bluuebunny/crossref_metadata_2025 huggingface dataset:
Immune Properties of Human Umbilical Cord Wharton's Jelly-Derived Cells
Authors: Weiss Mark L. , Anderson Cameron , Medicetty Satish , Seshareddy Kiran B. , Weiss Rita J. , VanderWerff Irene , Troyer Deryl , McIntosh Kevin R.
Published: August 2008

Cells isolated from Wharton's jelly, referred to as umbilical cord matrix stromal (UCMS) cells, adhere to a tissue-culture plastic substrate, express mesenchymal stromal cell (MSC) surface markers, self-renew, and are multipotent (differentiate into bone, fat, cartilage, etc.) in vitro. These properties support the notion that UCMS cells are a member of the MSC family. Here, the immune properties of UCMS cells are characterized in vitro. The overall hypothesis is that UCMS cells possess immune properties that would be permissive to allogeneic transplantation. For example, UCMS cells will suppress of the proliferation of “stimulated” lymphocytes (immune suppression) and have reduced immunogenicity (e.g., would be poor stimulators of allogeneic lymphocyte proliferation). Hypothesis testing was as follows: first, the effect on proliferation of coculture of mitotically inactivated human UCMS cells with concanavalin-A-stimulated rat splenocytes was assessed in three different assays. Second, the effect of human UCMS cells on one-way and two-way mixed lymphocyte reaction (MLR) assays was determined. Third, the expression of human leukocyte antigen (HLA)-G was examined in human UCMS cells using reverse transcription-polymerase chain reaction, since HLA-G expression conveys immune regulatory properties at the maternal-fetal interface. Fourth, the expression of CD40, CD80, and CD86 was determined by flow cytometry. Fifth, the cytokine expression of UCMS cells was evaluated by focused gene array. The results indicate that human UCMS cells inhibit splenocyte proliferation response to concanavalin A stimulation, that they do not stimulate T-cell proliferation in a one-way MLR, and that they inhibit the proliferation of stimulated T cells in a two-way MLR. Human UCMS cells do not inhibit nonstimulated splenocyte proliferation, suggesting specificity of the response. UCMS cells express mRNA for pan-HLA-G. UCMS cells do not express the costimulatory surface antigens CD40, CD80, and CD86. UCMS cells express vascular endothelial growth factor and interleukin-6, molecules previously implicated in the immune modulation observed in MSCs. In addition, the array data indicate that UCMS cells make a cytokine and other factors that may support hematopoiesis. Together, these results support previous observations made following xenotransplantation; for example, there was no evidence of frank immune rejection of undifferentiated UCMS cells. The results suggest that human UCMS will be tolerated in allogeneic transplantation.

Disclosure of potential conflicts of interest is found at the end of this article.
Enrichment of Putative Pancreatic Progenitor Cells from Mice by Sorting for Prominin1 (CD133) and Platelet-Derived Growth Factor Receptor β
Authors: Hori Yuichi , Fukumoto Miki , Kuroda Yoshikazu
Published: August 2008

Success in islet transplantation-based therapies for type 1 diabetes mellitus and an extreme shortage of pancreatic islets have motivated recent efforts to develop renewable sources of islet-replacement tissue. Although pancreatic progenitor cells hold a promising potential, only a few attempts have been made at the prospective isolation of pancreatic stem/progenitor cells, because of the lack of specific markers and the development of effective cell culture methods. We found that prominin1 (also known as CD133) recognized the undifferentiated epithelial cells, whereas platelet-derived growth factor receptor β (PDGFRβ) was expressed on the mesenchymal cells in the mouse embryonic pancreas. We then developed an isolation method for putative stem/progenitor cells by flow cytometric cell sorting and characterized their potential for differentiation to pancreatic tissue using both in vitro and in vivo protocols. Flow cytometry and the subsequent reverse transcription-polymerase chain reaction and microarray analysis revealed pancreatic epithelial progenitor cells to be highly enriched in the prominin1highPDGFRβ− cell population. During in vivo differentiation, these cell populations were able to differentiate into endocrine, exocrine, and ductal tissues, including the formation of an insulin-producing cell cluster. We established the prospective isolation of putative pancreatic epithelial progenitor cells by sorting for prominin1 and PDGFRβ. Since this strategy is based on the cell surface markers common to human and rodents, these findings may lead to the development of new strategies to derive transplantable islet-replacement tissues from human pancreatic stem/progenitor cells.

