The effects of riparian forest quality on allochthonous inputs and leaf litter retention in tropical headwater streams in Sabah, Malaysia

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Citation:
Cassell, C. (2017) The effects of riparian forest quality on allochthonous inputs and leaf litter retention in tropical headwater streams in Sabah, Malaysia. Unpublished masters thesis, Imperial College London.


Freshwater lotic ecosystems and their adjacent riparian zones are inherently linked through reciprocal ecological subsidies which strongly influence food web dynamics. Riparian disturbance associated with land use changes has been shown to negatively affect the biomass of terrestrial-aquatic energy fluxes, however few studies have been conducted in tropical forests. In the present study, the allochthonous inputs of terrestrial invertebrates and leaf litter were measured in five streams present across a land use gradient in Sabah, Malaysia. Stream environmental variables and the retentiveness of each stream were also measured. The allochthonous inputs (terrestrial invertebrates: 0.0039 - 0.023 g-1 m2 day-1, leaf litter: 0.008 - 1.66 g-1 m-1 day-1) were found to compare favourably to other tropical regions, although a marked biomass reduction was observed as the surrounding forest quality decreased. Streams with a higher riparian forest quality also exhibited greater average substrate sizes, canopy cover and biomass of retained organic matter. The importance of the oil palm industry in Malaysia continues to drive deforestation, with additional land demands projected to be five million hectares by 2020. Terrestrial-aquatic subsidies were shown to play an important role in maintaining chemical and physical habitats within streams, thus the present research highlighted a discernible threat towards freshwater ecosystems and suggested strict management practices should be implemented to protect riparian zones from further deforestation.