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Stream temperature governs many aquatic ecosystem processes and plays a key role in determining the distribution of cold‐water amphibians and cool‐ and cold‐water fish, including salmonids. Decades of research have focused on the effects of forestry and forest disturbance on stream temperature, and new projects are underway or being planned in jurisdictions including the Provinces of Alberta and British Columbia, Canada, and Washington State, USA. The objective of this paper is to provide a critical review of methodologies employed in previous studies. The review initially focuses on the range of metrics used to quantify stream thermal regimes and the factors that control stream temperature variability in time and space, then focuses on sampling and analytical methodologies used to quantify stream temperature response to forestry activity and forest disturbance. Empirical methods include sampling in time, space, or both, and may or may not include pre‐ and post‐harvest data. Process‐based mechanistic and hybrid empirical‐mechanistic models have also been applied. The advantages and disadvantages of these approaches are discussed, and recommendations provided to support the design and execution of future studies. [ABSTRACT FROM AUTHOR]

Stream temperature studies typically use either the Penman combination equation (PCE) or empirical wind functions to compute the latent heat flux, which can be an important control on daily maximum water temperature. The sensible heat flux is usually computed from the latent heat flux via the Bowen ratio or a bulk transfer model. Unfortunately, both the PCE and empirical wind functions involve challenges. The PCE is inappropriate for application to subdaily stream evaporation because, as implemented in many stream temperature studies, it does not account for energy associated with warming or cooling of the water column or bed heat fluxes. The PCE thus tends to overestimate evaporation under conditions typical of warm summer days during the diurnal warming phase, which is when evaporation is likely to be an important heat loss mechanism. Empirical wind functions involve substantial uncertainty given the broad range of coefficient values that have been reported in the literature and the lack of above‐stream meteorological data to use in their application. We provide suggestions for improving current practice and also identify research directions to support development of robust approaches to computing the latent and sensible heat fluxes. Key Points: The Penman combination equation is not appropriate for computing subdaily stream evaporationThere is considerable uncertainty associated with coefficients in empirical wind functions for computing evaporation and sensible heat fluxSuggestions for current practice and longer‐term research are provided [ABSTRACT FROM AUTHOR]

Stream surface albedo plays a key role in the energy balance of rivers and streams that are exposed to direct solar radiation. Most physically based analyses and models have incorporated a constant stream albedo between 0.03 and 0.10, based primarily on measurements from low-gradient streams with low suspended sediment concentrations. However, albedo should vary with solar elevation angle, suspended sediment concentration, aeration, and fraction of direct versus diffuse radiation. The objective of this study was to quantify the dependence of albedo of mountain streams on the controlling factors and to develop a predictive model for use in physically based analysis and modelling of stream temperature, especially for future climate and land-use scenarios. Stream surface albedo was measured at nine sites with a variety of gradients and suspended sediment characteristics in the southern Coast Mountains of British Columbia, Canada. As expected, albedo of low-gradient, non-white water (flatwater) streams increased with solar elevation angle, suspended sediment concentration, and proportion of diffuse to direct solar radiation, ranging between 0.025 during cloudy periods over clear water to 0.25 for turbid water at elevation angles of less than 20°. Albedo was enhanced in steep reaches or at channel steps and cascades where flow was visibly aerated, with a range of 0.09 to 0.33. In clear weather, albedo exhibited notable diurnal variability at flatwater sampling sites. For example, during late summer, surface albedo typically fluctuated between 0.08 and 0.15 on a daily basis at a flatwater site on the highly turbid, glacier-fed Lillooet River. Multiple regression models explained approximately 60% and 40% of the variance under cross validation for flatwater and white water data subsets, respectively, with corresponding root mean square errors of approximately 0.02 and 0.06. [ABSTRACT FROM AUTHOR]

There has been increasing attention over the last decade to the potential effects of glacier retreat on downstream discharge and aquatic habitat. This study focused on streamflow variability downstream of Bridge Glacier in the southern Coast Mountains of BC between 1979 and 2014, prior to and during a period in which the glacier experienced enhanced calving and rapid retreat across a lake-filled basin. Here we combined empirical trend detection and a conceptual-parametric hydrological model to address the following hypotheses: (1) streamflow trends in late summer and early autumn should reflect the opposing influences of climatic warming (which would tend to increase unit-area meltwater production) and the reduction in glacier area (which would tend to reduce the total volume of meltwater generated), and (2) winter streamflow should increase because of displacement of lake water as ice flows past the grounding line and calves into the lake basin. In relation to the first hypothesis, we found no significant trends in monthly discharge during summer. However, applying regression analysis to account for air temperature and precipitation variations, weak but statistically significant negative trends were detected for August and melt season discharge. The HBV-EC model was applied using time-varying glacier cover, as derived from Landsat imagery. Relative to simulations based on constant glacier extent, model results indicated that glacier recession caused a decline in mean monthly streamflow of 9% in August and 11% in September. These declines in late-summer streamflow are consistent with the results from our empirical analysis. The second hypothesis is supported by the finding of positive trends for December, January, and February discharge. Despite the modelled declines in late-summer mean monthly streamflow, recorded discharge data exhibited neither positive nor negative trends during the melt season, suggesting that Bridge Glacier may currently be at or close to the point of peak water. Further analysis of the impact of lake-terminating glaciers on downstream discharge is needed to refine the peak water model. [ABSTRACT FROM AUTHOR]

