High elevation mountain watersheds are undergoing rapid warming
and declining snow fractions worldwide, causing earlier and
quicker snowmelt. Understanding how this hydrologic shift
affects subsurface flow paths, biogeochemical reactions, and
solute export has been challenging due to the entanglement of
hydrological and biogeochemical processes. Coal Creek, a
high-elevation catchment (2,700 3,700 m, 53 km2) in Colorado, is
experiencing a higher rate of warming than surrounding low-lying
areas. This warming corresponds with dynamic and increased
responses from biogenic solutes and dissolved organic carbon
(DOC), whereas the behavior of geogenic solutes and dissolved
inorganic carbon (DIC) has remained relatively unchanged. DOC
has experienced the largest concentration increase (>3x), with
annual average flow weighted concentrations positively
correlated to average annual temperature. This suggests
temperature is the main driver of increasing DOC levels.
Although DOC and DIC response to warming is influenced by many
drivers, the relative contribution of each remains unknown. DOC
and DIC were analyzed to incorporate both carbon component
products of soil respiration (DOC and CO2) and to represent high
solute concentrations transported by shallow (DOC) versus deep
(DIC) subsurface flow. The contrasting behavior of these carbon
solutes indicates climate change and warming are driving changes
in organic matter decomposition and soil respiration. Modeling
results from the process-based model HBV-BioRT show increased
temperatures cause earlier snowmelt and streamflow generation
and lower peak discharge. As stream flow generation occurs
earlier, so do DOC flushing and DIC dilution events.
Additionally, post-snowmelt periods show greater DOC production
and concentrations under warming scenarios. Results indicated
increased production of DOC in post-snowmelt periods. DOC is
then flushed out by earlier snowmelt partitioned through the
shallow soil zone. Most process-based studies lack a
watershed-scale understanding of carbon transformation and flow
path alterations. This work demonstrates complex hydrologic and
biogeochemical coupling at the watershed scale to illustrate how
water flow paths and chemistry are responding to a changing
climate in highelevation mountain watersheds.
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The Importance of Capturing Topographic Features for Modeling Groundwater Flow and Transport in Mountainous Watersheds
Physics‐based distributed hydrological models that include groundwater are widely used to understand and predict physical and biogeochemical processes within watersheds. Typically, due to computational limitations, watershed modelers minimize the number of elements used in domain discretization, smoothing or even ignoring critical topographic features. We use an idealized model to investigate the implications of mesh refinement along streams and ridges for modeling three‐dimensional groundwater flow and transport in mountainous watersheds. For varying degrees of topographic complexity level (TCL), which increases with the level of mesh refinement, and geological heterogeneity, we estimate and compare steady state baseflow discharge, mean age, and concentration of subsurface weathering products. Results show that ignoring lower‐order streams or ridges diminishes flow through local flow paths and biases higher the contribution of intermediate and regional flow paths, and biases baseflow older. The magnitude of the bias increases for systems where permeability rapidly decreases with depth and is dominated by shallow flow paths. Based on a simple geochemical model, the concentration of weathering products is less sensitive to the TCL, partially due to the thermodynamic constraints on chemical reactions. Our idealized model also reproduces the observed emergent scaling relationship between the groundwater contribution to streamflow and drainage area, and finds that this scaling relationship is not sensitive to mesh TCL. The bias effects have important implications for the use of hydrological models in the interpretation of environmental tracer data and the prediction of biogeochemical evolution of stream water in mountainous watersheds.
more » « less- Award ID(s):
- 1830172
- NSF-PAR ID:
- 10453285
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 54
- Issue:
- 12
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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