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

Chapter One INTRODUCTION 1.1 Overview 2 1.2 Aims and Objectives 3 1.3 Organisation of Thesis 5 1 1.1 Overview Since the 19th century, development in Singapore has resulted in the loss of a rich natural environment. Where dense jungle once blanketed Singapore, with tropical rainforests covering 82% of the island, mangroves 13% and freshwater swamps 5% (Lu et al, 2005), today, Singapore is considered to be 100% urbanised (UNPD, 2008). While there are still green spaces in Singapore, over the past 190 years, 95% of the native rainforest in Singapore has been cleared (Castelletta et al, 2000). This has made protecting the last 5% of primary forests in Singapore crucial. Being one of the last remaining patches of primary forest on the island, and the oldest forest reserve in Singapore, Bukit Timah Nature Reserve (BTNR) “has survived against all odds to become a major source of scientific research, educational field trips and recreational enjoyment” (Waller, 2001: 133). Being only 8km from the city centre, surrounded by roads, including the eight lane Bukit Timah Expressway, and mere minutes walk away from several shopping centres, the urban pressure on the nature reserve is plain to see (Corlett, 1988). While, there is no risk that the reserve will be cleared for development (Lum and Sharpe, 1996), the reserve still faces many threats, including the isolation of the forest and the high pedestrian traffic within (Corlett, 1995a). In recent years, the National Parks Board (NParks), the government body that manages the reserve, is concerned that the Central Catchments Nature Reserve (containing BTNR) is becoming more affected by anthropogenic acidification. With domestic air pollution present, anthropogenic air pollution travelling into Singapore from the region already high, and pollution to increase as Southeast Asia (SEA) continues to industrialise, this issue is rising in importance. 2 Acidification brings with it a myriad of impacts, related not just to a direct lowering of pH levels in an ecosystem, but to the changes in the biogeochemical cycling of trace metals and nutrients caused by acid deposition. This includes affecting vegetation growth and a loss of species biodiversity. BTNR, being a primary forest, is particularly important. The acidification of BTNR is already suspected as a cause for the decline of Johora Singaporensis, an endemic freshwater crab species which lives within the forest streams. As such, in 2005, a stream-water chemistry monitoring programme was established in BTNR, located at Jungle Falls stream. This ongoing project is examining the water quality within the reserve, to see if the wildlife within is potentially being affected by acidification. This will then aid in the management of the forest reserve. Unfortunately, there is a lack of historical data monitoring the environmental changes within this stream, and thus, conditions of the stream prior to anthropogenic pollution are unknown. Supplementing this programme, this research plans to fill this gap in knowledge regarding the acidification history of the stream. 1.2 Aims and objectives The primary aim of this study is to employ paleolimnological analysis in order to evaluate the potential acidification of Jungle Falls stream, BTNR. In order to conduct this paleolimnological analysis, a selection of cores will be collected from a sediment accumulation behind a brick dam at Jungle Falls stream. As acidification issues within SEA are rising and there is currently a lack of scientific research in the area, a secondary aim of this study is to evaluate the potential for the use of paleolimnological indicators for acidification studies in the region and in tropical environments in general. 3 The aims are addressed through the following objectives: 1) Physical analysis of core a. To provide a stratigraphical description of the core using the Troels-Smith system. This would serve as a foundation for examining changing environmental conditions within the stream. b. To determine the organic carbon content of the core. As there should not be significant variations in organic carbon content within the sediments, with the environment at the reserve not changing radically over the last century, any variation present would provide a straightforward method to enable multiple cores to be correlated. 2) Biological analysis of core a. To examine the diatoms present within the core. As these microscopic algae are highly sensitive to environmental change, particularly acidification, changes in the diatom assemblage, moving from older to younger sediments, could be indicative of a lowering pH of the stream. 3) Geochemical analysis of core a. To quantify the vertical distribution of sulphur, lead, zinc, sodium, potassium, iron and manganese within the core. Sulphur, lead and zinc concentrations within a sedimentary profile would provide an insight into the levels and impact of atmospheric contamination into the stream. Sodium and potassium concentrations will aid in examining whether the concentrations of sulphur, lead and zinc are affected by changes in erosional intensity within the catchment. Iron and manganese levels are an indicator of whether sediment diagentic processes have an impact on sulphur, lead and zinc profiles. 4 1.3 Organisation of Thesis This thesis is divided into seven chapters. In this chapter, a general background of the research is given, along with the aims and objectives of this study. Following that, in chapter two, the issue of acid deposition is discussed, looking at its history, causes and impacts. It concludes by examining future trends of acid deposition in Asia. It is shown that acidification research within Asia is lacking and the problem is intensifying, making this study of the acidification of a tropical stream in Singapore highly pertinent. Chapter three discusses the difficulties faced by acidification researchers due to a lack of historical monitoring data and finding a suitable study site. This shortage of historical data has made paleolimnological analysis crucial in acidification research. It is, however, difficult to find a study site which is undisturbed and contains a record with the required time span and resolution, particularly in the tropics where there are fewer lakes than in temperate areas. Chapter three then examines the paleolimnological techniques employed in acidification research, looking at the rationale behind the techniques and providing examples of how they are applied. Chapter four is a background of the study site, combining the issues examined in chapter two and three into a Singaporean context. Information regarding the acidification problem in Singapore is provided, along with a description of BTNR and Jungle Falls stream within it. This elucidates why Jungle Falls stream is an ideal location for a study of acidification. Moving on to the primary data collection, chapter five details the methodology conducted in this study. Chapter six is a description and analysis of the results, demonstrating that there are signs of acidification within Jungle Falls stream. Chapter seven summarises this research and evaluates the contribution of this study to wider acidification studies within the region. Lastly, possible research extensions are suggested. 5  ... 190 years, 95% of the native rainforest in Singapore has been cleared (Castelletta et al, 2000) This has made protecting the last 5% of primary forests in Singapore crucial Being one of the last... combining the issues examined in chapter two and three into a Singaporean context Information regarding the acidification problem in Singapore is provided, along with a description of BTNR and. .. historical monitoring data and finding a suitable study site This shortage of historical data has made paleolimnological analysis crucial in acidification research It is, however, difficult to find a