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The role of spatial variability in water inputs on runoff source area dynamics has generally not received as much research attention as topography and soils; however, the influence of topography and forest cover on snow surface energy exchanges can result in asynchronous snowmelt throughout a catchment complicating the space-time patterns of runoff generation. This study investigates temporal variation in the relative importance of spatial controls on the occurrence, timing, and persistence of shallow groundwater response utilizing a highly distributed monitoring network in a snowmelt-dominated montane catchment in western Canada. The study findings indicate that 10 deep soil hydraulic conductivity is a first-order control on the distribution of sites that generate shallow groundwater response versus sites that experience only deep percolation. Upslope contributing area and slope gradient are first-order controls on the persistence of groundwater response during peak flow, recession flow, and low flow periods. Runoff source areas expand and contract throughout these periods according 15 to an interplay between catchment wetness and the spatial patterns of topographic convergence. However, controls on the differential timing, intensity, and quantity of snowmelt and controls on vertical versus lateral flux partitioning in the soil overwhelm the influence of topographic convergence on runoff source area dynamics during early spring freshet periods. The study findings suggest that various topographic indices and topography-based rainfall runoff models are not necessarily applicable to modelling snowmelt runoff source area dynamics during all streamflow periods for snowmelt-dominated montane catchments. [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]

Copyright of Canadian Water Resources Journal / Revue Canadienne des Ressources Hydriques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Glacier melt provides important contributions to streamflow in many mountainous regions. Hydrologic model calibration in glacier-fed catchments is difficult because errors in modelling snow accumulation can be offset by compensating errors in glacier melt. This problem is particularly severe in catchments with modest glacier cover, where goodness-of-fit statistics such as the Nash-Sutcliffe model efficiency may not be highly sensitive to the streamflow variance associated with glacier melt. While glacier mass balance measurements can be used to aid model calibration, they are absent for most catchments. We introduce the use of glacier volume change determined from repeated glacier mapping in a guided GLUE (generalized likelihood uncertainty estimation) procedure to calibrate a hydrologic model. We also explicitly account for changes in glacier area through the calibration and test periods. The approach is applied to the Mica basin in the Canadian portion of the Columbia River basin using the HBV-EC hydrologic model. Use of glacier volume change in the calibration procedure effectively reduced parameter uncertainty and helped to ensure that the model was accurately predicting glacier mass balance as well as streamflow. The seasonal and interannual variations in glacier melt contributions were assessed by running the calibrated model with historic glacier cover and also after converting all glacierized areas to alpine land cover in the model setup. Although glaciers in the Mica basin only cover 5% of the watershed, glacier ice melt contributes up to 25% and 35% of streamflow in August and September, respectively, and is particularly important during periods of warm, dry weather following winters with low accumulation and early snowpack depletion. The approach introduced in this study provides an effective and widely applicable approach for calibrating hydrologic models in glacier fed catchments, as well as for quantifying the magnitude and timing of glacier melt contributions to streamflow. [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]

Copyright of Canadian Water Resources Journal / Revue Canadienne des Ressources Hydriques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Context: Use of antiretroviral drugs, including protease inhibitors, for treatment of human immunodeficiency virus (HIV) infection has been anecdotally associated with hepatotoxicity, particularly in persons coinfected with hepatitis C or B virus.Objectives: To ascertain if incidence of severe hepatotoxicity during antiretroviral therapy is similar for all antiretroviral drug combinations, and to define the role of chronic viral hepatitis in its development.Design: Prospective cohort study.Setting: University-based urban HIV clinic.Patients: A total of 298 patients who were prescribed new antiretroviral therapies between January 1996 and January 1998, 211 (71%) of whom received protease inhibitors as part of combination therapy (median follow-up, 182 days) and 87 (29%) of whom received dual nucleoside analog regimens (median follow-up, 167 days). Chronic hepatitis C and B virus infection was present in 154 (52%) and 8 (2.7%) patients, respectively.Main Outcome Measure: Severe hepatotoxicity, defined as a grade 3 or 4 change in levels of serum alanine aminotransferase and aspartate aminotransferase, evaluated before and during therapy.Results: Severe hepatotoxicity was observed in 31 (10.4%) of 298 patients (95% confidence interval [CI], 7.2%-14.4%). Ritonavir use was associated with a higher incidence of toxicity (30%; 95% CI, 17.9% -44.6%). However, no significant difference was detected in hepatotoxicity incidence in other treatment groups, ie, nucleoside analogs (5.7%; 95% CI, 1.2%-12.9%), nelfinavir (5.9%; 95% CI, 1.2%-16.2%), saquinavir (5.9%; 95% CI, 0.15%-28.7%), and indinavir(6.8%; 95% CI, 3.0%-13.1 %). Although chronicviral hepatitis was associated with an increased risk of severe hepatotoxicity among patients prescribed nonritonavir regimens (relative risk, 3.7; 95% CI, 1.0-11.8), most patients with chronic hepatitis C or B virus infection (88%) did not experience significant toxic effects. Rate of severe toxicity with use of any protease inhibitor in patients with hepatitis C infection was 12.2% (13/107; 95% CI, 6.6%-19.9%). In multivariate logistic regression, only ritonavir (adjusted odds ratio [AOR], 8.6; 95% CI, 3.0-24.6) and a CD4 cell count increase of more than 0.05 x 10(9)/L (AOR, 3.6; 95% CI, 1.0-12.9) were associated with severe hepatotoxicity. No irreversible outcomes were seen in patients with severe hepatotoxicity.Conclusions: Our data indicate that use of ritonavir may increase risk of severe hepatotoxicity. Although hepatotoxicity may be more common in persons with chronic viral hepatitis, these data do not support withholding protease inhibitor therapy from persons coinfected with hepatitis B or C virus. [ABSTRACT FROM AUTHOR]