Meteorological observations at high elevations in mountainous regions are often lacking. One opportunity to fill this data gap is through the use of downscaled output from weather reanalysis models. In this study, we tested the accuracy of downscaled output from the North American Regional Reanalysis (NARR) against high-elevation surface observations at four ridgetop locations in the southern Coast Mountains of British Columbia, Canada. NARR model output was downscaled to the surface observation locations through three-dimensional interpolation for air temperature, vapour pressure and wind speed and two-dimensional interpolation for radiation variables. Accuracy was tested at both the 3-hourly and daily time scales. Air temperature displayed a high level of agreement, especially at the daily scale, with root mean square error (RMSE) values ranging from 0.98 to 1.21 °C across all sites. Vapour pressure downscaling accuracy was also quite high (RMSE of 0.06 to 0.11 hPa) but displayed some site specific bias. Although NARR overestimated wind speed, there were moderate to strong linear relations ( r2 from 0.38 to 0.84 for daily means), suggesting that the NARR output could be used as an index and bias-corrected. NARR output reproduced the seasonal cycle for incoming short-wave radiation, with Nash-Sutcliffe model efficiencies ranging from 0.78 to 0.87, but accuracy suffered on days with cloud cover, resulting in a positive bias and RMSE ranged from 42 to 46 Wm− 2. Although fewer data were available, incoming long-wave radiation from NARR had an RMSE of 19 Wm− 2 and outperformed common methods for estimating incoming long-wave radiation. NARR air temperature showed potential to assist in hydrologic analysis and modelling during an atmospheric river storm event, which are characterized by warm and wet air masses with atypical vertical temperature gradients. The incorporation of a synthetic NARR air temperature station to better represent the higher freezing levels resulted in increased predicted peak flows, which better match the observed run-off during the event. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We collected fish samples and measured physical habitat characteristics, including summer stream temperatures, at 156 sites in 50 tributary streams in two sampling areas (Upper Fraser and Thompson Rivers) in British Columbia, Canada. Additional watershed characteristics were derived from GIS coverages of watershed, hydrological and climatic variables. Maximum weekly average temperature (MWAT), computed as an index of summer thermal regime, ranged from 10 to 23 °C. High values of MWAT were associated with large, warm, low relief watersheds with a high lake influence. Measures of community similarity suggested that the fish community changed most rapidly through a lower transition zone at an MWAT of about 12 °C and an upper transition zone at an MWAT of about 19 °C. These results were confirmed using existing fisheries inventory data combined with predictions of MWAT from a landscape-scale regression model for the Thompson River watershed. For headwater sites in the Chilcotin River watershed (which drains into the middle Fraser River), the relative dominance of bull trout versus rainbow trout (based on inventory data) decreased with increasing predicted MWAT although the distinction was not as clear as for the Thompson River sites. The fish communities in these watersheds can be characterized in terms of very cold water (bull trout and some cold water species), cold water (salmonids and sculpins) and cool water (minnows and some cold water salmonids). The two transition zones ( ca 12 and 19 °C) can be used to identify thresholds where small changes in stream temperature can be expected to lead to large changes in fish communities. Such clear, quantifiable thresholds are critical components of a management strategy designed to identify and protect vulnerable fish communities in streams where poor land use practices, alone or in combination with climatic change, can lead to changes in stream temperatures. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A growing body of research on stream thermal regimes has highlighted the importance of heat advection associated with surface water and groundwater interactions, such as hyporheic exchange, groundwater discharge, and hillslope throughflow inputs. Existing catchment models that predict stream temperature use a variety of approaches to estimate throughflow temperatures, but none has been evaluated against field measurements of throughflow temperature. In this study, throughflow temperatures were monitored over two winters at 50 locations adjacent to a headwater stream (11 ha catchment area) located in the rain-on-snow zone of the Pacific Northwest. Existing approaches to estimate throughflow temperature under or overpredicted throughflow temperatures by up to 5°C, or were unable to represent the influence of transient snow cover. Therefore, a conceptual-parametric model that is computationally efficient was developed that simulates hillslope hydrology and throughflow temperatures. The model structure includes an upslope reservoir that drains into a downslope reservoir that, in turn, drains into the stream. Vertical and lateral energy and water fluxes are simulated using simplified process representations. The model successfully predicts throughflow temperatures and highlights the dominant role of throughflow advection and the influence of snow cover on stream thermal regimes during high flow periods and rain-on-snow events. [ABSTRACT FROM AUTHOR]

