Traumatic brain injury (TBI) can induce dysregulation of sleep. Sleep disturbances include hypersomnia and hyposomnia, sleep fragmentation, difficulty falling asleep, and altered ...electroencephalograms. TBI results in inflammation and altered hemodynamics, such as changes in blood brain barrier permeability and cerebral blood flow. Both inflammation and altered hemodynamics, which are known sleep regulators, contribute to sleep impairments post-TBI. TBIs are heterogenous in cause and biomechanics, which leads to different molecular and symptomatic outcomes. Animal models of TBI have been developed to model the heterogeneity of TBIs observed in the clinic. This review discusses the intricate relationship between sleep, inflammation, and hemodynamics in pre-clinical rodent models of TBI.
Following large‐scale surface oil sands mining, large tracts of the boreal forest in the Athabasca Oil Sands Region of Western Canada are legally required to be reclaimed. A greater understanding of ...how these novel ecosystems function and develop with regard to water use is crucial to aid in the development of regulatory practices and protocols based on information from ecosystem recovery. In this paper, a 12‐year (2003–2014) eddy covariance measurement record of latent and sensible heat fluxes and gross ecosystem productivity of carbon dioxide is analysed to evaluate how a reclaimed boreal forest has developed during its initial growth period. The study site is a reclaimed oil sands saline‐sodic clay shale overburden deposit that was topped with 100 cm of glacial till and 20 cm of peat mineral mix. The site was seeded with barley (Hordeum spp.) in 2001 to reduce erosion of the soil cover whereas aspen (Populus tremuloides Michx.) and spruce (Picea glauca Moench Voss) boreal tree species were planted in 2004. Changes in structure and function corresponded to the transition of dominant vegetation cover from early successional species to forest. Leaf area index increased from a growing season peak of 0.9 in 2003 to 4.0 in 2014 and was associated with an increased growing season gross ecosystem productivity (4.9 to 8.9 g C m−2 day−1), an increased evapotranspiration (1.6 to 3.4 mm day−1), and a decreased partitioning of energy to sensible heat (Bowen's ratio decreased from 1.1 to 0.4). Although canopy conductance increased throughout the 12 years, the shift from early successional species to trees with more conservative water use resulted in a decrease in conductance normalized by leaf area. Water use efficiency has increased slightly since 2008 with an average of 10.0 g CO2 kg−1 H2O for the last 6 years. No prolonged dry periods were observed during the study period. The functioning of this novel ecosystem is evolving as expected on the basis of the trends observed for other natural and disturbed boreal forests.
The higher midlatitudes of the northern hemisphere are particularly sensitive to change due to the important role the 0°C isotherm plays in the phase of precipitation and intermediate storage as ...snow. An international intercatchment comparison program called North‐Watch seeks to improve our understanding of the sensitivity of northern catchments to change by examining their hydrological and biogeochemical variability and response. Here eight North‐Watch catchments located in Sweden (Krycklan), Scotland (Girnock and Strontian), the United States (Sleepers River, Hubbard Brook, and HJ Andrews), and Canada (Dorset and Wolf Creek) with 10 continuous years of daily precipitation and runoff data were selected to assess daily to seasonal coupling of precipitation (P) and runoff (Q) using wavelet coherency, and to explore the patterns and scales of variability in streamflow using color maps. Wavelet coherency revealed that P and Q were decoupled in catchments with cold winters, yet were strongly coupled during and immediately following the spring snowmelt freshet. In all catchments, coupling at shorter time scales occurred during wet periods when the catchment was responsive and storage deficits were small. At longer time scales, coupling reflected coherence between seasonal cycles, being enhanced at sites with enhanced seasonality in P. Color maps were applied as an alternative method to identify patterns and scales of flow variability. Seasonal versus transient flow variability was identified along with the persistence of that variability on influencing the flow regime. While exploratory in nature, this intercomparison exercise highlights the importance of climate and the 0°C isotherm on the functioning of northern catchments.
Key Points
Color maps are a unique and novel way to visualize flow patterns and variability
Wavelet coherence identifies times and periods of precipitation-runoff coupling
The zero-degree mark is a critical factor that controls catchment function
A 58 ha mixed upland and lowland boreal plains
watershed called the Sandhill Fen Watershed was constructed between 2008 and
2012. In the years following wetting in 2013, methane emissions were
...measured using manual chambers. The presence of vegetation with aerenchymous
tissues and saturated soils were important factors influencing the spatial
variability of methane emissions across the constructed watershed.
