Distribution and cycling of terrigenous dissolved organic carbon in peatland-draining rivers and coastal waters of Sarawak, Borneo
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Published:2018-11-16
Issue:22
Volume:15
Page:6847-6865
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Martin PatrickORCID, Cherukuru NagurORCID, Tan Ashleen S. Y., Sanwlani Nivedita, Mujahid AazaniORCID, Müller MoritzORCID
Abstract
Abstract. South-East Asia is home to one of the world's largest stores of tropical
peatland and accounts for roughly 10 % of the global land-to-sea dissolved
organic carbon (DOC) flux. We present the first ever seasonally resolved
measurements of DOC concentration and chromophoric dissolved organic matter
(CDOM) spectra for six peatland-draining rivers and coastal waters in
Sarawak, north-western Borneo. The rivers differed substantially in DOC
concentration, ranging from 120–250 µmol L−1 (Rajang River) to
3100–4400 µmol L−1 (Maludam River). All rivers carried high
CDOM concentrations, with a350 in the four blackwater rivers between
70 and 210 m−1 and 4 and 12 m−1 in the other two rivers. DOC and CDOM
showed conservative mixing with seawater except in the largest river (the
Rajang), where DOC concentrations in the estuary were elevated, most likely
due to inputs from the extensive peatlands within the Rajang Delta. Seasonal
variation was moderate and inconsistent between rivers. However, during the
rainier north-east monsoon, all marine stations in the western part of our
study area had higher DOC concentrations and lower CDOM spectral slopes,
indicating a greater proportion of terrigenous DOM in coastal waters.
Photodegradation experiments revealed that riverine DOC and CDOM in Sarawak
are photolabile: up to 25 % of riverine DOC was lost within 5 days of
exposure to natural sunlight, and the spectral slopes of photo-bleached CDOM
resembled those of our marine samples. We conclude that coastal waters of
Sarawak receive large inputs of terrigenous DOC that is only minimally
altered during estuarine transport and that any biogeochemical processing
must therefore occur mostly at sea. It is likely that photodegradation plays
an important role in the degradation of terrigenous DOC in these
waters.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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