Summary
1. Diel variation in metabolism contributes to variation in oxygen (O2) concentrations in streams. This variation in O2 and other parameters (e.g. pH) can in turn affect the rates of ...microbial nitrogen (N) processing, concentrations of nitrogenous solutes and production of the greenhouse gas nitrous oxide (N2O). We investigated diel variability in emissions of N2O and the magnitude of short‐term variability in N solutes across 10 streams.
2. Nitrous oxide fluxes varied on average 2.3‐fold over diel cycles. Concentrations would be underestimated by sampling around noon, but N2O fluxes would not show a consistent bias. Time‐weighted mean daily N2O flux was strongly related to nitrate concentration (r2 = 0.58). Diel patterns in N2O and dissolved N species were often complex (rather than simple sinusoidal curves), probably reflecting complex underlying processes.
3. Reliance on samples obtained around noon would overestimate daily mean nitrate concentrations by 5% and underestimate ammonium by 32% (average bias across all streams and dates).
4. Dissolved organic N did not show consistent day–night variation. However, the magnitude of diel variability was similar to that observed for dissolved inorganic N. Organic and inorganic N concentrations were often similar. Both appear to be dynamic components of stream N budgets.
5. The Intergovernmental Panel on Climate Change (IPCC) relies upon an emission factor to estimate indirect agricultural N2O emissions from streams and ground water. The measured emission factor (defined as the ratio of concentrations of N2O‐N to ‐N) was typically below the recently revised IPCC default figure. Measured values varied on average 1.8‐fold over approximately 24‐h periods and were slightly higher at night than by day. The emission factor was actually highest in streams that were net sinks for N2O, highlighting a conceptual problem in the current IPCC method.
6. Typical sampling programmes rely on daytime‐only sampling, which might cause bias in results. In our study streams, the bias was generally small. Diel variation in nitrate concentrations was related to mean temperature; variation in ammonium and N2O concentrations was greatest at low concentrations of nitrite and ammonium.
A field study evaluated the performance of direct well recharge structures (DWRS) in order to harvest and filter farm runoff and its discharge into open dug wells to augment groundwater recharge. ...This was undertaken between 2016 and 2018 using a total of 11 wells in the Dharta watershed, situated in a semi-arid hardrock region of Udaipur district, Rajasthan, India. The depth to water level in each DWRS well was monitored weekly for 1 to 3 years before and after the DWRS was established, and water samples were taken for water quality analysis (pH, electrical conductivity (EC), total dissolved solids (TDS), turbidity, fluoride, and Escherichia coli) before and during the monsoon period. For each DWRS well, two control wells in close proximity were also monitored and sampled. Five of the DWRS established in 2018 also had flow meters installed in order to measure discharge from the filter to the well. The volume of water recharged through DWRS into individual wells during the 2018 monsoon ranged from 2 to 176 m3 per well. Although the mean rise in water levels over the monsoon was higher in DWRS wells than in nearby control wells, the difference was not significant. Values of pH, EC, TDS, and F decreased in DWRS and control wells as each monsoon progressed, whereas the turbidity of wells with DWRS increased slightly. There was no significant difference between DWRS and control wells for pH, EC/TDS, turbidity, or fluoride. The presence of E. coli in DWRS wells was higher than in control wells, however, E. coli exceeded drinking water guidelines in all sampled wells. On the basis of this study, it is recommended that rural runoff should not be admitted to wells that are used for, or close to, wells used for drinking water supplies, even though salinity and fluoride concentrations may be reduced. For this study, none of the 11 DWRS wells produced sufficient additional recharge to potentially increase dry season irrigation supplies to justify expenditure on DWRS. This even applies to the DWRS well adjacent to a small ephemeral stream that had a significantly larger catchment area than those drawing on farmers’ fields alone. An important and unexpected finding of this study was that no sampled open dug well met drinking water standards. This has led to a shift in local priorities to implement well-head water quality protection measures for wells used for drinking water supplies. It is recommended that parapet walls be built around the perimeter of such dug wells, as well as having covers be installed.
