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BACKGROUND: A model system described in International Organization for Standardization 9360 is the standard method for estimating the humidifying performance of heat and moisture exchangers (HMEs). However, there are no reliable bedside methods for evaluating the ongoing humidification performance of HMEs. Therefore, this study aimed to develop 2 clinically applicable methods for estimating the ongoing humidifying performance of HMEs and to evaluate their reliability in a model system. METHODS: Physiologically expired gas was simulated using a heated humidifier, and ventilation was delivered using a ventilator with constant flow through 3 different types of HMEs. Relative humidity (RH) was measured using a capacitive-type moisture sensor. Water content lost during expiration was calculated by integrating absolute humidity (AH), instantaneous gas flow measured at the expiratory outlet of the ventilator, and time. We also calculated the water content released and captured by the HMEs during tidal ventilation by integrating the difference in AH across the HMEs, instantaneous gas flow, and time. RESULTS: We found that the RH, temperature, and AH were almost constant on the expiratory outlet of the ventilator but rapidly varied near the HMEs. The water content lost by the 3 HMEs was associated with the manufacturer-reported values and inversely correlated with the calculated values of the water content exchanged by the HMEs. The water content released and captured by HMEs was closely correlated with the difference in HME weight measured at the end of inspiration and expiration; however, the water content captured by HMEs seemed to be overestimated. CONCLUSIONS: Our results demonstrated that our system was able to detect the differences in the performance of 3 models of HMEs and suggest that our method for calculating water loss is reliable for estimating the water retention performance of HMEs during mechanical ventilation, even in the presence of a constant flow. [ABSTRACT FROM AUTHOR]

Purpose: A method is proposed to quantify cerebral blood volume (vb$$ {v}_b $$) and intravascular water residence time (τb$$ {\tau}_b $$) using MR fingerprinting (MRF), applied using a spoiled gradient echo sequence without the need for contrast agent. Methods: An in silico study optimized an acquisition protocol to maximize the sensitivity of the measurement to vb$$ {v}_b $$ and τb$$ {\tau}_b $$ changes. Its accuracy in the presence of variations in T1,t$$ {\mathrm{T}}_{1,t} $$, T1,b$$ {\mathrm{T}}_{1,b} $$, and B1$$ {\mathrm{B}}_1 $$ was evaluated. The optimized protocol (scan time of 19 min) was then tested in a exploratory healthy volunteer study (10 volunteers, mean age 24 ±$$ \pm $$ 3, six males) at 3 T with a repeat scan taken after repositioning to allow estimation of repeatability. Results: Simulations show that assuming literature values for T1,b$$ {\mathrm{T}}_{1,b} $$ and T1,t$$ {\mathrm{T}}_{1,t} $$, no variation in B1$$ {\mathrm{B}}_1 $$, while fitting only vb$$ {v}_b $$ and τb$$ {\tau}_b $$, leads to large errors in quantification of vb$$ {v}_b $$ and τb$$ {\tau}_b $$, regardless of noise levels. However, simulations also show that matching T1,t$$ {\mathrm{T}}_{1,t} $$, T1,b$$ {\mathrm{T}}_{1,b} $$, B1+$$ {\mathrm{B}}_1^{+} $$, vb$$ {v}_b $$ and τb$$ {\tau}_b $$, simultaneously is feasible at clinically achievable noise levels. Across the healthy volunteers, all parameter quantifications fell within the expected literature range. In addition, the maps show good agreement between hemispheres suggesting physiologically relevant information is being extracted. Expected differences between white and gray matter T1,t$$ {\mathrm{T}}_{1,t} $$ (p < 0.0001) and vb$$ {v}_b $$ (p < 0.0001) are observed, T1,b$$ {\mathrm{T}}_{1,b} $$ and τb$$ {\tau}_b $$ show no significant differences, p = 0.4 and p = 0.6, respectively. Moderate to excellent repeatability was seen between repeat scans: mean intra‐class correlation coefficient of T1,t:0.91$$ {\mathrm{T}}_{1,t}:0.91 $$, T1,b:0.58$$ {\mathrm{T}}_{1,b}:0.58 $$, vb:0.90$$ {v}_b:0.90 $$, and τb:0.96$$ {\tau}_b:0.96 $$. Conclusion: We demonstrate that regional simultaneous quantification of vb$$ {v}_b $$, τb$$ {\tau}_b $$, T1,b,T1,t$$ {\mathrm{T}}_{1,b},{T}_{1,t} $$, and B1+$$ {\mathrm{B}}_1^{+} $$ using MRF is feasible in vivo. [ABSTRACT FROM AUTHOR]

Refinement of the governing equations for homogeneous isotropy in variable saturated porous media based on the basic equations for the seepage and temperature fields. Combined with the water exchange in the lateral hyporheic zone, a mathematical model of water and heat transport in the saturated-unsaturated zone of the lateral hyporheic zone of river-groundwater is established. The model was solved using COMSOL software and then validated by the measured data obtained from the test site. The simulation and validation results show that the model is effective in simulating the dynamics of hydrodynamic and temperature field changes in the river-groundwater lateral hyporheic zone under the conditions of water exchange, and that the mathematical model of hydrothermal transport can provide technical support for the in-depth study of hydrothermal exchange and pollutant migration processes in the riparian zone. [ABSTRACT FROM AUTHOR]

Sanmen Bay (SMB) is one of the important harbors in Zhejiang Province. It is a semi-enclosed shallow bay that has undergone large-scale land reclamation activities. Long-term reclamation has changed the hydrodynamic conditions of SMB, such as tide, residual current, tidal prism, water exchange capacity, and tidal asymmetry. In this study, three typical periods of numerical models, based on historical charts and remote sensing, were established to investigate the influence of reclamation activities on the hydrodynamic conditions of SMB from 1971 to 2020. These model results reveal that the amplitude and phase of M2, the main tidal components in SMB, decreased by ~0.1-0.3 m and ~ 5°-15°, respectively, over the last half-century. Additionally, under the influence of ~200 km2 reclamation, many hydrodynamic conditions in SMB also changed. This includes the reduction of a residual current and tidal prism, an increase in residence time, and a change in tidal asymmetry characteristics. The residence time in nearby Xiayangtu exhibited a downward trend from 2003 to 2020, because land reclamation squeezed, and thus, enhanced the residual current eddy. The water-exchange capacity of the bay became weaker with the reduction of tidal prism to one-third and an increase in residence time. The tidal asymmetry characteristic of SMB changed from half of flood dominant to fully flood dominant by the influence of shoreline and bathymetry, which raised the flood risk. Research on the response of the hydrodynamic environment to reclamation activities in SMB reminds the local government to reassess the impact of land reclamation on the hydrodynamic environment. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of the database of changes in the specific methane flux at various types of water reservoirs in Russia in which the authors participated. Measurements were carried out by the method of floating chambers in different periods of the annual hydroecological cycle. A comparison of the data with the results of foreign experience is given. An approach to the parameterization of specific methane flux for calculating the maximum possible methane emission from artificial reservoirs when developing quantitative quotas of greenhouse gas emissions is proposed. The estimation both in different phases of regime (stratification and homothermia) and for separate morphological parts of reservoirs differing in depth is offered. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effects of compartmental anisotropy on filtered exchange imaging (FEXI) in white matter (WM). Theory and Methods: FEXI signals were measured using multiple combinations of diffusion filter and detection directions in five healthy volunteers. Additional filters, including a trace‐weighted diffusion filter with trapezoidal gradients, a spherical b‐tensor encoded diffusion filter, and a T2 filter, were tested with trace‐weighted diffusion detection. Results: A large range of apparent exchange rates (AXR) and both positive and negative filter efficiencies (σ) were found depending on the mutual orientation of the filter and detection gradients relative to WM fiber orientation. The data demonstrated that the fast‐diffusion compartment suppressed by diffusional filtering is not exclusively extra‐cellular, but also intra‐cellular. While not comprehensive, a simple two‐compartment diffusion tensor model with water exchange was able to account qualitatively for the trends in positive and negative filtering efficiencies, while standard model imaging (SMI) without exchange could not. This two‐compartment diffusion tensor model also demonstrated smaller AXR variances across subjects. When employing trace‐weighted diffusion detection, AXR values were on the order of the R1 (=1/T1) of water at 3T for crossing fibers, while being less than R1 for parallel fibers. Conclusion: Orientation‐dependent AXR and σ values were observed when using multi‐orientation filter and detection gradients in FEXI, indicating that WM FEXI models need to account for compartmental anisotropy. When using trace‐weighted detection, AXR values were on the order of or less than R1, complicating the interpretation of FEXI results in WM in terms of biological exchange properties. These findings may contribute toward better understanding of FEXI results in WM. [ABSTRACT FROM AUTHOR]