Many efforts to model stream temperature by using an energy budget approach have not accounted for view factors in modelling stream surface radiative exchanges, used informal approaches for computing them, or relied on calibration, which is not applicable for prediction at unmonitored sites or for predicting the effects of changes in riparian vegetation. In this paper, equations are derived for calculating view factors on the basis of geometric considerations for streams with and without riparian forest. The solutions can accommodate vegetation overhanging the stream surface. Example calculations illustrate the substantial variability of view factors across the stream width, which has implications for the estimation of view factors from point-scale radiation measurements over the stream surface, and the important influence of overhanging vegetation on view factors for narrow streams. View factors computed from the geometric model agreed well with view factors computed from hemispherical photography for streams ranging from 1 to almost 50 m wide, indicating that the model appears to be reasonably robust to deviations from the simplified geometry assumed by the model. In addition to their use in modelling stream surface energy exchanges, the solutions could also be adapted for application to energy balance and microclimate modelling in linear forest openings, such as seismic lines used in oil and gas exploration. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10-min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired-catchment analysis revealed that partial-retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post-harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post-harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre-harvest regression models for shallow groundwater were not suitable for applying the paired-catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre-harvest year. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrologic classification is useful for data organization, transfer of model parameters and estimation of hydrologic sensitivity to disturbance and climatic change. Stream-flow regime has frequently been used as a basis for classification, typically by mapping regimes defined by stream-flow data from a gauging network. As an alternative, we hypothesized that ecological classification systems can predict stream-flow regime because they are based on the same characteristics that control run-off generation (soils, climate and topography). A multivariate regression tree (MRT) was used to relate stream-flow regime to the fractional coverages of the Biogeoclimatic Ecological Classification (BEC) zones within the catchment for gauged streams in British Columbia, Canada. Although the MRT identified a realistic set of regimes, only a small number of BEC zones were used as predictors, reflecting bias in the gauging network. To avoid this bias, we used a water balance model to compute mean monthly stream flow for 932 ungauged basins in British Columbia that were generated with areas between 10 and 1000 km2; these monthly stream flows were used to train an MRT model based on BEC zone coverages. This model predicted the regime at gauged basins nearly as accurately as the water balance model for pluvial, nival and glacier-supported nival regimes. Difficulties occurred in smaller basins and in specific regions where the local BEC zones were not included as predictors. Coastal hybrid nivo-pluvial regimes were poorly predicted. With further development, ecological classification systems could have great value as a tool for hydrologic classification for both research and operational applications. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study was motivated by an interest in understanding the potential effects of climate change and glacier retreat on late summer water temperatures in alpine areas. Fieldwork was carried out between July and September 2007 at Place Lake, located below Place Glacier in the southern Coast Mountains of British Columbia. Place Lake has an area of 72 000 m2, a single inlet and outlet channel, and an approximate residence time of 4 days. Warming between the inlet and outlet of the lake ranged up to 3 °C and averaged 1.8 °C, which exceeds the amount of warming that occurred over the 1 km reach of Place Creek between the lake outlet and tree line. Over a 23-day period, net radiation totalled about 210 MJ·m-2, with sensible heat flux adding another 56 MJ m-2. The latent heat flux consumed about 8% of the surface heat input. The dominant heat sink was the net horizontal advection associated with lake inflow and outflow. Early in the study period, temperatures between the surface and 6-m depth were dominantly at or above 4 °C and were generally neutral to thermally stable, whereas temperatures decreased with depth below 6 m and exhibited irregular sub-diurnal variations. The maximum outflow temperature of almost 7 °C occurred in this period. We hypothesize that turbidity currents associated with cold, sediment-laden glacier discharge formed an underflow and influenced temperatures in the deeper portion of the lake but did not mix with the upper layers. Later in the study period, the lake was dominantly well mixed with some near-surface stability associated with nocturnal cooling. Further research is required to examine the combined effects of sediment concentrations and thermal processes on mixing in small proglacial lakes to make projections of the consequences of glacier retreat on alpine lake and stream temperatures. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Stream surface albedo was measured at a location downstream of Place Glacier, Canada, in a steep bouldery channel. Portions of the water surface were visibly aerated as a result of the cascading flow even at lower discharges; at high flows, the stream was near-continuous whitewater. Albedo generally increased with discharge, from around 0.1 at the lower flows to 0.4 at the highest flows. This increase is consistent with the known effect of aeration on the reflectance of water. This discharge dependence of albedo needs to be accounted for in physically based models for predicting stream temperature to avoid biased predictions of net radiation. For steep proglacial streams that experience decreasing late-summer flows as a result of ongoing and future glacier recession, the associated decrease in albedo could promote higher stream temperatures, in addition to the effects of reduced flow depth and velocity. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lithologic transitions and glaciations create complex longitudinal profiles that control contemporary erosion and deposition processes. In areas with these characteristics, traditional morphometric approaches for predicting process domains, such as area-slope plots, can be augmented by considering other predictors measured from high resolution lidar-derived digital elevation models (DEMs). Ordinal logistic regression was used to model the distribution of hillslope, swale, colluvial channel, and fluvial channel domains, as identified during field surveys. The study area was a glaciated region of the Rocky Mountain foothills with a complex lithostructural setting. Relationships between domains and a suite of geographic information system-derived descriptors were explored. Predictors included profile anomalies measured at the reach and basin scale using a normalized stream length-gradient (SL/ k) index. Drainage area was the dominant factor controlling domains. A model with area as the only predictor was 82% accurate. Reach slope relations were not consistent. A model that also included lithology and basin-scale SL/ k index variation was 87% accurate. Domain transitions had larger area thresholds in basins with resistant conglomerate versus sandstone or shale formations and where SL/ k index was more variable along a profile. In a restricted model of hillslope, swale, and colluvial channel domains, profile curvature measured over 100 m was also related to domain occurrence. A model for regional-scale mapping applications with six additional predictors was 95% accurate. The results showed that ordinal logistic regression can be used to predict and map process domains in regions with complex physiography using descriptors measured from high -resolution DEMs. [ABSTRACT FROM AUTHOR]

