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Abstract Hyporheic exchange is critical to river corridor biogeochemistry, but decameter‐scale flowpaths (∼10‐m long) are understudied due to logistical challenges (e.g., sampling at depth, multi‐day transit times). Some studies suggest that decameter‐scale flowpaths should have initial hot spots followed by transport‐limited conditions, whereas others suggest steady reaction rates and secondary reactions that could make decameter‐scale flowpaths important and unique. We investigated biogeochemistry along a 12‐m hyporheic mesocosm that allowed for controlled testing of seasonal and spatial water quality changes along a flowpath with fixed geometry and constant flow rate. Water quality profiles of oxygen, carbon, and nitrogen were measured at 1‐m intervals along the mesocosm over multiple seasons. The first 6 m of the mesocosm were always oxic and a net nitrogen source to mobile porewater. In winter, oxic conditions persisted to 12 m, whereas the second half of the flowpath became anoxic and a net nitrogen sink in summer. No reactive hot spots were observed in the first meter of the mesocosm. Instead, most reactions were zeroth‐order over 12 m and 54 hr of transit time. Influent chemistry had less impact on hyporheic biogeochemistry than expected due to large amounts of in situ reactant sources compared to stream‐derived reactant sources. Sorbed or buried carbon likely fueled reactions with rates controlled by temperature and redox conditions. Each reactant showed different hyporheic Damköhler numbers, challenging the characterization of flowpaths being intrinsically reaction‐ or transport‐limited. Future research should explore the prevalence and biogeochemical contributions of decameter‐scale flowpaths in diverse field settings. 

Abstract We report exceptionally negative δ238U values for spring water (−2.5‰ to −0.8‰) and travertine calcite (−3.2‰ to −1.1‰) from an area where the Jemez lineament intersects the western margins of the Rio Grande rift, west-central New Mexico (southwestern United States). The highest anomalies come from the southern margins of the Valles Caldera and are related to upwelling CO2-charged spring water forming travertine mounds along joints and faults. The anomaly likely occurs due to CO2 lixiviation of uranium in a deep-seated reduced environment where 235U is preferentially leached along a long flow path through Precambrian granitic basement, resulting in spring water with exceptionally low δ238U values inherited by the calcite that precipitated near or at the surface at relatively low temperatures, i.e., ~40 °C (modern temperatures). The lowest δ238U values are preserved in settings where upwelling waters are least diluted by oxidized aquifer groundwaters. Given these low δ238U values in travertine are associated with and possibly indicators of upwelling CO2 related to tectonic and magmatic activity, studies such as ours may be used to identify this association far back in time. 

Abstract Urban centers around the world are grappling with the challenges associated with population increases, drought, and projected water shortages. Potable water reuse (i.e., purification of municipal wastewater for reuse as drinking water) is an option for supplementing existing water supplies. Public perception research on potable water reuse has predominantly employed surveys with multiple‐choice questions that constrain survey respondents to describe their concerns by choosing from several response options. This research examines hundreds of write‐in responses to a large public survey in Albuquerque, New Mexico, to provide a detailed analysis of residents' questions and concerns about potable water reuse. Findings demonstrate that allowing respondents to voice their actual concerns adds richness and nuance that cannot be obtained from multiple‐choice response data alone. Especially with controversial resource considerations, such as potable water reuse, planners would benefit from a full understanding of the problem before engaging with the community. 

Abstract Wildfires are increasing globally in frequency, severity, and extent, but their impact on fluvial networks, and the resources they provide, remains unclear. We combine remote sensing of burn perimeter and severity, in-situ water quality monitoring, and longitudinal modeling to create the first large-scale, long-term estimates of stream+river length impacted by wildfire for the western US. We find that wildfires directly impact ~6% of the total stream+river length between 1984 and 2014, increasing at a rate of 342 km/year. When longitudinal propagation of water quality impacts is included, we estimate that wildfires affect ~11% of the total stream+river length. Our results indicate that wildfire activity is one of the largest drivers of aquatic impairment, though it is not routinely reported by regulatory agencies, as wildfire impacts on fluvial networks remain unconstrained. We identify key actions to address this knowledge gap and better understand the growing threat to fluvial networks, water security, and public health risks. 

