High Flow Conditions Research Articles

Open-Source Code-Based Tidal Modeling of Tropical and Temperate Waters

Tidal energy is the most reliable and predictable form of renewable energy capable of ensuring energy security in coastal regions of the world. Many developing countries are prone to energy self-sufficiency due to a lack of tidal data, expensive commercial tidal modeling tools, and program codes. In the present study, an open-source finite element code along with available open-source data was used to predict the tidal resource potential of sites in both temperate and coastal waters. This paper also investigates the suitability of open-source code towards accurate tidal resource prediction and provides a comparative study on tidal resource prediction of sites in both temperate and coastal waters. Based on knowledge gained from tidal experts all around the globe, the straits of the Alderney race were selected as a temperate water site because of their high tidal flow conditions and high tidal energy resource potential. Singapore was selected as a tropical water site because of its low tidal flow conditions and lack of open-source tidal resource data in the tropical belt. From the results, temperate waters such as Alderney Race experience high tidal velocity in the range of 3.5–4.5 m/s with an average power density of about 15 kW/m2 in comparison with tropical waters such as Singapore that experiences tidal velocity in the range of 1–1.5 m/s with an average power density of about 1.5 kW/m2. The thrusting force behind the coastal dynamics is mainly due to tides, their interactions, and changes in seabed topography. The seabed roughness profile creates a drag force on the flow on the velocity field. Lack of understanding of the effects of seabed friction on tidal modeling might reduce the accuracy of the model prediction. Thus, the present study also focuses on the effects of seabed roughness on tidal prediction of Alderney race straits using the open-source finite element-based 2-dimensional depth average ocean model. It can be found that an increase in seabed friction reduces the flow velocity and thus the average power density of the location due to its major energy dissipating phenomenon for the energetic ocean flow.

Radiocesium leaching from litter during rainstorms in the Fukushima broadleaf forest

Forests are important sources of dissolved radiocesium (137Cs) discharge downstream. To improve understanding of dissolved 137Cs discharge processes during rainstorms, we investigated the relationship between rainfall-runoff hydrological processes and the discharge of 137Cs leached from litter. Leaching tests were conducted with broadleaf litter collected in the area where saturated overland flow was generated during rainstorms in a broadleaf-tree-dominated forest. According to the leaching test results, the 137Cs leaching rate was higher in the early stage of the test and decreased afterward. There was no significant difference in the overall results between the agitation and non-agitation cases. The 137Cs leaching rate from litter after the 24-h test was up to 33.7%. A large proportion of the original 137Cs activity was present even after the tests, as leaching from litter during rainstorms in the headwater area could be an additional source of dissolved 137Cs in the stream water. If mixing of 137Cs originating from groundwater, soil water, and rainfall with the hydrological processes is assumed, differences between the observed and estimated 137Cs in the surface runoff water became larger under high flow conditions. This analysis indicates additional 137Cs loading on surface runoff water during rainstorms, where saturated surface area can expand as the surface runoff rate increases. Contact area between surface runoff and litter accumulated on the forest floor should increase and accelerate 137Cs leaching from the litter. Therefore, 137Cs leaching in the saturated surface area that is temporarily formed during rainstorms can play a principal role in dissolved 137Cs discharge during rainfall-runoff events. Contaminated litter in the temporally saturated region of forested headwaters is an important factor contributing to elevated levels of dissolved 137Cs during rainstorms in the Fukushima area.

Large-Scale Particle Image Velocimetry to Measure Streamflow from Videos Recorded from Unmanned Aerial Vehicle and Fixed Imaging System