The objective of this study was to analyse stream temperature variability during summer in relation to both surface heat exchanges and reach-scale hydrology for two hydrogeomorphically distinct reaches. The study focused on a 1·5-km wildfire-disturbed reach of Fishtrap Creek located north of Kamloops, British Columbia. Streamflow measurements and longitudinal surveys of electrical conductivity and water chemistry indicated that the upper 750 m of the study reach was dominated by flow losses. A spring discharged into the stream at 750 m below the upper reach boundary. Below the spring, the stream was neutral to losing on three measurement days, but gained flow on a fourth day that followed a rain event. Continuous stream temperature measurements typically revealed a downstream warming along the upper 750 m of the study reach on summer days, followed by a pronounced cooling associated with the spring, with little downstream change below the spring. Modelled surface energy exchanges were similar over the upper and lower sub-reaches, and thus cannot explain the differences in longitudinal temperature patterns. Application of a Lagrangian stream temperature model provided reasonably accurate predictions for the upper sub-reach. For the lower sub-reach, accurate prediction required specification of concurrent flow losses and gains as a hydrological boundary condition. These findings are consistent with differences in the hydrogeomorphology of the upper and lower sub-reaches. The modelling exercise indicated that substantial errors in predicted stream temperature can occur by representing stream-surface exchange as a reach-averaged one-directional flux computed from differences in streamflow between the upper and lower reach boundaries. Further research should focus on reliable methods for quantifying spatial variations in reach-scale hydrology. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents a study which determines the stream temperature and riparian microclimate in a wildfire-disturbed area of Fishtrap Creek in Kamloops, British Columbia. The study uses net radiation model, and convective heat fluxes to examine the effects of the riparian wildfire on the radiation exchanges. The results show that air temperature was similar, the measured and modelled radiation were equal, and the difference in the surface energy fluxes were relatively minor.

Objectives While highly active antiretroviral therapy (HAART) decreases long-term morbidity and mortality, its short-term effect on hospitalization rates is unknown. The primary objective of this study was to determine hospitalization rates over time in the year after HAART initiation for virological responders and nonresponders. Methods Hospitalizations among 1327 HAART-naïve subjects in an urban HIV clinic in 1997–2007 were examined before and after HAART initiation. Hospitalization rates were stratified by virological responders (≥1 log10 decrease in HIV-1 RNA within 6 months after HAART initiation) and nonresponders. Causes were determined through International Classification of Diseases, 9th Revision (ICD-9) codes and chart review. Multivariate negative binomial regression was used to assess factors associated with hospitalization. Results During the first 45 days after HAART initiation, the hospitalization rate of responders was similar to their pre-HAART baseline rate [75.1 vs. 78.8/100 person-years (PY)] and to the hospitalization rate of nonresponders during the first 45 days (79.4/100 PY). The hospitalization rate of responders fell significantly between 45 and 90 days after HAART initiation and reached a plateau at approximately 45/100 PY from 91 to 365 days after HAART initiation. Significant decreases were seen in hospitalizations for opportunistic and nonopportunistic infections. Conclusions The first substantial clinical benefit from HAART may be realized by 90 days after HAART initiation; providers should keep close vigilance at least until this time. [ABSTRACT FROM AUTHOR]

Objective The aim of this study was to examine Emergency Department (ED) utilization and clinical and sociodemographic correlates of ED use among HIV-infected patients. Methods During 2003, 951 patients participated in face-to-face interviews at 14 HIV clinics in the HIV Research Network. Respondents reported the number of ED visits in the preceding 6 months. Using logistic regression, we identified factors associated with visiting the ED in the last 6 months and admission to the hospital from the ED. Results Thirty-two per cent of respondents reported at least one ED visit in the last 6 months. In multivariate analysis, any ED use was associated with Medicaid insurance, high levels of pain (the third or fourth quartile), more than seven primary care visits in the last 6 months, current or former illicit drug use, social alcohol use and female gender. Of those who used ED services, 39% reported at least one admission to the hospital. Patients with pain in the highest quartile reported increased admission rates from the ED as did those who made six or seven primary care visits, or more than seven primary care visits vs. three or fewer. Conclusions The likelihood of visiting the ED has not diminished since the advent of highly active antiretroviral therapy (HAART). More ED visits are to treat illnesses not related to HIV or injuries than to treat direct sequelae of HIV infection. With the growing prevalence of people living with HIV infection, the numbers of HIV-infected patients visiting the ED may increase, and ED providers need to understand potential complications produced by HIV disease. [ABSTRACT FROM AUTHOR]

Changes in air temperature, precipitation, and, in some cases, glacial runoff affect the timing of river flow in watersheds of western Canada. We present a method to detect streamflow phase shifts in pluvial, nival, and glacial rivers. The Kendall-Theil robust lines yield monotonic trends in normalized sequent 5-day means of runoff in nine river basins of western Canada over the period 1960-2006. In comparison to trends in the timing of the date of annual peak flow and the center of volume, two other less robust metrics often used to infer streamflow timing changes, our approach reveals more detailed structure on the nature of these changes. For instance, our trend analyses reveal extension of the warm hydrological season in nival and glacial rivers of western Canada. This feature is marked by an earlier onset of the spring melt, decreases in summer streamflow, and a delay in the onset of enhanced autumn flows. Our method provides information on streamflow timing changes throughout the entire hydrological year, enhancing results from previous methods to assess climate change impacts on the hydrological cycle. [ABSTRACT FROM AUTHOR]

Objectives The aim of the study was to determine the relationship between alcohol consumption and liver fibrosis as assessed by aspartate aminotransferase to platelet ratio index (APRI) in HIV-infected adults and to explore the relative contributions of alcohol and hepatitis C virus (HCV) to APRI among HIV/HCV-coinfected adults. Methods We performed a cross-sectional analysis of data from an observational clinical cohort. Alcohol consumption was categorized according to National Institute on Alcohol Abuse and Alcoholism guidelines. We defined significant liver disease as APRI>1.5, and used multinomial logistic regression to identify correlates of increased APRI. Results Among 1358 participants, 10.4% reported hazardous drinking. It was found that 11.6% had APRI>1.5, indicating liver fibrosis. Hazardous drinking was associated with increased APRI [adjusted relative risk ratio (RRR) 2.30; 95% confidence interval (CI) 1.26–4.17]. Other factors associated with increased APRI were male gender, viral hepatitis, and HIV transmission category of injecting drug use. Among coinfected individuals, 18.3% had APRI>1.5, and hazardous drinking was not associated with APRI. Among non-HCV-infected individuals, 5.3% had APRI>1.5 and hazardous drinking was associated with increased APRI (adjusted RRR 3.72; 95% CI 1.40–9.87). Conclusions Hazardous drinking is an important modifiable risk factor for liver fibrosis, particularly among non-HCV-infected patients. Clinicians and researchers must address alcohol use as the burden of liver disease increases among HIV-positive individuals. [ABSTRACT FROM AUTHOR]