Disclosure of potential conflicts of interest is found at the end of this article.
Feeder-Free Monolayer Cultures of Human Embryonic Stem Cells Express an Epithelial Plasma Membrane Protein Profile
Authors: Van Hoof Dennis , Braam Stefan R. , Dormeyer Wilma , Ward-van Oostwaard Dorien , Heck Albert J.R. , Krijgsveld Jeroen , Mummery Christine L.
Published: August 2008

Human embryonic stem cells (hESCs) are often cocultured on mitotically inactive fibroblast feeder cells to maintain their undifferentiated state. Under these growth conditions, hESCs form multilayered colonies of morphologically heterogeneous cells surrounded by flattened mesenchymal cells. In contrast, hESCs grown in feeder cell-conditioned medium on Matrigel instead tend to grow as monolayers with uniform morphology. Using mass spectrometry and immunofluorescence microscopy, we showed that hESCs under these conditions primarily express proteins belonging to epithelium-related cell-cell adhesion complexes, including adherens junctions, tight junctions, desmosomes, and gap junctions. This indicates that monolayers of hESCs cultured under feeder-free conditions retain a homogeneous epithelial phenotype similar to that of the upper central cell layer of colonies maintained on feeder cells. Notably, feeder-free hESCs also coexpressed vimentin, which is usually associated with mesenchyme, suggesting that these cells may have undergone epithelium-to-mesenchyme transitions, indicating differentiation. However, if grown on a “soft” substrate (Hydrogel), intracellular vimentin levels were substantially reduced. Moreover, when hESCs were transferred back to feeder cells, expression of vimentin was again absent from the epithelial cell population. These results imply that on tissue culture substrates, vimentin expression is most likely a stress-induced response, unrelated to differentiation.

Disclosure of potential conflicts of interest is found at the end of this article.
Case Management and Social Role Theory as Partners in Service Delivery
Authors: Blakely Thomas J. , Dziadosz Gregory M.
Published: August 2008

This article proposes a reorganized model of case management for persons with a serious psychiatric illness, including a substance abuse disorder. The model was designed as a response to the changing demands of federal law, public funding sources, and social work licensure requirements in some states. It partners case management with social role theory and uses the person-in-situation paradigm and social functioning as organizing concepts.

This model may be helpful for those adult mental health agencies serving this population who are faced with making adjustments to changing demands of federal law, public funding sources, and the requirements of social work licensure in some states, all of which place restrictions on service delivery. An important feature of the model is partnering case management with social role theory in a way that enhances the delivery of case management services. It is being implemented at Touchstone innovaré, a mental health agency serving adults who have a serious psychiatric condition or a co-occurring disorder.
Macroscopic Root Water Uptake Distribution Using a Matric Flux Potential Approach
Authors: de Jong van Lier Q. , van Dam J. C. , Metselaar K. , de Jong R. , Duijnisveld W. H. M.
Published: August 2008

Hydrological models featuring root water uptake usually do not include compensation mechanisms such that reductions in uptake from dry layers are compensated by an increase in uptake from wetter layers. We developed a physically based root water uptake model with an implicit compensation mechanism. Based on an expression for the matric flux potential (M) as a function of the distance to the root, and assuming a depth‐independent value of M at the root surface, uptake per layer is shown to be a function of layer bulk M, root surface M, and a weighting factor that depends on root length density and root radius. Actual transpiration can be calculated from the sum of layer uptake rates. The proposed reduction function (PRF) was built into the SWAP model, and predictions were compared to those made with the Feddes reduction function (FRF). Simulation results were tested against data from Canada (continuous spring wheat [(Triticum aestivum L.]) and Germany (spring wheat, winter barley [Hordeum vulgare L.], sugarbeet [Beta vulgaris L.], winter wheat rotation). For the Canadian data, the root mean square error of prediction (RMSEP) for water content in the upper soil layers was very similar for FRF and PRF; for the deeper layers, RMSEP was smaller for PRF. For the German data, RMSEP was lower for PRF in the upper layers and was similar for both models in the deeper layers. In conclusion, but dependent on the properties of the data sets available for testing, the incorporation of the new reduction function into SWAP was successful, providing new capabilities for simulating compensated root water uptake without increasing the number of input parameters or degrading model performance.
Horizontal Root Growth: Water Uptake and Stomatal Resistance under Microgravity
Authors: Kirkham M. B.
Published: August 2008

With the increased interest of plants in space, gravity cannot be ignored in studies of plant–water relations. Although photosynthesis has been measured on the International Space Station, apparently no published information exists concerning the stomatal resistance of plants in space. Growth is directly related to stomatal opening, which is controlled by hormones produced in the roots. The objective of this study was to determine the effect of gravity on plant water take and stomatal resistance. To simulate gravity‐free conditions, wheat plants (Triticum aestivum L. ‘Jagger’) were grown in columns oriented horizontally. Two experiments, each with a different depth of planting (3 cm or 3 mm), were performed in a growth room. Four columns (7 cm diam., 40 cm long), filled with a commercial potting mix were used in each experiment: two were placed horizontally and two were placed vertically. Stomatal resistance was measured with a steady‐state porometer. In the first experiment (3‐cm planting depth), plants in horizontal columns emerged poorly. In the second experiment (3‐mm planting depth), plants in horizontal columns emerged, but leaves often were plastered on the soil surface, making it difficult to determine stomatal resistance. In both experiments, roots in columns placed on their sides did not grow into the columns. Because the plants grown horizontally could not take up water, they wilted and died, and stomatal resistance readings were high (>50 s cm−1).
Matric Potential Measurements by Polymer Tensiometers in Cropped Lysimeters under Water‐Stressed Conditions
Authors: van der Ploeg Martine J. , Gooren Hermanus P. A. , Bakker Gerben , de Rooij Gerrit H.
Published: August 2008