The accuracy of river velocity measurements plays an important role in the effective management of water resources. Various methods have been developed to measure river velocity. Currently, image-based techniques provide a promising approach to avoid physical contact with targeted water bodies by researchers. In this study, measured surface velocities collected under low flow and high flow conditions in the Houlong River, Taiwan, using large-scale particle image velocimetry (LSPIV) captured by an unmanned aerial vehicle (UAV) and a terrestrial fixed station were analyzed and compared. Under low flow conditions, the mean absolute errors of the measured surface velocities using LSPIV from a UAV with shooting heights of 9, 12, and 15 m fell within 0.055 ± 0.015 m/s, which was lower than that obtained using LSPIV on video recorded from a terrestrial fixed station (i.e., 0.34 m/s). The mean absolute errors obtained using LSPIV derived from UAV aerial photography at a flight height of 12 m without seeding particles and with different seeding particle densities were slightly different, and fell within the range of 0.095 ± 0.025 m/s. Under high flow conditions, the mean absolute errors associated with using LSPIV derived from terrestrial fixed photography and LSPIV derived from a UAV with flight heights of 32, 62, and 112 m were 0.46 m/s and 0.49 m/s, 0.27 m, and 0.97 m/s, respectively. A UAV flight height of 62 m yielded the best measured surface velocity result. Moreover, we also demonstrated that the optimal appropriate interrogation area and image acquisition time interval using LSPIV with a UAV were 16 × 16 pixels and 1/8 s, respectively. These two parameters should be carefully adopted to accurately measure the surface velocity of rivers.

Regionalization of hydrological models for flow estimation in ungauged catchments in Ireland

Study RegionThe study area consists of 44 catchments across Ireland. Study FocusWe regionalize two hydrological models (GR4J and GR6J) to produce continuous discharge simulations and compare performance in simulating high, median and low flow conditions with other established approaches to prediction in ungauged basins and a simple benchmark of using the median parameter set across all catchments. These include K-nearest neighbor (KNN) and statistical methods for predicting flow quantiles using catchment characteristics. Different objective functions were selected for different parts of flow regime and the success of different methods for regionalizing hydrological model parameters; including multiple linear regression (MLR), non-linear regression (NL) and random forests (RF) were evaluated. New Hydrological insights for the RegionAll regionalization approaches perform well for average flow conditions. The GR4J model regionalized using RF performs best for simulating high flows, though all regionalized models underestimate the median annual flood. GR6J regionalized using RF performs best for low flows. While KNN and statistical approaches that directly leverage physical catchment descriptors provide comparable median performances across catchments, the spread in relative error across our sample is reduced using regionalized hydrological models. Our results highlight that the choice of hydrological model, objective functions for optimization and approach to linking model parameters and physical catchment descriptors significantly influence the success of regionalization for low and high flows.

Identifying Sources of Faecal Contamination in a Small Urban Stream Catchment: A Multiparametric Approach.

Small urban streams discharging in the proximity of bathing waters may significantly contribute to the deterioration of water quality, yet their impact may be overlooked. This study focuses on the Elm Park stream in the city of Dublin that is subject to faecal contamination by unidentified sources. The aim of the study was to identify a minimum number of “sentinel” sampling stations in an urban catchment that would provide the maximum amount of information regarding faecal pollution in the catchment. Thus, high-resolution sampling within the catchment was carried out over the course of 1 year at 11 stations. Faecal indicator bacteria were enumerated and microbial source tracking (MST) was employed to evaluate human pollution. In addition, ammonium, total oxidised nitrogen, and phosphorus levels were monitored to determine if these correlated with faecal indicator and the HF183 MST marker. In addition, the effect of severe weather events on water quality was assessed using automated sampling at one of the identified “sentinel” stations during baseflow and high flow conditions over a 24-h period. Our results show that this urban stream is at times highly contaminated by point source faecal pollution and that human faecal pollution is pervasive in the catchment. Correlations between ammonium concentrations and faecal indicator bacteria (FIB) as well as the human MST marker were observed during the study. Cluster analysis identified four “sentinel” stations that provide sufficient information on faecal pollution in the stream, thus reducing the geographical complexity of the catchment. Furthermore, ammonium levels strongly correlated with FIB and the human HF183 MST marker under high flow conditions at key “sentinel” stations. This work demonstrates the effectiveness of pairing MST, faecal indicators, and ammonium monitoring to identify “sentinel” stations that could be more rapidly assessed using real-time ammonium readouts to assess remediation efforts.

