Water Flow Regimes Research Articles

Power Performance Assessment of Vertical-Axis Tidal Turbines Using an Experimental Test Rig

This article presents the characteristic curves of a vertical-axis hydrokinetic tidal turbine of the Darrieus subtype aimed at meeting the electricity demand of port facilities located at harbors and estuaries with low water-speed conditions. The turbine was tested in the water-current flume of the University of Santiago de Compostela for several flow conditions with different water heights and water speeds. Blockage conditions were tested by examining the results from two groups of tests: with and without an accelerator device that restricts the flow around the rotor. The tip speed ratio and the power coefficient were used to characterize the performance of the turbine for each test. Finally, the results for open-field conditions were obtained by applying empirical expressions, which allowed us to assess the performance of the device in estuaries and harbors with known water-flow regimes.

Effects of Water Quality on Spatio-Temporal Diversity of Benthic Macro-Invertebrate Species along the Selected Shores of Lake Victoria, Homa-Bay County, Kenya

Human-induced landscape alterations impact the ecological integrity of water resources by adversely affecting fresh water ecosystems, water-quality, habitat structure, flow regime, and biotic interactions. For instance fresh-water Lake Victoria continues to be affected by massive discharge of waste-waters and other pollutants from the surrounding basin which interfere with the ecological balance leading to adverse impact on benthic macro-invertebrates especially along the lake shores. The objective of this study was to investigate the effect of water quality on the diversity of benthic macro-invertebrates along the shores of Lake Victoria in Homa-Bay County, Kenya. Samples were taken at various beaches including Oluch Kimira River Mouth, Homa Bay Sewage discharge point and Mbita East of course way shoreline and examined for water quality parameters and the species diversity of benthic macro-invertebrates at monthly intervals between September 2019 and Feb 2020. The study was conducted during dry and wet seasons to help determine any changes in waste water discharges, water quality and benthic macro-invertebrates’ characteristics. The results showed significant differences between various sites along the 3 different sites. During both wet and dry periods, Oluch Kimira and Homa Bay recorded low DO levels (4.0±0.46 to 6.2±0.19) MgL-1, while Mbita East of the course way throughout the period recorded DO level of (5.6±0.23 to 7.7±0.17) MgL-1. The mean concentration of Ammonia,NH4(µgL¯¹) during the dry season was (6.32 ±.3.55 to 8.79±3.02) and during the wet season 12.16± 0.92 to 22.50 ± 0.52. The county government should implement the findings of this study, which provides baseline data for evaluating the trends in water quality and related changes in benthic-macro invertebrates biodiversity in Lake Victoria shorelines in Homa Bay County. The findings will also help in making policy decisions in order to support environmental protection in Lake Victoria.

Verification of effectiveness and design procedure of gravel drains for liquefaction remediation

The current design practice of using gravel drains as a liquefaction countermeasure involves the selection of the drain spacing and drain diameter to keep the peak excess pore water pressure ratio low. As it has mostly been verified through small-scale 1 g shaking tests, its validity for the field-scale prototype has yet to be well investigated. In this study, a series of centrifuge tests was conducted to gain insight into the stress-dependent behavior of loose sand deposits with a level surface improved by gravel drains. Meanwhile, the current design procedure was validated with experimental data. The results revealed that the effects of gravel drains in suppressing the excess pore pressures depend significantly on the depth of the drains. The current design procedure has failed to elucidate the depth-dependent behavior of sand deposits. One of the important features of the mechanical properties of the soil used for the design of gravel drains was revealed through laboratory tests in which the coefficient of volumetric compressibility, mv, was found to be highly dependent on the stress level, while mv was assumed to be fixed in the design procedure. It was also found that the water flow regime in gravel drains can be a turbulent flow. The Reynolds number in drains increases from the bottom to the top, and the permeability coefficient decreases accordingly, resulting in more significant well resistance than expected based on the current design procedure. In the present study, when stress level-dependent mv and Reynolds number-dependent kw were used as input soil parameters, the axisymmetric diffusion equation, with consideration given to the well resistance, satisfactorily predicted the excess pore pressures in sand with gravel drains.

