3,150 research outputs found
Demographic and behavioural responses of the roe deer (Capreolus capreolus) to landscape modifications and landscape of fear
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Simulation of DNAPLs migration in saturated porous media by means of Lattice Boltzmann Models
No full textThe aim of the research is to implement a numerical model inspired by the Lattice Boltzmann (LB) theory able to simulate the complex scenario of contamination of DNAPLs (Dense Non Aqueous Phase Liquids) in saturated porous media.
Groundwater contamination is nowadays recognized as a serious environmental problem. Among different polluting substances, the contamination by NAPLs continues to persist as a significant problem in industrialized nations. More specifically, an accidental release at the ground surface of DNAPLs, which include a variety of organic compounds denser than water, can lead to long-term contamination of both the unsaturated and saturated zones.
Once released, the DNAPLs tend to migrate mainly vertically in the subsurface under gravity and capillary forces. Since they are slightly soluble in both water and air, they can exist in the subsurface as a separate and immiscible fluid phases and migrate to significant depths below the water table giving rise to aqueous phase plumes depending on the slow dissolution kinetics with persistence of the source for a long period. Furthermore, during DNAPLS migration in both unsaturated and saturated media, DNAPLs can be trapped by capillary forces in the porous medium (i.e. residual DNAPLS saturation).
Predicting the source localization, often unknown, and the fate of these organic chemicals in the subsurface is challenging. Because of the difficulty in defining the separate phases migration in porous media and the further complication of the soil heterogeneity, a significant effort has been carried out for the investigation of DNAPLs motion and transport by means of experimental tests and image analysis and fate and transport modeling mainly of the dissolved phases. Nevertheless, further effort is requested to model the separate phase motion in porous media.
On the basis of this context, numerical methods can be a support for understanding and investigating the fluids behavior in complex systems such as porous media. Different approaches to modeling flows through porous media can be considered. The classical macro-scale multiphase models however do not explicitly account for many important physical phenomena in which the phases are involved. As an alternative, a mesoscopic model known as Lattice Boltzmann (LB) has been successfully applied to saturated porous media and it has been widely used for its ability to deal with complex geometries as well as its capacity to simulate fluid flow and transport at the pore-scale. The LBM originates from the kinetic theory of gases and represents the microscopic phenomena by means of a statistical (macroscopic) description. The LBM has been shown to recover the conservation laws of mass, momentum and energy and the CFD community agrees that it has reached an high degree of maturity to solve the Navier- Stokes equations for incompressible fluids in single and multiphase environments.
Compared to traditional CFD, the LBMs lead to an easier implementation of multi-phase and multi-component flows and they are applied in many fields such as geologic storage of CO2, Petroleum Engineering or reactive and melting/dissolution phenomena. Even more dealing with multiphase fluids, LBMs provides several advantages compared to the traditional CFD, such as the ability to model the interface dynamics between the different phases and to simply handle the forcing terms involved in the non- wetting phase migration in a porous media e.g. capillary forces, viscous forces and buoyancy forces.
In the thesis, a multiphase multicomponent LB model is therefore presented to simulate DNAPLs migration in saturated porous media. Once described the main DNAPLs physical-chemical properties and the multiphase multicomponent LB theory, the implemented model is validated by means of different analytical solutions. Firstly, the interfacial tension phenomenon is analyzed by means of the bubble coalescence and the spinodal decomposition simulations: a sharp interface of few lattice nodes thickness is present between the two fluid phases in function of the tension parameter. The model has proved to recover the Young-Laplace Law, which correlates the pressure difference (at equilibrium) between the regions inside and outside a bubble of fluid 1 surrounded by the fluid 2, to 1/R, where R is the radius of the bubble. Then, the wettability effects are analyzed and validated by determining the contact angle measure and comparing it with the analytical solution in Huang et al. (2007). Finally, the multiphase Poiseuille flow is simulated and compared to the results obtained from Dou et al. (2012) .Different simulations varying the forces applied to the two fluids are then carried out to investigate the impacts of the drag forces, the viscosity effects and the velocity profiles in the channel.
Regarding the simulations of the DNAPLs migration in saturated porous media, the results obtained aimed to investigate the influence of the gravity, viscous and capillary forces on DNAPLs motion. Specifically, the role of these forces is characterized by means of different dimensionless numbers, which vary during the conducted simulation tests; the simulations results confirm that, once the DNAPL is released, an increase in contaminant amount and a more radial migration of DNAPL occurs in proximity of the release point when the capillary number “Ca” (ratio between the viscosity and the capillary forces) increases. Contrarily, when the Bond number “Bo” (ratio between the buoyancy and the capillary forces) exceeds the “Ca” number, the gravity assumes a “destabilizing” role leading to the formation of gravity driven fingers.
