Abstract
Dissolved carbon (C) leaching in and from soils plays an important role in C transport along the terrestrial-aquatic continuum. However, a global overview and analysis of dissolved carbon in soil solutions, covering a wide range of vegetation types and climates, is lacking. We compiled a global database on annual average dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in soil solutions, including potential governing factors, with 762 entries from 351 different sites covering a range of climate zones, land cover types and soil classes. Using this database we develop regression models to calculate topsoil concentrations, and concentrations versus depth in the subsoil at the global scale. For DIC, the lack of a proportional globally distributed cover inhibits analysis on a global scale. For DOC, annual average concentrations range from 1.7 to 88.3 (median = 25.27) mg C/L for topsoils (n = 255) and from 0.42 to 372.1 (median = 5.50) mg C/L for subsoils (n = 285, excluding lab incubations). Highest topsoil values occur in forests of cooler, humid zones. In topsoils, multiple regression showed that precipitation is the most significant factor. Our global topsoil DOC model ({mathrm{R}}^{2}=0.36) uses precipitation, soil class, climate zone and land cover type as model factors. Our global subsoil model describes DOC concentrations vs. depth for different USDA soil classes (overall ({mathrm{R}}^{2}=0.45). Highest subsoil DOC concentrations are calculated for Histosols.
Highlights
1.1 Scientific problemTerrestrial leached carbon (C) is commonly ignored in global C-cycle studies [1,2,3,4] leading to an inaccurate quantification of the terrestrial C budget [3, 5]
We present the first global database on annual average
Highest topsoil DOC concentrations occur in forests in humid continental climates, while topsoils of Histosols do not have higher DOC concentrations than other soil classes
Summary
1.1 Scientific problemTerrestrial leached carbon (C) is commonly ignored in global C-cycle studies [1,2,3,4] leading to an inaccurate quantification of the terrestrial C budget [3, 5]. Several studies show that leaching and transport through groundwater of dissolved C is a major C source to surface waters [6,7,8,9] These freshwaters are important active systems in the global C cycle, linking the land and the ocean [10]. Global inland waters are estimated to process between 1.9 and 5.1 Pg C year−1 [11], indicating the magnitude of the C flux into streams, rivers, lakes and reservoirs is fraught with uncertainties [11,12,13,14] This C flux from global terrestrial systems comprises litterfall from vegetation in floodplains and riparian zones of primarily headwaters, surface runoff, leaching from soils and processing via groundwater to surface waters.
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