Effects of periodic cavitation on steam–water flow regime transition and mixing near steam nozzle exit

Abstract Supersonic steam injection from underwater vehicles into surrounding bulk water exhibits the formation of coherent structures due to the interfacial interaction between the steam and water. The mixing between the two is a function of the rate of growth of shear layer. In present work, experimental study is conducted with minor contribution from the CFD, to highlight the phenomena associated to the high-pressure steam injection into a pool of water under the influence of periodic cavitation which occurs near the steam's nozzle exit with its opening being at right angle to the opening of the exit nozzle. PIV setup along with piezoelectric acoustic emission sensors as well as LM35 temperature sensors and pitot tubes were applied to characterize the growth of the shear layer as a function of periodic cavitation with a range of steam's operating pressure. Based on the normalized shear growth rate as well as the Strouhal number and the normalized pitot thickness, the effect of rising in the cavitation on the variations of the thickness of the shear layer was studied. It was observed that higher area under the influence of the shear layer was due to the domination of the coherent flow structures, which influenced improved mixing between the steam and water. Comparison of our data with the available shear growth rate in literature shows good agreement when compared as a function of Mach number.

Fish and flows: Abiotic drivers influence the recruitment response of a freshwater fish community throughout a regulated lotic system of the Murray‐Darling Basin, Australia

Abstract Fish assemblages in dryland rivers have life‐history strategies that have evolved in response to environmental conditions and triggers, particularly water temperatures and flow regimes. The regulation of rivers through the construction of dams, weirs and other water diversion structures has altered natural flow regimes and the associated ecological processes of river systems worldwide. Over a 3‐year period, using standardized fish sampling and daily otolith ageing, the recruitment of eight freshwater fish species was monitored in response to various abiotic drivers, including hydrology and water temperatures, throughout the Macquarie River, a large regulated river system of the Australian Murray‐Darling Basin. A data‐driven statistical classification system is provided that groups species into reproductive guilds, based on their recruitment response to hydrology and water temperature, specifically designed for use in environmental flow management. The eight species were grouped into three distinct reproductive guilds that showed similar recruitment responses to the abiotic drivers. Murray‐Darling rainbowfish, Murray cod, and eel‐tailed catfish were considered as a single guild, characterized by seasonal recruitment during a relatively narrow thermal window under low to moderate stable discharges. The second group included common carp, bony herring, and golden perch, which recruited primarily in association with larger flow events. Un‐specked hardyhead and Australian smelt formed a more differentiated guild, recruiting over a broad range of temperatures and discharges. Limitations associated with using a reproductive guild approach to simplify water management are discussed. This study highlighted important relationships among hydrology, water temperatures, and successful recruitment that can, in turn, be used to inform development of adaptive flow management plans and effective use of environmental water for the conservation management of native fish communities. Important considerations in the design of studies that aim to examine relationships between recruitment and abiotic drivers are also discussed.

Mechanistic understanding of the pollutant removal and transformation processes in the constructed wetland system.

Constructed wetland systems (CWs) are biologically and physically engineered systems to mimic the natural wetlands which can potentially treat the wastewater from the various point and nonpoint sources of pollution. The present study aims to review the various mechanisms involved in the different types of CWs for wastewater treatment and to elucidate their role in the effective functioning of the CWs. Several physical, chemical, and biological processes substantially influence the pollutant removal efficiency of CWs. Plants species Phragmites australis, Typha latifolia, and Typha angustifolia are most widely used in CWs. The rate of nitrogen (N) removal is significantly affected by emergent vegetation cover and type of CWs. Hybrid CWs (HCWS) removal efficiency for nutrients, metals, pesticides, and other pollutants is higher than a single constructed wetland. The contaminant removal efficiency of the vertical subsurface flow constructed wetlands (VSSFCW) commonly used for the treatment of domestic and municipal wastewater ranges between 31% and 99%. Biochar/zeolite addition as substrate material further enhances the wastewater treatment of CWs. Innovative components (substrate materials, plant species) and factors (design parameters, climatic conditions) sustaining the long-term sink of the pollutants, such as nutrients and heavy metals in the CWs should be further investigated in the future. PRACTITIONER POINTS: Constructed wetland systems (CWs) are efficient natural treatment system for on-site contaminants removal from wastewater. Denitrification, nitrification, microbial and plant uptake, sedimentation and adsorption are crucial pollutant removal mechanisms. Phragmites australis, Typha latifolia, and Typha angustifolia are widely used emergent plants in constructed wetlands. Hydraulic retention time (HRT), water flow regimes, substrate, plant, and microbial biomass substantially affect CWs treatment performance.

