freshwater ecosystem is currently not degraded by atmospheric pollution into the
catchment. Ultimately, there does appear to be a viable record of anthropogenic
acidification of Jungle Falls stream contained within the sedimentary record.
7.3 Contribution of Study to Wider Acidification Research
The secondary aim of this study was to evaluate the potential of
paleolimnological indicators in anthropogenic acidification studies within the
region and in tropical environments in general. Recall from chapter two that in the
late 1990s, following the completion of large-scale acidification research projects
in Europe and North America, along with a focus by developing countries on
economic development at the expense of environmental health, acidification
studies dropped sharply. However, the problem of acid deposition in Asia
persists.
As the majority of paleolimnological acidification studies were conducted
in temperate countries, where environmental processes differ, it is vital to
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investigate whether the techniques employed in Europe and North America are
transferrable to a tropical environment. This is the first time diatom and
geochemical analysis has been conducted in a freshwater acidification study in
Singapore, and literature on such paleolimnological acidification studies in Asia,
particularly SEA, are exceedingly rare. Thus, the methodologies employed in this
study had to be devised from scratch based on a literature review of similar
studies conducted in the temperate countries. As such, an evaluation of the
effectiveness of the selected techniques employed is necessary.
While diatom preservation would be an issue in tropical environments,
particularly with high temperatures, results obtained from this study are exciting.
A change in diatom assemblage can be seen moving from pre-anthropogenic
acidification conditions to modern day. This is in spite of the fact that air pollution
in Singapore has been carefully controlled and thus, Jungle Falls stream would
not be as heavily impacted by acidification as the freshwater ecosystems seen in
temperate studies.
Geochemical analysis has proved similarly useful in tracking the
acidification of freshwater ecosystems in the tropics - lead, zinc and sulphur
concentrations change with varying atmospheric contamination into the
catchment. The fact that lead levels remain low at the top of the core, even as
zinc and sulphur levels are increasing, demonstrates the accuracy of this signal.
This is because measurements of atmospheric pollution levels in Singapore show
that while lead pollution has decreased from 1981 to present (figure 4-3), sulphur
dioxide levels have increased from the late 1980s (figure 4-2).
It is crucial to measure other trace metals in a geochemical study to better
interpret down-core variations. Thus, for this study, because the series of dams
built at Jungle Falls stream would affect sediment supply levels into the stream,
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sodium
and
potassium
levels
were
measured.
Iron
and
manganese
concentrations were also determined to check if redox driven cycles affected
trace metal concentrations. It can be seen that changes in lead, zinc and sulphur
appear to vary above that of background environmental levels, a sign of the
anthropogenic pollution into the catchment. The diatom and geochemical data
complement well and reinforce each other, emphasising the value of using
multiple proxies in paleolimnological analyses.
7.4 Extensions of Research
This study has provided a good foundation for further acidification
research in Singapore and the region. It has shown the value of paleolimnological
indicators in tracking acidification, and this approach should be pursued further.
Firstly, more coring sites need to be found. An issue with the Jungle Falls coring
site is that the atmospheric contamination signal is intertwined with changing
hydrological processes due to the damming of the stream. More coring sites
would aid in verifying the Jungle Falls results, along with increasing the
knowledge about the extent of anthropogenic acidification in Singapore. The use
of caesium-137 to analyse the Jungle Falls core will also provide further
validation of the data interpretation in this study.
Secondly, a modern diatom dataset for Singapore and the region is
necessary. Most diatom studies conducted in Asia still refer to diatom keys from
Europe and North America. As mentioned in section 6.6.1, diatoms would have
different ecological parameters in different environments and in order to
accurately interpret the assemblages, a regional diatom database is paramount.
This would also aid in the development of a transfer function for the area, “a
mathematical formula that estimates environmental variables from diatom
species’ composition data” (Moser et al, 1996: 28), enabling quantitative analysis
which provides values for changes in environmental variables such as pH.
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Thirdly, concentrations of SCPs and PAHs could be analysed within the
Jungle Falls sediment core. As these particles are produced due to industrial
processes, it would give a clear indication of whether anthropogenic pollution is
being recorded within the sediment core. Lastly, the use of sulphur isotope
analysis in the Jungle Falls sediment core would also provide more data on
potential anthopogenic influences within the core. By looking at variations in the
34
S and
32
S stable isotopes of sulphur within a core, decreases in
34
S
concentrations accompany anthropogenic acidification, providing independent
information on the impact of anthropogenic pollution on a freshwater ecosystem
(Fry, 1990).
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... and Fragilaria bicapitata), and a lower abundance of taxa present in more acidic waters (Eunotia incisa and Eunotia flexuosa) Trace metal concentration begin increasing up-core and peak at 15cm... the diatom assemblage also changes at this depth, with levels of Eunotia vanheurckii, Eunotia curvata and Fragilaria bicapitata dropping and levels of Eunotia incisa and Eunotia flexuosa rising... time diatom and geochemical analysis has been conducted in a freshwater acidification study in Singapore, and literature on such paleolimnological acidification studies in Asia, particularly SEA,