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Title: Dissolved organic matter from tropical peatlands reduces shelf sea light availability in the Singapore Strait, Southeast Asia
Authors: Martin, Patrick
Sanwlani, Nivedita
Lee, Tiffany Wan Qi
Wong, Joel Meng Cheng 
Chang, Kristy Yi Wen
Wong, Elizabeth Wing-See 
Liew, Soo Chin 
Keywords: Coloured dissolved organic matter
Coral reefs
Dissolved organic carbon
Optical water quality
Tropical peatlands
Underwater light attenuation
Issue Date: 19-Aug-2021
Publisher: Inter-Research
Citation: Martin, Patrick, Sanwlani, Nivedita, Lee, Tiffany Wan Qi, Wong, Joel Meng Cheng, Chang, Kristy Yi Wen, Wong, Elizabeth Wing-See, Liew, Soo Chin (2021-08-19). Dissolved organic matter from tropical peatlands reduces shelf sea light availability in the Singapore Strait, Southeast Asia. Marine Ecology Progress Series 672 : 89-109. ScholarBank@NUS Repository.
Rights: Attribution 4.0 International
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. © 2021 The authors.
Source Title: Marine Ecology Progress Series
ISSN: 0171-8630
DOI: 10.3354/meps13776
Rights: Attribution 4.0 International
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