Objectives To define the incidence and risk factors for methicillin resistant Staphylococcus aureus (MRSA) bacteraemia in an HIV-infected population. Methods From January 1, 2000 to December 31, 2004, we conducted a retrospective cohort study. We identified all cases of Staphylococcus aureus bacteraemia (SAB), including MRSA, among patients enrolled in the Johns Hopkins Hospital out-patient HIV clinic. A conditional logistic regression model was used to identify risk factors for MRSA bacteraemia compared with methicillin-sensitive SAB and no bacteraemia in unmatched (1:1) and matched (1:4) nested case-control analyses, respectively. Results Of 4607 patients followed for a total of 11 020 person-years (PY) of follow-up, 216 episodes of SAB occurred (incidence: 19.6 cases per 1000 PY), including 94 cases (43.5%) which were methicillin-resistant. The incidence of MRSA bacteraemia increased from 5.3 per 1000 PY in 2000–2001 to 11.9 per 1000 PY in 2003–2004 ( P=0.001). Multivariate analysis demonstrated that independent predictors of MRSA bacteraemia ( vs. no bacteraemia) were injection drug use (IDU), end-stage renal disease (ESRD) and CD4 count <200 cells/μL. Conclusions MRSA bacteraemia was an increasingly common diagnosis in our HIV-infected cohort, especially in patients with history of IDU, low CD4 cell count and ESRD. [ABSTRACT FROM AUTHOR]

This study investigated the sensitivity of streamflow to changes in climate and glacier cover for the Bridge River basin, British Columbia, using a semi-distributed conceptual hydrological model coupled with a glacier response model. Mass balance data were used to constrain model parameters. Climate scenarios included a continuation of the current climate and two transient GCM scenarios with greenhouse gas forcing. Modelled glacier mass balance was used to re-scale the glacier every decade using a volume-area scaling relation. Glacier area and summer streamflow declined strongly even under the steady-climate scenario, with the glacier retreating to a new equilibrium within 100 years. For the warming scenarios, glacier retreat continued with no evidence of reaching a new equilibrium. Uncertainty in parameters governing glacier melt produced uncertainty in future glacier retreat and streamflow response. Where mass balance information is not available to assist with calibration, model-generated future scenarios will be subject to significant uncertainty. [ABSTRACT FROM AUTHOR]

The article discusses regime-dependent streamflow sensitivities to Pacific climate modes across the Georgia-Puget transboundary ecoregion in British Columbia, Canada and Washington State. A test which combines abundant salmonid habitat, rapid population growth, urbanization, and multiple national jurisdictions is discussed. The author states that the test is also hydrologically complex and heterogeneous as they contain at least three streamflow regimes including pluvial, nival, and hybrid. These regimes reflect differing elevation ranges within various watersheds.

Previous research has highlighted the relationship between snow accumulation and forest stand characteristics, as well as the effects of topography, but not the variability within stands. This study examined spatial patterns in snow accumulation within forest stands, their consistency from year to year, and the extent to which they can be predicted from commonly used stand measurements. Snow water equivalent (SWE) was measured on or near April 1, 1995 to 1997, and a forest inventory was completed at 64 points (15-m grid spacing) in each of nine stand types including mature and juvenile forests and clearcuts. Semivariograms revealed little evidence of spatial correlation among sample points, indicating that each sample could be considered statistically independent for analysis. Within the study stands, no strong spatial trends were evident through quadratic trend surface analysis. The within-stand coefficient of variation (CV) generally decreased with increasing mean accumulation. Spearman's rank correlation analysis and principal components analysis (PCA) indicated a weak to moderate similarity in snow accumulation patterns from year to year. Site-scale canopy measures do not appear to provide a reliable basis for parameterizing the variability of within-stand snow deposition. Through the fitting of general linear models (GLM), year alone accounted for 33% of the variability in snow water equivalent within stands, on average. Of the stand inventory variables measured, crown closure explained the largest proportion of the variability in SWE within each stand, but together with year never more than 43%. The strongest correlations between snow water equivalent and crown closure were found in those stands exhibiting the greatest consistency in interannual spatial patterns of snow accumulation. [ABSTRACT FROM AUTHOR]

A principal component analysis (PCA)-based synoptic typing scheme is used to assess the ability of the Canadian Centre for Climate Modelling and Analysis (CCCma) Coupled Global Climate Model (CGCM2) to reproduce daily mean-sea-level (MSL) synoptic patterns and their frequencies for the Pacific Northwest region of North America. Model output for the 'control' period 1961-1989 is compared against the climatology based on National Center for Environmental Prediction (NCEP) re-analysis data. Although CGCM2 is able to reproduce the full range and seasonality of 13 synoptic types it significantly under-represents three cold types and over-represents (by about 50%) three warm/wet winter types. This effect is most pronounced in winter months. Differences in frequencies between the CGCM2 runs (1961-1989 climatology and 1990-2100 IPCC SRES 'A2' greenhouse gases (GHG) and aerosol forcing scenario) are smaller than the differences between NCEP and CGCM2 synoptic type frequencies for the 1961-1989 control. Unresolved orographic influences and atmosphere-ocean coupling are cited as possible explanations for model deficiencies. Results suggest that application of CGCM2 output in downscaling studies examining regional impacts should take account of these potential biases. The approach adopted provides a methodology for not only assessing progress in emerging generations of more sophisticated higher resolution General Circulation Models (GCMs) (e.g. CGCM4 is under development), but also choosing the most appropriate model for regional downscaling studies. Copyright © 2006 Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