Contrasting distribution of REE and yttrium among particulate, colloidal and dissolved fractions during low and high flows in peri-urban and agricultural river systems

Understanding the possible consequences of anthropogenic activities on REY environmental fate and adverse effects on biota requires a detailed knowledge of their distribution between the particulate, colloidal and dissolved fractions. Such information is practically non-existent for peri-urban rivers having heavily populated basins and suffering from direct impacts from various human activities. The present study compared the distribution of REY among the particulate (>1000 nm), coarse colloidal (1000 nm – 220 nm), small colloidal (220 nm – 10 kDa) and dissolved (<10 kDa) water fractions in two peri-urban river basins having contrasted land uses (agricultural vs urban/industrial) under low and high flow conditions. Regardless of hydrological conditions, most of the REY were in the particulate fraction for both catchments. These results suggest erosion of soils as the main source of particulate REY in the two rivers, although a Nd anomaly of industrial origin occurred in the particulate and coarse colloidal fractions of the industrialized river basin. During low flow, the REY patterns of the dissolved fraction displayed marked Gd and Eu anomalies and a fractionation between Light REY and Heavy REY. Both characteristics reflect the influence of wastewater treatment plant effluents on the dissolved REY patterns in the two rivers. During high flow, the dissolved fraction acquired a less fractionated, more natural Light REY and Middle REY pattern, including much lower Gd and Eu positive anomalies. The REY fractionation of the coarse colloidal fraction was close to the particulate, while small colloids were depleted in Light REY and more similar to the dissolved fraction. These different patterns suggest a difference in the nature of REY bearing phases between the two colloidal fractions. The available results collectively show that a complete understanding of REY environmental fate and anomalies cannot be achieved from the sole study of filterable water fractions (typically <0.45 μm).

Effect of Inlet Section of Circular Section Spiral Case on Performance of Ultra-Low Specific Speed Diagonal Flow Turbine

Variation of section area at volute inlet is a key factor affecting turbine performance. By changing the inlet section of the turbine volute, the inlet angle of the guide vane is changed, so the guide vane parameters will also be changed, which will affect the turbine performance. In order to study the influence of different volute inlet section areas on the overall hydraulic performance of ultra-low specific speed diagonal flow turbine, this paper redesigns the volute inlet section area of an ultra-low specific speed diagonal flow turbine. On the premise of applying the same runner, seven different volute inlet circular sections are designed. The numerical simulation of the full flow channel is carried out for each scheme, and the influence of inlet circular section area of different volutes on hydraulic performance of the ultra-low specific speed diagonal flow turbine is analyzed and compared. The results show that with the increase of flow rate, the calculated head and runner loss of the turbine increase, and the hydraulic efficiency of the turbine first increases and then decreases. When the turbine runs under small flow conditions (less than rated flow), the hydraulic efficiency of the turbine increases with the decrease of the diameter of the inlet circular section of the volute. When the turbine operates under high flow condition (greater than rated flow), the hydraulic efficiency of the turbine decreases with the decrease of the diameter of the inlet circular section of the volute. Through comparative analysis of seven schemes, the optimum radius of the inlet circular section of volute for the ultra-low specific speed diagonal flow turbine is 127mm and the corresponding inlet angle of guide vane is 32°. At this time, the efficiency of the turbine is 81.59% and the calculated head is 4.821m. The flow pattern inside the turbine is more uniform without whirlpools. It provides a reference for future design of similar type turbines and selection of suitable volute inlet circular section area.

Variable fluid flow regimes alter human brain microvascular endothelial cell-cell junctions and cytoskeletal structure.