In many regions of the world, plant growth and productivity are limited by water deficits. As a result of more frequent and intense droughts, the area of land characterized as very dry has more than doubled since the 1970s. Consequently, understanding root water uptake under water‐stressed conditions is gaining importance. The performance of a recently developed polymer tensiometer (POT) designed to measure matric potentials down to −1.6 MPa was evaluated and compared with volumetric moisture content measurements in dry soil. Three irrigation intensities created severe, intermediate, and no water stress conditions in lysimeters with growing maize (Zea mays L.) plants. By monitoring matric potentials using POTs, levels of local water stress in our experiments were better defined. When the defined stress levels were reached, volumetric moisture measurements for this particular loam soil were below 0.1, thus less informative compared with matric potential measurements. The observed matric potential profiles indicate significant root water uptake between 0.3‐ and 0.5‐m depth in the later growth stages under water‐stressed conditions. The temporal pattern of matric potential profiles reflected changing root water uptake behavior under dry conditions. As the total soil water potential is a direct indication of the amount of energy required by plants to take up water, POTs may contribute to quantifying root water uptake in dry soils.
Species‐Level Impacts on Chaparral Root Zone Hydrology
Authors: Newman Brent D. , Graham Robert C.
Published: August 2008

A set of four unconfined (earthen‐walled) lysimeters in the San Dimas Experimental Forest near Los Angeles, CA, provides a unique opportunity to examine the effect of species‐level vegetation on root zone hydrology under highly controlled experimental conditions. The 28.1‐m2 by 2.1‐m deep lysimeters were specifically designed to minimize variation of all environmental conditions except vegetation. Monocultures of buckwheat (Eriogonum fasciculatum Benth. var. foliolosum Nutt.), chamise (Adenstomata fasciculatum Hooke & Arn.), scrub oak (Quercus dumosa Nutt.), and Coulter pine (Pinus coulteri D. Don.) were planted in 1946. In 1997 two sets of soil cores were sampled from each lysimeter to evaluate species level effects resulting from 50 yr of growth. The cores were analyzed for water content, soil water potential, and pore water chloride. The chloride mass balance approach was used to estimate long‐term average fluxes and residence times of water in the lysimeters. One core from each lysimeter was also analyzed for pore water stable isotope (δ2H) composition. Only small differences were observed between the four species in terms of the shapes of the depth profiles and the absolute values of the hydrologic characteristics and fluxes. However, some differences were statistically significant. For example, differences in some characteristics were found between the chamise and the other species. We also observed differences between the lowest aboveground biomass group (buckwheat and chamise) versus the highest aboveground biomass group (oak and pine). These results suggest that although species‐ and biomass‐level differences in root zone hydrologic behavior appear to be minor, there are detectible differences in how these vegetation types affect the water budget in chaparral ecosystems.
Changes in Soil Water Content Resulting fromRicinusRoot Uptake Monitored by Magnetic Resonance Imaging
Authors: Pohlmeier A. , Oros‐Peusquens A. , Javaux M. , Menzel M. I. , Vanderborght J. , Kaffanke J. , Romanzetti S. , Lindenmair J. , Vereecken H. , Shah N. J.
Published: August 2008

Magnetic resonance imaging (MRI) was used to study the soil water content changes caused by root water uptake. A 4‐wk‐oldRicinus communis carmencitawith a highly developed root system was planted in a cylindrical container filled with a model soil (99.5% fine sand, 0.5% clay), fully water saturated. The bottom and surface of the container were sealed so that water loss by factors other than transpiration via the leaves could be neglected. The water content of the soil was monitored for 3 wk using the MRI sequence SPRITE at an isotropic spatial resolution of 6.3 mm. In contrast to conventionally used MRI sequences, the T2* relaxation was monitored, temporally resolved, and extrapolated to zero. This procedure is a better measure of water content than a single signal at a given time point since it eliminates varying MRI relaxation times during soil desiccation. A linear correlation between the MRI‐determined and gravimetrically measured total water content proves the correctness of the monitoring and data evaluation procedure. Simultaneously, the root architecture was also imaged at 0.6 mm isotropic resolution by the MRI sequence constructive interference in steady state (CISS), which yielded a good contrast between soil and roots. The coregistration of both types of imaging (water content and root architecture) indicates that greater changes in water content took place in the bottom region and near the surface, where the highest root densities were found.
Effect of Local Soil Hydraulic Conductivity Drop Using a Three‐Dimensional Root Water Uptake Model
Authors: Schröder Tom , Javaux Mathieu , Vanderborght Jan , Körfgen Bernd , Vereecken Harry
Published: August 2008