The Baltic Sea is currently classified as 'affected by eutrophication'. In this study, water exchanges and net phosphorus flows in the Archipelago Sea and through the Åland Sea from the Baltic proper was estimated with the aid of a 3-D hydrodynamic model for the years 2000–2021. The modelling configuration is based on the Copernicus regional reanalysis data. W ater flowed from the Baltic proper to the Bothnian Sea at 669 km3/a and out from there at 879 km3/a. The inflow occurred in the deep-water layer (over 40 m), while the outflow occurred in the surface layer (0–40 m). With the inflow, 14,500 tons/a of phosphorus were transported during the years 2000–2014, but the amount increased to 20,300 tons per year from 2015 to 2021. At the same time, the winter-time concentrations of DIP in the Bothnian Sea almost doubled.   In the Archipelago Sea, the main flow direction of water was from south to north from 2000 to 2014. From 2015 to 2021, the net flow direction reversed, and water flowed from the Archipelago Sea to the Baltic proper in the surface layer at a rate of 140 km3/a. At the same time, the background loading of phosphorus entering the Archipelago Sea with the flows decreased significantly and the chlorophyll-a concentration decreased below the threshold for a good ecological status.   The U-turn in surface currents in the Archipelago Sea since 2015 may be related to variations in upwellings caused by climate change. [ABSTRACT FROM AUTHOR]

The blood–brain barrier (BBB) is a barrier protecting the brain and a milieu of continuous exchanges between blood and brain. There is emerging evidence that the BBB plays a major role in epileptogenesis and drug‐resistant epilepsy, through several mechanisms, such as water homeostasis dysregulation, overexpression of drug transporters, and inflammation. Studies have shown abnormal water homeostasis in epileptic tissue and altered aquaporin‐4 water channel expression in animal epilepsy models. This review focuses on abnormal water exchange in epilepsy and describes recent non‐invasive MRI methods of quantifying water exchange. Plain Language Summary: Abnormal exchange between blood and brain contribute to seizures and epilepsy. The authors describe why correct water balance is necessary for healthy brain functioning and how it is impacted in epilepsy. This review also presents recent MRI methods to measure water exchange in human brain. These measures would improve our understanding of factors leading to seizures. [ABSTRACT FROM AUTHOR]

Abstract The blood–brain barrier (BBB) is a barrier protecting the brain and a milieu of continuous exchanges between blood and brain. There is emerging evidence that the BBB plays a major role in epileptogenesis and drug‐resistant epilepsy, through several mechanisms, such as water homeostasis dysregulation, overexpression of drug transporters, and inflammation. Studies have shown abnormal water homeostasis in epileptic tissue and altered aquaporin‐4 water channel expression in animal epilepsy models. This review focuses on abnormal water exchange in epilepsy and describes recent non‐invasive MRI methods of quantifying water exchange. Plain Language Summary Abnormal exchange between blood and brain contribute to seizures and epilepsy. The authors describe why correct water balance is necessary for healthy brain functioning and how it is impacted in epilepsy. This review also presents recent MRI methods to measure water exchange in human brain. These measures would improve our understanding of factors leading to seizures.

Background: Colonoscopy is a common diagnostic and therapeutic method for assessing the lower gastrointestinal system. This study aimed to compare the differences between water immersion, water exchange and air insufflation colonoscopy under good bowel preparation conditions.methods: Randomized controlled trial study was conducted in 30 patients who performed a colonoscopy between January 2023 to July 2023 in internal medicine department, hepato-gasterontrology unit at Zagazig University Hospitals, equally divided into three groups; Group A: Air insufflation who were submitted to traditional method with minimal insufflation, with warm water used to wash residual stool. Group 2: Water immersion who were submitted to infusion with clean water to improve the visibility of the intestinal lumen. Group 3: Water exchange participants were subjected to infusion using an insertion strategy that included gasless insertion to the cecum, maximizing cleanliness during insertion, and preventing colon distension through excess water removal and residual air preparation. Results: there was no statistical significant difference regarding use of anesthetic drugs or time of procedure. Regarding result of colonoscopy (internal piles was the most prevalent result; 40%, 40% and 70% within air insufflation, water immersion and water exchange groups). Regarding cecal intubation time; difference is significant between air insufflation and water immersion group where time is significantly higher in air insufflation group as compared to water immersion group) p=0.001. Conclusion: Water exchange colonoscopy is superior to Water immersion, in reducing insertion pain, and cecal intubation time, minimizing sedation requirements. [ABSTRACT FROM AUTHOR]

Water exchange in the Luzon Strait (LS) is critical for layered circulation in the South China Sea (SCS); however, observational evidence of sandwich‐like water exchange is scarce. This study presents a comprehensive analysis of the meridional and zonal spatial patterns of water exchange in the upper and middle LS, along with its seasonal variations in a sigma–pi diagram using Argo profiles. As observed viewed from the perspective of SCS, inflow and outflow occur in the upper and middle layers, respectively. Upper‐layer Kuroshio intrudes into the SCS primarily in the northern and central regions of the LS, extending along the continental shelf into the inner SCS. A significant middle‐layer eastward outflow is evident at 26.7–27.56 kg/m3 (500–1,500 m) in the northern part of the strait, extending to 123°E. The Kuroshio intrusion intensifies during the winter, whereas the middle‐layer outflow is most pronounced in the autumn. Plain Language Summary: Understanding the circulation in marginal and inland seas is closely tied to comprehending the exchange of water between straits connecting neighboring oceans. The Luzon Strait, as a semi‐enclosed marginal sea, holds a pivotal role in shaping the layered circulation in the South China Sea. This study utilizes an extensive data set of Argo profiles to provide observational evidence of a layered zonal water exchange in the upper and middle Luzon Strait, offering detailed insights into the meridional and zonal patterns of water exchange and how they vary with the seasons. It reveals that inflow and outflow processes occur in the upper and middle layers observed viewed from the perspective of South China Sea, respectively. The upper‐layer intrusion of the Kuroshio is more prominent during the winter, while the middle‐layer outflow is most noticeable in the autumn. This research enhances our understanding of water exchange in the Luzon Strait and contributes to our knowledge of processes like water renewal, heat and salt budgets, and biogeochemical cycles in the South China Sea. Key Points: A novel insight into water exchange in the upper and middle Luzon Strait is provided using the sigma–pi diagramMeridional distribution of inflow (outflow) zonal water exchange in the upper (middle) Luzon Strait are describedUpper‐layer inflow was enhanced in winter, whereas middle‐layer outflow was significant during the autumn [ABSTRACT FROM AUTHOR]

The fluid transport of cerebrospinal fluid (CSF) and interstitial fluid in surrounding tissues plays an important role in the drainage pathway that facilitates waste clearance from the brain. This pathway is known as the glymphatic or perivascular system, and its functions are dependent on aquaporin‐4 (AQP4). Recently, magnetization transfer indirect spin labeling (MISL) magnetic resonance imaging (MRI) has been proposed as a noninvasive and noncontrast‐enhanced method for detecting water exchange between CSF and brain tissue. In this study, we first optimized the MISL sequence at preclinical 3 T MRI, and then studied the correlation of MISL in CSF with magnetization transfer (MT) in brain tissue, as well as the altered water exchange under AQP4 inhibition, using C57BL/6 mice. Results showed a strong correlation of MISL signal with MT signal. With the AQP4 inhibitor, we observed a significant decrease in MISL value (P < 0.05), suggesting that the hampered AQP4 activity led to decreased water exchange between CSF and brain tissue or the impairment of the glymphatic function. Overall, our findings demonstrate the potential application of MISL in assessing brain water exchange at 3 T MRI and its potential clinical translation. [ABSTRACT FROM AUTHOR]

