Hydroclimate drives seasonal riverine export across a gradient of glacierized high-latitude coastal catchments

Glacierized coastal catchments of the Gulf of Alaska (GoA) are undergoing rapid hydrologic fluctuations in response to climate change. These catchments deliver dissolved and suspended inorganic and organic matter to nearshore marine environments, however, these glacierized coastal catchments are relatively understudied and little is known about total solute and particulate fluxes to the ocean. We present hydrologic, physical, and geochemical data collected during April–October 2019–2021 from 10 streams along gradients of glacial fed to non-glacial (i.e., precipitation) fed, in one Southcentral and one Southeast Alaska region. Hydrologic data reveal that glaciers drive the seasonal runoff patterns. The ẟ18O signature and specific conductance show distinctive seasonal variations in stream water sources between the study regions apparently due to the large amounts of rain in Southeast Alaska. Total dissolved solids concentrations and yields were elevated in the Southcentral region, due to lithologic influence on dissolved loads, however, the hydroclimate is the primary driver of the timing of dissolved and suspended yields. We show the yields of dissolved organic carbon is higher and that the δ13CPOC is enriched in the Southeast streams illustrating contrasts in organic carbon export across the GoA. Finally, we illustrate how future yields of solutes and sediments to the GoA may change as watersheds evolve from glacial influenced to precipitation dominated. This integrated analysis provides insights into how watershed characteristics beyond glacier coverage control properties of freshwater inputs to the GoA and the importance of expanding study regions to multiple hydroclimate regimes.National Science Foundation. Sloan Indigenous Graduate Partnership Fellowship.Abstract -- Key points -- 1. Introduction -- 2. Study region -- 3. Methods -- 4. Results -- 5. Discussion -- 6. Conclusions -- Acknowledgments -- Conflict of interest -- Open research -- Supporting information -- References.Ye

Pronounced Water Age Partitioning Between Arid Andean Aquifers and Fresh-Saline Lagoon Systems

&amp;lt;p&amp;gt;The challenge of deciphering connections between groundwater systems and surface water bodies and by extension connections to hydroclimate represent major unsolved questions in the hydrology community. Within the UPH framework, under the Interfaces in hydrology theme, this includes aspects of both questions &amp;lt;em&amp;gt;twelve&amp;lt;/em&amp;gt; and &amp;lt;em&amp;gt;thirteen&amp;lt;/em&amp;gt;. In arid regions, disentangling these processes is an especially difficult challenge due to the large spatial and temporal scales over which these systems are integrated. Yet we must improve our understanding if we are to use water sustainably in these landscapes. In the dry Andes, very deep water tables develop groundwater flow paths with long transit times, often crossing topographic boundaries before emerging at basin floors. These factors combined with the complex evaporite stratigraphy in which surface and groundwaters interact make it quite difficult to close water budgets and quantify groundwater fluxes across hydrological boundaries. As a result, many fundamental questions about connections across these interfaces remain unresolved. This study presents a novel examination of processes controlling fluxes across critical boundaries (groundwater recharge, inter-catchment flow, and riparian/stream/aquifer exchange) by employing a comprehensive set of ~150 &amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt;H samples from waters across the entire dry Andes paired with a large dataset (&amp;gt;1,500 samples) of &amp;lt;sup&amp;gt;18&amp;lt;/sup&amp;gt;O, &amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;H in water and dissolved major ions.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We present an integrated process-based conceptual framework describing the dominant controls on water compartment connections intrinsic to these arid mountain systems. The large range in mean transit times and the persistence of hydrologic features here allow for reliable delineation of multiple distinct source and flow path groupings. Repeat sampling over several years provides further constraints on connections between these compartments and the modern hydroclimate. Our results outline a few novel findings regarding the hydrological attributes of these environments: i) most of the water sustaining both the regional and local hydrological systems is old (0-10 % modern and 100-10000 yrs old) yet modern water (days-10 yrs old) is critical to sustaining many surface water bodies. ii) transit time distributions in specific water compartments (Groundwaters, Springs, Streams, Saline lagoons, and Vegas) are remarkably stable over time and show consistent patterns across the entire plateau; iii) the existence of surface water bodies and their connection to groundwater compartments is regulated by persistent hydrological features (regional flow paths, hydrogeology, fresh-saline interfaces); and iv) sharp divergence in mean residence and transit time of source waters occurs over very short spatial scales (&amp;lt;&amp;lt;1km). &amp;amp;#160;By describing water age distributions and geochemical attributes of these features we define the dominant controls on several discrete water compartments and delineate clear distinctions between long-term average source waters and the decoupling of modern hydroclimate from the hydrologic system as a whole. This analysis represents a significant advancement in our understanding of controls on fluxes across boundaries in arid mountainous regions and freshwater-salt lagoon systems. An improved understanding of the primary controls on water source and transport will allow us to better protect communities and fragile ecosystems from the most damaging potential impacts of water extraction in these environments.&amp;lt;/p&amp;gt;</jats:p

Contemporary and relic waters strongly decoupled in arid alpine environments

Deciphering the dominant controls on the connections between groundwater, surface water, and climate is critical to understanding water cycles in arid environments. Yet, persistent uncertainties in the fundamental hydrology of these systems remain. The growing demand for critical minerals such as lithium and associated water demands in the arid environments in which they often occur has amplified the urgency to address these uncertainties. We present an integrated hydrological analysis of the Dry Andes region utilizing a uniquely comprehensive set of tracer data (3H, 18O/2H) for these environments, paired directly with physical hydrological observations. We find two strongly decoupled hydrological systems that interact only under specific hydrogeological conditions where preferential conduits exist. The primary conditions creating these conduits are laterally extensive fine-grained evaporite and/or lacustrine units and perennial flowing streams connected with regional groundwater discharge sites. The efficient capture and transport of modern or “contemporary” water (weeks to years old) within these conduits is the primary control of the interplay between modern hydroclimate variations and groundwater aquifers in these environments. Modern waters account for a small portion of basin budgets but are critical to sustaining surface waters due to the existence of these conduits. As a result, surface waters near basin floors are disproportionally sensitive to short-term climate and anthropogenic perturbations. The framework we present describes a new understanding of the dominant controls on natural water cycles intrinsic to these arid high-elevation systems that will improve our ability to manage critical water resources