Permafrost is a defining characteristic of the Arctic environment. However, climate warming is thawing permafrost in many areas leading to failures in soil structure called thermokarst. An extensive survey of a 600 km2 area in and around the Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds of which were new since ∼1980 when a high resolution aerial survey of the area was done. Most of these thermokarst features were associated with headwater streams or lakes. We have measured significantly increased sediment and nutrient loading from thermokarst features to streams in two well‐studied locations near the TLNRA. One small thermokarst gully that formed in 2003 on the Toolik River in a 0.9 km2 subcatchment delivered more sediment to the river than is normally delivered in 18 years from 132 km2 in the adjacent upper Kuparuk River basin (a long‐term monitoring reference site). Ammonium, nitrate, and phosphate concentrations downstream from a thermokarst feature on Imnavait Creek increased significantly compared to upstream reference concentrations and the increased concentrations persisted over the period of sampling (1999–2005). The downstream concentrations were similar to those we have used in a long‐term experimental manipulation of the Kuparuk River and that have significantly altered the structure and function of that river. A subsampling of other thermokarst features from the extensive regional survey showed that concentrations of ammonium, nitrate, and phosphate were always higher downstream of the thermokarst features. Our previous research has shown that even minor increases in nutrient loading stimulate primary and secondary production. However, increased sediment loading could interfere with benthic communities and change the responses to increased nutrient delivery. Although the terrestrial area impacted by thermokarsts is limited, the aquatic habitat altered by these failures can be extensive. If warming in the Arctic foothills accelerates thermokarst formation, there may be substantial and wide‐spread impacts on arctic stream ecosystems that are currently poorly understood.

Abstract:Lateral downslope flow in snow during snowmelt and rain-on-snow (ROS) events is a well-known phenomenon, yet its relevance to water redistribution at hillslope and catchment scales is not well understood. We used dye tracers, geophysical methods, and hydrometric measurements to describe the snow properties that promote lateral flow, assess the relative velocities of lateral flow in snow and soil, and estimate volumes of downslope flow. Results demonstrate that rain and melt water can travel tens of metres downslope along layers within the snowpack or at the snowpack base within tens of hours. Lateral flow within the snowpack becomes less likely as the snowpack becomes saturated and stratigraphic boundaries are destroyed. Flow along the base can be prevalent in all snowpack conditions. The net result of lateral flow in snow can be the deposition of water on the soil surface in advanced downslope positions relative to its point of origin, or direct discharge to a stream. Although both melt and ROS events can redistribute water to downslope positions, ROS events produced the most significant volumes of downslope flow. Direct stream contributions through the snowpack during one ROS event produced up to 12% of streamflow during the event. This can help explain rapid delivery of water to streams during ROS events, as well as anomalously high contributions of event water during snowmelt hydrographs. In catchments with a persistent snowpack, lateral redistribution of water within the snowpack should be considered a relevant moisture redistribution mechanism.

[1] Transient storage of solutes in hyporheic zones or other slow-moving stream waters plays an important role in the biogeochemical processes of streams. While numerous studies have reported a wide range of parameter values from simulations of transient storage, little field work has been done to investigate the correlations between these parameters and shifts in surface and subsurface flow conditions. In this investigation we use the stream properties of the Arctic (namely, highly varied discharges, channel morphologies, and subchannel permafrost conditions) to isolate the effects of discharge, channel morphology, and potential size of the hyporheic zone on transient storage. We repeated stream tracer experiments in five morphologically diverse tundra streams in Arctic Alaska during the thaw season (May-August) of 2004 to assess transient storage and hydrologic characteristics. We compared transient storage model parameters to discharge (Q), the Darcy-Weisbach friction factor ( f ), and unit stream power (w). Across all studied streams, permafrost active layer depths (i.e., the potential extent of the hyporheic zone) increased throughout the thaw season, and discharges and velocities varied dramatically with minimum ranges of eight-fold and four-fold, respectively. In all reaches the mean storage residence time (t stor ) decreased exponentially with increasing Q, but did not clearly relate to permafrost active layer depths. Furthermore, we found that modeled transient storage metrics (i.e., t stor , storage zone exchange rate (a OTIS ), and hydraulic retention (R h )) correlated better with channel hydraulic descriptors such as f and w than they did with Q or channel slope. Our results indicate that Q is the first-order control on transient storage dynamics of these streams, and that f and w are two relatively simple measures of channel hydraulics that may be important metrics for predicting the response of transient storage to perturbations in discharge and morphology in a given stream.Citation: Zarnetske, J. P., M. N. Gooseff, T. R. Brosten, J. H. Bradford, J. P. McNamara, and W. B. Bowden (2007), Transient storage as a function of geomorphology, discharge, and permafrost active layer conditions in Arctic tundra streams, Water Resour. Res., 43, W07410,

[1] Monitoring the snow water equivalent (SWE) is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage. There are currently no methods to remotely sense SWE with accuracy over large lateral distances in the steep and often forested terrain of mountain basins. Previous studies have shown that measurements of ground-penetrating radar (GPR) velocity can provide accurate estimates of SWE in dry snow. Introduction of liquid water into the snowpack results in a three-phase system that cannot be accurately characterized with GPR velocity alone. We show that measuring the frequency-dependent GPR signal attenuation and velocity provides a direct estimate of the complex dielectric permittivity. Because the imaginary component is a function only of liquid water content, we can utilize both the real and imaginary components of the permittivity to estimate liquid water content, snow density, and SWE using existing empirical relationships that are valid in the pendular regime. We tested this new method at two field sites and found that the estimates were accurate to within 12% of gravimetric methods in both a moist and a dry snowpack. GPR has the potential to provide SWE estimates across large lateral distances over a broad range of snow conditions.

ABSTRACT. We conducted two-dimensional continuous multi-offset georadar surveys on Bench Glacier, south-central Alaska, USA, to measure the distribution of englacial water. We acquired data with a multichannel 25 MHz radar system using transmitter-receiver offsets ranging from 5 to 150 m. We towed the radar system at 5-10 km h -1 with a snow machine with transmitter/receiver positions established by geodetic-grade kinematic differentially corrected GPS (nominal 0.5 m trace spacing). For radar velocity analyses, we employed reflection tomography in the pre-stack depth-migrated domain to attain an estimated 2% velocity uncertainty when averaged over three to five wavelengths. We estimated water content from the velocity structure using the complex refractive index method equation and use a three-phase model (ice, water, air) that accounts for compression of air bubbles as a function of depth. Our analysis produced laterally continuous profiles of glacier water content over several kilometers. These profiles show a laterally variable, stratified velocity structure with a low-watercontent ($0-0.5%) shallow layer ($20-30 m) underlain by high-water-content (1-2.5%) ice.