Quantifying changes in thermokarst lake extent is of importance for understanding the permafrost‐related carbon budget, including the potential release of carbon via lake expansion or sequestration ...as peat in drained lake basins. We used high spatial resolution remotely sensed imagery from 1950/51, 1978, and 2006/07 to quantify changes in thermokarst lakes for a 700 km2 area on the northern Seward Peninsula, Alaska. The number of water bodies larger than 0.1 ha increased over the entire observation period (666 to 737 or +10.7%); however, total surface area decreased (5,066 ha to 4,312 ha or −14.9%). This pattern can largely be explained by the formation of remnant ponds following partial drainage of larger water bodies. Thus, analysis of large lakes (>40 ha) shows a decrease of 24% and 26% in number and area, respectively, differing from lake changes reported from other continuous permafrost regions. Thermokarst lake expansion rates did not change substantially between 1950/51 and 1978 (0.35 m/yr) and 1978 and 2006/07 (0.39 m/yr). However, most lakes that drained did expand as a result of surface permafrost degradation before lateral drainage. Drainage rates over the observation period were stable (2.2 to 2.3 per year). Thus, analysis of decadal‐scale, high spatial resolution imagery has shown that lake drainage in this region is triggered by lateral breaching and not subterranean infiltration. Future research should be directed toward better understanding thermokarst lake dynamics at high spatial and temporal resolution as these systems have implications for landscape‐scale hydrology and carbon budgets in thermokarst lake‐rich regions in the circum‐Arctic.
Key Points
Landscape scale assessment of thermokarst lake expansion and drainage rates
Widespread drainage of thermokarst lakes in the continuous permafrost zone
Thermokarst lake dynamics impact the northern high latitude carbon cycle
Analysis of a 60 km segment of the Alaskan Beaufort Sea coast using a time‐series of aerial photography revealed that mean annual erosion rates increased from 6.8 m a−1 (1955 to 1979), to 8.7 m a−1 ...(1979 to 2002), to 13.6 m a−1 (2002 to 2007). We also observed that spatial patterns of erosion have become more uniform across shoreline types with different degrees of ice‐richness. Further, during the remainder of the 2007 ice‐free season 25 m of erosion occurred locally, in the absence of a westerly storm event. Concurrent arctic changes potentially responsible for this shift in the rate and pattern of land loss include declining sea ice extent, increasing summertime sea surface temperature, rising sea‐level, and increases in storm power and corresponding wave action. Taken together, these factors may be leading to a new regime of ocean‐land interactions that are repositioning and reshaping the Arctic coastline.
The balance of thermokarst lakes with bedfast‐ and floating‐ice regimes across Arctic lowlands regulates heat storage, permafrost thaw, winter‐water supply, and over‐wintering aquatic habitat. Using ...a time‐series of late‐winter synthetic aperture radar (SAR) imagery to distinguish lake ice regimes in two regions of the Arctic Coastal Plain of northern Alaska from 2003–2011, we found that 18% of the lakes had intermittent ice regimes, varying between bedfast‐ice and floating‐ice conditions. Comparing this dataset with a radar‐based lake classification from 1980 showed that 16% of the bedfast‐ice lakes had shifted to floating‐ice regimes. A simulated lake ice thinning trend of 1.5 cm/yr since 1978 is believed to be the primary factor driving this form of lake change. The most profound impacts of this regime shift in Arctic lakes may be an increase in the landscape‐scale thermal offset created by additional lake heat storage and its role in talik development in otherwise continuous permafrost as well as increases in over‐winter aquatic habitat and winter‐water supply.