The relic Lake Mogilnoe, separated from the Barents Sea by a sand and pebble dam, is located in the high Arctic on the Kildin island (Murmansk region). This lake is a classic example of a meromictic basin of marine origin. The data obtained during the 2018 expedition showed changes in the hydrochemical regime of the lake that have occurred over the past 20 years. Sulfide concentration in the monimolimnion of the lake was as high as 140 mg/L. A tendency for salinization of the surface waters to 7 g/L has been noted. The Lake Mogilnoe is characterized by a discrepancy between the halocline and thermocline levels. The chemocline zone in the lake is below the halocline level. In a narrow oxygen-containing layer between 3 and 7.5 m, aerobic microflora of the marine type and marine fauna were present. The bacterial plate was formed at the boundary of the sulfide layer at ~8 m and mainly consisted of green sulfur bacteria (GSB). Brown-colored GSB species containing bacteriochlorophyll e were predominant. The previously formed concept of anaerobic phototrophic bacteria (APB) biodiversity based on morphological characteristics was modified using metagenomic data obtained by analyzing DNA from two samples of lake water in the chemocline zone, and was also supplemented by identifying new GSB species. Molecular diagnostic data confirmed the absolute dominance of the brackish species of GSB Chlorobium phaeovibrioides. This is the first isolation and identification of brown- and green-colored Prosthecochloris aestuarii morphotypes from Lake Mogilnoe, as well as of bacteriochlorophyll c-containing Prosthecochloris sp. The taxonomic position of Pelodyction phaem, which was constantly present in the Lake Mogilnoe, is discussed in detail. Despite the partial isolation of the ecosystem of Lake Mogilnoe from the Barents Sea, the main properties of the dominant GSB species and Prosthecochlori aestuarii turned out to be similar to those of the phylotypes living in lakes on the White Sea coast. [ABSTRACT FROM AUTHOR]

Atmospheric frontal passage is a common meteorological event that can significantly affect hydrodynamics in coastal environments, including the hydrological connectivity between channels and floodplains that regulates material transport in river deltas. This study is focused on the influence of atmospheric cold fronts on the hydrological connectivity between channels and floodplains within the Wax Lake Delta using the Delft3D FM model. The results demonstrate a substantial effect of passing cold fronts on the exchange of water and transport fraction between the primary channels and floodplains. This impact is intricately connected to the morphodynamical characteristics of the floodplains, the intensity of cold fronts, river discharge, Coriolis force, and tidal currents. The passing cold fronts can enhance or reverse the direction of water exchange between channels and floodplains. For floodplains, the passage of cold fronts can lead to an increase in the rate of water exchange by as much as five times. In the WLD, a substantial fraction of water, 39-58%, is flowing through the floodplains to the bay at the delta front influenced by the prevailing discharge, although there is a significant spatial heterogeneity. Passing cold fronts can alter the transport distribution, depending on the phase of the front. An increase in river discharge tends to bolster floodplain connectivity and lessen the effects of cold fronts. Conversely, decreased river discharge results in reduced connectivity and exacerbates the fluctuations induced by cold fronts. Moreover, the findings indicate that from the apex to downstream, the contribution of channels decreases as they become shallower, while the role of the floodplains increases, leading to a less distinct demarcation between channels and floodplains. It has also been noted that an increase in river discharge correlates with an increased contribution from floodplains to transfer water to the bay. [ABSTRACT FROM AUTHOR]

A sorption–diffusion model of 137Cs absorption by bottom soils has been used to forecast 137Cs concentration in global fallouts and emergency release from the Chernobyl NPP in water of the deep (Hav = 30 m) Lake Onega. The natural conditions and the morphohydrological characteristics of the lake caused a rapid (2–3 years) transformation of 137Cs-polluted water to pseudoequilibrium concentrations. For 56 years (from 1964 to 2020), the concentration of 137Cs in water was determined with acceptable accuracy by a sorption-diffusion model of 137Cs adsorption by bottom soils with coefficients of sorption Kd = 4000 L/kg and diffusion D = 1.0 × 10–7 cm2/s. The effect of water exchange in the lake on 137Cs migration is taken into account in the characteristic of conditional exchange of Lake Onega water W = 16.4 years. The correctness of the forecast of water pollution by 137Cs was verified by comparison with experimental data and the conditions of 137Cs pollution of the waters of deep lakes in the northwestern Russia and Finnish Lapland. [ABSTRACT FROM AUTHOR]

A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea (AS) and the Bay of Bengal, i.e., the Preparis Channel (PC), the Ten Degree Channel (TDC), and the Great Channel (GC), based on the daily averaged simulation results ranging from 2010 to 2019. Spectral analysis and Empirical Orthogonal Function (EOF) methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms. The results of model simulation indicate that the net average transports of the PC and GC, as well as their linear trend, are opposite to that of the TDC. This indicates that the PC and the GC are the main inflow channels of the AS, while the TDC is the main outflow channel of the AS. The transport variability is most pronounced at surface levels and between 100 m and 200 m depth, likely affected by monsoons and circulation. A 182.4-d semiannual variability is consistently seen in all three channels, which is also evident in their second principal components. Based on sea level anomalies and EOF analysis results, this is primarily due to equatorial winds during the monsoon transition period, causing eastward movement of Kelvin waves along the AS coast, thereby affecting the spatiotemporal characteristics of the flow in the AS. The first EOF of the PC flow field section shows a split at 100 m deep, likely due to topography. The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series. Meanwhile, the first EOF of the GC flow field section indicates a stable surface inflow, probably influenced by the equatorial Indian Ocean's eastward current. [ABSTRACT FROM AUTHOR]

Study region: Dongting Lake Basin of China. Study focus: Dongting Lake is the first large-scale interconnected river–lake systems in the middle-lower reaches of the Yangtze River and the second-largest freshwater lake in China. Dam operation on the upper reaches of the Yangtze River dramatically affected the hydrological condition of Dongting Lake. Therefore, this study established a hydrodynamic-water age model to assess the effects of the Three Gorges Dam (TGD) on the spatiotemporal pattern of water age in Dongting Lake. New hydrological insights: The results show a significant spatial and temporal variation of water age in Dongting Lake. Water age in the floodway is lower than that in the shoal, meanwhile, water age in spring and summer is lower than that in autumn and winter. By establishing a hydrodynamic-water age model, several factors influencing water age in Dongting Lake were analyzed, i.e., the influences of the Jingjiang Three Outlets' triage from the Yangtze River, the water level of the mainstream of the Yangtze River, and the flow pattern. The TGD could influence the water age in Dongting Lake by altering the hydrodynamic conditions of the Yangtze River. Results from this study provide support for flood control and dispatch management of Dongting Lake and provides a reference for water exchange studies in other large shallow lakes.

