The influence of flow and bed slope on gas transfer in steep streams and their implications for evasion of CO2

The evasion of greenhouse gases (including CO2, CH4 and N2O) from streams and rivers to the atmosphere is an important process in global biogeochemical cycles, but our understanding of gas transfer in steep (> 10%) streams, and under varying flows is limited. We investigated gas transfer using combined tracer injections of SF6 and salt. We used a novel experimental design in which we compared four very steep (18.4-29.4%) and four moderately steep (3.7-7.6%) streams, and conducted tests in each stream under low flow conditions and during a high discharge event. Most dissolved gas evaded over short distances (~100 and ~200-400 m respectively), so accurate estimates of evasion fluxes will require sampling of dissolved gases at these scales to account for local sources. We calculated CO2 gas transfer coefficients (KCO2) and found statistically significant differences between larger KCO2 values for steeper (mean 0.465 min-1) streams compared to those with shallower slopes (mean 0.109 min-1). Variations in flow had an even greater influence. KCO2 was substantially larger under high (mean 0.497 min-1) compared to low flow conditions (mean 0.077 min-1). We developed a statistical model to predict KCO2 using values of streambed slope x discharge which accounted for 94 % of the variation. We show that two models using slope and velocity developed by Raymond et al. [2012] for streams and rivers with shallower slopes, also provide reasonable estimates of our CO2 gas transfer velocities (kCO2; m d-1). We developed a robust field protocol which could be applied in future studies

Sensitivity of Point of Care Ultrasound in Blunt Trauma Abdomen and Thorax at a Tertiary Care Center in Northern Kerala

BACKGROUND Road traffic accidents are the most common cause of thoracic and abdominal trauma. The role of point of care ultrasound especially in developing countries is gaining evidence in management of acutely ill. We wanted to test the reliability of Fast and E-Fast in blunt abdominal and thoracic trauma cases and evaluate their role in the management of RTAs. METHODS A cross sectional study was conducted over a 12-month period among patients presenting at Emergency Medicine Department at Government Medical College, Kannur (then known as Academy of Medical Sciences, Pariyaram). After clinical examination and recording details, fast and E-Fast was done in the emergency department by emergency physicians trained in ATLS using a standard curvilinear probe of 2 - 5 MHz using Sonosite M-Turbo portable ultrasound machine (Fujifilm Sonosite) and compared with the gold standard CT. The CT used was 16 slice Spiral CT scan machine by GE Healthcare (Chicago, Illinois, United States). Results on continuous measurements presented on mean + SD (min-max) and results on categorical measurements were presented in numbers (%). Sensitivity and specificity were computed for analysis. RESULTS The overall sensitivity of Fast is 72.8 % and the specificity is 92 %. The overall sensitivity and specificity of E-Fast are 87 % and 92.3 % respectively. The reliability of point of care ultrasound as a screening tool to triage patients with blunt abdominal and thoracic trauma is 100 %. CONCLUSIONS Fast and E-Fast are quite reliable as screening tools in the management of acutely ill blunt trauma abdomen and chest patients. KEYWORDS Point of Care, Ultrasound, Blunt Trauma, Sensitivity, Fast, E-Fast</jats:p

Outcome of early emergency intubation and early emergency dialysis in deliberate self-harm with formic acid in a tertiary care center in South India: A retrospective cohort study

OBJECTIVE: The objective is to evaluate the outcome of early emergency intubation and early dialysis in formic acid (FA) poisoning and to determine the clinical features associated with its mortality. METHODS: It is a retrospective cohort study of 78 patients who presented to the emergency medicine department from July 2008 to June 2015 with alleged history and clinical features of FA poisoning. The outcome of early intubation and early dialysis was studied in terms of 7-day and 30-day mortality. The outcome was compared in severe and not severe groups separately. Severity was graded according to Med-Tu chart used for corrosive poisoning. RESULTS: In the severe group (n = 53), early dialysis was done in 15 patients. There was 53% (n = 8) 30-day mortality. In the group where early dialysis was not done there was a significant increase in mortality 92.1% (n = 35). This was statistically significant with a P = 0.003. In a similar fashion 7-day mortality was analyzed in the severe group where mortality was higher when early dialysis was not done. In not severe group early dialysis has minimally decreased the mortality. Early intubation in severe group did not demonstrate any mortality benefit. Patients who were intubated early and not intubated early had equally high mortality. In not severe group, intubation could not make any significant difference in mortality. CONCLUSION: In this retrospective study, we observed that early dialysis in the severe group has a better outcome in terms of 7-day and 30-day mortality

