It is also in agreement with the observations of DOC increases with decrease in ionic strength (IS, Hruška et al., 2009). The latter is consistent with the observation of a significant reduction in acid anion concentrations (i.e., sulfate) in many catchments that show increases in DOC ( Monteith et al., 2007).
#DON CARBON ORIGIN DRIVER#
Lastly, recovery from acidification is put forth as a general driver for observed changes in stream water DOC ( Evans and Monteith, 2001 De Wit et al., 2007 Monteith et al., 2007 Hruška et al., 2009 Kang et al., 2018).
#DON CARBON ORIGIN DRIVERS#
Other suggested drivers include changes in nitrogen deposition ( Stuart, 2005) or land management practices ( Yallop and Clutterbuck, 2009). For example, some studies indicate that increases in DOC are consistent with a climate change driver including changing temperature or hydroclimatic conditions ( Freeman et al., 2001 Worrall and Burt, 2007 Eimers et al., 2008 Lepistö et al., 2008). Over the last few decades increased levels of dissolved organic carbon (DOC) have been observed in forested streams across the northern hemisphere ( Monteith et al., 2007 Porcal et al., 2009) and several processes have been proposed to explain observed patterns.
Overall, these results indicate that soil aggregates might be one important link between Critical Zone inputs (i.e., precipitation) and exports in streams. Landscape position impacted quality but not quantity of released DOC. These effects are attributed to aggregate dispersion due to expanding diffuse double layers in decreased IS solutions and to decreased bridging by divalent cations. Furthermore, higher DOC concentrations were found in Na + compared to Ca 2+ solutions of the same IS. In low IS solutions, extractable DOC concentrations were significantly higher, particle size (by laser diffraction) was significantly smaller and organic material was separated from mineral particles in scanning electron microscope observations. We monitored dynamic changes in soil particle size, aggregate architecture and composition, leachate DOC concentrations, dissolved organic matter (DOM) characteristics by fluorescence spectroscopy and trends in bioavailability. We performed aqueous soil extracts with solutions of different ionic strength (IS) and composition to simulate changes in soil solution. To test these hypotheses, we collected soils from two main landscape positions (hillslope and riparian zones) from the acid-impacted Sleepers River Research Watershed in northeastern Vermont. We hypothesize that soil aggregates are the main source of stream water DOC and that DOC release is greater in organic rich, riparian soils vs.
The exact nature of the mechanistic link between precipitation composition and stream water DOC is still widely debated in the literature. Over the past two decades, headwater streams of the northern hemisphere have shown increased amounts of dissolved organic carbon (DOC), coinciding with decreased acid deposition. 2US Geological Survey, Montpelier, VT, United States.1Environmental Biogeochemistry Lab, Department of Geology, University of Vermont, Burlington, VT, United States.Perdrial 1 *, Aaron Shavitz 1, Arianna Libenson 1, Maxwell Landsman-Gerjoi 1, Nicolas Perdrial 1, Jesse Armfield 1, Thomas Adler 1 and James B.
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