Nevertheless, median methane emissions were equal to or less than 0.51 mg CH4 m−2 h−1 even from the saturated organic soils in the
lowlands. Although overall methane emissions remained low, observations of
methane ebullition increased over the 3 study years. Ebullition events
occurred in 10 % of measurements in 2013, increasing to 21 % and 27 % of measurements in 2014 and 2015, respectively, at the plots with
saturated soils. Increasing metal ion availability and decreasing sulfur
availability was measured using buried ion exchange resins at both seasonal
and annual timescales potentially as a result of microbial reduction of
these ions. Using principle component analysis, methane fluxes had a
significant positive correlation to the leading principle component which
was associated with increasing ammonium, iron, and manganese and decreasing
sulfur availability (r=0.31, p<0.001). These results suggest
that an abundance of alternative inorganic electron acceptors may be
limiting methanogenesis at this time.
Permafrost strongly controls hydrological processes in cold regions. Our
understanding of how changes in seasonal and perennial frozen ground
disposition and linked storage dynamics affect runoff ...generation processes
remains limited. Storage dynamics and water redistribution are influenced by
the seasonal variability and spatial heterogeneity of frozen ground, snow
accumulation and melt. Stable isotopes are potentially useful for quantifying the
dynamics of water sources, flow paths and ages, yet few studies have employed
isotope data in permafrost-influenced catchments. Here, we applied the
conceptual model STARR (the Spatially distributed Tracer-Aided Rainfall–Runoff model), which facilitates fully distributed simulations of hydrological
storage dynamics and runoff processes, isotopic composition and water ages.
We adapted this model for a subarctic catchment in Yukon Territory, Canada,
with a time-variable implementation of field capacity to include the
influence of thaw dynamics. A multi-criteria calibration based on stream
flow, snow water equivalent and isotopes was applied to 3 years of data.
The integration of isotope data in the spatially distributed model provided
the basis for quantifying spatio-temporal dynamics of water storage and ages,
emphasizing the importance of thaw layer dynamics in mixing and damping the
melt signal. By using the model conceptualization of spatially and temporally
variable storage, this study demonstrates the ability of tracer-aided
modelling to capture thaw layer dynamics that cause mixing and damping of the
isotopic melt signal.
Abstract
As a consequence of increasing temperatures, a rapid increase in shrub vegetation has occurred throughout the circumpolar North and is expected to continue. Rates of shrub expansion are ...highly variable, both at the regional scale and within local study areas. This study uses repeat airborne LiDAR and field surveys to measure changes in shrub vegetation cover along with landscape-scale variations in a well-studied subarctic headwater catchment in Yukon Territory, Canada. Airborne LiDAR surveys were conducted in August 2007 and 2018, whereas vegetation surveys were conducted in summer 2019. Machine learning classification algorithms were used to predict shrub presence/absence in 2018 based on rasterized LiDAR metrics, with the best-performing model applied to the 2007 LiDAR to create binary shrub cover layers to compare between survey years. Results show a 63.3% total increase in detectable shrub cover >= 0.45 m in height between 2007 and 2018, with an average yearly expansion of 5.8%. These changes were compared across terrain derivatives to quantify the influence of topography on shrub expansion. Terrain comparisons show that shrubs are located in and are preferentially expanding into lower and flatter areas near stream networks, at lower slope positions and with a higher potential for topographic wetness. Overall, the findings from this research reinforce the documented increase in pan-Arctic shrub vegetation in recent years, quantify the variation in shrub expansion over terrain derivatives at the landscape scale, and demonstrate the feasibility of using LiDAR to compare changes in shrub properties over time.
Temperature can be used to trace groundwater flows due to thermal disturbances of subsurface advection. Prior hydrogeological studies that have used temperature‐depth profiles to estimate vertical ...groundwater fluxes have either ignored the influence of climate change by employing steady‐state analytical solutions or applied transient techniques to study temperature‐depth profiles recorded at only a single point in time. Transient analyses of a single profile are predicated on the accurate determination of an unknown profile at some time in the past to form the initial condition. In this study, we use both analytical solutions and a numerical model to demonstrate that boreholes with temperature‐depth profiles recorded at multiple times can be analyzed to either overcome the uncertainty associated with estimating unknown initial conditions or to form an additional check for the profile fitting. We further illustrate that the common approach of assuming a linear initial temperature‐depth profile can result in significant errors for groundwater flux estimates. Profiles obtained from a borehole in the Veluwe area, Netherlands in both 1978 and 2016 are analyzed for an illustrative example. Since many temperature‐depth profiles were collected in the late 1970s and 1980s, these previously profiled boreholes represent a significant and underexploited opportunity to obtain repeat measurements that can be used for similar analyses at other sites around the world.
Key Points
Repeated temperature‐depth profiles provide an excellent opportunity to study the transience of subsurface heat flow processes
The classic approach to infer ground water flow from temperature‐depth profiles disturbed by surface warming has serious shortcomings
Novel analytical approaches provide good estimates of groundwater flow when used on repeated temperature‐depth profiles
Progress in permafrost hydrology in the new millennium Woo, Ming-Ko; Kane, Douglas L.; Carey, Sean K. ...
Permafrost and periglacial processes,
April/June 2008, Letnik:
19, Številka:
2
Journal Article, Conference Proceeding
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