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

Hydrogeological controls on spatial patterns of groundwater discharge in peatlands

Peatland environments provide important ecosystem services including water and carbon storage, nutrient processing and retention, and wildlife habitat. However, these systems and the services they provide have been degraded through historical anthropogenic agricultural conversion and dewatering practices. Effective wetland restoration requires incorporating site hydrology and understanding groundwater discharge spatial patterns. Groundwater discharge maintains wetland ecosystems by providing relatively stable hydrologic conditions, nutrient inputs, and thermal buffering important for ecological structure and function; however, a comprehensive site-specific evaluation is rarely feasible for such resource-constrained projects. An improved process-based understanding of groundwater discharge in peatlands may help guide ecological restoration design without the need for invasive methodologies and detailed site-specific investigation. Here we examine a kettle-hole peatland in southeast Massachusetts historically modified for commercial cranberry farming. During the time of our investigation, a large process-based ecological restoration project was in the assessment and design phases. To gain insight into the drivers of site hydrology, we evaluated the spatial patterning of groundwater discharge and the subsurface structure of the peatland complex using heat-tracing methods and ground-penetrating radar. Our results illustrate that two groundwater discharge processes contribute to the peatland hydrologic system: diffuse lower-flux marginal matrix seepage and discrete higher-flux preferential-flow-path seepage. Both types of groundwater discharge develop through interactions with subsurface peatland basin structure, often where the basin slope is at a high angle to the regional groundwater gradient. These field observations indicate strong correlation between subsurface structures and surficial groundwater discharge. Understanding these general patterns may allow resource managers to more efficiently predict and locate groundwater seepage, confirm these using remote sensing technologies, and incorporate this information into restoration design for these critical ecosystems

Lithium Storage and Release From Lacustrine Sediments: Implications for Lithium Enrichment and Sustainability in Continental Brines

Abstract Despite current and projected future reliance on lithium (Li) as a resource, deficiencies remain in genesis models of closed‐basin Li brines. Subsurface geochemical interactions between water and bulk solid phases from lacustrine sediments, are shown here to be the most important process for brine genesis and sustainability of the Clayton Valley, NV brine deposit. A new subsurface basin model was developed and used to select Li‐bearing solids to test the release mechanisms for Li. Ash (20–350 ppm Li) and bulk sediments (1,000–1,700 ppm Li) samples across depths in the basin represent the majority of the subsurface Li‐bearing materials. Temperature dependent (25°C–95°C) batch reaction experiments using low‐salinity groundwater from the basin indicate a positive relationship between the amount of Li released and temperature. Four‐step sequential extractions on a subset of bulk sediments indicate most Li is released from water and weak acid‐soluble portions with approximately 30% of the total Li contained in the sediments released overall. We conceptualize that Li is released from these samples via three mechanisms: (a) release of adsorbed Li; (b) cation exchange of Li and Mg and; (c) possible minor release from the silicate structure at elevated temperatures. Based on these results and the abundance of Li‐bearing sediments in the subsurface we estimate the mean Li mass in the basin materials to be between 24.4 and 58.0 Mt which provides a continuous supply from water‐rock interactions. This is now the largest known accumulation of Li in a basin‐fill continental setting on a global scale

Summary of hydrophysical data and results used in this work.

Summary of hydrophysical data and results used in this work.</p

Surface and groundwaters in the Dry Andes analyzed for ³H, δ¹⁸O, and δ²H in this study (n = 142).

Pie charts represent the percent modern content, colored outlines show general water type groupings, and colored dots show sample sites by their physical water type. The black crosses are precipitation sample sites. Black outlines show internally drained basins, blue solid lines are perennial streams, and blue dashed lines are intermittent streams. Important features (salars, mountains, rivers) are noted along with their elevations. (a) Map of the Salar de Atacama basin and the northern Puna region to the east, where pie charts represent the average content of inflow zones and surface waters to display all data (see Moran et al., 2022). (b) Map of the southern Puna where each pie chart represents one sample. (c) A schematic cross-section of salar-basin floor hydrogeological systems describing the physical water classifications. The basemap for (a) and (b) is World Imagery (ESRI), and the locator map is the National Geographic Style Map with country borders; they can be accessed here: https://doc.arcgis.com/en/data-appliance/2022/maps/world-imagery.htm, and https://www.arcgis.com/home/item.html?id=f33a34de3a294590ab48f246e99958c9, respectively.</p