This study examined the effects of glacier cover on summer streamflow across British Columbia, Canada, by applying nonparametric tests to assess trends in August discharge. Field-significant negative streamflow trends were found for glacierized catchments but not for those lacking glaciers. Effects of interannual climatic variations were accounted for by regressing August streamflow against August temperature and precipitation and July streamflow (to account for carryover storage). Trend analyses of the regression residuals suggested first-order stationarity for unglacierized basins, but revealed widespread negative trends for glacier-fed rivers, particularly from 1976 to 1996, consistent with the effects of glacier retreat. [ABSTRACT FROM AUTHOR]

We investigated the potential for glacier- and snowmelt-fed rivers to respond differently to the Arctic Oscillation (AO) by applying nonparametric statistical techniques to standardized and deseasonalized monthly hydrometric data from eight watersheds in southwest Yukon and northwest British Columbia, Canada. We first extracted regionally coherent glacial and nival hydroclimatic signals from the station data using empirical orthogonal function analysis. The annually averaged glacial and nival principal component time series were mutually uncorrelated, suggesting a decoupling of interannual streamflow variability between the two fluvial regimes. Moreover, glacial and nival rivers showed selective teleconnectivity to the AO; the annual glacial signal was significantly positively correlated to the AO index, whereas the nival signal was not. Composite analyses of annual hydrographs, performed using data from individual hydrometric stations, were consistent with the EOF-correlation results and provided details of related changes in hydrologic seasonality. In particular, positive-phase AO events are associated with positive glacial streamflow anomalies in late spring and early summer and an earlier freshet in nival rivers with little or no net change in annual flow. Parallel composite analyses of locally available homogeneous temperature and precipitation station data suggested that the hydrologic behaviour largely arises from the combination of AO-related late spring to early summer temperature anomalies and the presence or absence of a glacial reservoir potentially available for melting. Synoptic-scale correlation mapping of sea-level pressure fields reinforced these inferences. The results provide significant additional evidence that watershed glacierization can control the fundamental nature and patterns of regional-scale spatiotemporal water resource variability resulting from low-frequency climatic forcing. Copyright © 2005 Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

We investigated fine-scale genetic structuring in the rare and vulnerable Mallorcan midwife toad Alytes muletensis using eight polymorphic microsatellite markers. The current range of this amphibian is restricted to some 19 sites of which six are derived from reintroductions, all located in the mountain ranges of Mallorca. We sampled tadpoles from 14 pools covering 10 natural sites and two reintroduction sites for microsatellite DNA analyses. Relatively high levels of genetic variation were found in most pools ( HE = 0.38–0.71, allelic richness = 2.6–6.2). Only at one pool has the population recently gone through a bottleneck. Dispersal between pools in different torrents does not occur whereas downstream dispersal between pools within the same torrent does happen at low frequencies. This occasional exchange of individuals does not lead to neighbouring pools in the same torrent being panmictic. This can be concluded because all FST values (0.12–0.53) differ significantly from zero and structure analyses identified neighbouring pools as separate populations. Furthermore, assignment and migration tests showed little exchange between neighbouring pools. If upstream locations or complete torrents go extinct, they are unlikely to be recolonized naturally. For conservation purposes, reintroductions of tadpoles to sites where local extinctions have occurred may therefore be advisable. [ABSTRACT FROM AUTHOR]

Alterations in body shape and composition are associated with HIV/AIDS. Wasting remains prevalent; increasingly, lipodystrophy is reported. Obesity is also epidemic in the USA. In this study, we sought to characterize the body changes reported by women attending a US urban clinic, and to evaluate contributing factors using inexpensive methods that are readily available in clinical practice. In an urban Maryland clinic, a cross-section of HIV-infected women were evaluated by self report, anthropomorphic measurements, bioelectric impedance analysis (BIA) and chart review; they were categorized as no change, lipodystrophy, weight loss/wasting or weight gain/obesity. One hundred and sixty-one women were evaluated: 144 (89%) were African-American; 100 (62%) had used intravenous drugs and 40 (25%) were actively injecting drugs, while 39 (24%) smoked crack. Ninety-five (59%) were on highly active antiretroviral therapy (HAART) for a median period of 11.7 months [interquartile range (IQR)=4.5–24.2]. Since starting current HAART or in the previous year, 12 (7.4%) reported lipodystrophy changes, 85 (52.8%) weight gain, 27 (16.8%) overall weight loss, and 37 (23.0%) no change. Lipodystrophy was associated with higher CD4 percentage ( P=0.03), lower frequency of crack use ( P=0.04) and higher educational level ( P=0.03). Weight loss correlated with longer duration of infection ( P=0.01), select BIA results and increased rate of crack use ( P=0.005). Weight gain was associated with higher fat mass ( P=0.005), higher peak viral load ( P=0.02), and lower rate of intravenous drug use ( P=0.03). Self-reported changes in body shape were common. Obesity and complications of illicit drug use were more prevalent than lipodystrophy in this inner-city population of HIV-positive women. [ABSTRACT FROM AUTHOR]

Focuses on winter streamflow regimes in northern catchments to evaluate water supply and to assess the vulnerability of aquatic habitat. Objective of this study including a synoptic analysis of winter streamflow measurements archived by Water Survey of Canada for rivers in Yukon Territory, Canada; Evidence suggesting an abrupt decrease in discharge at freeze-up; Data from case studies indicating that discharge can fluctuate around a smooth recession trend as a result of transient storage and release of water behind ice jams; How a storage-depletion model provided a reasonable fit to most of the observed measurements; View that the tendency to poorer model fit in smaller catchments could reflect a problem with data reliability; Findings suggest further advances in understanding winter streamflow variability will require frequent measurements on a range of streams over a number of winters.

