DOC fluorescence properties and degradation in the Changjiang River Network, China: implications for estimating in-stream DOC removal
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Dissolved organic carbon (DOC) in large river networks is an important carbon pool in the global biogeochemical cycle. DOC compositions vary spatially at global and regional scales, which influences DOC degradation and subsequent in-stream removal in river networks. The Changjiang River Network (CRN) is the third largest river system worldwide and plays an important role in DOC transformation and transportation. However, the relationships between DOC composition and degradation, as well as the quantification of in-stream removal, remain poorly understood. In this study, we chose the CRN to study spatial patterns of DOC fluorescence, as proxies for chemical composition, and degradation. Laboratory degradation experiments were conducted to explore DOC degradability and mechanisms of photodegradation and microbial respiration. We found that DOC fluorescence properties and degradation showed significant spatial differences in the lower reaches of the CRN. DOC with higher proportions of humic acid-like materials showed higher photodegradability. In degradation experiments, the total DOC loss was 49.1–66.0% over about the first 6 to 7 days. Microbial respiration removed 33.0–47.3% of total DOC, while photodegradation removed 9.0–35.3%. The relative contributions of photodegradation and microbial respiration to DOC degradation varied with different DOC fluorescence properties. The experimental values of DOC decay rate constants were 0.217–0.250 d−1. Our study improves understanding of DOC degradability, linking to its composition and providing a reference for estimating DOC in-stream removal in large river networks.
KeywordsDissolved organic carbon Fluorescence properties Microbial respiration Photodegradation In-stream removal The Changjiang River Network
The work by Weijin Yan in this study was supported by the National Key Research and Development Program of China through Grant 2016YFA0601004, and the National Natural Science Foundation of China (41877483, 21177126). The work by Yuchun Wang was supported by the National Natural Science Foundation of China (91647208, U1802241).
- Dalmagro HJ, Johnson MS, de Musis CR, Lathuilliere MJ, Graesser J, Pinto OB, Couto EG (2017) Spatial patterns of DOC concentration and DOM optical properties in a Brazilian tropical river-wetland system. J Geophys Res Biogeosci 122:1883–1902. https://doi.org/10.1002/2017jg003797 CrossRefGoogle Scholar
- Eckard RS, Pellerin BA, Bergamaschi BA, Bachand PAM, Bachand SM, Spencer RGM, Hernes PJ (2017) Dissolved Organic Matter Compositional Change and Biolability During Two Storm Runoff Events in a Small Agricultural Watershed. Journal of Geophysical Research-Biogeosciences 122:2634–2650. https://doi.org/10.1002/2017jg003935 CrossRefGoogle Scholar
- Fellman JB, Hood E, D’Amore DV, Edwards RT, White D (2009) Seasonal changes in the chemical quality and biodegradability of dissolved organic matter exported from soils to streams in coastal temperate rainforest watersheds. Biogeochemistry 95:277–293. https://doi.org/10.1007/s10533-009-9336-6 CrossRefGoogle Scholar
- Liu K-K, Yan W, Lee H-J, Chao S-Y, Gong G-C, Yeh T-Y (2015) Impacts of increasing dissolved inorganic nitrogen discharged from Changjiang on primary production and seafloor oxygen demand in the East China Sea from 1970 to 2002. J Mar Syst 141:200–217. https://doi.org/10.1016/j.jmarsys.2014.07.022 CrossRefGoogle Scholar
- Lonborg C, Álvarez-Salgado XA, Davidson K, Martínez-García S, Teira E (2010) Assessing the microbial bioavailability and degradation rate constants of dissolved organic matter by fluorescence spectroscopy in the coastal upwelling system of the Ría de Vigo. Mar Chem 119:121–129. https://doi.org/10.1016/j.marchem.2010.02.001 CrossRefGoogle Scholar
- Osburn CL, Oviedo-Vargas D, Barnett E, Dierick D, Oberbauer SF, Genereux DP (2018) Regional groundwater and storms are hydrologic controls on the quality and export of dissolved organic matter in two tropical rainforest streams, Costa Rica. J Geophys Res Biogeosci 123:850–866. https://doi.org/10.1002/2017jg003960 CrossRefGoogle Scholar
- Pellerin BA, Saraceno JF, Shanley JB, Sebestyen SD, Aiken GR, Wollheim WM, Bergamaschi BA (2012) Taking the pulse of snowmelt: in situ sensors reveal seasonal, event and diurnal patterns of nitrate and dissolved organic matter variability in an upland forest stream. Biogeochemistry 108:183–198. https://doi.org/10.1007/s10533-011-9589-8 CrossRefGoogle Scholar
- Wang H, Jiao R, Wang F, Zhang L, Yan W (2016) Dissolved organic carbon content and characteristics in relation to carbon dioxide partial pressure across Poyang Lake wetlands and adjacent aquatic systems in the Changjiang basin. Environ Pollut 219:714–723. https://doi.org/10.1016/j.envpol.2016.07.012 CrossRefGoogle Scholar
- Zhang LJ, Xue M, Wang M, Cai WJ, Wang L, Yu ZG (2014) The spatiotemporal distribution of dissolved inorganic and organic carbon in the main stem of the Changjiang (Yangtze) River and the effect of the Three Gorges Reservoir. J Geophys Res Biogeosci 119:741–757. https://doi.org/10.1002/2012jg002230 CrossRefGoogle Scholar