The coupling of soil and root water fluxes at the plant scale is a particularly challenging task. Numerical three‐dimensional plant‐scale models exist that consider these soil–root interactions. The influence of the hydraulic conductivity drop at the microscopic scale and especially the effect on root water uptake is not yet assessed in such models. In this study, an analytical approach describing the hydraulic conductivity drop from the bulk soil to the soil–root interface for a three‐dimensional plant‐scale model was derived and validated by numerical means. With these tools, quantification of the local hydraulic conductivity drop with time was possible. Furthermore, the effect of the hydraulic conductivity drop on the time occurrence of plant stress was evaluated. Root water uptake was assessed, with and without considering the hydraulic conductivity drop around single roots in a three‐dimensional plant‐scale model in terms of total water uptake at the root collar under different soil and root properties. It was shown that the total root water uptake was strongly affected, especially under conditions where the radial root hydraulic conductivity, which regulates root water uptake, was larger than the soil hydraulic conductivity, which regulates water flow in the soil. These findings were backed up by numerical validation of the model using mesh refinement. Incorporation of the hydraulic conductivity drop around individual roots in a three‐dimensional plant‐scale model can solve problems with greater accuracy for larger grid resolutions, and with smaller computational times, than not considering the hydraulic conductivity drop.
The Shallowest Possible Water Extraction Profile: A Null Model for Global Root Distributions
Authors: Schenk H. Jochen
Published: August 2008

The factors that shape vertical root distributions in different soils and under different climates and vegetation are poorly understood. This makes it difficult to parameterize root profiles in vegetation‐, hydrology, biogeochemistry‐, or global circulation models. Recently, it has been proposed that vertical root distributions in the vadose zone could be predicted from soil water infiltration and extraction patterns as a function of climatic variability, soil, and vegetation characteristics. A number of ecological factors favor shallow over deep roots, suggesting that root profiles of plant communities may tend to be as shallow as possible and as deep as needed to fulfill evapotranspirational demands. To test this hypothesis, a stochastic, one‐dimensional soil water infiltration and extraction model (SWIEM) was developed that simulates soil water infiltration through 600 discrete soil layers to a depth of 6 m. Water input is simulated in Monte Carlo fashion based on site‐specific long‐term precipitation data. Water extraction proceeds from the top down, with extraction depths determined by potential evapotranspiration (PET) and the vertical distribution of soil water. The resulting shallowest possible water extraction profile was tested against nine measured root profiles from long‐term ecological research sites in different biomes. Two other approaches, based on mean root distributions for biomes and an empirical regression model, were also compared to the observed root distributions. Soil water extraction patterns predicted by the SWIEM model matched observed vertical root distributions better than the other two approaches. These findings show that vertical root distributions in different biomes tend to approach the shallowest possible shape, thereby creating a useful null model for future research on root distributions and a promising tool for parameterization of global models.
Microsensing of Water Dynamics and Root Distributions in Sandy Soils
Authors: Segal Eran , Kushnir Tammar , Mualem Yechezkel , Shani Uri
Published: August 2008

Comprehensive understanding of water and nutrient transport in the rhizosphere is important because water use is a major societal and environmental concern. Studying these processes has been slow, however, due to historical neglect of belowground research and the fact that soil is not transparent to many research tools. We investigated two independent and noninvasive methods that have the potential to expand our knowledge of root water uptake. The magnetic resonance imaging technique was used to simultaneously generate three‐ and two‐dimensional, high‐resolution images of a seedling's root system and the soil water content distribution in the rhizosphere of sandy soils. A quantitative measurement of soil moisture in the rhizosphere and specifically at the root–soil interface was applied, taking into account the cylindrical nature of roots and the radial water flow toward root surfaces. This protocol enabled a dynamic study of water depletion patterns around a single root as a result of root water uptake. In the second method, a pliable‐tip microtensiometer (PTMT) was introduced as a reliable tool to measure soil water pressure heads in a small volume of sandy soil. A set of PTMTs combined with a growth chamber, which allows roots to grow in a predetermined location, was used to measure the water status at the soil–root interface and in the bulk soil with time.
Water Uptake and Hydraulics of the Root Hair Rhizosphere
Authors: Segal Eran , Kushnir Tammi , Mualem Yechezkel , Shani Uri
Published: August 2008

