04 Jan 2023
04 Jan 2023
Status: this preprint is currently under review for the journal BG.

Massive corals record deforestation in Malaysian Borneo through sediments in river discharge

Walid Naciri1, Arnoud Boom1, Matthew J. Payne1, Nicola Browne3, Noreen J. Evans2, Philip Holdship4, Kai Rankenburg2, Ramasamy Nagarajan5,6, Bradley J. McDonald2, Jennifer McIlwain3, and Jens Zinke1,3 Walid Naciri et al.
  • 1School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH, United Kingdom
  • 2School of Earth and Planetary Sciences / John de Laeter Centre, Curtin University, Bentley, WA 6102, Australia
  • 3Molecular and Life Sciences, Curtin University, Bentley, WA 6102, Australia
  • 4School of Earth Sciences, Oxford University, Oxford, OX1 2JD, United Kingdom
  • 5Department of Applied Sciences (Applied Geology), Curtin University Malaysia, Miri, 98009, Malaysia
  • 6Curtin Malaysia Research Institute, Curtin University Malaysia, Miri, 98009, Malaysia

Abstract. Logging of tropical primary forests is a widely acknowledged global issue threatening biodiversity hotspots and indigenous communities leading to significant land erosion and decreased soil stability. The downstream effects of logging on human coastal communities include poor water quality and increased sedimentation. Quantifying the impacts of historical deforestation within a watershed requires accurate data from river discharge or satellite images, which are rarely available prior to the 1980’s. In the absence of these in-situ measurements, proxies have successfully produced accurate, long-range, historical records of temperature, hydrological balance, and sediment discharge in coastal and oceanic environments. We present a 30 year, monthly resolved Ba/Ca proxy record of sediment in river discharge as measured from the skeletal remains of massive corals Porites sp. from northern Malaysian Borneo. We make the comparison with local instrumental hydrology data, river discharge and rainfall, to test the reliability of the Ba/Cacoral proxy. Our results show that averaging five records into two composites results in significant positive correlations with river discharge (r = 0.5 and r = 0.59) as well as a difference in correlations strength coherent with distance from the river mouth, with the composite closer to the river mouth displaying a higher correlation. More importantly, Porites sp. corals from this region recorded a very similar upward trend to that of river discharge on multi decennial time scales. The lack of similar increase, and overall stability in the precipitation record suggests that the river discharge’s trend recorded by corals is linked to the increasing land use associated with ever–growing deforestation. We argue that massive corals in this region are therefore valuable archives of past hydrological conditions and accurately reflect changes in land use patterns.

Walid Naciri et al.

Status: open (until 15 Feb 2023)

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Walid Naciri et al.

Walid Naciri et al.


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Short summary
In this study, we tested the ability of massive boulder-like corals to act as archives of land use in Malaysian Borneo to palliate the lack of accurate instrumental data on deforestation before the 1980s. We used mass spectrometry to measure trace elements ratios in coral cores to use as proxy for sediment in river discharge. Results showed an extremely similar increase between our proxy and the river discharge instrumental record demonstrating the use of these corals as reliable archives.