Abstract. Degradation of tropical peats is a global concern due to large Carbon emission and loss of biodiversity. The degradation of tropical peats usually starts when the government drains and clears peat forests into open peats used for food crops, oil palm and industrial timber plantations. Major properties of tropical peat forests are high in Water Contents (WC), Loss on Ignition (LOI) and Total Organic Carbon (TOC), and low in peat pH, Dry Bulk Density (DBD), and Total Nitrogen (TN). In this study, we investigated impacts of drainage and land use change on these properties. We collected peat samples from peat forests, logged over peat forest, industrial timber plantation, community agriculture, and oil palms. We used independent t-tests and oneway ANOVA to analyze mean differences of the research variables. We found that peat pH, DBD, and TN tend to increase. A significant decrease of C/N ratio in oil palm and agriculture sites importantly denotes a high rate of peat decompositions. Water contents, LOI, and TOC are relatively constants. We suggest that changes in pH, DBD, TN and atomic C/N ratio are important indicators for assessing tropical peat degradation. We infer that land use change from tropical peat forests intoCorrespondence to: G. Z. Anshari (gzanshari@live.untan.ac.id) cleared and drained peats used for intensive timber harvesting, oil palms and industrial timber plantations in Indonesia has greatly degraded major ecological function of tropical peats as Carbon storage.

Abstract. Worldwide, peatlands are important sources of dissolved organic matter (DOM) and trace metals (TMs) to surface waters, and these fluxes may increase with peatland degradation. In Southeast Asia, tropical peatlands are being rapidly deforested and drained. The blackwater rivers draining these peatland areas have high concentrations of DOM and the potential to be hotspots for CO2 release. However, the fate of this fluvial carbon export is uncertain, and its role as a trace metal carrier has never been investigated. This work aims to address these gaps in our understanding of tropical peatland DOM and associated elements in the context of degraded tropical peatlands in Indonesian Borneo. We quantified dissolved organic carbon and trace metal concentrations in the dissolved and fine colloidal (<0.22 µm) and coarse colloidal (0.22–2.7 µm) fractions and determined the characteristics (δ13C, absorbance, fluorescence: excitation-emission matrix and parallel factor – PARAFAC – analysis) of the peatland-derived DOM as it drains from peatland canals, flows along the Ambawang River (blackwater river) and eventually mixes with the Kapuas Kecil River (whitewater river) before meeting the ocean near the city of Pontianak in West Kalimantan, Indonesia. We observe downstream shifts in indicators of in-stream processing. An increase in the δ13C of dissolved organic carbon (DOC), along with an increase in the C1∕C2 ratio of PARAFAC fluorophores, and a decrease in SUVA (specific UV absorbance) along the continuum suggest the predominance of photo-oxidation. However, very low dissolved oxygen concentrations also suggest that oxygen is quickly consumed by microbial degradation of DOM in the shallow layers of water. Blackwater rivers draining degraded peatlands show significantly higher concentrations of Al, Fe, Pb, As, Ni and Cd compared to the whitewater river. A strong association is observed between DOM, Fe, As, Cd and Zn in the dissolved and fine colloid fraction, while Al is associated with Pb and Ni and present in a higher proportion in the coarse colloidal fraction. We additionally measured the isotopic composition of lead released from degraded tropical peatlands for the first time and show that Pb originates from anthropogenic atmospheric deposition. Degraded tropical peatlands are important sources of DOM and trace metals to rivers and a secondary source of atmospherically deposited contaminants.

Abstract. Worldwide, peatlands are important sources of dissolved organic matter (DOM) and trace metals (TM) to surface waters and these fluxes may increase with peatland degradation. In Southeast Asia, tropical peatlands are being rapidly deforested and drained. The black rivers draining these peatland areas have high concentrations of DOM, and the potential to be hotspots for CO2 release. However, the fate of this fluvial carbon export is uncertain, and its role as a trace metal carrier has never been investigated. This work aims to address these gaps in our understanding of tropical peatland DOM and associated elements in the context of degraded tropical peatlands of Indonesian Borneo. We quantified dissolved organic carbon and trace metals concentrations in the dissolved and fine colloidal (

&lt;p&gt;Worldwide, peatlands are important sources of dissolved organic matter (DOM) and trace metals (TM) to surface waters and these fluxes may increase with peatland degradation. In Southeast Asia, tropical peatlands are being rapidly deforested and drained. The black rivers draining these peatland areas have high concentrations of DOM. However, the fate of this fluvial carbon export is uncertain, and its role as a trace metal carrier has never been investigated. This work aims to address these gaps in our understanding of tropical peatland DOM and associated elements in the context of degraded tropical peatlands of Indonesian Borneo. We quantified dissolved organic carbon and trace metals concentrations in the dissolved, fine colloidal and coarse colloidal fractions and determined the characteristics (optical and isotopic) of the peatland-derived DOM as it drains from peatland canals, flows along black river and eventually mixes with the Kapuas Kecil River before meeting the ocean near the city of Pontianak in West Kalimantan, Indonesia. Black rivers draining degraded peatlands show significantly higher concentrations of Al, Fe, Pb, As, Ni, and Cd, compared the white river. A strong association is observed between DOM, Fe, As, Cd and Zn in the dissolved and fine colloid fraction, while Al is associated to Pb and Ni and present in a higher proportion in the coarse colloidal fraction. We additionally measured the isotopic composition of lead released from degraded tropical peatlands for the first time and show that Pb originates from anthropogenic atmospheric deposition. Degraded tropical peatlands are important sources of DOM and trace metals to rivers and a secondary source of atmospherically deposited contaminants.&lt;/p&gt;

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