Plant roots consist of various functional zones; the root cap and beyond the lateral root formation region have very low water permeability due to immature water conduit and root suberization, respectively. The root hair zone, which is located between these regions, is the most permeable zone, where both radial and axial conductivities are high, and has been suggested to play a role in water uptake enhancement. The conventional understanding of root hair function is that root hairs increase root surface area, thereby enhancing water and nutrient uptake. Yet, modeling the soil water status between root hairs shows that the soil water potential there reaches a value close to that of the root in a very short time. The corresponding low water content values within the inter‐root‐hair domain indicates limited mass water flow and ion diffusion rate toward the root. Consequently, we conclude that when the plant transpires (daytime), root hairs do not increase water and nutrient uptake by increasing root surface area. Instead we used both magnetic resonance imaging technology, for measurements and analysis of spatial and dynamic changes in water content in the rhizosphere, and numerical modeling to show that: (i) root hairs function mostly by water uptake through the root hair tip plane; (ii) the growth of root hairs, perpendicular to the root surface, expands the apparent diameter of the cylinder that is characterized by the root water potential, thereby increasing the effective surface area of the root for water uptake; and (iii) the growth of needle‐shaped root hairs requires minimal investment in biomass with less mechanical resistance compared with alternative strategies that require larger root diameter or root length.
A Fully Transient Model for Long‐Term Plutonium Transport in the Savannah River Site Vadose Zone: Root Water Uptake
Authors: Demirkanli Deniz I. , Molz Fred J. , Kaplan Daniel I. , Fjeld Robert A.
Published: August 2008

Improved understanding of flow and radionuclide transport in vadose zone sediments is fundamental to future planning involving radioactive materials. To that end, long‐term experiments were conducted at the Savannah River Site in South Carolina, where a series of lysimeters containing sources of plutonium (Pu) in different oxidation states was placed in the shallow subsurface and exposed to the environment for 2 to 11 yr. Then, sediment Pu activity concentrations were measured along vertical cores taken from the lysimeters. Results showed anomalous activity distributions below the source, with significant migration of Pu above the source. A previously developed reactive transport model with surface‐mediated redox reactions successfully simulated the lysimeter results below the source, assuming a steady, net downward flow. To simulate more realistic field conditions, a transient variably saturated flow model with root water uptake is developed and coupled to the reactive transport model. Overall, the fully transient analysis shows results nearly identical to the much simpler steady flow analysis. Thus, the surface‐mediated redox hypothesis remains consistent with the below‐source experimental data, the most important variable affecting transport being the oxidation state of the source material. However, none of the models studied could produce the upward Pu transport observed in the data. The hydraulic and chemical mechanisms tested as potential causes for upward migration—a modified root distribution, hysteresis, and air‐content dependent oxidation—yielded little or no enhancement of the upward Pu movement. This suggests another transport mechanism such as root Pu uptake and translocation in the transpiration stream.
Wetting Solution and Electrical Double Layer Contributions to Bulk Electrical Conductivity of Sand–Clay Mixtures
Authors: Mojid M. A. , Cho H.
Published: August 2008

This study investigated the contributions of the wetting liquid and electrical double layers (EDLs) to the bulk electrical conductivity (σ) of sand–clay mixtures. The conductivity is small at small water content due to few conductive pathways and low ionic mobility. The fully expanded state of the EDLs provided the largest σ in distilled water but not in salt solutions. At small water content, σ increases following a logarithmic function, but changes linearly at large water content after reaching a transitional large value. This conductivity increases with increasing electrical conductivity of the wetting solution (σw) exponentially at small water content, but linearly at large water content. Existing bulk electrical conductivity models described the measured σ values well and resulted in stable values of the electrical formation factor (F) and dimensionless parameter. Due to considerable leach cations in the clay, the cations in the bulk solution exerted negligible influence on the surface conductivity (σs). Although F is independent of σw, the confounding effect of shrink–swell in the samples with changing σw shows an apparent dependency of F on σw The surface mobility of the counterions decreased nonlinearly with increasing water‐filled porosity (ϕ), and also with increasing σw The cementation exponent (m) decreased monotonically from −4.4 at ϕ = 0.22 to −94.1 at ϕ = 0.93 in the samples wetted with distilled water. With increasing σw, m also increased. The value of m for three samples wetted with salt solutions of σw = 0.878, 1.273, and 1.572 S m−1 ranged from 2.1 to 2.5 at ϕ = 0.22 and 4.1 to 5.3 at ϕ = 0.93.
Semianalytical Solution for Two‐Phase Flow in Porous Media with a Discontinuity
Authors: Fučík Radek , Mikyška Jirí , Beneš Michal , Illangasekare Tissa H.
Published: August 2008

We present a benchmark solution for one‐dimensional porous media with heterogeneity involving two soils separated by a sharp interface. A similar problem was discussed previously by other researchers; however, only a diffusion term was considered in their models. The proposed solution allows the inclusion of advection terms in a limited way. This solution is useful in the verification of more complex numerical models of multiphase flow developed for general applications involving heterogeneous aquifers. A derivation of the semianalytical solution for heterogeneous porous media is presented and its existence and uniqueness are discussed. A computationally efficient algorithm and several computational results are presented.
Role of snow in the hydrology of a High Arctic riparian wetland
Authors: Young Kathy L.
Published: August 2008