The Cold Region Critical Zone in Transition: Responses to Climate Warming and Land Use Change

Global climate warming disproportionately affects high-latitude and mountainous terrestrial ecosystems. Warming is accompanied by permafrost thaw, shorter winters, earlier snowmelt, more intense soil freeze-thaw cycles, drier summers, and longer fire seasons. These environmental changes in turn impact surface water and groundwater flow regimes, water quality, greenhouse gas emissions, soil stability, vegetation cover, and soil (micro)biological communities. Warming also facilitates agricultural expansion, urban growth, and natural resource development, adding growing anthropogenic pressures to cold regions’ landscapes, soil health, and biodiversity. Further advances in the predictive understanding of how cold regions’ critical zone processes, functions, and ecosystem services will continue to respond to climate warming and land use changes require multiscale monitoring technologies coupled with integrated observational and modeling tools. We highlight some of the major challenges, knowledge gaps, and opportunities in cold region critical zone research, with an emphasis on subsurface processes and responses in both natural and agricultural ecosystems.

Flow Regime Visualization and Identification of Air–Water Two-Phase Flow in a Horizontal Helically Coiled Rectangular Channel

Experiments of flow regime visualization and identification of air–water two-phase flow were conducted in a horizontal helically coiled rectangular channel. The test superficial liquid and gas velocities are 0.09–2 m/s and 0.18–16 m/s, respectively. Flow regimes were observed with a high-speed video camera and the corresponding local and average void fractions were measured with an electric conductivity probe method and with a quick-close valve method, respectively. Four main flow regimes including unsteady pulsating flow, bubbly flow, intermittent flow, and annular flow were observed. The bubbly flow identification criteria depend on more than 90% bubbles whose chord length was smaller than the channel equivalent diameter. The annular flow identification criteria is the local void fraction in the gas core larger than 0.97. Then the flow regimes and their transition mechanisms are analyzed. Furthermore, new transition criteria among these flow regimes have been proposed. The results show that the critical transition average void fraction from bubbly to intermittent flow is 0.23. A complete air–water flow regime map has been developed for the horizontal helically coiled rectangular channel and the map predicts the observed flow regimes well.

Changes in the Behavior of Long-Term Waterflow Variations in the Middle Part of Yakutia under the Global Warming Conditions

Currently, not only the expected future climatic changes but also the associated changes in the long-term waterflow regime are popular research objectives. However, such studies, as a rule, are focused on large water bodies of a regional or even subplanetary significance. Also, the estimates obtained for the expected changes in the waterflow regime are of the most common nature. They are certainly important in terms of assumptions on the main trends in the development of the situation with water resources on a macro-regional scale but do little in assessing the risks of water use or even living safety (if people live near a water body) in the foreseeable future in respect of relatively small and medium-sized water bodies. The study identifies and evaluates the specifics of the waterflow regime response to global warming for rivers, the basins of which are compactly located within a single natural and climatic zone - the middle part of Yakutia. This approach allows adequately comparing the parameters of changes in the behavior of long-term waterflow variations for different rivers.For all rivers in the middle part of Yakutia, a significant increase in water content has been detected after 1987 (taken as the year preceding the start of the climate warming period), however, for the rivers of the western part of the region, this increase is associated not with a change in the behavior of long-term waterflow variations but with the onset of a high-water phase of a long-term natural cycle there. An increase in the annual waterflow variations was recorded for almost all rivers.Changes in the behavior of long-term waterflow variations after 1987 led to the loss of stationarity of the annual waterflow time series in the overwhelming majority of cases.It has been established that for rivers located in the middle part of Yakutia, a change in the behavior of long-term waterflow variations, which is presumably associated with global warming, can manifest itself in two main forms: a) in some cases, extremely high annual waterflow against the background of the typical regime of long-term variations - 1-2 cases (for the period from 1987 to 2018) lasting 1-3 years; b) the onset of a relatively long (5 years or more) period with an increased annual water content against the background of a violated of the cyclical behavior of long-term water content variations, which is typical for a given river. Herewith, for the rivers of the western region zone, the absence of pronounced changes in the behavior of long-term waterflow variations has been detected.

Predicting the effects of reservoir water level management on the reproductive output of a riparian songbird.

