Abstract
The concentrations of dissolved organic carbon (DOC) and its light-absorbing fraction (chromophoric dissolved organic matter; CDOM) in surface waters, particularly those draining organic-rich peatlands, have dramatically increased over the past decade due to climate change and human disturbance. To explore the spatiotemporal dynamics of DOC and CDOM in surface waters of the northeastern Qinghai-Tibetan Plateau, we collected water samples from two rivers in the Zoige alpine wetland and from two rivers in its adjacent alpine-gorge region, during wet and dry seasons. DOC concentration ranged from 4.82 mg·L−1 to 47.83 mg·L−1, with a mean value of 15.04 mg·L−1, 2.84 times higher than the global average. The Zoige rivers had higher DOC concentration and highly terrigenous CDOM. Significantly higher DOC concentration was observed for the Zoige rivers in the wet season compared to the dry season. In contrast, the alpine-gorge rivers had higher DOC levels in the dry season. No significant correlations were observed between DOC and CDOM at all rivers due to the influence of autochthonous sources on the alpine-gorge rivers and intensive photochemical degradation of terrigenous DOM in the Zoige rivers. Significant relationships between CDOM and specific ultraviolet absorbance at 254 nm (SUVA254) and between CDOM/DOC and SUVA254 were observed, indicating that the aromaticity of DOM in the rivers was mainly determined by CDOM. Moreover, the DOC/CDOM properties of the Hei River indicate critical human-induced water quality degradation. High DOC level and high browning degree were found in rivers in the Zoige alpine wetland, indicating that large amounts of terrigenous DOC were released to the aquatic systems of the region.
Highlights
Dissolved organic matter (DOM), operationally measured as dissolved organic carbon (DOC)and defined as the organic fraction in solution that passes through a 0.45 μm filter [1], is a ubiquitous component in soils and natural waters which establishes a connection between terrestrial and aquatic carbon pools [2,3]
The purpose of this study is to explore the spatiotemporal dynamics of DOC and chromophoric dissolved organic matter (CDOM), in relation to the browning of surface waters, in the Zoige wetland, northeastern Qinghai-Tibetan
Concluding from the research conducted by Liu et al [33] and our results, the wide fluctuation ranges of CDOM and CDOM properties along the Bai River can be attributed to the unequal input intensity of terrigenous sources, while the autochthonous impacts on the Zagunao River and the Min
Summary
Dissolved organic matter (DOM), operationally measured as dissolved organic carbon (DOC)and defined as the organic fraction in solution that passes through a 0.45 μm filter [1], is a ubiquitous component in soils and natural waters which establishes a connection between terrestrial and aquatic carbon pools [2,3]. DOC is related to the energy supply, light penetration, the biogeochemical cycles of carbon (C) and elements coupled to C, and the transportation of metals and nonpolar organic contaminants in waters [4,5,6], and plays an important role in environmental processes in aquatic ecosystems. Humic substances absorb ultraviolet and short-wave visible light, and any increase of them contributes to the brown coloration in waters [8,11]. Colored or chromophoric dissolved organic matter (CDOM), defined by the component of DOM capable of absorbing light in the range from the ultraviolet to visible wavelength in natural water systems, mostly consists of humic substances [4,12]. Algal-derived DOM contains fewer colored components than
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