Key Points
Thermokarst lake ice regimes vary with ice thickness and water balance
Thinning ice trend explains a shift from bedfast‐ to floating‐ice lakes
Floating‐ice lakes enhance heat storage, permafrost thaw, and winter habitat
Snowmelt‐dominated runoff regimes have defined northern Alaskan rivers. Discharge records from three watersheds within the National Petroleum Reserve in Alaska (NPR‐A) span 19 years and capture three ...notable periods of changing runoff. In the first, 2001–2008, mean annual runoff (MAR) averaged 90 mm, characterized by sharp snowmelt runoff and summer drought. Over the next 7 years, larger MAR averaged 120 mm driven by high and early snowmelt runoff. The most recent 4 years, 2016–2019, had even higher MAR of 163 mm with high and sustained late summer flows. Hydrograph analysis suggests a shift toward rainfall‐dominated runoff in the most recent period compared to snowmelt‐dominated hydrographs in the previous two. Declining sea ice appears closely linked to increasing late summer precipitation and a shift toward rainfall runoff. Future development in the NPR‐A will require continued hydrological monitoring and planning to mitigate flood and erosion hazards, permafrost degradation, and ecosystem impairment.
Plain Language Summary
Water is expected to cycle more rapidly as the Arctic climate warms, yet it is uncertain whether conditions will get wetter or dryer. Watershed runoff, measured in the form of river flow, captures the balance of precipitation and evaporation over wide land areas to detect how the water cycle is changing. Historically, arctic river flows are supplied mainly by spring snowmelt and become quite low during summers with limited rainfall. River flow records from three watersheds in northern Alaska over the last 19 years provide evidence that total water inputs from snow and rain are increasing relative to water losses from evaporation. Most recently, contributions from rainfall have increased greatly, and this may be related to enhanced moisture supply from more ice‐free conditions of the Arctic Ocean. Higher river flows that come later in the summer may affect erosion and sedimentation, frozen soils, fish habitat, and human infrastructure.
Key Points
Arctic Coastal Plain watershed runoff regimes are traditionally snowmelt‐dominated
Discharge records show increasing annual runoff over the past 19 years and much higher rainfall runoff contributions over the last 4 years
Increasing ice‐free ocean conditions correspond to higher rainfall runoff, yet attribution of hydrologic responses remain uncertain
Multi-center, prospective, cohort study.
To assess the validity and reliability of the Spinal Cord Independence Measure (SCIM III) in measuring functional ability in persons with spinal cord injury ...(SCI).
Inpatient rehabilitation hospitals in the United States (US).
Functional ability was measured with the SCIM III during the first week of admittance into inpatient acute rehabilitation and within one week of discharge from the same rehabilitation program. Motor and sensory neurologic impairment was measured with the American Spinal Injury Association Impairment Scale. The Functional Independence Measure (FIM), the default functional measure currently used in most US hospitals, was used as a comparison standard for the SCIM III. Statistical analyses were used to test the validity and reliability of the SCIM III.
Total agreement between raters was above 70% on most SCIM III tasks and all κ-coefficients were statistically significant (P<0.001). The coefficients of Pearson correlation between the paired raters were above 0.81 and intraclass correlation coefficients were above 0.81. Cronbach's-α was above 0.7, with the exception of the respiration task. The coefficient of Pearson correlation between the FIM and SCIM III was 0.8 (P<0.001). For the respiration and sphincter management subscale, the SCIM III was more responsive to change, than the FIM (P<0.0001).
Overall, the SCIM III is a reliable and valid measure of functional change in SCI. However, improved scoring instructions and a few modifications to the scoring categories may reduce variability between raters and enhance clinical utility.