Riparian wetlands are narrow strips of saturated and vegetated ground forming critical links between dry ground and waterways. The hydrology of a riparian wetland situated within a polar oasis landscape near Eastwind Lake, Ellesmere Island, Nunavut (80°80′N, 85°35′W) was investigated in 2006 using a combination of fieldwork and modelling. Supplemental information from 2005 was also employed. This study showed that deep snow in the nearby stream channel does not promote a period of extended over-bank flooding but instead initially serves as a dam blocking most streamwater from entering and flooding the wetland. It was not until the snow dam melts and disintegrates in response to favourable weather conditions that the wetland becomes flooded and fully recharged. This was a delay of three weeks from the previous year. For the remainder of the 2006 growing season, contributions of meltwater from late-lying snow beds located within and adjacent to the stream channel and near the headwaters were essential for maintaining saturated conditions in the wetland.
Case study of a large summer flood on the North Slope of Alaska: bedload transport
Authors: McNamara J. P. , Oatley J. A. , Kane D. L. , Hinzman L. D.
Published: August 2008

The relative importance of snowmelt versus rain-generated floods on sediment transport in arctic streams is largely unknown because studies documenting either event-type are rare. An August 2002 precipitation event produced the largest discharge level (snowmelt or rain) over the previous ten-year period of hydrologic and geomorphologic monitoring in the Upper Kuparuk River, Alaska providing an opportunity to document the geomorphologic response to of an arctic stream to an extreme event. In this study we document the geomorphologic response and estimate the bedload transport rate using the virtual velocity method. This flood mobilized virtually the entire bed, with the exception of random boulders greater than 0.5 m. The channel cross-section and water edge survey data illustrate the considerable morphologic response generated by the flood. The magnitude of this response resulted in only a 13% tracer rock recovery rate. The total bedload transport was estimated to be 870 m3 of bed material through the study cross sections. Channel morphology, and therefore habitat, is maintained by large and infrequent summer rain events. These events, particularly when they occur in the late summer months, when active layer depth is at its greatest, have the potential to generate orders of magnitude more bedload transport than a snowmelt runoff event. It is unclear, however, if the lack of significant bedload transport during snowmelt is due to protection by bedfast ice or if flows are insufficient.
Seasonal dynamics of dissolved nitrogen exports from two High Arctic watersheds, Melville Island, Canada
Authors: Lafrenière Melissa , Lamoureux Scott
Published: August 2008

This study examines the magnitude and seasonal patterns of dissolved N export during the 2006 melt season from two small watersheds on Melville Island, in the Canadian High Arctic. The dominant N species was dissolved organic nitrogen (DON), comprising >80% of the seasonal nitrogen flux from both rivers. The total DON and dissolved inorganic nitrogen (DIN, NH4++NO3−) yields from the catchments were similar (183 and 204 kg DON, and 46–42 kg DIN): however, on a per unit area basis the West catchment had greater yields of both DON and DIN. There were also differences in the temporal patterns and concentrations of the N species between the catchments, which may be a function of inter-catchment differences in vegetation cover. Low end-of-season DIN concentrations in the West river suggest there is strong biogeochemical retention of inorganic N in this catchment during the growing season relative to the East catchment, where stream NO3− concentrations increase through July. A decrease in DOC:DON ratios in the East river at the end of season also indicates a change in the composition of dissolved organic matter in this river that is not evident in the West river. The results illustrate that there can be large differences in the processes controlling nitrogen between two adjacent and similar catchments.
Climate, glacier mass balance and runoff (1993–2005) for the Mittivakkat Glacier catchment, Ammassalik Island, SE Greenland, and in a long term perspective (1898–1993)
Authors: Mernild S. H. , Kane D. L. , Hansen B. U. , Jakobsen B. H. , Hasholt B. , Knudsen N. T.
Published: August 2008

Climate, glacier mass balance and runoff are investigated in the Low-Arctic Mittivakkat Glacier catchment on Ammassalik Island, Southeast Greenland. High-resolution meteorological data from the catchment covering 1993–2005 and standard synoptic meteorological data from the nearby town of Tasiilaq (Ammassalik) from 1898–2005 are used. Within the catchment, gradients and variations are observed in meteorological conditions between the coastal and the glacier areas. During the period 1993–2005 about 15% lower annual solar radiation was observed in the coastal area. Further, decreasing mean annual air temperatures (MAAT) occur in the coastal area, indicating an approximately 20-d shorter thawing period. The higher lying glacier area, in contrast, experiences an increasing MAAT, an approximately 40-d longer thawing period and a 60-d longer snow-free period. The Mittivakkat Glacier net mass balance has been almost continuously negative, corresponding to an average loss of glacier volume of 0.4% yr−1. The total catchment runoff is averaging 1973±281 mm w.eq. yr−1, and around 30% of the runoff is explained by glacier net loss. Over the 106 years (1898–2004) MAAT has, on average, increased significantly in the catchment by 1.3°C. However, time periods of considerable variability occur. All seasons show increasing air temperatures, with the highest increase during winter season. The period 1995–2004 was the warmest 10-yr period within the last 60 yr, and 1936–1946 the warmest within the last 106 years. The calculated glacier net mass balance indicates an average glacier loss of 550±530 mm w.eq. yr−1, and 89 out of 105 mass balance years show a negative net mass balance. For the 106-yr period average runoff was estimated to be 1957±254 mm w.eq. yr−1.
Analysis of cold season streamflow response to variability of climate in north-western North America
Authors: Woo Ming-ko , Thorne Robin
Published: August 2008