Dams and reservoirs alter natural water flow regimes with adverse effects on natural ecosystems. Quantifying and reducing these effects are important as global demands for energy and water, and the number of dams and reservoir, increase. However, costs and logistic constraints typically preclude experimental assessment of reservoir effects on the environment. We developed a stochastic individual-based model (IBM), parameterized using empirical data, to estimate the annual productivity of yellow warblers that breed in riparian habitat within the footprint of the Arrow Lakes Reservoir in British Columbia, Canada. The IBM incorporated information on breeding phenology, nest site selection, brood parasitism, daily nest survival, re-nesting probabilities and post-fledging survival. We used the IBM to estimate the effect of four different water management scenarios on annual productivity. We found that the IBM accurately estimated average nest success (0.39 ± 0.10 SD), the proportion of females that produced at least one fledgling during a breeding season (0.56 ± 0.11), and annual fledging success (2.06 ± 0.43) under current conditions. The IBM estimated that reservoir operations currently reduce the annual productivity of this population by 37%, from an average of 1.62 to 1.06 independent young/female. Delaying when reservoir water levels reach 435m asl (the minimum elevation occupied by yellow warblers) by approximately 2 weeks was predicted to increase annual productivity to 1.44 independent young/female. The standardized effect on annual productivity of reducing the maximum elevation of the reservoir so that yellow warbler habitat is not inundated (Cohen's d = 1.52) or delaying when water is stored (Cohen's d = 0.83) was primarily driven by inundation effects on post-fledging survival. Reservoir operation effects on breeding birds will be species specific, but this IBM can easily be modified to allow the environmental impacts on the entire breeding bird community to be incorporated into water management decisions.

Populations of a widespread hexacoral have trophic plasticity and flexible syntrophic interactions across the Indo-Pacific Ocean

Benthic cnidarians are suspension feeders that ingest items ranging from particulate organic matter to macrozooplankton. Additionally, many species receive photosynthetic products from associated endosymbiotic microalgae (Symbiodiniaceae). Although benthic cnidarians are ubiquitous to reef ecosystems, variation in their nutrition acquisition strategy across distinct environments is poorly understood. In this study, we evaluated the trophic niche and symbiotic interactions of the widespread species Palythoa tuberculosa (Hexacorallia: Zoantharia) inhabiting depths ranging from the intertidal to 35 m across three Indo-Pacific regions, using carbon and nitrogen stable isotope ratios and isotopic niche metrics. Our results revealed that populations in shallow (0-8 m) and deep zones (down to 35 m) had distinct niche placements and overlap with the endosymbionts’ niches across all regions. Associated Symbiodiniaceae were identified as Cladocopium. Contradicting the paradigm of a more productive endosymbiosis in shallower waters, P. tuberculosa had less isotopic niche overlap with its endosymbionts in shallow reefs (0–9%) but a higher niche overlap in deep waters (up to 70%). Among regions, this was most evident in Dongsha Atoll, South China Sea, which has comparatively high influence of internal waves and, thus, high concentrations of plankton. The low niche overlap with endosymbionts in shallow waters indicated that P. tuberculosa may have a high heterotrophic performance, which partially explains the species’ resilience during bleaching events. Regarding the distinct niche placements across depths, lower δ13C in the shallower zone could be due to light-driven effects on fixation by the endosymbionts. Additional non-exclusive explanations include that water flow regimes and nocturnal feeding behavior could enable P. tuberculosa populations to ingest more/distinct prey items, with lower δ13C, in the shallow compared to the deep zone. The nutritional plasticity of P. tuberculosa likely contributes to its widespread distribution and provides an advantage under a warming climate that will affect cnidarian-endosymbiont relationships.

Impacts alum DWTPs sludge discharge and changes in flow regime of the Nile River on the quality of surface water and cultivated soils in Fayoum watershed, Egypt

Discharge of Drinking Water Treatment Plants sludge directly on surface waters without any treatment is becoming an important issue in most countries around the world, behavior is not only affecting on the water quality, but also on soil and crops. This study investigated the effect of discharge of alum sludge and the variation in the level of the Nile water (flow regime) on water and soil qualities. The water samples were analyzed for physical, chemical and microbiological parameters. In winter (closure season), the mean values of EC, TDS, major ions, pH, DO and total algae count were higher than in summer. In summer (flooding season), it was noticed that the mean values of SiO2, metals, COD, BOD, TOC, nutrients and bacteriological parameters exceed winter season values. Moreover, the concentrations of Al, Fe, Mn were above WHO permissible limits and the concentrations of aggregate organic parameters exceed the FAO permissible limits in sites near the areas of sludge discharge. Most of water samples exceed the national guidelines. For soil, our findings showed that the concentrations of metals in soil samples collected from areas irrigated from canals receiving alum sludge are more (two-three times) than their concentrations from the pure sites. However, Pb concentration in the contaminated soil reaches ten times more than in the pure one. The management of sludge disposal becomes an urgent priority to save waterways, soil and crops from pollution. Finally, the variation in water flow during the winter closure period with reduction by ≈15 BCM is similar to the same reduction in the Nile flow when the Grand Ethiopian Renaissance Dam starts operation. This indicates that the long-term reduction in water flow due to the construction of this dam may cause serious environmental changes in the Nile River in Egypt.

