This paper uses the energetics framework developed by Scotti and White to provide a critical assessment of the widely used Thorpe-scale method, which is used to estimate dissipation and mixing rates ...in stratified turbulent flows from density measurements along vertical profiles. This study shows that the relevant displacement scale in general is not the rms value of the Thorpe displacement. Rather, the displacement field must be Reynolds decomposed to separate the mean from the turbulent component, and it is the turbulent component that ought to be used to diagnose mixing and dissipation. In general, the energetics of mixing in an overall stably stratified flow involves potentially complex exchanges among the available potential energy and kinetic energy associated with the mean and turbulent components of the flow. The author considers two limiting cases: shear-driven mixing, where mixing comes at the expense of the mean kinetic energy of the flow, and convective-driven mixing, which taps the available potential energy of the mean flow to drive mixing. In shear-driven flows, the rms of the Thorpe displacement, known as the Thorpe scale is shown to be equivalent to the turbulent component of the displacement. In this case, the Thorpe scale approximates the Ozmidov scale, or, which is the same, the Thorpe scale is the appropriate scale to diagnose mixing and dissipation. However, when mixing is driven by the available potential energy of the mean flow (convective-driven mixing), this study shows that the Thorpe scale is (much) larger than the Ozmidov scale. Using the rms of the Thorpe displacement overestimates dissipation and mixing, since the amount of turbulent available potential energy (measured by the turbulent displacement) is only a fraction of the total available potential energy (measured by the Thorpe scale). Corrective measures are discussed that can be used to diagnose mixing from knowledge of the Thorpe displacement. In a companion paper, Mater et al. analyze field data and show that the Thorpe scale can indeed be much larger than the Ozmidov scale.
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Abstract
The mixing efficiency observed in stratified turbulent boundary layers is considered within the framework of the Monin–Obukhov similarity theory. It is shown that the efficiency within the ...layer increases with distance from the boundary. Near the boundary, the efficiency is proportional to the distance from the boundary scaled with the Monin–Obukhov length. Far from the boundary, the efficiency relaxes to a value that depends on the overall thickness of the layer relative to the Monin–Obukhov layer. This value approaches 1/6 when the thickness is larger than 1/2 of the Monin–Obukhov length. The same analysis shows that the buoyancy Reynolds number cannot be used to unequivocally predict the efficiency. The −1/2 scaling between the efficiency and buoyancy Reynolds number that has been observed in field measurements and experiments is shown to depend on an extra dimensional scale and thus is not universal.
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The present dataset contains information about aquatic macroinvertebrates and environmental variables collected before and after the implementation of a small "run-of-river" hydropower plant on the ...Saldur stream, a glacier-fed stream located in the Italian Central-Eastern Alps. Between 2015 and 2019, with two sampling events per year, we collected and identified 34,836 organisms in 6 sampling sites located within a 6 km stretch of the stream. Given the current boom of the hydropower sector worldwide, and the growing contribution of small hydropower plants to energy production, data here included may represent an important - and long advocated - baseline to assess the effects that these kinds of powerplants have on the riverine ecosystem. Moreover, since the Saldur stream is part of the International Long Term Ecological Research network, this dataset also constitutes part of the data gathered within this research programme. All samples are preserved at Eurac Research facilities.
We report on near‐bottom waves of elevation with amplitude nearly half the 25 m water column, very steep, and propagating into a sheared turbulent wave‐guide. The waves contained trapped cores ...transporting parcels of water shoreward. These large waves depart strongly from weakly‐nonlinear and weakly‐nonhydrostatic conditions and challenge established paradigms. They can also represent an important factor in the across‐shore transport of plankton and contaminants.
Despite very limited in their extension - about 1% of the total surface of our planet – freshwater habitats greatly contribute to the biodiversity of Earth, since 10% of the known species and 33% of ...the vertebrates inhabit freshwaters.
However, continuous monitoring of habitats and biodiversity – not only aquatic – is considered as a complex task due to the long-term perspective these monitoring programs should have, and the connected required financial needs.
Here, within the framework of a regional-scale program of biodiversity monitoring started in the mountainous region of the Autonomous Province of Bolzano/Bozen (Italy) – including terrestrial and aquatic habitats – we present a dataset covering the first year of the fieldwork campaign aiming at sampling and identifying the benthic macroinvertebrates inhabiting the running-waters of the region.
First, we developed a GIS model with the aim of classifying all the running-waters of the region on the base of their water origin, elevation, mean discharge, slope, and geology of the catchment. After having identified a final set of 12 different stream types, 10 sampling points per each type were selected throughout the region, 2 of which – defined as “reference points” – were scheduled to be sampled each year, in order to keep a “year-by-year” temporal resolution in addition to a long-term one. Thus, every year, 48 points are sampled: 24 “reference points” (2 sites x 12 stream types), and 24 additional sites whose re-sampling is scheduled to happen every 4 years. In summary, in a 4 year-period all the 120 sites are sampled, and the same sampling campaign is planned to be repeated every 4 years, in order to build an ecological time series in a long-term perspective.
At each site, we collect benthic macroinvertebrates through a kick-net sampler (mesh size 500 µm), following a detailed protocol involving, among other aspects, characterization and quantification of the habitats present in the stretch selected for the sampling, as well as measurement of the water velocity associated to each habitat. The benthic samples are then sorted in the lab – with no application of sub-sampling – and identified mostly to family or genus level using appropriate literature.