Permeable type shore connection structure was first applied in the Dalian Bay Subsea Tunnel Project. Numerical simulation method is used to calculate the flow field and water exchange after the construction of the shore connection structure of Dalian Bay subsea tunnel, and the results were compared with the traditional impermeable type. The research results show that the water flow in the permeable type shore connection structure will produce obvious flow across the direction of the tunnel, which can improve the water exchange on both sides of the tunnel and promote the exchange of surrounding water. The permeable type structure has the value of promotion and application. [ABSTRACT FROM AUTHOR]

The bidirectional mass exchange between the Marmara Sea and the Aegean Sea provides one part of the critical hydrodynamic links between the Black Sea and the Mediterranean Sea. In this study, we examined exchange in the Dardanelles based on a 3-D numerical model simulation covering an 11-year period under realistic atmospheric forcing. The model includes the Black Sea, the Marmara Sea, and a part of the Aegean Sea to include the remote effects of basin dynamics. The main features as one-, two-, and three-layered flow structures are successfully reproduced by the model in comparison to earlier observations. It is found that the strait is subject to submaximal exchange by only one control near the Nara Pass. According to long-term modeling results, most variability occurs on synoptic time scales, and wind stress has a dominant role in those variations. The seasonal and interannual variability of exchange flow is relatively low and displays a close relationship with freshwater input to the Black Sea. [ABSTRACT FROM AUTHOR]

Purpose: Guidelines recommend measuring myocardial extracellular volume (ECV) using T1‐mapping before and 10–30 min after contrast agent administration. Data are then analyzed using a linear model (LM), which assumes fast water exchange (WX) between the ECV and cardiomyocytes. We investigated whether limited WX influences ECV measurements in patients with severe aortic stenosis (AS). Methods: Twenty‐five patients with severe AS and 5 healthy controls were recruited. T1 measurements were made on a 3 T Siemens system using a multiparametric saturation‐recovery single‐shot acquisition (a) before contrast; (b) 4 min post 0.05 mmol/kg gadobutrol; and (c) 4 min, (d) 10 min, and (e) 30 min after an additional gadobutrol dose (0.1 mmol/kg). Three LM‐based ECV estimates, made using paired T1 measurements (a and b), (a and d), and (a and e), were compared to ECV estimates made using all 5 T1 measurements and a two‐site exchange model (2SXM) accounting for WX. Results: Median (range) ECV estimated using the 2SXM model was 25% (21%–39%) for patients and 26% (22%–29%) for controls. ECV estimated in patients using the LM at 10 min following a cumulative contrast dose of 0.15 mmol/kg was 21% (17%–32%) and increased significantly to 22% (19%–35%) at 30 min (p = 0.0001). ECV estimated using the LM was highest following low dose gadobutrol, 25% (19%–38%). Conclusion: Current guidelines on contrast agent dose for ECV measurements may lead to underestimated ECV in patients with severe AS because of limited WX. Use of a lower contrast agent dose may mitigate this effect. [ABSTRACT FROM AUTHOR]

Purpose: To demonstrate an analytic formula giving the time dependence of the diffusional kurtosis for the Kärger model (KM) with an arbitrary number of exchanging compartments and its application in estimating the mean KM water exchange rate. Theory and Methods: The general formula for the kurtosis is derived from a power series solution for the multi‐compartment KM. A lower bound on the exchange rate is established from the observation that the kurtosis is always a logarithmically convex function of time. Both the kurtosis time dependence and the lower bound are illustrated with numerical calculations. The lower bound is also applied to previously published data for the time dependence of the kurtosis in both brain and tumors. Results: The kurtosis for the multi‐compartment KM is given by a sum in which each term is associated with an eigenvector of the exchange rate matrix. The lower bound is determined from the most negative value for the logarithmic derivative of the kurtosis with respect to time. In the cerebral cortex, the lower bound is found to vary from 15 to 76 s−1, depending on the experimental details, while for the tumors considered, it varies from 2 to 4 s−1. Conclusion: The time dependence of the kurtosis for the multi‐compartment KM has a simple analytic solution that allows a lower bound for the mean KM water exchange rate to be determined directly from experiment. This may be useful in tissues with complex microstructure that is difficult to model explicitly. [ABSTRACT FROM AUTHOR]

Macrochloa tenacissima (M. tenacissima), or esparto, is a perennial tussock grass that coexists with Pinus halepensis (P. halepensis) in semi-arid Mediterranean woodlands. This research was carried out to explore diurnal transpiration at leaf level in esparto grass under different levels of pine–esparto competition and in contrasting environmental soil water conditions. The measurement period spanned from the summer of 2020 to the spring of 2021. The relationship between transpiration and competition was conducted in open and closed P. halepensis stands, and the type of leaf (green, senescent) and the maturity of the esparto grass were taken into account. We observed a higher control of transpiration in green leaves, and the correlations between the transpiration and pine competition were noted exclusively in this type of leaf. Our results demonstrated a significant impact of pine competitors (closed stands) on the transpiration of esparto grass, particularly during seasons characterized by scenarios of high water demand: the summer drought period and the commencement of the growing and flowering period (spring). Furthermore, our findings revealed a greater response to transpiration in mature bushes compared to young ones under severe water stress, indicating a higher adaptation to drought by esparto as it ages. Although our results confirmed that PAR increased transpiration in all seasons and in both stands, which is attributable to the heliophilia of esparto grass, the site effects on transpiration could also be attributable to competition for water, especially during periods of drought. These results may have important implications for the dynamics and management of these semi-arid mixed woodlands, as well as the planning of reforestation programs aimed at restoring esparto grass formations. [ABSTRACT FROM AUTHOR]

The purpose of the study is to identify the relationship between drought resistance indicators and the yield of potato plants under unfavorable conditions. A xeromorphic leaf structure is considered to be a diagnostic sign of plant drought resistance. The objects of the study were 24 potato varieties. Planting of seeds, preplanting tillage, harvesting, and crop recording were carried out in the period of 2020–2022 on the territory of the Samara Research Institute of Agriculture (branch of the Samara Scientific Center, Russian Academy of Sciences). Growing conditions for 2021 and 2022 were characterized by elevated temperatures and insufficient moisture. The number and size of stomata per unit leaf area were chosen as the criterion for xeromorphism. The studied varieties were divided into two groups (n = 12 each) according to the number of stomata. In the first group, the average number of stomata was 26 000 pcs./cm2 of leaf, and that in the second group was 35 000 pcs. (F = 41, p = 0.03). More developed structural features of xeromorphism and the accumulation of certain types of metabolites in the second group of varieties led to a 1.6 times greater yield than in the first less xeromorphic group (F = 9, p = 0.004). The second group was characterized by a large number of mesophyll cells per unit leaf area (584 000 pcs./cm2 vs. 557 000 pcs.), high content of phospholipids (36 mg/g dry weight vs. 31 mg/g), dry weight (0.19 vs. 0.17 g/g wet weight), and the ratio of membrane lipids to membrane proteins (1.4 vs. 1.2). In the less xeromorphic group of plants, the level of oxidative stress, assessed by LPO products, was 0.050 μM/g fresh weight and was 12% higher than in the more xeromorphic group (F = 6, p = 0.08). The revealed positive correlation between yield and xeromorphic genotypes indicates the prospects of using this criterion in potato breeding or creating a variety model. [ABSTRACT FROM AUTHOR]

Atmospheric frontal passage is a common meteorological event that can significantly affect hydrodynamics in coastal environments, including the hydrological connectivity between channels and floodplains that regulates material transport in river deltas. This study is focused on the influence of atmospheric cold fronts on the hydrological connectivity between channels and floodplains within the Wax Lake Delta using the Delft3D FM model. The results demonstrate a substantial effect of passing cold fronts on the exchange of water and transport fraction between the primary channels and floodplains. This impact is intricately connected to the morphodynamical characteristics of the floodplains, the intensity of cold fronts, river discharge, Coriolis force, and tidal currents. The passing cold fronts can enhance or reverse the direction of water exchange between channels and floodplains. For floodplains, the passage of cold fronts can lead to an increase in the rate of water exchange by as much as five times. In the WLD, a substantial fraction of water, 39-58%, is flowing through the floodplains to the bay at the delta front influenced by the prevailing discharge, although there is a significant spatial heterogeneity. Passing cold fronts can alter the transport distribution, depending on the phase of the front. An increase in river discharge tends to bolster floodplain connectivity and lessen the effects of cold fronts. Conversely, decreased river discharge results in reduced connectivity and exacerbates the fluctuations induced by cold fronts. Moreover, the findings indicate that from the apex to downstream, the contribution of channels decreases as they become shallower, while the role of the floodplains increases, leading to a less distinct demarcation between channels and floodplains. It has also been noted that an increase in river discharge correlates with an increased contribution from floodplains to transfer water to the bay.