Ecological risk assessment of environmental stress and bioactive chemicals to riverine fish populations: An individual-based model of smallmouth bass Micropterus dolomieu✰

• A modeling framework is developed to assess population-level effects of temperature, flow and chemicals. • The framework includes three modules: biological model module, effect module and population model. • The framework is demonstrated with an individual-based model of smallmouth bass. • Warm summer water temperatures and year-round high flows have the most severe impacts. • Exposure to estrogenic endocrine disrupting compounds substantially reduces population size. Ecological risk assessments play an important role in environmental management and decision-making. Although empirical measurements of the effects of habitat changes and chemical exposure are often made at molecular and individual levels, environmental decision-making often requires the quantification of management-relevant, population-level outcomes. In this study, we generalized a modeling framework to evaluate population-level ecological risk of environmental stress and bioactive chemicals. The modeling framework includes (1) a biological model module that incorporates complex and interacting biological and ecological processes, and environmental stochasticity, (2) an effect module that links the impacts of environmental changes and chemical exposure to individual characteristics, and (3) a population module that makes decisions on the choice of population-level properties to best capture the effects and thus to track in the model based on the target species and the research and management interest. This framework is a 3-module procedure that provides an alternative way for researchers to organize, present and communicate the risk assessment modeling studies. To demonstrate this framework, we used a socioeconomically important riverine fish species, smallmouth bass Micropterus dolomieu , as the model species. We developed an individual-based model as the biological model module. We evaluated the impacts of changing water temperature and flow regimes, and the impacts of exposure to estrogenic endocrine disrupting compounds (EEDC) on smallmouth bass populations in the Chesapeake Bay Watershed, USA. Warm summer water temperatures and year-round high flows had the most severe impacts on the smallmouth bass population. An increase in exposure level to EEDC, both year-round and in summer months, substantially reduced population size, spawner and recruit abundance, and the proportion of quality-length individuals. Acute exposure to EEDC was more detrimental to the population than chronic exposure. Acute exposure during spawning season had the most severe impacts. This modeling framework can be extended to other species, environmental factors and chemicals, and can be used to inform management and conservation decisions.

Specific climate classification for Mediterranean hydrology and future evolution under Med-CORDEX regional climate model scenarios

Abstract. The Mediterranean region is one of the most sensitive regions to anthropogenic and climatic changes, mostly affecting its water resources and related practices. With multiple studies raising serious concerns about climate shifts and aridity expansion in the region, this one aims to establish a new high-resolution classification for hydrology purposes based on Mediterranean-specific climate indices. This classification is useful in following up on hydrological (water resource management, floods, droughts, etc.) and ecohydrological applications such as Mediterranean agriculture. Olive cultivation is the characteristic agricultural practice of the Mediterranean region. The proposed approach includes the use of classic climatic indices and the definition of new climatic indices, mainly precipitation seasonality index Is or evapotranspiration threshold SPET, both in line with river flow regimes, a principal component analysis to reduce the number of indices, K-means classification to distribute them into classes, and finally the construction of a decision tree based on the distances to class kernels to reproduce the classification without having to repeat the whole process. The classification was set and validated by WorldClim-2 at 1 km high-resolution gridded data for the 1970–2000 baseline period and 144 stations' data over 30 to 120 years, both at monthly time steps. Climatic classes coincided with a geographical distribution in the Mediterranean ranging from the most seasonal and driest class 1 in the south to the least seasonal and most humid class 5 in the north, showing the climatic continuity from one place to another and enhancing the visibility of change trends. The MED-CORDEX ALADIN and CCLM historical and projected data at 12 and 50 km resolution simulated under the RCP4.5 and 8.5 scenarios for the 2070–2100 period served to assess the climate change impact on this classification by superimposing the projected changes on the baseline grid-based classification. RCP scenarios increase the seasonality index Is by +80 % and the aridity index IArid by +60 % in the north and IArid by +10 % without Is change in the south, hence causing the wet season shortening and river regime modification with the migration north of moderate and extreme winter regimes instead of early spring regimes. The ALADIN and CCLM regional climate models (RCMs) have demonstrated an evolution of the Mediterranean region towards arid climate. The classes located to the north are slowly evolving towards moderate coastal classes, which might affect hydrologic regimes due to shorter humid seasons and earlier snowmelts. These scenarios might look favourable for Mediterranean cultivation; however, the expected impact on water resources and flow regimes will surely expand and directly hit ecosystems, food, health, and tourism, as risk is interconnected between domains. This kind of classification might be reproduced at the global scale, using the same or other climatic indices specific to each region, highlighting their physiographic characteristics and hydrological responses.

