4.4 Future research directions
Ground-truthing model outputs by collecting samples or deploying sensors
in every reach is logistically impossible even for a small
sub-catchment. Our RCM approach already incorporates a model-experiment
(Modex) loop (Serbin et al. 2021), where laboratory measurements of
sediments collected within the Columbia River Basin were used to
parameterize biogeochemical rates in the model. We suggest implementing
a subsequent ModEx loop, where our allometry estimates can identify
sub-catchments that may function as biogeochemical control points
(sensu Bernhardt et al. 2017). For instance, by examining
residuals in Figure 2 for each regression line fit, we could iteratively
identify which reaches adhered most poorly to scaling relationships
(where the largest positive residuals represent respiration hot spots)
and target field sampling campaigns to confirm whether outliers are due
to high respiration or heterogeneity poorly captured by the model.
Predictions of how hyporheic respiration allometrically scales across
watersheds that can generalize between basins will dramatically improve
our ability to model and therefore forecast how biogeochemical processes
influencing, and influenced by, aquatic metabolism will respond to
natural or anthropogenic changes in watershed dynamics. Our findings
present an initial attempt to characterize how hyporheic respiration
scales allometrically with watershed area across two environmentally
distinct basins. We found that, while some commonalities exist in
allometric scaling patterns and relationships to watershed
characteristics, particularly precipitation and elevation,
basin-specific patterns suggest that the factors driving hyporheic
respiration scaling require additional study. We suggest future studies
incorporate a larger number of study basins to more effectively assess
generalizability of patterns and relationships to watershed
characteristics. Further, incorporation of key disturbances, including
non-perenniality, wildfires, and urbanization, whose downstream impacts
increasingly influence, and are influenced by, surface and hyporheic
biogeochemical processes (Lawrence et al. 2013; Zhao et al. 2021; Ball
et al. 2021; DelVecchia et al. 2022), will improve our ability to model
the hyporheic zone and more accurately represent river corridor function
in earth system models.
Acknowledgements: The authors thank Francisco Guerrero for
contributions in conceptualization and analysis to an earlier draft of
this manuscript. This research was supported by the U.S. Department of
Energy (DOE), Office of Biological and Environmental Research (BER),
Environmental System Science (ESS) Program as part of the River Corridor
Science Focus Area (SFA) at the Pacific Northwest National Laboratory
(PNNL). PNNL is operated by Battelle Memorial Institute for the DOE
under Contract No. DE-AC05-76RL01830. The authors declare no conflict of
interest.
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