The human brain microvasculature is constantly exposed to variable fluid flow regimes and their influence on the endothelium depends in part on the synchronous cooperative behavior between cell-cell junctions and the cytoskeleton. In this study, we exposed human cerebral microvascular endothelial cells to a low laminar flow (1 dyne⋅cm-2 ), high laminar flow (10 dyne⋅cm-2 ), low oscillatory flow (±1 dyne⋅cm-2 ), or high oscillatory flow (±10 dyne⋅cm-2 ) for 24 hr. After this time, endothelial cell-cell junction and cytoskeletal structural response was characterized through observation of zonula occludens-1 (ZO-1), claudin-5, junctional adhesion molecule-A (JAM-A), vascular endothelial cadherin (VE-Cad), and F-actin. In addition, we also characterized cell morphology through measurement of cell area and cell eccentricity. Our results revealed the greatest change in junctional structure reorganization for ZO-1 and JAM-A to be observed under low laminar flow conditions while claudin-5 exhibited the greatest change in structural reorganization under both low and high laminar flow conditions. However, VE-Cad displayed the greatest structural response under a high laminar flow, reflecting the unique responses each cell-cell junction protein had to each fluid flow regime. In addition, cell area and cell eccentricity displayed most significant changes under the high laminar flow and low oscillatory flow, respectively. We believe this study will be useful to the field of cell mechanics and mechanobiology.

MO164NOVEL PARAMETERS TO ASSESS ENDOTHELIAL DYSFUNCTION BY PULSE WAVE ANALYSIS

Abstract Background and Aims Pulse wave morphology changes under the high flow condition of reactive hyperaemia. We hypothesized, that those alterations may be able to indicate endothelial dysfunction. Method We recorded digitized pulse waves measured tonometrically with the SphygmoCor® device of 64 persons, 41 kidney transplant recipients and 23 healthy individuals, under normal conditions (NC) and under reactive hyperaemia (RH). Using matlab®, we calculated novel parameters, which had a temporal relationship with 3 charactereristic points (PO) of the normalized pulse wave, namely the maximum of the antegrade wave (1), the diacrotic notch (2) and the first diastolic inflection point (3). The following parameters were calculated: Mean slope between PO 1 and 2 (λ2), area under the curve (AUC) in the systole (Asys), AUC between PO 1 and 3 (A13), AUC between PO 1 and 2 (A12) and AUC between PO 2 and 3 (A23). Parameters were analyzed as their difference under reactive hyperaemia and under normal conditions. Also the maximum of the instantaneous difference of normalized pulse waves under NC und RH (Dmax) was analyzed. Endothelial function was evaluated by duplex sonography using ROC-analysis of peak systolic and end-diastolic flow difference under NC and RH. Results ROC-assessment of endothelial dysfunction as indicated by systolic peak flows demonstrated AUCs of 0.733 for λ2 (p=0.002), 0.751 for Dmax (p&amp;lt; 0.001), 0.698 for Asys (p=0.006), 0.648 for A13 (p=0.077), 0.678 for A12 (p=0.027) and 0.732 for A23 (p=0.001). For the diastole the values were 0.753 for λ2 (p=0.003), 0.733 for Dmax (p=0.002) 0.670 for Asys (p=0.038), 0.566 for A13 (p=0.495), 0.664 for A12 (p=0.091) and 0.722 for A23 (p=0.015) respectively. Conclusion Pulse wave analysis under the condition of reactive hyperaemia probably is useful to assess endothelial function in kidney transplant recipients.

Numerical and Experimental Analysis of Flow and Pulsation in Hump Section of Siphon Outlet Conduit of Axial Flow Pump Device

In order to study the variation law of the flow field and pressure fluctuation in the hump section of the siphon outlet conduit, the flow field characteristics and frequency spectrum characteristics of the flow field were analyzed by combining a physical model test and numerical simulation under the conditions of the interaction between the axial flow pump and siphon outlet conduit, and the influence of the residual circulation at the outlet of the guide vane on the siphon outlet flow was investigated. Based on the influence of the flow field and hydraulic loss in the conduit, the equivalent surface method based on the Q criterion was used to analyze the vortex structure in the siphon outlet conduit and to analyze the internal vortex state. The results showed that with the increase of the flow rate, the intensity of the vortices in the cross-section of the hump section of the siphon outlet conduit decreased gradually, the average velocity circulation decreased gradually and the axial velocity distribution uniformity increased and tended to be stable; water flow stratification existed under three characteristic conditions with no circulation, and the hydraulic loss was greater with the circulation flow while it had a circulation under the small flow condition. Under the low flow rate conditions, the hydraulic loss was 6.6 times higher under the condition of circulation than without. Under a high flow condition, it was 1.3 times. Under the condition of a small flow rate, the vortex structure was distributed centrally at the inlet of the flow conduit, and under the other two characteristic conditions, the vortex structure mostly appeared as a strip; the pressure fluctuation in the hump section had obvious periodicity, and with the increase of the flow rate, the maximum pressure fluctuation amplitude in the hump section decreased gradually; with the decrease of the rotational speed, the pressure amplitude at the same measuring point in the hump section decreased gradually and at the optimum condition. Under the following conditions, the mean value of the pressure amplitude at the top of the hump section was reduced by 69.63%, and the mean value of the pressure amplitude at the bottom of the hump section was reduced by 63.5%. Under all the calculation conditions, the main frequency of pulsation at each measuring point of the hump section was twice the frequency of the rotation.