Flow distribution imaging and sensing for leaks in pipelines using decimated signal diagonalization

Control and monitoring of pipelines, dedicated to liquids transportation and distribution, are generally performed by active and passive techniques. With active techniques, we intend the possibility of using external sources to target pipelines and/or liquid inside the infrastructure. The used radiation can be partly reflected by the liquid and pipeline. Passive techniques are related to spontaneous emissions from liquids within the pipelines. However, capturing water displacements and fluctuations within the pipeline, by means of sensors and transducers, is somehow a passive technique. This latter is here illustrated thanks to pressure sensors mounted on an experimental pipeline. The basic idea is to detect leaks but also to monitor water flow regime by means of imaging without using a camera. That is possible thanks to the algorithm here developed and based on 2D/3D Decimated Signal Diagonalization (DSD). It is a technique used in nuclear magnetic resonance, and susceptible to bring to excellent results if water flow within a pipeline is considered as blood flow inside an artery or a vein. The approach has been applied to an experimental hydraulic circuit.

Sensitivity of Streamflow Metrics to Infiltration‐Based Stormwater Management Networks

AbstractAs stormwater control measures (SCMs) capture surface runoff from impervious areas, a shift in the water balance and flow regime components may emerge in urban watersheds, but the amount of SCM treatment needed to detectably shift these components may vary. We used the Soil and Water Assessment Tool (SWAT) hydrologic model to assess the sensitivity of 16 hydrologic metrics as an increasingly dense rain garden SCM network was applied across the West Creek watershed, near Cleveland, Ohio (USA). As the area treated by SCMs increased, annual baseflow increases matched decreases in surface runoff, while water yield and evapotranspiration changes remained small. The stream's peak response to rainfall decreased with SCM implementation across storm sizes, ranging from the threshold rainfall depth (4.8 mm) to values higher than the design storm of a single rain garden (19 mm). SCM networks draining >20% of directly connected impervious area (DCIA) significantly decreased the magnitude of discharges with a return period of less than 1 year, the percentage of time above mean flow, and flashiness. Recession slopes and annual 1‐ and 7‐day low flows exhibited a slight response that fell within uncertainty limits of the model. Water balance and rainfall response metrics exhibited the greatest sensitivity to different intensities of stormwater management, while infrequent high and low flows were resistant to detectable change even at high levels of SCM treatment when model uncertainty was included.

Analysis of water management in PEM fuel cell stack at dead-end mode using direct visualization

Abstract Polymer electrolyte membrane fuel cells (PEMFC) have the ability to be operated with open-end and dead-end modes. At the open-end mode the extra reactants are essential for obtaining the specified current density. The removal of impurities from channels at the dead-end mode at a specific period of time is a very important issue. Water accumulation leads to the non-uniform distribution of reactant flow in individual fuel cell plate and within the fuel cell assembly, which can result in the voltage instabilities and electrodes degradation. In this work, a transparent PEMFC stack has been suggested and designed to explore water flow within the cell through direct visualization as the simplest and most reliable tool for water management studies. Design steps are explained in details within the manuscript and the performance of PEMFC stack at open-end and dead-end modes is compared. The effect of liquid water flow regime on voltage and pressure variation is investigated. The different losses at stack and single cell are compared and analyzed. In addition, an empirical correlation has been extracted for setting the purge parameters in PEM fuel cell stacks at dead-end mode which can be useful for further research works in the field of dead-end PEMFC.