Previous studies have correlated interannual streamflow fluctuations with changes in the climate. We note that decadal shifts in climate forcing can impart a stronger signal on streamflow than does the long-term climatic trend. In north-western North America, the Pacific Decadal Oscillation (PDO), which is strong in the cold season, may exert influence on interannual variations in spring high flows. In the 20th century, several major shifts in the PDO have been recognized. However, the rivers of Alaska, Yukon, Northwest Territories, British Columbia and Alberta have variable response to such climate signals. An analysis of the flow of rivers in this region indicates that a number of rivers draining the Pacific coast are positively correlated with PDO and some rivers in the interior correlate negatively. Not all river flows correlate with the PDO because factors such as location, topography and storage can overwhelm the climatic influence. Given these considerations, the interpretation of long-term trends in streamflow should take account of the interdecadal climatic shifts and basin characteristics that affect flow generation.
Apparent recent trends in hydrologic response in permafrost regions of northwest Canada
Authors: Janowicz J. Richard
Published: August 2008

Yukon air temperature trends have been observed to change over the last several decades with an increase in both summer and winter air temperatures. An assessment of streamflow response was carried out to determine if there are apparent trends in permafrost regions as a result of the observed temperature changes. Degrading permafrost places a greater reliance on the interaction between surface and subsurface processes. Annual mean, maximum and minimum flows were assessed using the Mann–Kendall test to statistically validate observed trends. Annual mean flows are observed to have slight positive trends over the last three decades within continuous and discontinuous permafrost zones, with variable results within sporadic permafrost regions. These results are generally in keeping with similar trends in annual precipitation, which has increased slightly. Though not generally statistically significant, annual peak flows have largely decreased within continuous permafrost regions, and lesser so within discontinuous regions. Results are variable within sporadic permafrost zones. These trends are likely associated with increased annual precipitation; however, it is conceivable that there may be increased infiltration amounts as a result of degrading permafrost. Winter low flows have experienced significant apparent changes over the last three decades. The greatest changes in winter low flows appear to be occurring within the continuous permafrost zone, where flows from the majority of sampled streams have increased. Winter low flows trends in streams within the discontinuous permafrost zone generally exhibit positive significant trends, but are more variable. Winter streamflow trends within the sporadic permafrost zone are not consistent.
Invasive Non-Native Solidago Species in Latvia: Expansion History and Current Distribution
Authors: Priede Agnese
Published: August 2008

Invasive Non-NativeSolidagoSpecies in Latvia: Expansion History and Current Distribution

Two non-nativeSolidagoL. species of North-American origin are aggressive plant invaders in most of Europe.Solidago canadensisoccurs frequently in most of temperate Europe, whileS. gigantealags behind in north and east Europe. For the first time the distribution and history of expansion of bothSolidagospecies in Latvia were studied and reviewed in maps. The distribution data were gathered mainly in field surveys (2004-2007); other data sources include herbarium materials, literature and unpublished data. Both the widespreadS. canadensisand rareS. giganteaare well adapted to a wide range of habitats mostly occurring in human-disturbed habitats in the vicinity of settlements and transportation routes. Over the last century, the dispersal success of goldenrods had been greatly facilitated by land use changes, human alteration of ecosystems, and development of transportation networks.
Concepts of Rurality and Urbanity as Analytical Categories in Multidimensional Research
Authors: Kūle Laila
Published: August 2008

Concepts of Rurality and Urbanity as Analytical Categories in Multidimensional Research

This paper is a review of the concepts of rurality and urbanity and of various approaches to their differentiation. The author reviews the continuum and dichotomy of rurality and urbanity and the challenges that occur when seeking to differentiate between them. The author has reviewed the descriptive approach, which is based on empirical data, as well as the social approach, which is based on various social agents and different ways of perceiving space. The author has evaluated various approaches to studying rural-urban separation, focusing on the challenges that are created by contemporary developments in society. New forms of populated areas are emerging, and they do not correspond to this binary separation. Both rural and urban areas are becoming increasingly multidimensional and interactions between them more intensive. "Urban" and "rural" are abstractions and metaphors that are needed to ensure human communications which enables the bridging of knowledge from one area of science or politics to another. That is particularly relevant for interdisciplinary research such as spatial and environmental studies. In the conclusion, the author reviews the way in which rurality and urbanity are studied by researchers in Latvia.
Premise of Optimal Water Management in Latvia
Authors: Zaķis Gunārs , Ernšteins Raimonds
Published: August 2008