Water striders (family Gerridae): mercury sentinels in small freshwater ecosystems

To circumvent some of the previous limitations associated with contaminant-monitoring programs, we tested the suitability of the water strider (Hemiptera: Gerridae) as a mercury sentinel by comparing total mercury concentrations in water striders and brook trout (Salvelinus fontinalis) from a variety of stream sites in New Brunswick, Canada. There was a strong association between the two variables across sites (r2 = 0.81, P < 0.001) in systems where both atmospheric deposition and a point source (an abandoned gold mine) were likely contributing to ambient mercury levels. In a small stream draining the gold mine tailings pile, water striders had mercury concentrations an order of magnitude higher than those from reference locations. Temporal variation at three southern New Brunswick stream sites was non-significant. These results suggest that water strider mercury levels accurately quantify food chain entry of the element. The use of sentinel species holds great potential for expanding contaminant-monitoring programs. Water striders accurately reflect the entry of mercury in food chains of small freshwater systems.No Full Tex

Spatiotemporal variability of the gas transfer coefficient (KCO2) in boreal streams: implications for large scale estimates of CO2 evasion

Boreal streams represent potentially important conduits for the exchange of carbon dioxide (CO2) between terrestrial ecosystems and the atmosphere. The gas transfer coefficient of CO2 (KCO2) is a key variable in estimating this source strength, but the scarcity of measured values in lotic systems creates a risk of incorrect flux estimates even when stream gas concentrations are well known. This study used 114 independent measurements of KCO2 from 14 stream reaches in a boreal headwater system to determine and predict spatiotemporal variability in KCO2. The KCO2 values ranged from 0.001 to 0.207 min−1 across the 14 sites. Median KCO2 for a specific site was positively correlated with the slope of the stream reach, with higher gas transfer coefficients occurring in steeper stream sections. Combining slope with a width/depth index of the stream reach explained 83% of the spatial variability in KCO2. Temporal variability was more difficult to predict and was strongly site specific. Variation in KCO2, rather than pCO2, was the main determinant of stream CO2 evasion. Applying published generalized gas transfer velocities produced an error of up to 100% in median instantaneous evasion rates compared to the use of actual measured KCO2 values from our field study. Using the significant relationship to local slope, the median KCO2 was predicted for 300,000 km of watercourses (ranging in stream order 1–4) in the forested landscape of boreal/nemoral Sweden. The range in modeled stream order specific median KCO2 was 0.017–0.028 min−1 and there was a clear gradient of increasing KCO2 with lower stream order. We conclude that accurate regional scale estimates of CO2 evasion fluxes from running waters are possible, but require a good understanding of gas exchange at the water surface

Dissolved inorganic carbon export across the soil/stream interface and its fate in a boreal headwater stream

The aim of this investigation was to determine the lateral export of dissolved inorganic carbon (DIC) from soils of a Swedish boreal forest to a first order stream and to estimate the partitioning of this DIC into CO2 evasion from the stream surface and the DIC pool exported down through the catchment by streamwater. The groundwater entering the stream was supersaturated with CO2 with values as high as 17 times equilibrium with the atmosphere. Up to 90% of the estimated daily soil DIC export to the stream was emitted to the atmosphere as CO2 within 200 m of the water entering the stream. The annual DIC export from the soil to the stream was estimated to be 3.2 ((0.1) g C m-2 yr-1 (normalized to catchment size). Ninety percent of the variation in soil DIC export could be explained by the variation in groundwater discharge and the DIC concentrations per se,were of minor importance. Asignificant correlation (R2 ) 0.74, P < 0.01) between soil DIC export and CO2 emission from the stream surface suggests that emission dynamics were primarily driven by the export of terrestrial DIC and that in-stream processes were less important. Our results reveal that current budget estimates of lateral DIC export from soils to aquatic conduits need to be revised because they do not account for conditions prevailing in headwater streams. Any quantification of lateral stream C export and CO2 emissions from freshwater systems must include headwater streams as well as the lower parts of the aquatic conduit