Background: Recently, the ENDOANGEL (EN) system, a computer-assisted detection technique, and water exchange (WE) assisted colonoscopy have both been shown to increase the colorectal adenoma detection rate (ADR). Objectives: The aim of this study was to compare the ADR between EN- and WE-assisted colonoscopy. Design: This was a retrospective study. Methods: Data from patients who underwent either EN- or WE-assisted colonoscopy between October 2021 and August 2022 were analysed consecutively. The primary outcome measure was the ADR. Results: The ADR was found to be similar between the EN and WE groups, with 80 out of 199 (40.2%) patients in the EN group compared to 78 out of 174 (44.8%) patients in the WE group [1.21; 95% confidence interval (CI), 0.80–1.83]. In the analysis using stabilized inverse probability treatment weighting after adjustment for confounding factors, both colonoscopy methods had similar performance in terms of ADR (1.41; 95% CI, 0.88–2.27). Conclusion: EN was found to be comparable to WE in terms of ADR during colonoscopy, and both methods may be effectively used in clinical practice. [ABSTRACT FROM AUTHOR]

Larval cod require live prey as food, and prey concentration (PC) and feeding frequency (FF) often affect their growth and survival. Apart from this, water exchange rates/water flow (WER/WF) and water current (WC) also affect the prey resident time in the tank and larval/early juvenile behaviour, respectively. High water current is also known to induce stress in finfish larvae, and this stress response is believed to be dependent on larval developmental stage. Thus, we conducted a study to evaluate three larval rearing protocols varying in prey concentration, feeding frequency, and water current/exchange rate. Three protocols were used: low prey concentration (PC), low feeding frequency (FF), and low water flow (protocol 1); medium PC, medium FF, and medium WF (protocol 2); and high PC, high FF, and high WF (protocol 3) (see Table 1). Larvae were sampled periodically for growth and cortisol measurements. Cortisol extraction and radioimmunoassay (RIA) were conducted using methods previously validated for cod larvae. Larvae reared using protocols 2 and 3 were significantly bigger and heavier than larvae reared using protocol 1. Rearing protocol had a significant effect on the cortisol level in larval cod. Larvae showed a developmental stage-dependent stress response. Protocol 2 had significantly higher survival than protocols 1 and 3. Our results indicate that an intermediate PC, FF, and WF (protocol 2) is suitable during cod larval rearing. [ABSTRACT FROM AUTHOR]

Formation of the Kanda Bay resulted from construction of a railway dam (1916) and subsequent isolation of the sea lagoon from the main basin of the Kandalaksha Gulf, White Sea. Decreased action of tidal flows, which mix the water column of the lagoon, altered the hydrological regime of the basin. Decreased water exchange resulted in formation of oxygen-depleted near-bottom water and to sulfide contamination. A freshwater lake was, however, preserved in the southern part of the Kanda Bay. The composition of microbial communities was studied for the near-bottom water horizons at different sides of the Kanda Bay. The oxygen regime in this layer was found to change, with increasing concentrations of sulfide and methane and active processes of sulfate reduction and methane oxidation. The composition of the microbial community changed noticeably, with lower abundance of true marine and freshwater microorganisms and development of bacteria and archaea predominant in microbial communities of anoxic water in meromictic basins. Among the microbial diversity, indicator species with increased abundance were revealed. These are archaea of the genera Methanoregula and Methanosaeta (phylum Halobacterota). The sulfur cycle microorganisms, which were the indicators of stagnant marine water, included anoxygenic phototrophic bacteria of the class Chlorobia, (Chlorobium phaeovibrioides, Pelodictyon phaeoclathratiforme), Chloroflexi of the genus Chloronema, nonsulfur purple bacteria related to the genus Rhodoferax, colorless sulfur bacteria of the family Beggiatoaceae, and sulfur oxidizers of the genus Thiobacillus. Archaea of the genus Nitrosopumilus (phylum Crenarchaeota) and bacteria of the genus Woeseia may be considered opposites to the indicator microorganisms, since they were found only in the open sea water. In our opinion, stable water exchange through the dam will result in the stable composition of the Kanda Bay microbial community, with only seasonal variations and year-to-year fluctuations. The negative scenario supports prediction of conversion of the Kanda Bay into a stratified basin with anoxic near-bottom water and the microbial community similar to that found in meromictic lakes. [ABSTRACT FROM AUTHOR]

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Background: Water exchange across blood–brain barrier (BBB) (WEXBBB) is an emerging biomarker of BBB dysfunction with potential applications in many brain diseases. Several MRI methods have been proposed to measure WEXBBB, but evidence remains scarce whether different methods can produce comparable WEXBBB. Purpose: To explore whether dynamic contrast‐enhanced (DCE)‐MRI and vascular water exchange imaging (VEXI) could produce comparable WEXBBB in high‐grade glioma (HGG) patients. Study Type: Prospective cross‐sectional. Subjects: 13 HGG patients (58.4 ± 9.4 years, 9 females, 4 WHO III and 9 WHO IV). Field Strength/Sequence: A 3 T, spoiled gradient‐recalled‐echo DCE‐MRI and VEXI containing two pulsed‐gradient spin‐echo blocks separated by a mixing block. Assessments: The enhanced tumor and contralateral normal‐appearing white matter (cNAWM) volume‐of‐interests (VOIs) were drew by two neuroradiologists. And whole‐brain NAWM and normal‐appearing gray matter (NAGM) without tumor‐affected regions were segmented by automated segmentation algorithm in FSL. Statistical Tests: Student's t‐test was used to evaluate parameters difference between cNAWM and tumor, NAGM and NAWM, respectively. The correlation between vascular water efflux rate constant (kbo) from DCE‐MRI and apparent exchange rate across BBB (AXRBBB) from VEXI was evaluated by Pearson correlation. P < 0.05 was considered statistically significant. Results: Compared with cNAWM, both kbo and AXRBBB were significantly reduced in tumor (kbo = 3.50 ± 1.18 sec−1 vs. 1.03 ± 0.75 sec−1; AXRBBB = 3.54 ± 1.11 sec−1 vs. 1.94 ± 1.04 sec−1). Both kbo and AXRBBB showed significantly higher values in NAWM than NAGM (kbo = 3.50 ± 0.59 sec−1 vs. 2.10 ± 0.56 sec−1; AXRBBB = 3.35 ± 0.77 sec−1 vs. 2.07 ± 0.52 sec−1). The VOI‐averaged kbo and AXRBBB were also linearly correlated in tumor, NAWM, and NAGM (r = 0.59). Data Conclusion: DCE‐MRI and VEXI showed comparable and correlated WEXBBB in HGG patients, suggesting that the consistence and reliability of these two MRI methods in measuring WEXBBB. Evidence Level: 2. Technical Efficacy: Stage 1. [ABSTRACT FROM AUTHOR]

The self-purification capacity of semi-closed bays is closely related to the exchange process of open sea water. In recent years, with the enhancement of human development activities, environmental problems such as eutrophication, weak hydrodynamics, and poor water exchange capacity have appeared in the bays. In this paper, the water exchange time and flow field in Jiaozhou Bay (JZB) were investigated using the environmental fluid dynamics code with a coupled dye module. Specifically, Jiaozhou Bay was divided into seven zones to explore the effect mechanism of a monsoon on the water exchange process. A detailed analysis was performed on the current water exchange status in the highly polluted northeastern region of the bay and its influence on the surrounding areas. Based on the definition of the average residence time and considering the effect of the tracer release moment, the distribution of the water exchange time in the bay under three circumstances was obtained. Results showed that the timing of the tracer release exerted minimal influence on the average residence time. The water exchange process was influenced by a combination of astronomical and meteorological factors. The overall exchange capacity of the bay was strongest under the impact of a winter monsoon and tides, followed by a summer monsoon and tides, and the weakest exchange occurred under the influence of tides alone. Moreover, both summer and winter monsoons greatly facilitated water exchange in the heavily polluted northeastern region. However, pollutants from this region had a significant impact on surrounding areas during a summer monsoon. Changes in the structure and intensity of residual flow fields were the primary causes of exchange rate discrepancies. [ABSTRACT FROM AUTHOR]

