Distribution and cycling of terrigenous dissolved organic carbon in peatland-draining rivers and coastal waters of Sarawak, Borneo

Abstract

<p><strong>Abstract.</strong> 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<sup>−1</sup> (Rajang river) to 3,100–4,400 µmol L<sup>−1</sup> (Maludam river). All rivers carried high CDOM concentrations, with <i>a</i><sub>350</sub> in the four blackwater rivers between 70–210 m<sup>−1</sup>, and 4–12 m<sup>−1</sup> 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. Photo-degradation experiments revealed that riverine DOC and CDOM in Sarawak are photo-labile: up to 25 % of riverine DOC was lost within five 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 photo-degradation plays an important role in the degradation of terrigenous DOC in these waters.</p>

Composition and cycling of dissolved organic matter from tropical peatlands of coastal Sarawak, Borneo, revealed by fluorescence spectroscopy and parallel factor analysis

“…The full processed dataset is available in Supplement Data Table 1. All raw data files, MATLAB scripts for EEM correction and PARAFAC analysis are available through the NTU data repository, DR-NTU, at doi:10.21979/N9/RCYCIT (Zhou, 2019) and https://doi.org/10.21979/N9/0RLSDU (Martin, 2018).…”

“…CDOM concentrations (in the blackwater rivers) (Martin et al, 2018); at the marine stations, this most likely reflects the low nutrient concentrations that are typical of tropical seas.…”

“…Changes in DOC (a-d), C1-C5 Fmax (e-x), FI (y-ab) and HIX (ac-af) of samples from Rajang River in June and September, from seawater of eastern region and from Samunsam River during the photodegradation experiment. DOC data are taken fromMartin et al (2018).…”

Distribution and Flux of Dissolved Iron of the Rajang and Blackwater Rivers at Sarawak, Borneo

“…4b). As evidenced by the water color, these peat-draining rivers are characterized by extremely high levels of terrigenous DOM (Martin et al, 2018;Zhou et al, 2018).Given such high concentrations of DOM and the positive https://doi.org/10.5194/bg-2019-204 Preprint. Discussion started: 18 June 2019 c Author(s) 2019.…”

Dissolved inorganic nitrogen in a tropical estuary at Malaysia: transport and transformation

“…8B). Photo-degradation in tropical rivers also accelerates the decomposition of DON and benefits accumulation of NH4 + in surface river water (Martin et al, 2018). In Lassa branch, a clear DON consumption and the possibility for the occurrence of ammonification was obtained ( Fig.…”