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]

Background: In clinical trials, highly active antiretroviral therapy (HAART) reduces plasma HIV-1 RNA levels to less than 500 copies/mL in 60% to 90% of patients with HIV-1 infection. The performance of such therapy outside of the clinical trial setting is unclear.Objective: To determine factors associated with failure to suppress HIV-1 RNA levels and adverse drug reactions in a cohort of patients in whom protease inhibitor-containing therapy was begun in a large urban clinic.Design: Retrospective cohort study.Setting: Johns Hopkins HIV Clinic in Baltimore, Maryland.Patients: 273 protease inhibitor-naive patients began taking a protease inhibitor regimen containing at least one other antiretroviral drug to which the patients had not previously been exposed.Measurements: Demographic variables, plasma HIV-1 RNA levels, CD4+ lymphocyte counts, and adverse drug reactions.Results: Levels of HIV-1 RNA were undetectable in 42% of the cohort at 1 to 90 days, in 44% at 3 to 7 months, and in 37% at 7 to 14 months. Factors associated with failure to suppress viral load at two or more time points included higher rates of missed clinic appointments, nonwhite ethnicity, age 40 years or younger, injection drug use, lower baseline CD4+ lymphocyte count, and higher baseline viral load. In a multivariate model, only higher rates of missed clinic appointments were independently associated with viral suppression at 1 year. Ritonavir was associated with adverse drug reactions about twice as frequently as indinavir or nelfinavir, and women experienced significantly more adverse effects than men.Conclusions: Unselected patients in whom HAART is started in a clinic setting achieve viral suppression substantially less frequently than do patients in controlled clinical trials. Missed clinic visits were the most important risk factor for failure to suppress HIV-1 RNA levels. Studies are needed to identify interventions that maximize the performance of HAART in inner-city clinics. [ABSTRACT FROM AUTHOR]

As part of an institution-wide program to enhance the education of physicians in diagnosing and treating alcohol dependence and abuse, a comprehensive survey was conducted in which all new admissions to the adult inpatient services of The Johns Hopkins Hospital were screened for alcoholism. The prevalence of screen-positive alcoholism, by department, was as follows: medicine (25%), psychiatry (30%), neurology (19%), obstetrics-gynecology (12.5%), and surgery (23%). Detection rates by the house staff and faculty physicians caring for those patients who screened positively were less than 25% in surgery and obstetrics-gynecology, between 25% and 50% in neurology and medicine, and greater than 50% in psychiatry. However, physicians were less likely to identify as alcoholic those patients with higher incomes, higher education, or private medical insurance; women; and those who denied heavy alcohol intake. Physician-instituted treatment rates for those patients diagnosed by the physician as having nonrecovered alcoholism were less than 50% in surgery and obstetrics-gynecology, between 50% and 75% in medicine and neurology, and 100% in psychiatry. The extent to which the physicians intervened while the patient was hospitalized correlated with the patient's reported change in alcohol use after discharge. Recommendations based on these data are being incorporated into the medical education curriculum. [ABSTRACT FROM AUTHOR]