A technique for quantifying regional blood–brain barrier (BBB) water exchange rates using contrast‐enhanced arterial spin labelling (CE‐ASL) is presented and evaluated in simulations and in vivo. The two‐compartment ASL model describes the water exchange rate from blood to tissue, kb, but to estimate kb in practice it is necessary to separate the intra‐ and extravascular signals. This is challenging in standard ASL data owing to the small difference in T1 values. Here, a gadolinium‐based contrast agent is used to increase this T1 difference and enable the signal components to be disentangled. The optimal post‐contrast blood T1 (T1,bpost) at 3 T was determined in a sensitivity analysis, and the accuracy and precision of the method quantified using Monte Carlo simulations. Proof‐of‐concept data were acquired in six healthy volunteers (five female, age range 24–46 years). The sensitivity analysis identified the optimal T1,bpost at 3 T as 0.8 s. Simulations showed that kb could be estimated in individual cortical regions with a relative error ϵ<1% and coefficient of variation CoV=30%; however, a high dependence on blood T1 was also observed. In volunteer data, mean parameter values in grey matter were: arterial transit time tA=1.15±0.49 s, cerebral blood flow f=58.0±14.3 mL blood/min/100 mL tissue and water exchange rate kb=2.32±2.49 s−1. CE‐ASL can provide regional BBB water exchange rate estimates; however, the clinical utility of the technique is dependent on the achievable accuracy of measured T1 values. [ABSTRACT FROM AUTHOR]

Purpose. The paper is purposed at studying the dynamics and reasons of the Black Sea water inflows to the Sea of Azov, as well as the features of their seasonal variability. Methods and Results. Medium and high resolution satellite data, and also the results of numerical modeling the salinity field of the Azov-Black Sea basin for 2008-2009 by the high resolution (1 km) NEMO model were used. The analysis showed that the transparent and salty Black Sea waters were recorded most frequently in the southern and southeastern parts of the Azov Sea during a cold season. Based on the satellite measurements, the maximum number of inflows was observed in November and March, and the minimum one – from June to October. Similar results were obtained from the data of numerical calculations for 2008-2009: in winter, intense salt water inflows to the Sea of Azov (the flow exceeds 20 tons/s) are observed in a third of cases, and in some cases, the estimated salt flux attains 60 tons/s, whereas in summer their number is close to zero. Further the Black Sea waters move predominantly in a cyclonic direction, sometimes reaching the basin center. In some cases, high density gradients induce the development of an intense cyclonic eddy near the strait at the front of the Black Sea water inflows. The simulation data made it possible to assess the relationship between the wind and the salt fluxes to the Sea of Azov. It is shown that this relationship is of a cubic nature that is partly explained by increase of the inflowing water salinity caused by the intensified vertical mixing during the storms. Conclusions. The main hydrodynamic reasons for the Black Sea water inflows to the Sea of Azov and their seasonal variability are the following: 1) intense wind transfer during the south winds; 2) frontal currents at the boundary of upwellings near the Kerch Peninsula during the western and southwestern winds; 3) orbital currents of the passing anticyclones which are able to induce a northerly water transport in the strait at any wind conditions.

Water exchange between the different compartments of a heterogeneous specimen can be characterized via diffusion magnetic resonance imaging (dMRI). Many analysis frameworks using dMRI data have been proposed to describe exchange, often using a double diffusion encoding (DDE) stimulated echo sequence. Techniques such as diffusion exchange weighted imaging (DEWI) and the filter exchange and rapid exchange models, use a specific subset of the full space DDE signal. In this work, a general representation of the DDE signal was employed with different sampling schemes (namely constant b1, diagonal and anti-diagonal) from the data reduction models to estimate exchange. A near-uniform sampling scheme was proposed and compared with the other sampling schemes. The filter exchange and rapid exchange models were also applied to estimate exchange with their own subsampling schemes. These subsampling schemes and models were compared on both simulated data and experimental data acquired with a benchtop MR scanner. In synthetic data, the diagonal and near-uniform sampling schemes performed the best due to the consistency of their estimates with the ground truth. In experimental data, the shifted diagonal and near-uniform sampling schemes outperformed the others, yielding the most consistent estimates with the full space estimation. The results suggest the feasibility of measuring exchange using a general representation of the DDE signal along with variable sampling schemes. In future studies, algorithms could be further developed for the optimization of sampling schemes, as well as incorporating additional properties, such as geometry and diffusion anisotropy, into exchange frameworks.

The Baltic Sea is currently classified as ‘affected by eutrophication’. In this study, water exchanges and net phosphorus flows in the Archipelago Sea and through the Åland Sea from the Baltic proper was estimated with the aid of a 3-D hydrodynamic model for the years 2000–2021. The modelling configuration is based on the Copernicus regional reanalysis data. Water flowed from the Baltic proper to the Bothnian Sea at 669 km3/a and out from there at 879 km3/a. The inflow occurred in the deep-water layer (over 40 m), while the outflow occurred in the surface layer (0–40 m). With the inflow, 14,500 tons/a of phosphorus were transported during the years 2000–2014, but the amount increased to 20,300 tons per year from 2015 to 2021. At the same time, the winter-time concentrations of DIP in the Bothnian Sea almost doubled. In the Archipelago Sea, the main flow direction of water was from south to north from 2000 to 2014. From 2015 to 2021, the net flow direction reversed, and water flowed from the Archipelago Sea to the Baltic proper in the surface layer at a rate of 140 km3/a. At the same time, the background loading of phosphorus entering the Archipelago Sea with the flows decreased significantly and the chlorophyll-a concentration decreased below the threshold for a good ecological status. The U-turn in surface currents in the Archipelago Sea since 2015 may be related to variations in upwellings caused by climate change.

The Neva Bay is a body of water located between the delta of the Neva River and Kotlin Island. The goal of the study was to develop a method for numerical modeling of the shallow water equation in the Neva Bay, based on the finite element method. To achieve this goal, we solved a number of tasks. First, we selected characteristic periods in the history of the Neva Bay and formed numerical modeling options while determining boundary conditions. Secondly, we determined the geometric characteristics of the computational domain for modeling options and formed a finite element mesh for each of the options. Then, we found a numerical solution of hydrodynamic problems in terms of determining values of current velocity vectors. Finally, we conducted a comparative analysis of the results of solving the hydrodynamic problem of the structure of currents in the Neva Bay in different periods of history. The changes in the velocity field occurred because of the construction of the fairway and the dams for the Complex of flood protection structures (CFPS) in St. Petersburg. Today there is practically no water flow south of the Sea Canal. Water exchange between the Neva Bay and the Gulf of Finland is carried out due to culvert structures in the northern part of the CFPS and navigation facilities. The average flow of the Neva River during the calculation period did not change and was about 2500 m3/s (depends on the water level in Lake Ladoga); an increase in speeds occurs north of the Sea Canal.

As a coastal area, Bohai Bay plays an important role in the economic development and urbanization of its neighboring cities. However, its water exchange capacity has been affected by the reclamation. This study uses Delft3D to contrast the water exchange processes before and after reclamation in Bohai Bay. To find out the change of water exchange in Bohai Bay after reclamation, TRACLUS, a trajectory clustering method, is used to obtain the representative trajectories for comparison in the water exchange processes. The influence from hydrodynamics is described by comparing the residual current distribution in the water exchange processes. The comparison of the representative trajectory distribution shows that the local water exchange around the new shoreline has been reduced. The change of residual current distribution shows a similar feature to the change of trajectory distribution after reclamation. This phenomenon means that water transport has been hindered by the inward shorelines built during the reclamation period, so the water exchange has been weakened in the coastal areas. [ABSTRACT FROM AUTHOR]

