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| Titel |
Contextualising impacts of logging on tropical rainforest catchment sediment dynamics using the stratigraphic record of in-channel bench deposits |
| VerfasserIn |
Will Blake, Rory Walsh, Kawi Bidin, Kogila Annammala |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112587
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| Publikation (Nr.) |
 EGU/EGU2015-12749.pdf |
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| Zusammenfassung |
| It is widely recognised that commercial logging and conversion of tropical rainforest to oil
palm plantation leads to enhanced fluvial sediment flux to the coastal zone but the
dynamics of delivery and mechanisms that act to retain sediment and nutrients within
rainforest ecosystems, e.g. riparian zone and floodplain storage, are poorly understood
and underexploited as a management tool. While accretion of lateral in-channel
bench deposits in response to forest clearance has been demonstrated in temperate
landscapes, their development and value as sedimentary archives of catchment
response to human disturbance remains largely unexplored in tropical rainforest river
systems.
Working within the Segama River basin, Sabah, Malaysian Borneo, this study aimed to
test the hypothesis that (1) lateral bench development in tropical rainforest rivers
systems is enhanced by upstream catchment disturbance and that (2) the sedimentary
record of these deposits can be used to infer changes in sediment provenance and
intensification of sediment flux associated with logging activities. Sediment cores
were taken from in-channel bench deposits with upstream catchment contributing
areas of 721 km2 and 2800 km2 respectively. Accretion rates were determined
using fallout 210Pb and 137Cs and the timing of peak accumulation was shown to
correspond exactly with the known temporal pattern of logging and associated fluvial
sediment response over the period 1980 to present following low pre-logging rates.
Major and minor element geochemistry of deposits was used to assess the degree of
weathering that deposited sediment had experienced. This was linked to surface
(heavily weathered) and subsurface (less weathered) sediment sources relating to
initial disturbance by logging and post-logging landsliding responses respectively. A
shift in the dominant source of deposited material from surface (i.e. topsoil) to
subsurface (i.e. relatively unweathered subsoil close to bedrock) origin was observed to
coincide with the increase in accretion rates following logging of steep headwater
slopes.
Coherence of sedimentary, monitoring and observational evidence demonstrates that
in-channel bench deposits offer a previously unexplored sedimentary archive of
catchment response to logging in tropical rainforest systems and a tool for evaluating
the erosional responses of ungauged basins. In-channel bench development due to
catchment disturbance may augment ecosystem services provided by the riparian
corridors of larger rivers and process knowledge gained from sedimentary archives can
be used to underpin future riparian and catchment forest management strategies. |
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