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Title: Water‐rock interactions drive chemostasis
Abstract

The western U.S. is experiencing shifts in recharge due to climate change, and it is currently unclear how hydrologic shifts will impact geochemical weathering and stream concentration–discharge (CQ) patterns. Hydrologists often useCQanalyses to assess feedbacks between stream discharge and geochemistry, given abundant stream discharge and chemistry data. Chemostasis is commonly observed, indicating that geochemical controls, rather than changes in discharge, are shaping streamCQpatterns. However, fewCQstudies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of importantCQcontrols such as coupled mineral dissolution and clay precipitation and subsequent cation exchange. Here, we use field observations—including groundwater age, stream discharge, and stream and groundwater chemistry—to analyseCQrelations in the Manitou Experimental Forest in the Colorado Front Range, USA, a site where chemostasis is observed. We combine field data with laboratory analyses of whole rock and clay x‐ray diffraction and soil cation‐extraction experiments to investigate the role that clays play in influencing stream chemistry. We use Geochemist's Workbench to identify geochemical reactions driving stream chemistry and subsequently suggest how climate change will impact streamCQtrends. We show that as groundwater age increases,CQslope and stream solute response are not impacted. Instead, primary mineral dissolution and subsequent clay precipitation drive strong chemostasis for silica and aluminium and enable cation exchange that buffers calcium and magnesium concentrations, leading to weak chemostatic behaviour for divalent cations. The influence of clays on streamCQhighlights the importance of delineating geochemical controls along flowpaths, as upgradient mineral dissolution and clay precipitation enable downgradient cation exchange. Our results suggest that geochemical reactions will not be impacted by future decreasing flows, and thus where chemostasis currently exists, it will continue to persist despite changes in recharge.

 
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NSF-PAR ID:
10489844
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Hydrological Processes
Volume:
38
Issue:
2
ISSN:
0885-6087
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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