Water exchange between the different compartments of a heterogeneous specimen can be characterized via diffusion magnetic resonance imaging (dMRI). Many analysis frameworks using dMRI data have been proposed to describe exchange, often using a double diffusion encoding (DDE) stimulated echo sequence. Techniques such as diffusion exchange weighted imaging (DEWI) and the filter exchange and rapid exchange models, use a specific subset of the full space DDE signal. In this work, a general representation of the DDE signal was employed with different sampling schemes (namely constant b1, diagonal and anti-diagonal) from the data reduction models to estimate exchange. A near-uniform sampling scheme was proposed and compared with the other sampling schemes. The filter exchange and rapid exchange models were also applied to estimate exchange with their own subsampling schemes. These subsampling schemes and models were compared on both simulated data and experimental data acquired with a benchtop MR scanner. In synthetic data, the diagonal and near-uniform sampling schemes performed the best due to the consistency of their estimates with the ground truth. In experimental data, the shifted diagonal and near-uniform sampling schemes outperformed the others, yielding the most consistent estimates with the full space estimation. The results suggest the feasibility of measuring exchange using a general representation of the DDE signal along with variable sampling schemes. In future studies, algorithms could be further developed for the optimization of sampling schemes, as well as incorporating additional properties, such as geometry and diffusion anisotropy, into exchange frameworks. [ABSTRACT FROM AUTHOR]

Purpose. The work is purposed at studying the synoptic variability of hydrophysical parameters in the basins of the Azov and Black seas induced by the water masses inflow through the strait; at that the inflowing water features differ from the analogous ones in the above-noted basins. Methods and Results. The results of numerical modeling of circulation in the cascade of seas (the Azov – Black – Marmara seas) for 2008–2009 were analyzed. Regional configuration of the NEMO numerical modeling platform and the results of the ERA5 atmospheric reanalysis were used. The main results were obtained for the configuration with the ~ 1.1 km spatial resolution of the computational grid. The processes of the Azov Sea waters inflow to the Black Sea and their further evolution, as well as the analogous processes with Black Sea waters in the Azov Sea basin are demonstrated. The estimates of water and salt exchange through the Kerch Strait are represented. Conclusions. Regular change of the water transfer direction through the strait conditioned by the wind significant variability constitutes the basic mechanism for the changes in water exchange between the basins. Having being analyzed, the events with the exceeding average annual values in the unidirectional salt flows through the Kerch Strait permitted to identify significant salt inflows to the Sea of Azov. The portion of such events ranges from 20–25 to almost 70 % of the total number of inflows.

Fissures and conduits are main void of karstic aquifer. Karst aquifers are highly vulnerable to contamination as water exchange between fissure system and conduit system greatly influences the karstification of limestone terrains, heterogeneity of karstic aquifer, and spring flow regime. A two-dimensional tank model was constructed, and a corresponding numerical model (MODFLOW-2005 Conduit Flow Process Mode 1, CFPM1) was developed to explore the effects of rainfall intensity and intrinsic structure of karst system (hydraulic conductivity of fissures and conduit diameter) on conduit-matrix water exchange. Nine different scenarios were designed to quantitatively simulate the spatial and temporal variability of water exchange between the fissures and conduits. The study reproduced the area of fissure water recharging to conduit (recharge zone), the area of conduit water discharging to fissure water (discharge zone) and the area of fissure water moving laterally (transport zone) in both physical model and numerical model. The results from rainfall scenarios show a relatively stable ratio of exchange zone (recharge zone and discharge zone) with increasing rainfall intensity, indicating that conduit-matrix water exchange is not sensitive to rainfall intensity, and conduit water discharging to fissure water is just a short-term phenomenon. It is also found that an increase in hydraulic conductivity of fissure system enhances extensiveness of water transport, but restrains conduit-matrix water exchange. However, the enlargement of conduit can prompt the extent of conduit-matrix water exchange. A positive feedback between the extent of conduit-matrix water exchanges and karstification can be confirmed. These findings might be essential for better understanding groundwater flow dynamics in karst aquifers.

Macrochloa tenacissima (M. tenacissima), or esparto, is a perennial tussock grass that coexists with Pinus halepensis (P. halepensis) in semi-arid Mediterranean woodlands. This research was carried out to explore diurnal transpiration at leaf level in esparto grass under different levels of pine–esparto competition and in contrasting environmental soil water conditions. The measurement period spanned from the summer of 2020 to the spring of 2021. The relationship between transpiration and competition was conducted in open and closed P. halepensis stands, and the type of leaf (green, senescent) and the maturity of the esparto grass were taken into account. We observed a higher control of transpiration in green leaves, and the correlations between the transpiration and pine competition were noted exclusively in this type of leaf. Our results demonstrated a significant impact of pine competitors (closed stands) on the transpiration of esparto grass, particularly during seasons characterized by scenarios of high water demand: the summer drought period and the commencement of the growing and flowering period (spring). Furthermore, our findings revealed a greater response to transpiration in mature bushes compared to young ones under severe water stress, indicating a higher adaptation to drought by esparto as it ages. Although our results confirmed that PAR increased transpiration in all seasons and in both stands, which is attributable to the heliophilia of esparto grass, the site effects on transpiration could also be attributable to competition for water, especially during periods of drought. These results may have important implications for the dynamics and management of these semi-arid mixed woodlands, as well as the planning of reforestation programs aimed at restoring esparto grass formations.

Riparian zones in alluvial rivers have important functions such as hydrological regulation and environmental purification. This study investigated the groundwater flow processes of the Shishou reach in the Middle Yangtze River (MYR), which can provide an important basis and reference for planning and management of the riverbanks. Soil gradation measurements and groundwater level monitoring were firstly carried out in the Shishou reach in 2021. Afterwards, numerical simulations were conducted of the groundwater flow processes under the influence of the varying river stage. Based on these numerical tests, the influencing range of riparian groundwater flow was investigated, and variation characteristics of riparian groundwater level at locations with different topographic features were quantitatively analyzed. Measured data and calculation results show that riparian groundwater level was significantly affected by river stage, given that the hydrological synchronization at 10 m away from the bank marginal was almost the same, and the peak at 20 m had a delay of only one day. With the increasing distance from the bank marginal, the response of groundwater level to in- channel water level became slower, with the peak being flattened. The impact zone of groundwater flow variation could extend to about 1 400—1 600 m away from the bank marginal. The annual variation of groundwater level outside this range was less than 5% of the maximum variation of in-channel water level. The unit channel-length water volume seeping into bank was about 5 000 m 3 / m during the 2021 rising and flood- peak periods, and the water volume discharging from the bank was about 3 000 m 3 / m during the 2021 recession period. Compared with the straight reach, the response of groundwater level at the convex side to in- channel water level was faster with a higher peak value and an opposite phenomenon was observed at the concave side. As the process of rainfall infiltration was considered, the calculated runoff coefficient was about 0. 80 in the study area. Compared with the case without rainfall infiltration, variation characteristics of groundwater level were almost unchanged, but the unit channel-length water volume seeping into and discharging from the river banks were both equal to about 4 000 m 3 / m in 2021. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate potential modeling paradigms and the impact of relaxation time effects on human blood‐brain barrier (BBB) water exchange measurements using FEXI (BBB‐FEXI), and to quantify the accuracy, precision, and repeatability of BBB‐FEXI exchange rate estimates at 3 T$$ \mathrm{T} $$. Methods: Three modeling paradigms were evaluated: (i) the apparent exchange rate (AXR) model; (ii) a two‐compartment model (2CM$$ 2\mathrm{CM} $$) explicitly representing intra‐ and extravascular signal components, and (iii) a two‐compartment model additionally accounting for finite compartmental T1$$ {\mathrm{T}}_1 $$ and T2$$ {\mathrm{T}}_2 $$ relaxation times (2CMr$$ 2{\mathrm{CM}}_r $$). Each model had three free parameters. Simulations quantified biases introduced by the assumption of infinite relaxation times in the AXR and 2CM$$ 2\mathrm{CM} $$ models, as well as the accuracy and precision of all three models. The scan–rescan repeatability of all paradigms was quantified for the first time in vivo in 10 healthy volunteers (age range 23–52 years; five female). Results: The assumption of infinite relaxation times yielded exchange rate errors in simulations up to 42%/14% in the AXR/2CM$$ 2\mathrm{CM} $$ models, respectively. Accuracy was highest in the compartmental models; precision was best in the AXR model. Scan–rescan repeatability in vivo was good for all models, with negligible bias and repeatability coefficients in grey matter of RCAXR=0.43$$ {\mathrm{RC}}_{\mathrm{AXR}}=0.43 $$ s−1$$ {\mathrm{s}}^{-1} $$, RC2CM=0.51$$ {\mathrm{RC}}_{2\mathrm{CM}}=0.51 $$ s−1$$ {\mathrm{s}}^{-1} $$, and RC2CMr=0.61$$ {\mathrm{RC}}_{2{\mathrm{CM}}_r}=0.61 $$ s−1$$ {\mathrm{s}}^{-1} $$. Conclusion: Compartmental modelling of BBB‐FEXI signals can provide accurate and repeatable measurements of BBB water exchange; however, relaxation time and partial volume effects may cause model‐dependent biases. [ABSTRACT FROM AUTHOR]

