2020 ESA Annual Meeting (August 3 - 6)

LB 8 Abstract - Assessing the impact of acidification and recovery on dissolved organic carbon (DOC) mobilization from a snow dominated, forested headwater catchment

Caitlin Bristol1, Thomas Adler1, Lindsey Stinson1, Bryan Stozenburg1, Kristen Underwood2, Donna, M. Rizzo2, Hang Wen3, Li Li4, Adrian Harpold5, Gary Sterle5, James B. Shanley6 and Julia N. Perdrial1, (1)Geology, University of Vermont, Burlington, VT, (2)Civil and Environmental Engineering, University of Vermont, Burlington, VT, (3)Civil and Environmental Engineering, Pennsylvania State University, University Park, PA, (4)CEE, Pennsylvania State University, PA, (5)Natural Resources and Environmental Science, University of Nevada, Reno, NV, (6)NH-VT Water Science Center, USGS, Montpelier, VT
Abstract Text:

Background/Question/Methods: In the last few decades, several studies reported increased amounts of dissolved organic carbon (DOC) in forested streams and attributed this increase to recovery from acidification and climate change. Sleepers River Research Watershed (SRRW) in northeastern Vermont, provides an extensive dataset showing significant increases in DOC exports over the past two decades. During snowmelt, topsoils are flushed extensively, leading to significant DOC exports in a short amount of time. In this research, we sample soil cores over winter to investigate the DOC liberation process under changing solution chemistry and to assess snowmelt DOC characteristics (i.e. composition and biodegradability). Soil cores are subjected to solutions of varying pH and ionic strength and allowed to interact with the soil for several minutes before being drained gravitationally. We analyze the effluent for DOC concentrations, fluorescence characteristics, and perform soil incubations under controlled conditions to assess biodegradability.

Results/Conclusions: Our experiments found that samples from the first sampling trip in February released almost double the amount of DOC compared to samples from in mid-March, which could indicate that intermittent thaw or rain on snow events already led to DOC losses after the first sampling period. This was confirmed with discharge data from the USGS indicating a rain event just prior to the March sampling. This makes sense because snowmelt and rain on snow events flush labile carbon from soils, so as expected we found the highest amounts of DOC to be leached out from pre-snowmelt soil cores. Secondly, because low pH and high ionic strength destabilize soil aggregates (leading to carbon sequestration), we expected and found a reversal of these conditions to lead to DOC liberation from aggregates and highest DOC concentrations in recovery solutions. Thirdly, because labile DOC is not microbially processed extensively in cold conditions and accumulates under the snowpack, we expected and found that DOC from pre-snowmelt cores is mostly plant-derived (e.g. low fluorescence index) and be highly biodegradable.