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The unprecedented expansion of lithium mining in closed‐basin brines is sparking concerns that mine‐related brine abstraction will stress freshwater resources and harm sensitive wetland ecosystems. These fears stoke preexisting conflicts between indigenous communities, governments, and mining interests. However, until now there has not been a comprehensive evaluation of how groundwater flux to wetlands in these systems responds to brine and freshwater abstraction to support these concerns. This study characterizes the hydrogeologic relationship between both brine and freshwater abstraction and groundwater discharge to wetlands in closed‐basin brine systems utilizing groundwater‐flow models representing three closed‐basin brine system endmembers. The models show that regardless of hydrogeologic conditions, fresh groundwater abstraction has a 200%–2,300% larger impact than halite brine abstraction on groundwater‐dependent wetlands over a 200‐year period. The primary control mechanisms for groundwater discharge response to abstraction are proximity to the abstraction point and density‐driven storage flux, which magnifies the impacts of freshwater abstraction and buffers the impacts of brine abstraction. Observations of changes in wetland vegetation near existing lithium brine mines show a 90% reduction in vegetated wetland area in response to freshwater abstraction but no observable change in response to brine abstraction, in agreement with the results of the modeling study. These findings demonstrate that minimizing freshwater use is more effective at protecting groundwater‐dependent wetlands than limiting brine drawdowns in closed‐basin brine systems.

Demand for lithium for batteries is growing rapidly with the global push to decarbonize energy systems. The Salar de Atacama, Chile holds ∼42% of the planet's reserves in the form of brine hosted in massive evaporite aquifers. The mining of these brines and associated freshwater use has raised concerns over the environmental responsibility of lithium extraction, yet large uncertainties remain regarding fundamental aspects of governing hydrological processes in these environments. This incomplete understanding has led to the perpetuation of misconceptions about what constitutes sustainable or renewable water use and therefore what justifies responsible allocation. We present an integrated hydrological assessment using tritium and stable oxygen, and hydrogen isotopes paired with remotely sensed and terrestrial hydroclimate data to define unique sources of water distinguished by residence time, physical characteristics, and connectivity to modern climate. Our results describe the impacts of prolonged drought on surface and groundwaters and demonstrate that nearly all inflow to the basin is composed of water recharged >65 years ago. Still, modern precipitation is critical to sustaining important wetlands around the salar. Recent large rain events have increased surface water and vegetation extents and terrestrial water storage while mining‐related water withdrawals have continued. As we show, poor conceptualizations of these complex hydrological systems have perpetuated the misallocation of water and the misattribution of impacts. These fundamental issues apply to arid regions globally. Our new framework for hydrological assessment in these basins moves beyond calculating gross inputs‐outputs at a steady state to include all compartmentalized stores that constitute “modern” budgets. Plain Language Summary Lithium is a critical resource for the green energy transition as the primary component in lithium‐ion batteries. Most of the planet's resources occur in water‐scarce environments, like Salar de Atacama, Chile where almost half the world's supply exists. Large amounts of very salty groundwater and some freshwater is extracted to recover the lithium. Yet, persistent gaps remain in our understanding of how water moves in these environments and therefore the impacts its extraction may have on surrounding ecosystems. We employ a combination of satellite and ground‐based hydroclimatological data to assess the system. Our results show that prolonged drought and a subsequent wetter period are the primary drivers of surface hydrology changes and that most of the water here is very old, highlighting the shortcomings of current water allocations. This work presents a data‐driven framework that allows water sustainability and lithium extraction to be adequately assessed in these arid regions. Key Points Freshwater inflows and the modern water budget at Salar de Atacama are dominated by relic groundwater A drought coincident with increases in groundwater extraction complicates the attribution of specific anthropogenic environmental impacts Freshwater use and allocated water rights at Salar de Atacama appear to not meet sustainable metrics

Understanding the impacts of glacier change on riverine ecosystems is limited by a lack of multi-year studies in glacierized mountain catchments quantifying the magnitude and stoichiometry of riverine biogeochemical yields. Here we evaluate riverine concentration-discharge relationships using the power function between daily runoff and element yields and stoichiometry across 10 catchments of varying glacial coverage within two climatically distinct regions in the Gulf of Alaska. Our multi-year study showed that biogeochemical stoichiometry and concentration-discharge relationships for dissolved carbon, nitrogen, and phosphorus varied significantly with catchment glacier coverage across both regions. This stoichiometric variability could drive regional differences in proglacial riverine food webs given that high trophic levels in low productivity rivers are generally driven by bottom-up controls. The coherence of our findings across the Gulf of Alaska suggests that observed patterns in concentration-discharge relationships are likely globally generalizable to catchments in which discharge is dominated by glacier ice and/or snowmelt. Concentration-discharge relationships for dissolved carbon, nitrogen, and phosphorus in Gulf of Alaska rivers are driven by glacier catchment coverage, according to analysis of water samples from the Gulf of Alaska.

More than half the world’s lithium resources are found in brine aquifers in Chile, Argentina, and Bolivia. Lithium brine processing requires freshwater, so as lithium exploration increases, accurate estimates of freshwater availability are critical for water management decisions in this region with limited water resources. Here we calculate modern freshwater inflows, such as groundwater recharge and streamflow, for 28 active or prospective lithium-producing basins. We use regional water budget assessments, field streamflow measurements, and global climate and groundwater recharge datasets. Using the freshwater inflow estimates, we calculate water scarcity using the Available Water Remaining methodology. Among all 28 basins, freshwater inflows range from 2 to 33 mm year −1 . Our results reveal that commonly used global hydrologic models overestimate streamflow and freshwater availability substantially, leading to inaccurate water scarcity classifications. Surface freshwater inflow to the Lithium Triangle of South America, a key resource for many lithium processes, has been overestimated substantially, according to a basin-scale water availability assessment in 28 basins relevant for lithium mining.

Accelerated modifications to the hydrology, driven by global climate change, will alter the timing and amount of freshwater discharged from coastal catchments to the intertidal and nearshore habitats of the Gulf of Alaska. Coastal glacierized catchments are important sources of both inorganic and organic matter to the nearshore ecosystem. The Gulf of Alaska is an ecologically diverse ecosystem, that supports commercial, mariculture, and subsistence lifestyles. However, the coastal catchments of the Gulf of Alaska are relatively understudied with respect to solute generation, seasonal cycles of major cations and anions, and chemical weathering regimes. To close the knowledge gap, the present study utilizes a unique set of stream samples compiled from field-based activities and the USGS NWIS from stream sites across the Gulf of Alaska watershed. First, we find that watershed characteristics such as slope, elevation and relief drive the variation in concentration-discharge relationships, while glacier coverage controls solute yields. Second, though glaciers control overall solute yields, the climate dictates the timing of seasonal solute yields. Additionally, we find across the Gulf of Alaska lithology and climate are important controls on major cation and anion concentrations. Finally, we implement a solute mass balance model to estimate fractional contributions to solute flux from silicate, carbonate and precipitation. We find that carbonate weathering is the dominant source of weathering derived solutes, however there are several streams across the Gulf of Alaska in which silicate weathering is an important source of solutes. Overall, the results of this work illustrate the variability in stream chemistry across the Gulf of Alaska, and changing climate regimes will alter the fluxes of solutes and nutrients in the future.