Objective: To examine the impact of a policy restricting reimbursement for Medicaid anti-ulcer drugs on anti-ulcer drug use and peptic-related hospitalizations.Data Sources/study Setting: In addition to U.S. Census Bureau data, all of the following from Florida: Medicaid anti-ulcer drug claims data, 1989-1993; Medicaid eligibility data, 1989-1993; and acute care nonfederal hospital discharge abstract data (Medicaid and non-Medicaid), 1989-1993.Study Design: In this observational study, a Poisson multiple regression model was used to compare changes, after policy implementation, in Medicaid reimbursement for prescription anti-ulcer drugs as well as hospitalization rates between pre- and post-implementation periods in Medicaid versus non-Medicaid patients hospitalized with peptic ulcer disease.Principal Findings: Following policy implementation, the rate of Medicaid reimbursement for anti-ulcer drugs decreased 33 percent (p < .001). No associated increase occurred in the rate of Medicaid peptic-related hospitalizations.Conclusions: Florida's policy restricting Medicaid reimbursement for anti-ulcer drugs was associated with a substantial reduction in outpatient anti-ulcer drug utilization without any significant increase in the rate of hospitalization for peptic-related conditions. [ABSTRACT FROM AUTHOR]

The TOPMODEL concept provides a simple method for parameterizing the effect of topography on the distribution of subsurface moisture and runoff production, and has been incorporated into models of catchment hydrology and forest ecology. Most evaluations of the TOPMODEL concept have been based on comparisons of stream flow hydrographs and do not necessarily provide a test of the predictions of subsurface flow and saturated source area dynamics. The objective of this study was to evaluate whether water table predictions based on the TOPMODEL concept agree with observed water table depths for a shallow forest soil in a small subcatchment drained by an ephemeral stream. Observed water table depths were fitted well by a linear statistical model that is mathematically consistent with the TOPMODEL assumptions and that specifies time and location effects independently. That is, the water table does not change shape but shifts uniformly up or down in response to changes in saturated zone storage. Residuals from the fitted model were generally less than 10 cm in absolute value, compared to observed ranges of water table depths up to 100 cm. The TOPMODEL concept predicts that the relation between the estimated location effects for the wells and the values of In ( a/tan β) should be linear, where a is the drainage area per unit contour length, and tan β is the surface slope. Regression analysis revealed that the fitted linear relation was statistically significant ( P=0.001), but weak ( R2= 0.26). This weak fit could be caused by (1) significant spatial variability in soil transmissivity (assumed negligible in many applications of TOPMODEL) and/or (2) errors in specifying In ( a/tan β) from a digital elevation model of the surface topography. Considering the increasingly common application of the TOPMODEL concept in hydrologic and ecological models, further research should be carried out to specify more clearly the bounds of applicability of its underlying assumptions and to identify workable extensions and modifications to the concept, where necessary. [ABSTRACT FROM AUTHOR]

The objective of this study was to describe the spatial and temporal structure of spring snowpack anomalies in British Columbia, Canada, and to relate the anomaly patterns to climatic fluctuations. Cluster analysis was used to identify relatively homogeneous groups of snow course sites, based on the April 1 snowpack measurements, for the periotd 1966-1992. Time series of cluster-averaged anomalies were then computed. Synoptic-scale circulation types were defined by applying a correlation-based map classification technique to gridded data sets of surface pressure and 500-hPa height levels. Frequencies of the circulation types were calculated for each winter (November to March). Total precipitation and mean temperature for each winter were calculated from monthly data from 16 climate stations. Snowpack anomalies from 1966 to 1976 were dominated by two patterns: one characterized by generally heavier-than-average snowpacks over most of the province and the other by heavier-than-average snowpacks in the south and lighter-than-average in the north. From 1977 to 1992, snowpack conditions were generally either lighter than average over the whole province or were heavier than average in the north and lighter than average in the south. Snowpack and precipitation were generally correlated, although at some stations it appears that high winter temperatures, likely causing more midwinter melt and more rain, can act to reduce the snowpack. The differences in anomaly patterns and frequencies of synoptic types between the 1966-1976 and 1977-1992 periods accord with decadal-scale shifts in sea surface temperatures and atmospheric circulation patterns over the North Pacific, as reported in the literature. The shift in snowpack anomaly patterns following 1976 is consistent with reported shifts in glacier mass balance and rates of retreat and with streamflow fluctuations. [ABSTRACT FROM AUTHOR]

A response by Armina A. Chaudhry to a letter to the editor about the Aspartate aminotransferase to platelet radio index (APRI) score which is inappropriate for assessment of liver fibrosis in HIV-infected patients with hazardous drinking.