In addition, at each site, water samples are collected and analyzed within the same day, through a spectrophotometer, looking for a set of chemical species of nitrogen and phosphorous.
Currently, across the entire European river network, there are an estimated 0.74 barriers per kilometer of river length, with hydropower production being the main cause of riverine habitat ...fragmentation. On the one hand, policy actions have been proposed by different institutions to limit this impact. On the other hand, the compelling need to produce energy from renewable/sustainable resources is further boosting the impoundment of rivers, since, globally, small hydropower plants are expected to contribute greatly to future energy needs. While a few studies have already analyzed the environmental impact of small hydropower plants by researching the structural communities of benthic macroinvertebrates, none have thus far assessed the potential impacts related to the functional diversity of these communities. Here, following a “Before-After-Control-Impact (BACI)” scheme, we implemented different methodologies to study the functional diversity of benthic communities sampled across 4 sites in a fish-free, glacier-fed stream of the Italian Central-Eastern Alps for 5 consecutive years. More specifically, the sampling sites were chosen in an area near the weir of a small “run-of-river” hydropower plant, which constituted the structure from which water was diverted to the turbine. Specific goals were to assess the potential variation in the functional traits of benthic macroinvertebrates in relation to the weir’s presence, investigate whether a variation in trait distribution was caused by alterations in the abundances of common and rare taxa, and quantify functional diversity in space and time through the application of specific indices. Our initial hypothesis of finding significant differences among the sampling sites after the start-up of the hydropower plant was not confirmed by our results, since the benthic communities at all sites continued to exhibit a largely similar set of traits and, consequently, functional diversity. Our results highlighted the need for a better understanding of the relationships between effect traits and ecological processes to establish thresholds from which a shift in these processes may occur. Hence, a better understanding of the assets and liabilities of already established small hydropower plants may be a guide for more conscious decisions concerning the establishment of new ones and/or changes in the management of already existing ones.
The term odontogenic sinusitis (OS) has proved less and less suitable to describe a series of pathological conditions related to dental procedures. We have introduced the term and classification ...‘sinonasal complications of dental disease or treatment’ (SCDDT). This study aimed to review our cases and evaluate whether the classification used is applicable to everyday clinical practice. The sample was composed of patients treated for SCDDT from 2002 to 2018 in our Department of Otorhinolaryngology. All presented signs and symptoms of sinusitis and had a recent history of dental disease or treatment. All patients underwent multidisciplinary evaluation, flexible endoscopy and computed tomography (CT) scan. Patients were allocated into three groups depending on the aetiology of the complication, following the classification proposed by Felisati et al. The sample comprised 480 patients (44% men, 56% women) with a mean age of 52.36 years. Of these, 43 patients (9%) belonged to group 1 (class A), 105 (21%) to group 2 (50, 2A; 5, 2B; 27, 2C; 23, 2D) and 332 (70%) to group 3 (119, 3A; 213, 3B). A total of 454 patients (94.5%) had unilateral maxillary opacification, while only 26 cases (5.4%) started as bilateral inflammation. Nine of the latter cases (34.6%) presented a bilateral odontogenic focus, while the other 17 (65.4%) had a history of unilateral dental pathology. The results of this study suggest that SCDDT is a complex entity that needs a careful diagnostic approach based on CT scans and presurgical endoscopy.
This paper considers the initial stage of radiatively driven convection, when the perturbations from a quiescent but time-dependent background state are small. Radiation intensity is assumed to decay ...exponentially away from the surface, and we consider parameter regimes in which the depth of the water is greater than the decay scale of $e$ of the radiation intensity. Both time-independent and time-periodic radiation are considered. In both cases, the background temperature profile of the water column is time-dependent. A linear analysis of the system is performed based on these time-dependent profiles. We find that the perturbations grow in time according to $\exp (\sigma (t) t)$, where $\sigma (t)$ is a time-dependent growth rate. An appropriately defined Reynolds number is the primary dimensionless number characterising the system, determining the wavelength, vertical structure and growth rate of the perturbations. Simulations using a Boussinesq model (the Stratified Ocean Model with Adaptive Refinement) confirm the linear analysis.
Abstract This paper provides a framework that unifies the characteristics of Langmuir turbulence, including the vortex force effect, velocity scalings, vertical flow structure, and crosswind spacing ...between surface streaks. The widely accepted CL2 mechanism is extended to explain the observed maximum alongwind velocity and downwelling velocity below the surface. Balancing the extended mechanism in the Craik-Leibovich equations, the scalings for the along-wind velocity u , cross-wind velocity v , and vertical velocity w are formulated as Here, U f is the friction velocity, U s is the Stokes drift on the surface, and La = ( U f / U s ) 1/2 is the Langmuir number. Simulations using the Stratified Ocean Model with Adaptive Refinement in Large Eddy Simulation mode (LES-SOMAR) validate the scalings and reveal physical similarity for velocity and crosswind spacing. The horizontally averaged velocity along the wind ū/U on the surface grows with time, whereas v/V and w/W are confined. The root mean square (rms) of w peaks at w rms /W ≈ 0.85 at a depth of 1.3 Zs , where Zs is the e -folding scale of the Stokes drift. The crosswind spacing L grows linearly with time but is finally limited by the depth of the water H , with maximum L/H = 3.3. This framework agrees with measurement collected in six different field campaigns.
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