Differential compartmentalization of BMP4/NOGGIN requires NOGGIN trans-epithelial transport.

Using self-organizing human models of gastrulation, we previously showed that (1) BMP4 initiates the cascade of events leading to gastrulation, (2) BMP4 signal reception is restricted to the basolateral domain, and (3) in a human-specific manner, BMP4 directly induces the expression of NOGGIN. Here, we report the surprising discovery that in human epiblasts, NOGGIN and BMP4 were secreted into opposite extracellular spaces. Interestingly, apically presented NOGGIN could inhibit basally delivered BMP4. Apically imposed microfluidic flow demonstrated that NOGGIN traveled in the apical extracellular space. Our co-localization analysis detailed the endocytotic route that trafficked NOGGIN from the apical space to the basolateral intercellular space where BMP4 receptors were located. This apical-basal transcytosis was indispensable for NOGGIN inhibition. Taken together, the segregation of activator/inhibitor into distinct extracellular spaces challenges classical views of morphogen movement. We propose that the transport of morphogen inhibitors regulates the spatial availability of morphogens during embryogenesis.

Catchment landscape components alter relationships between discharge and stream water nutrient ratios in the Xitiao River Basin China

The terrestrial environment of a watershed is a source of potential carbon (C), nitrogen (N), and phosphorus (P) exports, and the hydrological regime provides the mechanism to turn the potential exports into reality when water is available. However, the extent to which the terrestrial environment alters the strength and nature of streamflow in transporting stream water nutrient ratios remains largely unknown. This study combined monthly stream discharge data with synchronously sampled stream water C:N:P ratios in 14 catchment streams in the Xitiao River Basin (XRB) in Zhejiang Province, China. The transport effect of streamflow on C:N:P ratios varied depending on the nutrient element, flow condition, and terrestrial environment. In the lower reaches of the XRB, there were negative relationships between C:N ratios, C:P ratios and watershed discharge, and positive relationships between N:P ratios and watershed discharge in both high and low flow conditions. In the middle and upper reaches of the XRB, the C:N-discharge relationship changed from negative to positive when the streamflow conditions altered from low to high flow. The C:P- and N:P-discharge relationships were negative regardless of high or low flows, but the regression coefficient significantly decreased with increasing streamflow. The C:N-discharge correlation over the course of the year shifted from negative to positive, as urban areas expanded within the catchment. The C:P-discharge relationship altered from negative to positive with more cropland and wetland but from positive to negative with a greater forest percentage and mean percentage slope. Our results indicate that changes in the terrestrial environment (e.g., the proportion of a particular land cover within a watershed) generally produced a threshold flow above which the coupling relationships between element fluxes from the terrestrial to riverine ecosystem changed sharply.

Animal blood in translational research: How to adjust animal blood viscosity to the human standard.

