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Glacial meltwater contributions to streams depend on watershed characteristics that impact water quantity and quality, with potential changes as glaciers continue to recede. The purpose of our study was to investigate the influence of glacier and bedrock controls on water chemistry in glacial streams, focusing on a range of small to large watersheds in Alaska. Southcentral Alaska provides an ideal study area due to diverse geologic characteristics and varying amounts of glacial coverage across watersheds. To investigate spatial and temporal variability due to glacial coverage and bedrock type, we analyzed water samples (n= 343) from seven watersheds over 2 years for major and trace element concentrations and water stable isotopes. We found variable water chemistry across the glacial rivers related to glacial coverage and the relative amount of metamorphic, sedimentary, and igneous bedrock. Some sites had elevated concentrations of harmful trace elements like As and U from glacier melt or groundwater. Longitudinal (upstream to downstream) variability was apparent within each river, with increasing inputs from tributaries, and groundwater altering the water chemistry relative to glacier meltwater contributions. The water chemistry and isotopic composition of river samples compared with endmember sources suggested a range from glacier-dominated to groundwater-dominated sites along stream transects. For example, water chemistry in the Knik and Matanuska rivers (with large contributing glaciers) was more influenced by glacier meltwater, while water chemistry in the Little Susitna River (with small glaciers) was more influenced by groundwater. Across all rivers, stream chemistry was controlled by glacier inputs near the headwaters and groundwater inputs downstream, with the water chemistry reflecting bedrock type. Our study provides a greater understanding of geochemical and hydrological processes controlling water resources in rapidly changing glacial watersheds. 

Abstract The glacial meltwater streams in the McMurdo Dry Valleys (MDVs), Antarctica only flow during the austral summer and contain abundant algal mats which grow at the onset of flow. Their relative abundance in stream channels of this polar desert make the streams biogeochemical hot spots. The MDVs receive minimal precipitation as snow, which is redistributed by wind and deposited in distinct locations, some of which become persistent snow patches each year. Previous studies identified that MDV streamflow comes from a combination of glacier ice and snow, although snow was assumed to contribute little to the overall water budget. This study uses a combination of satellite imagery, terrain analysis, and field measurements to determine where snow patches accumulate and persist across MDV watersheds, and to quantify the potential hydrologic and biogeochemical contributions of snow patches to streams. Watersheds near the coast have the highest snow‐covered area and longest snow persistence. Many of these snow patches accumulate within the stream channels, which results in the potential to contribute to streamflow. During the summer of 2021–2022, stream channel snow patches had the potential to contribute anywhere between <1% and 90% of the total annual discharge in Lake Fryxell Basin streams, and may increase with different hydrometeorological conditions. On average the potential inputs from snow patches to streamflow was between 12% and 25% of the annual discharge during the 2021–2022 season, as determined by snow area and SWE. Snow patches in the majority of the watersheds had higher nitrogen and phosphorous concentrations than stream water, and six streams contained snow with higher N:P ratios than the average N:P in the stream water. This suggests that if such patches melt early in the summer, these nutrient and water inputs could occur at the right time and stoichiometry to be crucial for early season algal mat growth. 

Abstract. The McMurdo Dry Valleys (MDVs) of Antarctica are a polar desertecosystem consisting of alpine glaciers, ice-covered lakes, streams, andexpanses of vegetation-free rocky soil. Because average summer temperaturesare close to 0 ∘C, theMDV ecosystem in general, and glacier melt dynamics in particular, are both closely linked to the energy balance. A slightincrease in incoming radiation or change in albedo can have large effects onthe timing and volume of meltwater. However, the seasonal evolution orspatial variability of albedo in the valleys has yet to fully characterized.In this study, we aim to understand the drivers of landscape albedo changewithin and across seasons. To do so, a box with a camera, GPS, andshortwave radiometer was hung from a helicopter that flew transects four to fivetimes a season along Taylor Valley. Measurements were repeated over threeseasons. These data were coupled with incoming radiation measured at sixmeteorological stations distributed along the valley to calculate thedistribution of albedo across individual glaciers, lakes, and soilsurfaces. We hypothesized that albedo would decrease throughout the australsummer with ablation of snow patches and increasing sediment exposure on theglacier and lake surfaces. However, small snow events (<6 mm waterequivalent) coupled with ice whitening caused spatial and temporalvariability of albedo across the entire landscape. Glaciers frequentlyfollowed a pattern of increasing albedo with increasing elevation, as well asincreasing albedo moving from east to west laterally across the ablationzone. We suggest that spatial patterns of albedo are a function of landscapemorphology trapping snow and sediment, longitudinal gradients in snowfallmagnitude, and wind-driven snow redistribution from east to west alongthe valley. We also compare our albedo measurements to the MODIS albedo productand found that overall the data have reasonable agreement. The mismatch inspatial scale between these two datasets results in variability, which isreduced after a snow event due to albedo following valley-scale gradients ofsnowfall magnitude. These findings highlight the importance of understandingthe spatial and temporal variability in albedo and the close coupling ofclimate and landscape response. This new understanding of landscape albedocan constrain landscape energy budgets, better predict meltwater generationon from MDV glaciers, and how these ecosystems will respond to changingclimate at the landscape scale. 

Abstract Glaciers of the McMurdo dry valleys (MDVs) Antarctica are the main source of streamflow in this polar desert. Because summer air temperatures hover near 0°C small changes in the energy balance strongly affect meltwater generation. Here we demonstrate that increased surface roughness, which alters the turbulent transfer of energy between the ice surface and atmosphere, yields a detectable increase in meltwater runoff. At low elevations on the glaciers, basin‐like topography became significantly rougher over 13 years between repeat lidar surveys, yielding greater melt. In contrast, the smoother ice at higher elevation exhibited no detectable change in roughness. We pose a conceptual model of the cycle of glacier surface change as a result of climate forcing whereby glacier surfaces transition from being dominated by sublimation to becoming increasingly melt‐dominated, which is reversible under prolonged cool periods. This research advances our understanding of warm season effects on polar glaciers. 

Abstract As glaciers around the world rapidly lose mass, the tight coupling between glaciers and downstream ecosystems is resulting in widespread impacts on global hydrologic and biogeochemical cycling. However, a range of challenges make it difficult to conduct research in glacierized systems, and our knowledge of seasonally changing hydrologic processes and solute sources and signatures is limited. This in turn hampers our ability to make predictions on solute composition and flux. We conducted a broad water sampling campaign in order to understand the present‐day partitioning of water sources and associated solutes in Alaska's Wolverine Glacier watershed. We established a relationship between electrical conductivity and streamflow at the watershed outlet to divide the melt season into four hydroclimatic periods. Across hydroclimatic periods, we observed a shift in nonglacial source waters from snowmelt‐dominated overland and shallow subsurface flow paths to deeper groundwater flow paths. We also observed the shift from a low‐ to high‐efficiency subglacial drainage network and the associated flushing of water stored subglacially with higher solute loads. We used calcium, the dominant dissolved ion, from watershed outlet samples to estimate solute fluxes for each hydroclimatic period across two melt seasons. We found between 40% and 55% of Ca²⁺export occurred during the late season rainy period. This partitioning of the melt season coupled with a characterization of the chemical makeup and magnitude of solute export provides new insight into a rapidly changing watershed and creates a framework to quantify and predict changes to solute fluxes across a melt season.