Beaded streams are widespread in permafrost regions and are considered a common thermokarst landform. However, little is known about their distribution, how and under what conditions they form, and ...how their intriguing morphology translates to ecosystem functions and habitat. Here we report on a circum-Arctic survey of beaded streams and a watershed-scale analysis in northern Alaska using remote sensing and field studies. We mapped over 400 channel networks with beaded morphology throughout the continuous permafrost zone of northern Alaska, Canada, and Russia and found the highest abundance associated with medium to high ground-ice content permafrost in moderately sloping terrain. In one Arctic coastal plain watershed, beaded streams accounted for half of the drainage density, occurring primarily as low-order channels initiating from lakes and drained lake basins. Beaded streams predictably transition to alluvial channels with increasing drainage area and decreasing channel slope, although this transition is modified by local controls on water and sediment delivery. The comparisons of one beaded channel using repeat photography between 1948 and 2013 indicate a relatively stable landform, and 14C dating of basal sediments suggest channel formation may be as early as the Pleistocene–Holocene transition. Contemporary processes, such as deep snow accumulation in riparian zones, effectively insulate channel ice and allows for perennial liquid water below most beaded stream pools. Because of this, mean annual temperatures in pool beds are greater than 2 °C, leading to the development of perennial thaw bulbs or taliks underlying these thermokarst features that range from 0.7 to 1.6 m. In the summer, some pools thermally stratify, which reduces permafrost thaw and maintains cold-water habitats. Snowmelt-generated peak flows decrease rapidly by two or more orders of magnitude to summer low flows with slow reach-scale velocity distributions ranging from 0.01 to 0.1 m s−1, yet channel runs still move water rapidly between pools. The repeating spatial pattern associated with beaded stream morphology and hydrological dynamics may provide abundant and optimal foraging habitat for fish. Beaded streams may create important ecosystem functions and habitat in many permafrost landscapes and their distribution and dynamics are only beginning to be recognized in Arctic research.
Modeling studies examining the effect of lakes on regional and global climate, as well as studies on the influence of climate variability and change on aquatic ecosystems, are surveyed. Fully coupled ...atmosphere—land surface—lake climate models that could be used for both of these types of study simultaneously do not presently exist, though there are many applications that would benefit from such models. It is argued here that current understanding of physical and biogeochemical processes in freshwater systems is sufficient to begin to construct such models, and a path forward is proposed. The largest impediment to fully representing lakes in the climate system lies in the handling of lakes that are too small to be explicitly resolved by the climate model, and that make up the majority of the lake-covered area at the resolutions currently used by global and regional climate models. Ongoing development within the hydrological sciences community and continual improvements in model resolution should help ameliorate this issue.
Watersheds draining the Arctic Coastal Plain (ACP) of Alaska are dominated by permafrost and snowmelt runoff that create abundant surface storage in the form of lakes, wetlands, and beaded streams. ...These surface water elements compose complex drainage networks that affect aquatic ecosystem connectivity and hydrologic behavior. The 4676 km2 Fish Creek drainage basin is composed of three watersheds that represent a gradient of the ACP landscape with varying extents of eolian, lacustrine, and fluvial landforms. In each watershed, we analyzed 2.5-m-resolution aerial photography, a 5-m digital elevation model, and river gauging and climate records to better understand ACP watershed structure and processes. We show that connected lakes accounted for 19 to 26% of drainage density among watersheds and most all channels initiate from lake basins in the form of beaded streams. Of the > 2500 lakes in these watersheds, 33% have perennial streamflow connectivity, and these represent 66% of total lake area extent. Deeper lakes with over-wintering habitat were more abundant in the watershed with eolian sand deposits, while the watershed with marine silt deposits contained a greater extent of beaded streams and shallow thermokarst lakes that provide essential summer feeding habitat. Comparison of flow regimes among watersheds showed that higher lake extent and lower drained lake-basin extent corresponded with lower snowmelt and higher baseflow runoff. Variation in baseflow runoff among watersheds was most pronounced during drought conditions in 2007 with corresponding reduction in snowmelt peak flows the following year. Comparison with other Arctic watersheds indicates that lake area extent corresponds to slower recession of both snowmelt and baseflow runoff. These analyses help refine our understanding of how Arctic watersheds are structured and function hydrologically, emphasizing the important role of lake basins and suggesting how future lake change may impact hydrologic processes.
Summary
Background
GSK2894512 is a topically delivered investigational drug being developed for treatment of atopic dermatitis and psoriasis.