Abstract Background Carotid endarterectomy (CEA) has been performed since the 1950s and remains one of the most common surgical procedures in the United States. The procedure is performed by ...cardiothoracic, general, neurologic, and vascular surgeons. This study uses data from the National Surgical Quality Improvement Program (NSQIP) to examine the outcomes after CEA when performed by general or vascular surgeons. Materials and methods Data included 34,493 CEAs from years 2005 to 2010 recorded in the NSQIP database. Primary outcomes measured were length of stay, 30-d mortality, surgical site infection, cerebrovascular accident, myocardial infarction, and blood transfusion requirement. Secondary outcomes measured were the remaining intraoperative outcomes from the NSQIP database. Results After controlling for patient and surgical characteristics, patients treated by general surgeons did not have a significantly different LOS or 30-d mortality than those treated by vascular surgeons. Patients of general surgeons had nearly twice the risk of acquiring a surgical site infection (odds ratio OR = 1.94; P = 0.012), >1.5 times the risk of cerebrovascular accident (OR = 1.56; P = 0.008), and >1.8 times the risk of blood transfusion (OR = 1.85; P = 0.017) than those of vascular surgeons. Patients of general surgeons had less than half the risk of having a myocardial infarction (OR = 0.34; P = 0.031) than those of vascular surgeons. Conclusions Surgical specialty is associated with a wide range of postoperative outcomes after CEA. Additional research is needed to explore practice and cultural differences across surgical specialty that may lead to outcome differences.
Well-clogging remains a major operational issue, particularly in light of the increased attention being given to the reuse of reclaimed water through the method of aquifer storage and recovery (ASR) ...in seasonally arid regions. At a reclaimed water ASR trial site in a limestone aquifer at Bolivar in South Australia, rates of clogging were related to the quality of the injectant over a 4 year study period, during which time water quality generally improved due to advancements in pretreatment. Rates of clogging within a 4
m radius of the ASR well, defined by changes in the relative intrinsic permeability of the aquifer, were enhanced at higher levels of turbidity, total nitrogen (N
TOT) and pH due to their resultant effects on particle filtration, microbial growth, and calcite dissolution, respectively. Water quality changes due to the movement of the injectant to an observation well at a radius of 4
m verified these processes. At this site acceptably low rates of short- and long-term clogging were achieved for turbidity
<
3 NTU, N
TOT
<
10
mg/L and pH
<
7.2. A mass balance model that incorporated these three processes consistently reproduced the observed permeability changes for related column experiments and provided estimates of model parameters. When applied to the field trial, the model reproduced some but not all of the major long-term clogging trends and demonstrated that the extent of clogging is largely driven by the interaction and relative dominance of the three key processes as affected by variations in the source water quality.
Investment in the small-scale enhancement of groundwater recharge through check dams and other recharge structures in rural India is on the order of USD 1 billion/year. However, for any catchment, ...the optimal capacity of check dams is unknown, and the impacts on downstream flows are rarely determined. This paper describes a method that can be applied to plan recharge augmentation in catchments that have at least one monitored check dam. It was applied in the Dharta catchment of the Aravalli Hills in Udaipur district, Rajasthan, India, where four check dams in an ephemeral stream were monitored by farmers over seven years. For the last three years of this study, the hydrology of two of these check dams was affected by 19 new check dams established upstream. A basic hydrologic model, WaterCress, was calibrated on monitored check-dam storages and used to assess the impacts of the new structures on recharge from those downstream. Then, the model was rerun with a range of capacities of upstream check dams to determine the effects of check-dam capacity on (1) the recharge from the downstream check dam, (2) the total recharge from all check dams, and (3) the frequency of spill from the downstream check dam. Using the available economic information, the benefit–cost ratio was calculated for a range of check-dam capacities. This showed a decline in economic efficiency with each new check dam and defined the optimal capacity. Monsoon size was found to be consequential to results, and longer hydrological records yield more reliable results. The study showed that monitoring check dams, rainfall, and groundwater levels is key to deciding whether additional check dams are economically beneficial.