Implementation of the EU ecological flow policy in Italy with a focus on Sardinia

River ecosystems are characterised by a naturally high level of hydrodynamic perturbations which create aquatic-terrestrial habitats indispensable for many species, as well as for the human beings' welfare. Environmental degradation and habitat loss caused by increasing anthropogenic pressures and global change affect freshwater aquatic ecosystems worldwide and have caused changes in water flow regimes and channels morphologies. These, in turn, decreased the natural flow capacity and reduced habitat availability, thus causing severe degradation of rivers' ecological integrity. The ecological flow (e-flow) is commonly intended as the quantity, timing, duration, frequency and quality of water flows required to sustain freshwater, estuarine and near‐shore ecosystems and the human livelihoods and well‐being. Maintaining the e-flow represents a potential tool for restoring and managing river ecosystems, to preserve the autochthonous living communities, along with environmental services and cultural/societal values. In the last decade, methods for the determination of the e-flow in European rivers moved from a simply hydrological approach towards establishing a linkage between the hydrological regime and the good ecological status (GES) of the water bodies, as identified by the European Water Framework Directive (WFD; 2000/60/EC). Each Member State is required to implement and integrate into the River Basin Management Plans (RBMP) a methodology for the determination of the e-flow, ensuring that rivers can achieve and maintain the GES. The competent river basin authorities have thus to ascertain whether national methodologies to can be applied to different river typologies and basin environment characteristics. In this context, we narratively review the e-flow assessments in the heterogeneous Italian territory, in particular on a water scant region such as Sardinia, by analysing laws, guidelines and focusing on study cases conducted with micro and meso-scale hydraulic-habitat approaches. In the sight of a more ecological-based application of national e-flow policy, we suggest that meso-habitat methods provide a valuable tool to overcome several limitations of current e-flow implementation in the Italian territory. However, to face future challenges, such as climate change adaptation, we stress the need for further experimental studies to update water management plans with greater attention for nature conservation.

Demographic history, range size and habitat preferences of the groundwater amphipod Niphargus puteanus (C.L. Koch in Panzer, 1836)

Niphargus puteanus is the oldest described species of its genus and, in the past, was used as a taxonomic annotation for any subterranean amphipod record. For that reason, no clear knowledge exists about its actual range size and habitat preferences. We here applied a molecular taxonomic and phylogeographical approach based on mitochondrial and nuclear DNA to shed light on its distribution and to infer its demographic history. Furthermore, we analysed aquifer types and water flow regimes to provide a clearer picture of the species’ ecological requirements.Our results indicate that N. puteanus is widely distributed north of the Alps, having its core range in the geomorphological natural region of the ‘South German Scarplands’ (SGS). Additionally, isolated satellite populations exist in the Taunus and the Sauerland, and two single individuals were collected in Luxembourg and in Austria, respectively. The species’ maximal distribution range reaches 756 km between the two single-specimen records and 371 km within the SGS. A very high haplotype diversity was observed, revealing the presence of seven haplotype groups. All the haplogroups were present in the SGS and exhibited distinct spatial-genetic patterns. We thus inferred a high degree of population isolation, with the SGS being a potential long-term refugium for N. puteanus. Historical drift of specimens along major riverine networks (Rhine, Danube) may provide an evolutionary dispersal mechanism explaining the formation of satellite populations.From an ecological perspective, populations of N. puteanus were found to be closely associated with fast-flowing spring environments within fissured aquifers. This species should therefore be classified as both crenophile and stygophile, effectively exploiting resources of surface as well as subsurface spring waters.

Experimental and Model‐Based Investigation of the Effect of the Free‐Surface Flow Regime on the Detection Threshold of Warm Water Inflows

AbstractHeat has been used as a tracer to identify and quantify groundwater inflows into streams. Over the last decade, a few methods have used fiber‐optic distributed temperature sensing to facilitate assessment of such inflows into small streams. However, these methods focused mainly on the groundwater percentage and the thermal contrast between groundwater and surface water without considering the flow regime of the surface water. In this study, artificial water inflows into a controlled flume were examined using fiber‐optic distributed temperature sensing to quantify the thermal anomalies induced as a function of the flow regime (turbulent or laminar). Computer simulations were then performed to widen the range of the parameters tested and provide insight into the physical processes involved. Experiments conducted under the turbulent regime were in accordance with results and uncertainties of previous studies. Under the laminar regime, however, the inflow‐induced thermal anomalies were always smaller than those under the turbulent regime for a given inflow percentage. Therefore, the actual inflow percentage may be underestimated when using a classic method under a laminar regime.