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In this manuscript, I provide ideas that may help early‐career colleagues on their paths in science, especially in research and academia. I discuss the inevitability of failure at times, the importance of finding great collaborators and mentors and making time for the things that bring you joy in your life, and suggest a few practices that I hope make us more pleasant human beings. I share a few difficulties I've navigated and advice I've shared with my students, postdocs, and early‐career colleagues through the years. I hope such thoughts are useful, and help others find the joy in being a scientist.

 

Two major barriers hinder the holistic understanding of subsurface critical zone (CZ) evolution and its impacts: (a) an inability to measure, define, and share information and (b) a societal structure that inhibits inclusivity and creativity. In contrast to the aboveground portion of the CZ, which is visible and measurable, the bottom boundary is difficult to access and quantify. In the context of these barriers, we aim to expand the spatial reach of the CZ by highlighting existing and effective tools for research as well as the “human reach” of CZ science by expanding who performs such science and who it benefits. We do so by exploring the diversity of vocabularies and techniques used in relevant disciplines, defining terminology, and prioritizing research questions that can be addressed. Specifically, we explore geochemical, geomorphological, geophysical, and ecological measurements and modeling tools to estimate CZ base and thickness. We also outline the importance of and approaches to developing a diverse CZ workforce that looks like and harnesses the creativity of the society it serves, addressing historical legacies of exclusion. Looking forward, we suggest that to grow CZ science, we must broaden the physical spaces studied and their relationships with inhabitants, measure the “deep” CZ and make data accessible, and address the bottlenecks of scaling and data‐model integration. What is needed—and what we have tried to outline—are common and fundamental structures that can be applied anywhere and used by the diversity of researchers involved in investigating and recording CZ processes from a myriad of perspectives.

 

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 (C–Q) patterns. Hydrologists often useC–Qanalyses 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 streamC–Qpatterns. However, fewC–Qstudies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of importantC–Qcontrols 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 analyseC–Qrelations 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 streamC–Qtrends. We show that as groundwater age increases,C–Qslope 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 streamC–Qhighlights 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.

 

Abstract. Many studies in ecohydrology focusing on hydrologictransport argue that longer residence times across a stream ecosystem shouldconsistently result in higher biological uptake of carbon, nutrients, andoxygen. This consideration does not incorporate the potential forbiologically mediated reactions to be limited by stoichiometric imbalances.Based on the relevance and co-dependences between hydrologic exchange,stoichiometry, and biological uptake and acknowledging the limited amountof field studies available to determine their net effects on the retentionand export of resources, we quantified how microbial respiration iscontrolled by the interactions between and the supply of essential nutrients (C, N, and P)in a headwater stream in Colorado, USA. For this, we conducted two rounds ofnutrient experiments, each consisting of four sets of continuous injectionsof Cl− as a conservative tracer, resazurin as a proxy for aerobicrespiration, and one of the following nutrient treatments: (a) N, (b) N+C,(c) N+P, or (d) C+N+P. Nutrient treatments were considered to be knownsystem modifications that alter metabolism, and statistical tests helpedidentify the relationships between reach-scale hydrologic transport andrespiration metrics. We found that as discharge changed significantlybetween rounds and across stoichiometric treatments, (a) transient storagemainly occurred in pools lateral to the main channel and was proportional todischarge, and (b) microbial respiration remained similar between rounds andacross stoichiometric treatments. Our results contradict the notion thathydrologic transport alone is a dominant control on biogeochemicalprocessing and suggest that complex interactions between hydrology, resourcesupply, and biological community function are responsible for drivingin-stream respiration.