Premise of Optimal Water Management in Latvia

The development of water management in Latvia was broadly investigated with a focus on identifying the main managerial problems when analysing all factors affecting water administration and management optimisation prospects. Combined sociological research was performed using traditional and also case study research methodologies to produce systemic assessment of institutional and human resource capacities and managerial impact on the organisational ability of municipalities and the provision of water supply and waste water treatment services by companies and utilities. Alternative water management models and their applications were also elaborated and evaluated. To provide rational use of water resources in Latvia and to meet the requirements of the EU legislation, it is necessary to change the water management system in the country, but, most important, to develop principles of systemic integration and coordinated cooperation with respecting historically formed conditions, and, to introduce an optimal water management model comprising a set of management preconditions—approaches, principles, structural components and set of tools into complement institutional capacities.
Amenity Migration in Postsocialist Metropolis: The Case of Rīga Agglomeration
Authors: Bērziņš Māris , Krišjāne Zaiga
Published: August 2008

Amenity Migration in Postsocialist Metropolis: The Case of Rīga Agglomeration

Over the last ten years, the metropolitan area of Rīga has seen a population increase, while the number of people actually living in the city of Rīga has declined. The aim of this paper is to analyse the process of deconcentration in the Rīga agglomeration, linking these to motivation for migration and changes in the territorial distribution of places of residents. The study analyses factors that lead people to choose a specific place of residence. A comparison of motivation for migration in Rīga and in the zones of its agglomeration shows that there are significant differences in terms of a job as a motivation factor. More important in selecting a new home are the purchase or construction of property, the desire for an attractive environment, and the ability to move into a better home. Efforts to improve quality of life are more distinct in the internal zone of the agglomeration, which means that environmental amenities play a more important role there than in the external zone.
A New Tristichopterid (Pisces, Sarcopterygii) from the Devonian of Latvia
Authors: Zupiņš Ivars
Published: August 2008

A New Tristichopterid (Pisces, Sarcopterygii) from the Devonian of Latvia

A new species of tristichopterid sarcopterygians, Eusthenopteron kurshi, sp. nov., the earliest representative of the family reported to this date from the territory known as the Main Devonian Field, is described from the well-known fossil locality of Latvia, the Lode clay quarry (Upper Givetian/Lower Frasnian). One complete skeleton and several disarticulated bone elements of the head and shoulder girdle have been found. The material reveals some morphologic features like a relatively short parietal shield in the cranial roof and rather asymmetric caudal fin. Characteristic features for the species are a front end of the squamosal extending comparatively far anteriorly and opercular being twice as high as the subopercular.
Approaches for Management of Chemical Substances: Challenges and Solutions
Authors: Kazerovska Kristīne , Kļaviņš Māris , Dipāne Judīte
Published: August 2008

Approaches for Management of Chemical Substances: Challenges and Solutions

This article analyses the development of approaches for management of chemical substances in the frame of current reform of chemicals policy at the European Union level with regard to implementation of REACH Regulation No. 1907/2006. REACH is considered as an integrated approach to the control of the production, import and use of chemicals in the European Union, especially of those chemical substances with the most hazardous properties. The new approach covers both the strengths of old and new chemical policies, also requires revision of existing understandings about chemical production, import and use: responsibilities of all involved actors, the chemicals supply chain, and information flow within chemicals supply chain.
Roles of Reflex Activity and Co-contraction During Assessments of Spasticity of the Knee Flexor and Knee Extensor Muscles in Children With Cerebral Palsy and Different Functional Levels
Authors: Pierce Samuel R , Barbe Mary F , Barr Ann E , Shewokis Patricia A , Lauer Richard T
Published: August 2008

Background and Purpose

Spasticity is a common impairment in children with cerebral palsy (CP). The purpose of this study was to examine differences in passive resistive torque, reflex activity, coactivation, and reciprocal facilitation during assessments of the spasticity of knee flexor and knee extensor muscles in children with CP and different levels of functional ability.

Subjects

Study participants were 20 children with CP and 10 children with typical development (TD). The 20 children with CP were equally divided into 2 groups: 10 children classified in Gross Motor Function Classification Scale (GMFCS) level I and 10 children classified in GMFCS level III.

Methods

One set of 10 passive movements between 25 and 90 degrees of knee flexion and one set of 10 passive movements between 90 and 25 degrees of knee flexion were completed with an isokinetic dynamometer at 15°/s, 90°/s, and 180°/s and concurrent surface electromyography of the vastus lateralis and medial hamstring muscles.

Results

Children in the GMFCS level III group demonstrated significantly more peak knee flexor torque with passive movements at 180°/s than children with TD. Children in the GMFCS level I and level III groups demonstrated significantly more repetitions with medial hamstring muscle activity, vastus lateralis muscle activity, and co-contraction than children with TD during the assessment of knee flexor spasticity at a velocity of 180°/s.

Discussion and Conclusion

Children with CP and more impaired functional mobility may demonstrate more knee flexor spasticity and reflex activity, as measured by isokinetic dynamometry, than children with TD. However, the finding of increased reflex activity with no increase in torque in the GMFCS I group in a comparison with the TD group suggests that reflex activity may play a less prominent role in spasticity.