Objectives
To investigate, in a phase I clinical trial, ...the spatial biodistribution and residency of GSK2894512 within the epidermis and dermis of healthy human participants noninvasively using fluorescence lifetime imaging microscopy (FLIM).
Methods
Two topical drug formulations containing GSK2894512 1% were applied to the right and left forearms of six participants for seven consecutive days, followed by seven days of observation for residency. FLIM images were obtained daily throughout the study, approximately every 24 h. During the treatment phase of the study, images were collected from each participant pretreatment, reflecting the residual dose from the previous day. Three punch biopsies from each participant of one formulation was obtained from the treated region during the post‐treatment follow‐up period between days 8 and 14 for comparison with FLIM results.
Results
Cellular and subcellular features associated with different epidermal and dermal layers were visualized noninvasively, down to a depth of 200 μm. Results yielded three‐dimensional maps of GSK2894512 spatial distribution and residency over time. This fluorescence data provided a marker that was used as a monitor for day‐to‐day variance of drug presence and residency postapplication.
Conclusions
The results suggest FLIM could be a viable alternative to skin biopsies without the usual patient discomfort and limitations, thereby enabling the direct measurement of skin distribution through longitudinal monitoring. These results are the first step in establishing the unique capabilities that multiphoton imaging could provide to patients through noninvasive drug detection.
What's already known about this topic?
Fluorescence lifetime imaging (FLIM) has been used to image noninvasively cellular features in humans.
FLIM has demonstrated the potential to monitor morphological and metabolic changes at the subcellular level that occur in patients with skin cancer and atopic dermatitis.
Its potential for wider utilization in dermal drug discovery or dermatological disease monitoring has seen limited development.
What does this study add?
This is a first‐of‐its‐kind clinical study in which FLIM was used to monitor drug distribution and residency.
It is a first step in establishing the unique capabilities multiphoton imaging could provide to patients via noninvasive drug detection.
More information was generated per patient while reducing patient burden and population size using FLIM.
Imaging end points can be utilized to improve patient outcomes through improved monitoring capabilities.
What is the translational message?
Optical imaging can assess the heterogeneity of pharmacokinetic responses to topical drugs with optical signatures.
Advanced nonlinear optical imaging techniques can provide label‐free contrast in skin, which allows investigation of the efficacy of a topical treatment by monitoring structural/functional changes in skin.
Personalized therapeutic approaches may be possible by visualizing the distribution, residency and clearance of anti‐inflammatory drugs.
Commercial imaging systems facilitate the translation of nonlinear optical imaging techniques into clinical applications.
Linked Comment: Jeong and Evans. Br J Dermatol 2018; 179:1245–1246.
Respond to this article
The formation, growth, and decay of freshwater ice on lakes and
rivers are fundamental processes of northern regions with wide-ranging
implications for socio-ecological systems. Ice thickness at the ...end of
winter is perhaps the best integration of cold-season weather and climate,
while the duration of thick and growing ice cover is a useful indicator for
the winter travel and recreation season. Both maximum ice thickness (MIT)
and ice travel duration (ITD) can be estimated from temperature-driven ice
growth curves fit to ice thickness observations. We simulated and analyzed
ice growth curves based on ice thickness data collected from a range of
observation programs throughout Alaska spanning the past 20–60 years to
understand patterns and trends in lake and river ice. Results suggest
reductions in MIT (thinning) in several northern, interior, and coastal
regions of Alaska and overall greater interannual variability in rivers
compared to lakes. Interior regions generally showed less variability in MIT
and even slightly increasing trends in at least one river site. Average ITD
ranged from 214 d in the northernmost lakes to 114 d across
southernmost lakes, with significant decreases in duration for half of
sites. River ITD showed low regional variability but high interannual
variability, underscoring the challenges with predicting
seasonally consistent river travel. Standardization and analysis of these
ice observation data provide a comprehensive summary for understanding
changes in winter climate and its impact on freshwater ice services.
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