The study is focused on variations of air temperature in the basin of the Volga reservoirs, the total inflow into the water bodies, their water exchange, water level and temperature, and the heat content of water mass in open-water period under various climate conditions. The object of the analysis is the long-term series of hydrometeorological data processed by statistical methods. It is shown that the present-day air temperature has increased by 1.3‒1.8°C compared with the period before 1976. The rate of warming was on the average 0.50°C/10 years. The volume of annual inflow increased by 12.4%. Three low-water and 4 high-water phases were identified in the reservoirs of the Upper Volga, including 29–31 low-water, 25–31 high-water, and 8–16 medium-water years. During the low-water phases, the volume of inflow into the reservoirs is 10–28% less than the long-term average, while in high-water years, it is 4–20% higher. The coefficient of water exchange in the reservoirs decreased or increased by 5–13% relative to the values obtained earlier. An increase in the winter and a decrease in the spring inflow were recorded in the reservoirs of the Upper Volga and in the Kuibyshev Reservoir. A tendency toward an increase in the normal annual water level was observed in the reservoirs in the upper part of the Volga and in the Kuibyshev Reservoir, while in the lower Volga, the normal annual level somewhat decreased. In low-water phases, the reservoir levels were on the average 17 cm below and in the high-water phases, 10 cm above the normal annual value. An increase in air temperature during the warm season in the reservoir water areas, on the average by 1.2°C, led to a synchronous increase in the temperature of the water mass by 1.1°C. At the same time, the heat content of the water mass of the reservoirs increased, on the average, by 24% in the upper part of the Volga and by as little as 2–11% in its lower part. [ABSTRACT FROM AUTHOR]

Connecting the Bohai Sea (BS) and Yellow Sea (YS), the Bohai Strait is vital in controlling physical‐biogeochemical conditions in the East Asian marginal seas. In August 2019, Typhoon Lekima moved northward inland into eastern China and caused drastic water exchange through the Bohai Strait. The specific variation and underlying dynamics involved were investigated with observations and high‐resolution numerical simulations. Volume transport featured an intense inflow followed by an intense outflow, with a fluctuation magnitude of 1.88 Sv, which was much greater than the seasonal‐interannual variations. The corresponding current patterns presented three phases: strait‐wide inflow, strait‐wide outflow, and outflow in the south and inflow in the north. The strait‐wide inflow was driven by strong east‐northeasterly winds through local Ekman dynamics. The strait‐wide outflow resulted from the dynamic adjustment of ocean currents accompanying the rapid weakening of easterly winds. The third current pattern was part of a large‐scale cyclonic circulation in the BS and North YS and was governed by different factors in the southern and northern straits. Further comparisons indicated that transport caused by winter storms and other typhoons in the year had opposite phase variations to that caused by Lekima. The underlying dynamics mainly involved local Ekman dynamics and/or remote wind forcing via the propagation of coastal trapped waves but could differ greatly from events. Finally, we found that to a large extent, geostrophic transport derived from the sea surface height difference across the Bohai Strait could be used as actual transport during synoptic weather events. Plain Language Summary: The Bohai Strait is the only passage connecting the Bohai Sea and the Yellow Sea. Water exchange through the Bohai Strait plays a vital role in influencing physical‐biogeochemical conditions in the East Asian marginal seas and thus the socioeconomic development of coastal countries. In August 2019, Typhoon Lekima moved northward inland into eastern China and caused drastic water exchange through the Bohai Strait, which was much stronger than the seasonal‐interannual variations. This is the first time that water exchange variation through the Bohai Strait and underlying dynamics caused by typhoons have been investigated in detail. In addition, the transport fluctuations and underlying dynamics caused by winter storms and other typhoons in the year were compared to provide a comprehensive understanding of this high‐interest research topic. A general conclusion was that during different synoptic weather events, the underlying dynamics mainly involved local Ekman dynamics and/or remote wind forcing via the propagation of coastal trapped waves but could differ significantly from events. Finally, we found that to a large extent, geostrophic transport derived from the sea surface height difference across the Bohai Strait could be used as actual transport during synoptic weather events. Key Points: Typhoon Lekima caused stronger water exchange through the Bohai Strait than winter‐spring storms and seasonal‐interannual variationsCurrent patterns in the Bohai Strait presented three phases controlled by different dynamicsGeostrophic transport derived from the sea level difference across the strait could be used as actual transport during synoptic events [ABSTRACT FROM AUTHOR]

Gangnan Reservoir is an important water source of Shijiazhuang, the seat of northern China’s Hebei Province. The irregular shape of the reservoir makes it easy for water to stop flowing in bays, forming dead water areas. Serious water quality problems will ensue. To disclose the influence of a water diversion project on the water exchange in Gangnan Reservoir, this paper sets up a hydrodynamic and water exchange model for the reservoir based on the convection–diffusion theory. According to different diversion flows and wind fields, a total of 12 working conditions was configured to numerically simulate the water exchange in the reservoir. The results show that: the diversion flow is the main factor affecting the water exchange rate. In the main reservoir areas, the water exchange rate increases gradually, finally, it can reach a relatively high level. In the bay areas, the water exchange rate is relatively small, and affected by the diversion flow and the bay location. The wind field has different impacts on the water exchange rate in the main reservoir areas and the bay areas. The impact is small in the former areas, yet significant in the latter areas. When it is not windy, the residence time decreases with the increase of the flow. When it is windy, the wind field of each direction shortened the residence time in the bay areas, while increased that in the main reservoir areas. Furthermore, the transport and diffusion law of water pollutants in Gangnan Reservoir was analyzed by the connectivity matrix: When the main reservoir areas are polluted, the pollutants greatly affect the main reservoir areas; When the bay areas are polluted, the pollutants only affect some adjacent water bodies. The research findings provide scientific reference for the diversion operation of Gangnan Reservoir.

Eggs are a vulnerable stage because they are sensitive to thermal and hydric conditions and yet cannot behaviourally avoid stressful environments. A general mechanistic model of egg development in natural nests requires microclimatic predictions of temperature, humidity, radiation (if above ground) and water potential (if buried in soil) to be integrated with models of heat and water exchange of the egg and the metabolism of the developmental process. Although all the required pieces for such a model now exist, they have not been integrated into a general modelling framework.We developed such an integration using NicheMapR package for mechanistic niche modelling. Specifically, we took an existing general model of egg water exchange and connected it with the microclimate model in NicheMapR to simulate nest thermal and hydric environments, including the effects of soil water potential on liquid and vapour exchange and moisture‐mediated soil thermal conductivity on heat exchange. We then used the Dynamic Energy Budget model within the ectotherm model of NicheMapR as the mechanistic engine for the developmental process, allowing the explicit computation of the dynamics of metabolic heat production and all aspects of mass exchange.We illustrate the modelling framework using existing laboratory and field data on reptiles, insects, and birds. We show that it can capture laboratory observations of water exchange and metabolic heat production and how it can be used to map potential development and water uptake under natural conditions at the continental scale.The modelling framework can be used to interpret laboratory experiments and allows strong inferences to be made about the abiotic constraints on egg development in natural nests under past, present, and future environmental change. [ABSTRACT FROM AUTHOR]