SPATIAL VARIATION AND DRIVERS OF STREAM SEDIMENT ACIDITY IN SINGAPORE’S FRESHWATER SWAMP FORESTS
CHIA JIA MIN, SANDRA
CHIA JIA MIN, SANDRA
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Abstract
Forest stream sediments serve important ecological functions such as growing mediums for aquatic flora, habitat for aquatic fauna and acidity regulation. Although sediments have traditionally been studied for pollution monitoring, recent studies have characterized spatial variation in forest sediment for ecological conservation purposes. This study investigates the drivers of and spatial variation of sediment acidity in a freshwater swamp forest in Singapore. Sediment grab samples from 20 meter reaches in three streams were obtained. These were analysed for clay content, organic matter content, base cation values and aluminium values. Results indicate that sediment acidity was similar within separate streams of the upper catchment but significantly less acidic in the middle catchment stream confluence. Of the variables considered, sediment acidity was found to be predominantly driven by aluminium and stream depth. Aluminium, an acidic cation, influenced acidity by blocking adsorption of base cations to sediments. More acidic sediments tended to contain larger amounts of aluminium. Deeper parts of the stream were likely to have more complex surfaces, accumulating smaller sediments and organic matter. This provided more surface area for the adsorption of acidic cations, making sediments acidic. Though the variables considered explained sediment acidity to a large degree in tropical forests, they did so only to a medium extent for freshwater swamp forest sediment. This suggests differences in variables governing sediment acidity in the two forest types. However, stream depth and aluminium are ultimately still significant in controlling sediment acidity and should be managed with care to ensure effective conservation of freshwater swamp forests in Singapore.
Keywords
sediment acidity, sediment chemistry, Nee Soon Swamp Forest, spatial variability, acidity drivers
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2019
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