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Marine Ecology Progress Series

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MEPS 672:89-109 (2021)  -  DOI:

Dissolved organic matter from tropical peatlands reduces shelf sea light availability in the Singapore Strait, Southeast Asia

Patrick Martin1,*, Nivedita Sanwlani1,5, Tiffany Wan Qi Lee1, Joel Meng Cheng Wong2,3, Kristy Yi Wen Chang1,4, Elizabeth Wing-See Wong2, Soo Chin Liew2

1Asian School of the Environment, Nanyang Technological University, 639798 Singapore
2Centre for Remote Imaging, Sensing, and Processing, National University of Singapore, 119076 Singapore
3Present address: Department of Environmental Systems Science, ETH Zürich, 8092 Zürich, Switzerland
4Present address: Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, 637551 Singapore
5Present address: Satellite Research Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, 637553 Singapore
*Corresponding author:

ABSTRACT: Shelf seas provide valuable ecosystem services, but their productivity and ecological functioning depend critically on sunlight transmitted through the water column. Anthropogenic reductions in underwater light availability are thus a serious threat to coastal habitats. The flux of light-absorbing coloured dissolved organic matter (CDOM) from land to sea may have increased world-wide, but how this has altered the availability and spectral quality of light in shelf seas remains poorly known. We present time-series data from the Sunda Shelf in Southeast Asia, where the monsoon-driven reversal in ocean currents supplies water enriched in CDOM from tropical peatlands for part of the year, resulting in 5- to 10-fold seasonal variation in light absorption by CDOM. We show that this terrigenous CDOM can dominate underwater light absorption at wavelengths up to 500 nm, and shift the underwater irradiance spectrum towards longer wavelengths. The seasonal presence of terrigenous CDOM also reduces the 10% light penetration depth by 1-5 m, or 10-45%. We estimate that on average 0.6 m, or 25%, of this terrigenous CDOM-mediated shoaling might be attributable to the enhanced input of dissolved organic matter following peatland disturbance. The seasonal change in the light environment is correlated with changes in phytoplankton absorption spectra that suggest a photo-acclimation response, and we infer that terrigenous CDOM likely contributes to limiting the depth distribution of photosynthetic corals. The results reveal an ecologically important but largely overlooked impact of human modifications to carbon fluxes that is likely increasingly important in coastal seas.

KEY WORDS: Coral reefs · Optical water quality · Underwater light attenuation · Coloured dissolved organic matter · Dissolved organic carbon · Tropical peatlands

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Cite this article as: Martin P, Sanwlani N, Lee TWQ, Wong JMC, Chang KYW, Wong EWS, Liew SC (2021) Dissolved organic matter from tropical peatlands reduces shelf sea light availability in the Singapore Strait, Southeast Asia. Mar Ecol Prog Ser 672:89-109.

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