Animal blood is used in mock circulations or in forensic bloodstain pattern analysis. Blood viscosity is important in these settings as it determines the driving pressure through biomedical devices and the shape of the bloodstain. However, animal blood can never exactly mimic human blood due to erythrocyte properties differing among species. This results in the species‐specific shear thinning behavior of blood suspensions, and it is therefore not enough to adjust the hematocrit of an animal blood sample to mimic the behavior of human blood over the entire range of shear rates that are present in the body. In order to optimize experiments that require animal blood, we need models to adapt the blood samples. We here offer mathematical models derived for each species using a multi linear regression approach to describe the influence of shear rate, hematocrit, and temperature on blood viscosity. Results show that pig blood cannot be recommended for experiments at low flow conditions (<200 s−1) even though erythrocyte properties are similar in pigs and humans. However, pig blood mimics human blood excellently at high flow condition. Horse blood is unsuitable as experimental model in this regard. For several studied conditions, sheep blood was the closest match to human blood viscosity among the tested species.

The association between hemodynamics and wall characteristics in human intracranial aneurysms: a review.

Hemodynamics plays a key role in the natural history of intracranial aneurysms (IAs). However, studies exploring the association between aneurysmal hemodynamics and the biological and mechanical characteristics of the IA wall in humans are sparse. In this review, we survey the current body of literature, summarize the studies' methodologies and findings, and assess the degree of consensus among them. We used PubMed to perform a systematic review of studies that explored the association between hemodynamics and human IA wall features using different sources. We identified 28 publications characterizing aneurysmal flow and the IA wall: 4 using resected tissues, 17 using intraoperative images, and 7 using vessel wall magnetic resonance imaging (MRI). Based on correlation to IA tissue, higher flow conditions, such as high wall shear stress (WSS) with complex pattern and elevated pressure, were associated with degenerated walls and collagens with unphysiological orientation and faster synthesis. MRI studies strongly supported that low flow, characterized by low WSS and high blood residence time, was associated with thicker walls and post-contrast enhancement. While significant discrepancies were found among those utilized intraoperative images, they generally supported that thicker walls coexist at regions with prolonged residence time and that thinner regions are mainly exposed to higher pressure with complex WSS patterns. The current body of literature supports a theory of two general hemodynamic-biologic mechanisms for IA development. One, where low flow conditions are associated with thickening and atherosclerotic-like remodeling, and the other where high and impinging flow conditions are related to wall degeneration, thinning, and collagen remodeling.

The Effects of Exchange Flow on the Karst Spring Hydrograph under the Different Flow Regimes: A Synthetic Modeling Approach

In this study, a synthetic modeling approach is proposed to quantify the effect of the amount and direction of the exchange flow on the karstic spring discharge fluctuations under different hydrologic conditions corresponding to high and low flow conditions. We hypothesis that the spring discharge fluctuations constitute a valuable proxy to understand the internal processes of the karst system. An ensemble of spring hydrographs was synthetically produced to highlight the effect of exchange flow by exploring the plausible range of variability of coefficients of exchange flow, conduit diameter, and matrix hydraulic conductivity. Moreover, the change of the rate of point recharge through the karst conduit allows for the quantifying of the sensibility of the spring hydrograph to the directions of exchange flow. We show that increasing the point recharge lies to a remarkable linear recession coefficient (β) as an indication of the conduit flow regime. However, a reduction in and/or lack of the point recharge caused the recession coefficient to change to exponential (α) due to the dominant effect of the matrix restrained flow regime and/or conduit-influenced flow regime. The simulations highlight that the exchange flow process from the conduit to the matrix occurred in a short period and over a restricted part of the conduit flow regime (CFR). Conversely, the exchange flow dumped from the matrix to the conduit occurs as a long-term process. A conceptual model is introduced to compare spring hydrographs’ characteristics (i.e., the peak discharge, the volume of baseflow, and the slope of the recession curve) under the various flow conditions with the directions of the exchange flow between the conduit and the matrix.

