River Dynamics Control Transit Time Distributions and Biogeochemical Reactions in a Dam‐Regulated River Corridor

Xuehang Song; Xingyuan Chen; John M. Zachara; Jesus D. Gomez-Velez; Pin Shuai; Huiying Ren; Glenn E. Hammond

doi:10.1029/2019WR026470

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River Dynamics Control Transit Time Distributions and Biogeochemical Reactions in a Dam‐Regulated River Corridor

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River Dynamics Control Transit Time Distributions and Biogeochemical Reactions in a Dam‐Regulated River Corridor

Xuehang Song, Xingyuan Chen, John M. Zachara, Jesus D. Gomez-Velez, Pin Shuai, Huiying Ren and Glenn E. Hammond

Water resources research, Vol.56(9), p.n/a

09/2020

DOI: 10.1029/2019WR026470

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Abstract

Transit time distributions (TTDs) exert important controls on biogeochemical processes in watershed systems. TTDs are often assumed to follow time‐invariant exponential, lognormal, or heavy‐tailed power law distributions in headwater or low‐order streams. However, under dynamic hydrological forcing, transit time could exhibit more complex distribution patterns with strong spatial and temporal variability. In this study, we used a numerical particle tracking approach to characterize TTDs along the Hanford Reach of the Columbia River under the influences of river stage fluctuations and evaluate the associated effects on biogeochemical reaction potentials within the river corridor. Particle tracking was conducted using velocity fields simulated by high‐resolution three‐dimensional groundwater flow models that capture both the river stage fluctuations and physical heterogeneity. Our results revealed that multifrequency flow variations led to multimodal TTDs that varied in time and space. Such characteristics can only be captured by multiyear numerical simulations supported by multiyear field monitoring. Dam‐induced high‐frequency (subweekly) flow variations increased additional hydrologic exchange flows with short (subweekly) transit times, which accounted for up to 44% of reactant consumption in the river corridor along the Hanford Reach. The dam‐induced river stage fluctuations have more significant impacts on faster biogeochemical reactions because they cause a larger fraction of shorter transit times. Numerical particle tracking provides an efficient alternative for characterizing TTDs for large complex systems where in situ field experiments are not feasible. Such a numerical approach is thus essential for improving large‐scale biogeochemical modeling from watersheds to basins. Key Points River stage fluctuations lead to highly dynamic, multimodal transit time distributions Dam‐induced high‐frequency river stage variations have higher impacts on faster biogeochemical reactions Numerical particle tracking can effectively characterize complex transit time distributions

biogeochemical reaction

dam operation

hydrological exchange zone

hydropeaking

surface water‐groundwater interactions

transit time distributions

Details

Title: Subtitle: River Dynamics Control Transit Time Distributions and Biogeochemical Reactions in a Dam‐Regulated River Corridor
Creators: Xuehang Song - Pacific Northwest National Laboratory
Xingyuan Chen - Pacific Northwest National Laboratory
John M. Zachara - Pacific Northwest National Laboratory
Jesus D. Gomez-Velez - Vanderbilt University
Pin Shuai - Pacific Northwest National Laboratory
Huiying Ren - Pacific Northwest National Laboratory
Glenn E. Hammond - Pacific Northwest National Laboratory
Resource Type: Journal article
Publication Details: Water resources research, Vol.56(9), p.n/a
DOI: 10.1029/2019WR026470
ISSN: 0043-1397
eISSN: 1944-7973
Number of pages: 25
Grant note: DOE: (DE‐AC05‐76RL01830; DE‐AC02‐05CH11231)
Language: English
Date published: 09/2020
Academic Unit: Civil and Environmental Engineering
Record Identifier: 9984962533902771

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