This study examined the spatial and temporal variability of throughflow in a shallow forest oil in terms of the controls exerted by topography, soil properties and the shape of the water table. Hillslope outflow was measured at nine troughs installed at a road cut, and hydraulic head was measured at 37 piezometers installed to the confining till surface at the base of the soil. At the lowest flows, the distribution of throughflow across the hillslope conformed reasonably to thedistribution of upslope contributing area computed from the topography of the confining basal till layer. At higher flows, however, the distribution of throughflow shifted, partly as a result of changes in the orientation in flow tubes as the piezometric surface changed. At high flows, surface topography appeared to provide a reasonable proxyfor the shape of the water table. Shunting of water through discretemacropores, however, can apparently overwhelm topographic controls on throughflow, at least for slope widths less than about 10 m. Effective hydraulic conductivities computed at the scale of the troughs varied over two orders of magnitude and displayed no consistent relationship with the thickness of the saturated layer. Estimates at the plotscale (c. 10 m hillslope width) were far less variable, and for higher flows displayed an approximately linear relationship with saturated zone thickness. [ABSTRACT FROM AUTHOR]

The Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH) demonstrated the efficacy of hydroxyurea in reducing the rate of painful crises compared to placebo. We used resource utilization data collected in the MSH to determine the cost-effectiveness of hydroxyurea. The MSH was a randomized, placebo-controlled double-blind clinical trial involving 299 patients at 21 sites. The primary outcome, visit to a medical facility, was one of the criteria to define occurrence of painful crisis. Cost estimates were applied to all outpatient and emergency department visits and inpatient hospital stays that were classified as a crisis. Other resources for which cost estimates were applied included hospitalization for chest syndrome, analgesics received, hydroxyurea dosing, laboratory testing, and clinic visits for management of patient care. Annualized differential costs were calculated between hydroxyurea- and placebo-receiving patients. Hospitalization for painful crisis accounted for the majority of costs in both arms of the study, with an annual mean of $12,160 (95% CI: $9,440, $14,880) for hydroxyurea and $17,290 (95% CI: $13,010, $21,570) for placebo. The difference in means was $5,130 (95% CI: $60, $10,200; P = 0.048). Chest syndrome was the next largest cost with a mean difference of $830 (95% CI: $-340, $2,000; P = 0.16). The hydroxyurea arm was also associated with lower costs for emergency department visits, transfusion, and use of opiate analgesics. In total, the annual average cost per patient receiving hydroxyurea was $16,810 (95% CI: $13,350, $20,270) and the annual average costs per patient receiving placebo was $22,020 (95% CI: $17,340, $26,710). The difference in means was $5,210 (95% CI: $-610, $11,030; P = 0.21). The cost of hydroxyurea with the more intensive monitoring required when using this drug appears to be more than offset by decreased costs for medical care of painful crisis and analgesic use. Although the total cost difference was not significant statistically, these results suggest that hydroxyurea therapy is cost-effective compared to placebo in the management of adult patients with sickle cell anemia. If hydroxyurea can prevent development of chronic organ damage, long-term savings may be even greater.

Approximately 150 human immunodeficiency virus (HIV)-infected patients with a thrombotic microangiopathy (TMA)-like syndrome have been reported in the literature since the early 1980s. The prevalence of a TMA-like syndrome in our hospitalized patients was determined to discern whether it is a more common occurrence than previously recognized and, if possible, to delineate risk factors for its occurrence. A total of 350 patients admitted consecutively to the Johns Hopkins Hospital HIV inpatient service were assessed from May 1, 1996 through February 1, 1997. These patients were evaluated for the presence of anemia, thrombocytopenia, fragmented erythrocytes on peripheral blood smear (schistocytosis), renal dysfunction, neurologic dysfunction, and fever. The association of a TMA-like syndrome with demographic and clinical factors was analyzed. Schistocytosis was present in 24% of the patients and a TMA-like syndrome (anemia, thrombocytopenia, schistocytosis + renal dysfunction or neurologic dysfunction, and fever) was present in 7% of the patients. The patients who had a TMA-like syndrome were more likely to have a low CD4 lymphocyte count or CD4 percentage, Centers for Disease Control and Prevention stage C disease, and have bacterial sepsis. Age, race, HIV risk group, other diagnoses, and prescribed drugs were not associated. Patients were more likely to die if they had a TMA-like syndrome, independently of level of immunosuppression. Schistocytosis and a TMA-like syndrome are relatively common in hospitalized HIV-infected patients. This syndrome may contribute to mortality and morbidity, particularly in patients with more advanced disease.

The objective of this study was to report the frequency of disulfiram-related elevations of four commonly used hepatic screening chemistries using a retrospective record review design. An inpatient alcoholism program was selected for the setting. Patients who had initial laboratory values within the normal range started daily supervised doses of disulfiram, then underwent follow-up testing after 2 and 4 weeks on the drug. The study population consisted of 108 patients receiving disulfiram and 27 patients who did not receive disulfiram (controls). The four screening serum chemistries performed were aspartate aminotransferase (SGOT), alanine aminotransferase (SGPT), alkaline phosphatase, and gamma-glutamyl transferase. Twenty-seven (25%) of the 108 patients who were taking 250 mg of disulfiram a day for 2 to 4 weeks had disulfiram-related elevations in alanine aminotransferase above the upper limit of normal, as opposed to one elevation in 27 patients (4%) for whom disulfiram was not prescribed. In the 108 patients (with initially normal serum chemistries) who were prescribed disulfiram, 32 were discontinued from the drug at 2 weeks and an additional 11 were discontinued from the drug at 4 weeks because of one or more abnormal serum chemistries. Alanine aminotransferase was the most specific and sensitive indicator of the four screening chemistries performed.