Geochemistry of natural acid rock drainage in the Judith Mountains, Montana, part 2: Seasonal and spatial trends in Chicago Gulch

Three streams radially draining Red Mountain, a prominent peak in the Judith Mountains of central Montana, are naturally acidic in their headwaters and experience a rise in pH as they transition from hydrothermally altered quartz monzonite to sedimentary bedrock in their lower reaches. A previous study (Williams et al., 2015) examined the geochemistry of two of these streams, Armells Creek and Collar Gulch, using detailed synoptic sampling with continuous tracer-injection. Here we present results of two synoptic sampling events in the third stream, Chicago Gulch. Data are compared between the three watersheds, and estimates of solute flux (load divided by watershed area) are presented.Filtered and unfiltered metal concentrations and loads are quantified with distance downstream in Chicago Gulch under low-flow (August) and high-flow (May) conditions. Headwater streams in the watershed have pH < 4 and extensive deposits of ferricrete and Fe-bog deposits. Weakly acidic springs (pH > 4) contain >10 mg/L of Fe2+ which quickly oxidizes and precipitates as hydrous ferric oxide (HFO), releasing protons that lower the pH of the stream. Geochemical modeling suggests the actively forming HFO is a mix of schwertmannite and ferrihydrite, both of which are slowly converting to goethite which cements the ferricrete deposits. White, hydrous aluminum oxide (HAO) flocs form where stream pH transitions from <5 to >5, and a comparison of filtered and unfiltered samples indicates strong partitioning of Cu and Pb into the suspended particles. Dissolved loads of Zn, Cd, Mn, and Tl (thallium) diminish slightly in the lower reaches of Chicago Gulch where pH rises above 7.All water samples collected in the upper reaches of Chicago Gulch exceed the US-EPA water quality standards for protection of aquatic life for Pb, Cd, Zn, and Cu, and human health standards for Tl. Lead concentrations are especially high in the headwaters of Chicago Gulch, indicating the possible presence of an unmined Pb-sulfide deposit. Estimates of the load of dissolved sulfate at baseflow conditions in each stream on Red Mountain, normalized to their respective surface areas of hydrothermally altered bedrock, are remarkably similar, and indicate a steady state pyrite oxidation rate of 11.9 mol FeS2/h/km2. Prediction of pre-modern pH using the methods of Nimick et al. (2009) indicates that the current pH regimes of all three streams draining Red Mountain are broadly similar to conditions when ancient ferricretes were deposited. Because the Judith Mountains were never glaciated in the Pleistocene, it is possible that similar hydro-geochemical conditions have existed in the area for 10's to 100's of thousands of years.

Hydrological and biogeochemical controls on temporal variations of dissolved carbon and solutes in a karst river, South China

BackgroundUnderstanding the responses of riverine dissolved carbon dynamics and chemical weathering processes to short-term climatic variabilities is important to understand the Surface-Earth processes under ongoing climate change. Temporal variations of solutes and stable carbon isotope of dissolved inorganic carbon (δ13CDIC) were analysed during a hydrological year in the Guijiang River, South China. We aimed to unravel the chemical weathering processes and carbon dynamics in karst areas under ongoing climate changes.ResultsSignificant positive relationships were found between weathering rates and climatic factors (i.e. temperature and discharge) over the hydrological year. The total flux of CO2 consumption (760.4 × 103 mol/km2/year) in the Guijiang River was much higher than the global mean flux, with a higher CO2 consumption capacity in the Guijiang River relative to most other global rivers. Chemical weathering fluxes in this karst area showed high sensitivity to global climate change. CO2 evasion during the warm–wet seasons was much lower than those during cold–dry seasons. Light δ13CDIC values occurred under high-flow conditions, corresponding with the high temperatures in high-flow seasons. IsoSource modelling revealed that biological carbon could account for 53% of all dissolved inorganic carbon (DIC), controlling the temporal carbon variabilities.ConclusionThis study quantitatively evaluated the temporal variations in CO2 fluxes and carbon cycling of karstic river systems and demonstrated that riverine carbon cycling will have a higher sensibility to ongoing global climate change. High discharges accelerate solutes transport, with relatively large quantities of 13C-depleted carbon being flushed into rivers. Meanwhile, high temperatures also accelerate organic carbon mineralisation, producing high content of soil CO2, whose influx can shift the 13C-depleted values in the high-flow seasons. Taken together, biological carbon influx should be responsible for the temporal carbon dynamics.

