Impact of forest disturbance, fragmentation and restoration on erosion and sediment sources and transport within the Segama river catchment, Eastern Sabah

• Main Author: Kogila Vani Annammala
• Format: Thesis
• Language: English; English
• Published: 2015
• Subjects: SD390.5-390.7 Forest meteorology. Forest microclimatology
• Online Access: https://eprints.ums.edu.my/id/eprint/39470/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/39470/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/39470/

This research focuses on terrain of contrasting land-use in Eastern Sabah, Malaysian Borneo. Differences in soil erosion rate were assessed between primary forest (Danum Valley),naturally regenerating selectively logged forest and rehabilitated logged forest (Malua), and oil palm plantation land and adjacent forest fragments at the Sabahmas Plantation of Wilmar International. Second part of this research uses multi-proxy sediment fingerprinting approach to reconstruct changes in sedimentation rate and the relative contributions of different sub-catchments to the downstream sediment budget of the large Segama catchment over the past 150 years. Networks of 50-70 erosion bridge transect sites were established in the various land-use types on slopes of 0-50o to study on erosion pattern. Downstream evidence was derived from a sediment core on high lateral bench on the Lower Segama below the confluence of the Urik tributary. Bed-sediment samples were taken from channel-margin sites at low flow for the major upstream tributary catchments (the hypothesized sediment sources) of the Segama River. The core sectioned materials were analysed for (i) fallout radionucides 137Cs and 210Pb (ii) particle size distributions and (iii) major and minor elemental composition (by X-Ray Fluorescence). Results indicated that logged forest rehabilitated by enrichment planting experienced much reduced erosion (1.22 mm yr-1 and less) compared with un-rehabilitated logged forest (1.48-8.55 mm yr-1) and primary forest 0.18 mm yr-1. Within the oil palm areas, erosion rates at sites without conservational measures were high (6.38-43.72 mm yr-1), whereas sites with soil conservation practices, erosion rates were 0.31-5.31 mm yr-1. Recent enrichment of the downstream sediment with alkali and alkaline earth elements were apparent. These elements are considered as mobile elements during weathering and are more susceptible to retention, sorption at top of the core may be linked to increased inputs from sections of the catchment that have been recently disturbed (e.g. converted to oil palm). Input of fallout 210Pb in the middle and upper sections of the core profile marked dilution of activity concentration by periods of enhanced rates of accretion. Concentrations of 137Cs were measured at mass depths of 8.86 and 58.64 kg m-2, however a third peak was not achieved thus the dating using 137Cs could not be performed. Using only results from 210Pb dating, the peaks and troughs were found to tally with the known history of logging within the Segama catchment. The use of radiochronology in combination with sediment fingerprinting capable of revealing changes in the sedimentation rate and the relative contributions from different parts of the upstream catchment with their land-uses and land management practices.