Purpose: Drug therapies for patients with human immunodeficiency virus (HIV) infection are associated with adverse events that can potentially limit their effectiveness. We sought to quantify the incidence of these events in clinical practice and determine whether there were demographic and clinical differences in adverse event rates for these drugs.Patient and Methods: We calculated specific and overall adverse event rates from use of zidovudine, didanosine, zalcitabine, cotrimoxazole, and dapsone in an observational urban cohort of 1,450 HIV-infected patients with a CD4+ count of 500 cells/mm3 or less. We compared adverse event rates by gender, race, age, injecting drug use, and CD4+ count.Results: Overall adverse event rates in order of incidence were dapsone, 16.2 per 100 person-years (PY); didanosine, 24.1 per 100 PY; zidovudine, 26.3 per 100 PY; cotrimoxazole, 26.3 per 100 PY; and zalcitabine, 37.0 per 100 PY. Rates increased significantly with decline in CD4+ count from > 200 to < 100 cells/mm3 for all drugs but dapsone. In addition, women were more likely than men to have an adverse event for didanosine (relative risk [RR] = 2.7, P = 0.03) and from cotrimoxazole (RR 1.5; P = 0.05). Whites were at greater risk than blacks for adverse events from cotrimoxazole (RR = 1.6, P = 0.03). Only 22 of 357 total events (6%) required hospitalization, and there were no deaths.Conclusions: Adverse events from antiretroviral drugs and Pneumocystis carinii pneumonia prophylaxis that interrupt therapy are relatively common, although serious events requiring hospitalization are rare. Adverse event rates increase progressively with decline in CD4+ count. The gender and race of the patient modify the risk of adverse events for some drugs. [ABSTRACT FROM AUTHOR]

Objective: To determine the effect of contemporary clinical care on the natural history of opportunistic disease in an urban population infected with human immunodeficiency virus (HIV).Setting: Urban university HIV clinic.Design: Retrospective and prospective observational study.Patients: 1246 HIV-infected patients with CD4+ counts of 300 cells/mm3 or less.Measurements: Incidence rates and Kaplan-Meier estimates of the probability of developing opportunistic disease with time, distribution of the CD4+ counts at which opportunistic disease develops, survival after the development of opportunistic disease, and the association between preventive drug therapies and the occurrence of opportunistic infection.Results: The most common opportunistic disease was Candida esophagitis, which had an incidence of 13.3 events per 100 person-years and a 3-year Kaplan-Meier probability of 0.30. Pneumocystis carinii pneumonia, Mycobacterium avium complex bacteremia, cytomegalovirus, and the acquired immunodeficiency syndrome dementia complex occurred at rates of 5 to 9 events per 100 person-years and 3-year Kaplan-Meier probabilities of 0.15 to 0.22. Toxoplasmosis, cryptococcal meningitis, herpes zoster, the wasting syndrome, and Kaposi sarcoma occurred at rates of about 2 to 4 events per 100 person-years and with 3-year Kaplan-Meier probabilities of 0.05 to 0.10. Non-Hodgkin lymphoma, M. tuberculosis infection, progressive multifocal leukoencephalopathy, and cryptosporidiosis were the least common disorders, with an incidence of about 1 to 2 events per 100 person-years and a 3-year Kaplan-Meier probability less than 0.05. Only the incidences of cryptococcal meningitis, secondary P. carinii pneumonia, and herpes zoster decreased (P < 0.05) between 1989-1992 and 1993-1995. Fluconazole use was associated with a decreased relative rate of 0.49 (P = 0.06) for cryptococcal meningitis and a decreased relative rate of 0.61 (P = 0.005) for esophageal candidiasis. Rifabutin use was associated with a decreased relative rate of 0.37 (P = 0.002) for M. avium complex bacteremia, and trimethoprim-sulfamethoxazole use was associated with decreased relative rates of 0.33 (P = 0.02) for secondary P. carinii pneumonia and 0.55 (P = 0.08) for primary P. carinii pneumonia. Candidiasis, herpes zoster, and M. tuberculosis infection first occurred at a median CD4+ count greater than 100 cells/mm3, but all other opportunistic diseases first occurred at a median CD4+ count less than 50 cells/mm3. Median survival after diagnosis varied from 35 days for non-Hodgkin's lymphoma to 680 days for herpes zoster.Conclusions: In the patients studied, the incidences of secondary P. carinii pneumonia, cryptococcal meningitis, and herpes zoster have declined in the past 5 years. The incidences of primary P. carinii pneumonia and Kaposi sarcoma appear to be declining compared with historical estimates. However, although these and other opportunistic diseases continue to be relatively frequent complications of HIV infection, they are first occurring at more advanced immunosuppression than in the past. Continued efforts are needed to develop effective strategies for preventing opportunistic disease in very advanced HIV infection. [ABSTRACT FROM AUTHOR]