Determination of multi-pesticide residues in vegetable products using a “reduced-scale” Quechers method and flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry

The aim of the present research was the development of an analytical method for the determination of multi-pesticide residues (88 target analytes) in four vegetable products (tomatoes, cucumbers, sweet red peppers and iceberg lettuce) using a “reduced-scale” QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry. In particular, the suitability of flow modulation [with relatively high second-dimension gas flow conditions (8 mL min−1)] for trace analyte determination was evaluated.The samples were prepared according to the QuEChERS procedure as reported by the official European Union method, namely EN 15662:2018, based on the use of 3 g of vegetable product. Matrix-matched calibration processes were carried out for all the samples. The figures-of-merit determined were recovery, linearity, precision, limits of detection (LoDs), and limits of quantification (LoQs). Specifically, recoveries were in the 53-160% range, regression coefficients were between 0.9156 and 0.9999, the LoDs were in the 0.1-6.3 μg kg−1 range, the LoQs were in the 3.0-21.0 μg kg−1 range, and coefficients of variation were between 1 and 28% (at the 50 μg kg−1 level).

Magnitude and drivers of CO2 and CH4 emissions from an arid/semiarid river catchment on the Chinese Loess Plateau

River systems are major sources of greenhouse gases (GHG). However, simultaneous CO2 and CH4 emissions from arid/semiarid rivers remain poorly studied. Here we investigated CO2 and CH4 emissions (diffusion + ebullition) and their potential sources and drivers in an arid/semiarid catchment on the Chinese Loess Plateau. The river water CO2 partial pressure (pCO2) averaged 885 ± 415 µatm and did not show a significant change along the stream network due to strong carbonate buffering. Groundwater inputs played a dominant role in controlling pCO2 which exhibited a pronounced seasonal variation. In-stream decomposition of organic matter mobilized by soil erosion was also an important contributor. The streams were consistently oversaturated in CH4, ranging between 0.06 and 0.77 µmol L−1. Both gas emissions exhibited significant seasonal variations, which were collectively controlled by gas concentration gradient across the water–air interface and flow dynamics. The mean CO2 and CH4 efflux were 55 mmol m−2 d–1 and 346 µmol m−2 d–1, respectively, with the highest efflux in August (high flow conditions) for both gases. River impoundment resulted in greatly reduced pCO2 due to enhanced primary production but elevated CH4 concentrations because of anaerobic degradation of organic-rich sediments. Reservoirs acted as a smaller CO2 source but a stronger CH4 source than flowing rivers. Ebullition was an important pathway of CH4 emissions in both lotic and lentic ecosystems, contributing 36 ± 23% and 55 ± 19% to the total CH4 emissions from rivers and reservoirs, respectively. Urban wastewater discharges modified riverine carbon cycling and created local hotspots of GHG production and emissions, which will be globally significant given the increasing human impacts worldwide. Our results reinforce the urgency to account for arid/semiarid rivers in future GHG emission estimates. Future work to better understand the impacts of groundwater inflows and aquatic ecosystem processes in controlling GHG dynamics is also needed.

Computational evaluation of geometric effects on aerodynamic performance of circulation control airfoils

The geometric effects of Coanda trailing edges on the aerodynamic performance of an airfoil are numerically evaluated for a range of different freestream Mach numbers and momentum coefficients. A Circulation control (CC) airfoil with a circular trailing edge (ACTE) proves to have better control effectiveness at low subsonic freestream speeds (Mach = 0.1). A CC airfoil having an elliptic trailing edge (AETE) outperforms the ACTE at high subsonic flow conditions. The occurrence of C μ-stall for the AETE is greatly postponed, and meanwhile the maximum net lift coefficient increment achieved for the AETE (Δ C L = 0.51) is slightly higher than that of the ACTE (Δ C L = 0.50) at Mach 0.6. Compared to the ACTE, the AETE is found to have better control consistency at different operating velocities and better control stability when the Coanda jet is supersonic. Through careful consideration of the aerodynamic performance and the control effects, the most appropriate axial ratio for an AETE ellipse is within the interval from 1.5 to 2. Finally, the flow field instability phenomenon and the jet detachment induced by the supersonic Coanda jet are investigated. A self-sustained shock-wave instability phenomenon without jet detachment is first observed in this paper.