Sources and selective preservation of organic matter in the karst watershed: evidence from sediment records in a plateau
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RESEARCH ARTICLE
Sources and selective preservation of organic matter in the karst watershed: evidence from sediment records in a plateau deep lake, Southwestern China Runyu Zhang 1 & Liying Wang 1 & Jingan Chen 1 Received: 7 May 2020 / Accepted: 10 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Human activities have greatly altered terrestrial carbon (C) dynamics associated with vegetation cover and land use changes, thereby influencing the C sink in downstream ecosystems. However, the transport and preservation of organic C from soils that experience serious erosion in the karst area are scarce, particularly at catchment scales. In this study, chemical characteristics of organic matter (OM) isolated from the topsoil, overlying water, and lake sediments, as well as subsequent source identification, were inferred from the molecular, spectroscopic, and carbon isotopic (δ13C) signatures in a typical karst catchment, Southwestern China. The results indicated that the elemental compositions of the calcareous soil and paddy soil significantly differed from the yellow soil. High similarities existed in the fluorescence spectra of humic substances (HS) extracted from the front two soil types with those of lake sediments, indicating the homogeneous nature of OM molecular structure. The C/N ratios of six dissolved OM fractions and sedimentary HS along with δ13C values consistently reflected the primary terrestrial source. It was estimated to account for 60% of total organic C in sedimentary OM by end-member mixing modeling in accordance with soil erosion intensity and large recharge coefficient of this catchment. The evolution of soil loss and lake productivity can be well deduced from sediment records of organic C content, C/N ratio, and the specific information of HS. This research highlighted that the composition, source, and fate of OM in the karst lake was mainly dominated by the terrestrial C flux, rather than in-lake production. Furthermore, soil type and erosion intensity have significant effects on the nature of eroded OM and ultimate preservation. Keywords Karst watershed . Soil erosion . Carbon sink . Humic substances . Sediment record
Introduction Karst topography is one of the most fragile and vulnerable environments because of the low pedogenesis and high permeability underlying the carbonate rocks (Jiang et al. 2014). It represents 7–12% of the global land surface and is widely distributed in the Mediterranean coast, Southwest China, Northern Vietnam, Indiana and Kentucky of the USA, Cuba, and Jamaica (Li et al. 2016). As one of the three largest conResponsible editor: Kitae Baek * Runyu Zhang [email protected] 1
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
tinuous and well-developed karst landforms in the world, Southwest China amounted to 2.5% of the global karst area, about 540 000 km2 (Luo et al. 2016). Over the past several centuries, excessive deforestation and reclaimi
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