Abstract Urban communities around the world are grappling with the challenges associated with population increases, drought, and projected water shortages. With a substantial global shortfall between water supply and demand expected by 2030, water planning strategies must adapt to a new reality characterized by higher temperatures and less precipitation, requiring new ways of thinking about water management, use, and governance. Commonplace strategies such as water conservation and nonpotable water reuse might not be sufficient to adequately stretch water supplies in water‐scarce parts of the industrialized world. In the United States, planned potable water reuse (i.e., purification of domestic wastewater for reuse as drinking water) is emerging as a way forward to mitigate water shortages without significant changes to lifestyle, behavior, or infrastructure. But potable reuse is not the only solution: paradigm shifting and disruptive options that more holistically address water scarcity, such as composting toilets and market‐based approaches to water use, are also gaining traction, and they could be pursued alongside or instead of potable water reuse. However, these options would require more significant changes to lifestyles, behavior, infrastructure, and governance. While all of the options considered offer advantages, they each come with new concerns and challenges related to cost, public perception, social norms, and policy. The goal of this work is to consider a number of plausible solutions to water scarcity—partial and complete, traditional and disruptive—to stimulate forward‐looking thinking about the increasingly common global problem of water scarcity. This article is categorized under:Engineering Water > Sustainable Engineering of WaterEngineering Water > Planning Water 

Wildfires significantly alter hydrological and biogeochemical processes, impacting downstream water quality and posing risks to ecosystems and human communities. Following the 2022 Hermit’s Peak-Calf Canyon (HPCC) wildfire in New Mexico, the largest wildfire recorded in the state of New Mexico, we deployed high-resolution in-situ sensors at three locations along a > 160 km fluvial network to investigate event-scale solute transport dynamics and their environmental drivers. Our objective was to evaluate how post-fire runoff events influenced water quality behavior across spatial (headwaters to mid- and high-order streams) and temporal (event to seasonal) gradients. We found that acute water quality impacts were most severe near the burn area, where turbidity reached ~8,500 FNU and dissolved oxygen fell below regulatory thresholds. These extremes, largely missed by traditional discrete sampling, were strongly driven by storm event size and seasonal variability. In contrast, farther downstream, solute export behavior was better predicted by longer-term indicators such as time since the fire and vegetation recovery metrics. Our analysis reveals distinct spatial shifts in concentration-discharge behavior that depend on the water quality parameter type, event features, and site position in the watershed. These findings highlight the need for longitudinal, high-frequency monitoring to detect and anticipate wildfire-induced water quality risks and inform more adaptive, spatially targeted watershed management strategies. 

The benthic biolayer is a shallow zone of reactive streambed sediments, widely believed to contribute disproportionately to whole‐stream reactions such as aerobic respiration and contaminant transformation. Quantifying the relative contribution of the biolayer to whole‐stream reactions remains challenging because it requires that hyporheic zone solute transport and reaction heterogeneity are explicitly captured within a single modeling framework. Here, we use field experiments and modeling to quantify the biolayer's aerobic reactivity relative to other stream compartments. We co‐injected and monitored several fluorescent tracers, including the reactive tracer resazurin, into a controlled experimental stream. We characterized reactive transport in the water column and at multiple depths in the hyporheic zone by fitting all data to a new mobile‐immobile model, using resazurin‐to‐resorufin conversion as an indicator of aerobic bioreactivity. Results show that the biolayer converted 8 times more resazurin to resorufin than all other stream compartments, and 80% of this conversion occurred within 2 reach advection times. This hotspot and hot moment behavior is attributed to the biolayer's ability to rapidly acquire, transiently retain, and rapidly degrade stream‐borne solutes. The model analysis shows that the majority of raz‐to‐rru conversion occurs in the biolayer across streams with a wide range of biolayer structural properties, including streams with a biolayer that is less reactive than deeper regions of the hyporheic zone. Together, our results show that the biolayer is a common feature of streams and rivers that should be considered in network‐scale models of aerobic reactivity. 

Abstract Sensor‐based, semicontinuous observations of water quality parameters have become critical to understanding how changes in land use, management, and rainfall‐runoff processes impact water quality at diurnal to multidecadal scales. While some commercially available water quality sensors function adequately under a range of turbidity conditions, other instruments, including those used to measure nutrient concentrations, cease to function in high turbidity waters (> 100 nephelometric turbidity units [NTU]) commonly found in large rivers, arid‐land rivers, and coastal areas. This is particularly true during storm events, when increases in turbidity are often concurrent with increases in nutrient transport. Here, we present the development and validation of a system that can affordably provide Self‐Cleaning FiLtrAtion for Water quaLity SenSors (SC‐FLAWLeSS), and enables long‐term, semicontinuous data collection in highly turbid waters. The SC‐FLAWLeSS system features a three‐step filtration process where: (1) a coarse screen at the inlet removes particles with diameter > 397 μm, (2) a settling tank precipitates and then removes particles with diameters between 10 and 397 μm, and (3) a self‐cleaning, low‐cost, hollow fiber membrane technology removes particles ≥ 0.2μm. We tested the SC‐FLAWLeSS system by measuring nitrate sensor data loss during controlled, serial sediment additions in the laboratory and validated it by monitoring soluble phosphate concentrations in the arid Rio Grande river (New Mexico, U.S.A.), at hourly sampling resolution. Our data demonstrate that the system can resolve turbidity‐related interference issues faced by in situ optical and wet chemistry sensors, even at turbidity levels > 10,000 NTU.