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Browsing by Author "Shanley, James B."

Now showing 1 - 3 of 3
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    Cross-regional prediction of long-term trajectory of stream water DOC response to climate change
    Laudon, Hjalmar; Buttle, J.; Carey, S. K.; McDonnell, J.; McGuire, Kevin J.; Seibert, J.; Shanley, James B.; Soulsby, C.; Tetzlaff, D. (American Geophysical Union, 2012-09-22)
    There is no scientific consensus about how dissolved organic carbon (DOC) in surface waters is regulated. Here we combine recent literature data from 49 catchments with detailed stream and catchment process information from nine well established research catchments at mid- to high latitudes to examine the question of how climate controls stream water DOC. We show for the first time thatmean annual temperature (MAT) in the range from -3 to +10 degrees C has a strong control over the regional stream water DOC concentration in catchments, with highest concentrations in areas ranging between 0 and +3 degrees C MAT. Although relatively large deviations from thismodel occur for individual streams, catchment topography appears to explain much of this divergence. These findings suggest that the long-term trajectory of stream water DOC response to climate change may be more predictable than previously thought.
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    Flushing of distal hillslopes as an alternative source of stream dissolved organic carbon in a headwater catchment
    Gannon, John P.; Bailey, Scott W.; McGuire, Kevin J.; Shanley, James B. (American Geophysical Union, 2015-10-01)
    We investigated potential source areas of dissolved organic carbon (DOC) in headwater streams by examining DOC concentrations in lysimeter, shallow well, and stream water samples from a reference catchment at the Hubbard Brook Experimental Forest. These observations were then compared to high-frequency temporal variations in fluorescent dissolved organic matter (FDOM) at the catchment outlet and the predicted spatial extent of shallow groundwater in soils throughout the catchment. While near-stream soils are generally considered a DOC source in forested catchments, DOC concentrations in near-stream groundwater were low (mean52.4 mg/L, standard error50.6 mg/L), less than hillslope groundwater farther from the channel (mean55.7 mg/L, standard error50.4 mg/L). Furthermore, water tables in near-stream soils did not rise into the carbon-rich upper B or O horizons even during events. In contrast, soils below bedrock outcrops near channel heads where lateral soil formation processes dominate had much higher DOC concentrations. Soils immediately downslope of bedrock areas had thick eluvial horizons indicative of leaching of organic materials, Fe, and Al and had similarly high DOC concentrations in groundwater (mean514.5 mg/L, standard error50.8 mg/L). Flow from bedrock outcrops partially covered by organic soil horizons produced the highest groundwater DOC concentrations (mean520.0 mg/L, standard error54.6 mg/L) measured in the catchment. Correspondingly, stream water in channel heads sourced in part by shallow soils and bedrock outcrops had the highest stream DOC concentrations measured in the catchment. Variation in FDOM concentrations at the catchment outlet followed water table fluctuations in shallow to bedrock soils near channel heads. We show that shallow hillslope soils receiving runoff from organic matter-covered bedrock outcrops may be a major source of DOC in headwater catchments in forested mountainous regions where catchments have exposed or shallow bedrock near channel heads.
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    Use of color maps and wavelet coherence to discern seasonal and interannual climate influences on streamflow variability in northern catchments
    Carey, S. K.; Tetzlaff, D.; Buttle, J.; Laudon, Hjalmar; McDonnell, J.; McGuire, Kevin J.; Seibert, J.; Soulsby, C.; Shanley, James B. (American Geophysical Union, 2013-10-01)
    The higher midlatitudes of the northern hemisphere are particularly sensitive to change due to the important role the 0 degree C isotherm plays in the phase of precipitation and intermediate storage as snow. An international intercatchment comparison program called North-Watch seeks to improve our understanding of the sensitivity of northern catchments to change by examining their hydrological and biogeochemical variability and response. Here eight North-Watch catchments located in Sweden (Krycklan), Scotland (Girnock and Strontian), the United States (Sleepers River, Hubbard Brook, and HJ Andrews), and Canada (Dorset and Wolf Creek) with 10 continuous years of daily precipitation and runoff data were selected to assess daily to seasonal coupling of precipitation (P) and runoff (Q) using wavelet coherency, and to explore the patterns and scales of variability in streamflow using color maps. Wavelet coherency revealed that P and Q were decoupled in catchments with cold winters, yet were strongly coupled during and immediately following the spring snowmelt freshet. In all catchments, coupling at shorter time scales occurred during wet periods when the catchment was responsive and storage deficits were small. At longer time scales, coupling reflected coherence between seasonal cycles, being enhanced at sites with enhanced seasonality in P. Color maps were applied as an alternative method to identify patterns and scales of flow variability. Seasonal versus transient flow variability was identified along with the persistence of that variability on influencing the flow regime. While exploratory in nature, this intercomparison exercise highlights the importance of climate and the 0 degree C isotherm on the functioning of northern catchments.