Interest is growing in preventing readmissions as payers start to link reimbursement to readmission rates. The purpose of this study was to assess factors that contribute to 30‐day readmission rates ...for women undergoing mastectomy for breast cancer. Data from the Pennsylvania Health Care Cost Containment Council were queried for women undergoing mastectomy for breast cancer during 2011 (n = 2,919). The outcomes measured were length of stay (LOS) and 30‐day readmission. Univariate comparisons between characteristics of readmitted (n = 172) and nonreadmitted patients were performed using t‐tests and chi‐square tests. Readmission was modeled using logistic regression; LOS was modeled using linear regression and controlled for potential confounders. In multivariate analyses, patients with peripheral vascular disease were more likely to be readmitted (OR 4.36, p = 0.002). Increased LOS was also associated with increased odds of readmission (OR 1.26, p = <0.0001). Since LOS was an important predictor of readmission we also estimated determinants of LOS using linear regression. The occurrence of reconstructive surgery (p = <0.0001) and renal disease (p < 0.0001) were highly predictive of longer LOS. This study showed peripheral vascular disease and longer lengths of stay were associated with higher odds of readmission in women undergoing mastectomy. Clinicians should be cognizant that optimizing a patient's vascular status before mastectomy may lead to lower rates of readmission. Additional research is needed to determine whether the relationship between readmissions and length of hospital stay is a causative versus associative phenomenon since LOS is a modifiable factor that may lead to lower readmissions.
The purpose of this study was to compare the cost-effectiveness of the National Surgical Quality Improvement Program (NSQIP) at an academic medical center between the first 6 months and through the ...first and second years of implementation.
The NSQIP has been extended to private-sector hospitals since 1999, but little is known about its cost-effectiveness.
Data included 2229 general or vascular surgeries, 699 of which were conducted after NSQIP was in place for 6 months. We estimated an incremental cost-effectiveness ratio (ICER) comparing costs and benefits before and after the adoption of NSQIP. Costs were estimated from the perspective of the hospital and included hospital costs for each admission plus the total annual cost of program adoption and maintenance, including administrator salary, training, and information technology costs. Effectiveness was defined as events avoided. Confidence intervals and a cost-effectiveness acceptability curve were computed by using a set of 10,000 bootstrap replicates. The time periods we compared were (1) July 2007 to December 2007 to July 2008 to December 2008 and (2) July 2007 to June 2008 to July 2008 to June 2009.
The incremental costs of the NSQIP program were $832 and $266 for time periods 1 and 2, respectively, yielding ICERs of $25,471 and $7319 per event avoided. The cost-effectiveness acceptability curves suggested a high probability that NSQIP was cost-effective at reasonable levels of willingness to pay.
In these data, not only did NSQIP appear cost-effective, but also its cost-effectiveness improved with greater duration of participation in the program, resulting in a decline to 28.7% of the initial cost.
Decreases in exchangeable base cation reservoirs, base cation export, and lake concentrations have been reported for acid-sensitive regions in Europe and eastern North America. These decreases have ...produced smaller than anticipated increases in alkalinity in surface waters in response to reductions in sulphate emissions and may have ecological consequences. This study presents annual export rates of Ca, Mg, K, and Na from 20 forested catchments between 1978 and 1998 and concentrations in seven downstream lakes between 1975 and 2005 in an acid-sensitive region of central Ontario, Canada. In contrast to monovalent cation export, decreases in divalent cation export continued after an extended dry period ended. Lake concentration trends showed three distinct periods. The first period (1975-1976 to 1982-1983) coincided with high runoff and was characterized by relatively high Ca, Mg, and K concentrations. This was followed by a 10-year period of fluctuations around the long-term mean. Concentrations then dropped below the long-term means and remained 5%-20% below the means until 2004-2005. The latter trend in lake concentrations suggests that export likely remained low but stable after May 1998 (the last month for which export data are available). Na increased between 250% and 350% in Dickie and Harp lakes as a result of road salt contamination.
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