The influence of the hydraulic gradient on DNAPLs migration is also investigated. When a hydraulic gradient is applied, the separate phase shift towards the water flow direction occurs and the pooled DNAPL accumulated above the fine lenses is less. However, the DNAPL phase is also able to move backwards the flow direction when the hydraulic gradient does not let it to exceed the capillary pressure between the pores situated downgradient, explaining the not totally removal of pools over the fine lens even with higher hydraulic gradients. Finally, “trapped DNAPLs” are present: the gravity-driven fingers extend between the pores until they are too long and break. The disconnected mass can be immobilize as blobs and ganglia for the capillary forces.
It can be concluded that the development of a model that reproduces the motion of immiscible fluids starting from the microscale- mesoscopic scale is of particular interest and importance. On one hand, it can be useful to investigate the DNAPLs scenario of contamination as well as the reactions and physical microscale processes that significantly influence their macroscale behavior; on the other hand, it is worth to underline its potential use as a tool to support any projects of environmental remediation, in which the identification of the source of contamination and the prediction migration dynamics of contaminants in porous media are essential in selecting the best remediation technology to apply. Although further research and investigation are needed to simulate the DNAPLs migration paths in real contaminated sites, the LB method can provide good results in such a field. The model can therefore be applied to investigate the migration behavior of these separate phases in saturated porous media. However, further effort has to be spent in order to provide a tool able to simulate greater contaminated domains: the potential use of upscaling techniques, without losing the intrinsic microscopic information provided by the LB model, can be suggested
Changes in Wolf Occupancy and Feeding Habits in the Northern Apennines: Results of Long-Term Predator–Prey Monitoring
No full textThe comprehension of the factors that have influenced the recent changes in wolf (Canis lupus) range and diet that have occurred in our study area, characterized by a highly heterogeneous landscape, can shed light on their current process of expansion toward the plain. Wolf presence was monitored using a standardized protocol from 2007 to 2022 by carrying out eight monitoring sessions organized in seasonal surveys, during which, we collected wolf presence data. To model wolf range dynamics, we used dynamic occupancy models considering land cover types and wild ungulate abundances as covariates. Moreover, we studied the wolf diet through scat analysis, identifying the consumed items from undigested remains. Wolf occupancy in the study area progressed from mountains to lower hills gradually; the observed range dynamics were driven by prey abundance and human presence: in particular, the probability of colonization increased with roe deer (Capreolus capreolus) abundance, whereas the probability of extinction increased with urban areas. The wolf diet showed a gradual shift from the prevalent consumption of wild boar (2007–2008 and 2011–2012) to the prevalent consumption of roe deer (continuously increasing from 2015 onward). Our results might be related to a specific adaptation of the predator to the local ecology of the most consumed species: the roe deer
Wolf predation on wild ungulates: How slope and habitat cover influence the localization of kill sites
No full textBased on data collected along the Ligurian Apennines and Alps (N-W Italy), we analysed the main environmental and human-related factors influencing the distribution of kill sites of the wolf Canis lupus. We mapped and digitized 62 kill sites collected during 2007-2016. Around each kill site, we defined a buffer corresponding to the potential hunting area of wolves. We compared kill site plots and an equal number of random plots. We formulated a model of kill site distribution following an approach presence versus availability by binary logistic regression analysis; we tested the hypothesis that wolf choice of kill sites is influenced by the physiography and the land use of the area. Among the preyed wild ungulates, we identified 23 roe deer Capreolus capreolus, 18 fallow deer Dama dama, 16 wild boars Sus scrofa, and 5 chamois Rupicapra rupicapra. Binary logistic regression analysis showed a negative effect of the road density, the urban areas, the mixed forests, and a positive effect of steep slopes and open habitats. Prey are more vulnerable to predators under certain conditions and predators are capable of selecting for these conditions. Wolves achieved this by selecting particular habitats in which to kill their prey: they preferred steep, open habitats far from human presence, where wild ungulates are more easily detectable and chasable
Recent Changes in Wolf Habitat Occupancy and Feeding Habits in Italy: Implications for Conservation and Reducing Conflict with Humans
No full textBehind wolf predation on wild ungulates: environmental factors influencing the distribution of kill sites in Northern Italy
No full textPredation is a hierarchical process whereby predators are constrained to kill prey within the area they select
while hunting. Therefore kill sites are not randomly distributed, rather where kill sites occur is a function of prey
distribution and predictability and environmental factors that influence prey detection, access, or the success of
an attack [1]. Wolves (Canis lupus) are considered generalist apex predators, preying mainly on wild ungulates.
Being socially organized in packs, usually consisting of the breeding pair and their offspring, wolves roam within
their exclusive territory and cooperate during the hunt. Wolves are well adapted for cursorial predation with
chases ranging from 100 m to more than 5 km [2].
The aim of this research is to identify the main environmental factors influencing the distribution of wolf kill sites,
so at the same time determine which factors influenced the vulnerability of prey once the hunt began.
The study was carried out in Liguria (5343 km2 region in Northern Italy; Fig. 1) The wild ungulate community
includes the wild boar (Sus scrofa) and the roe deer (Capreolus capreolus), widely distributed with high
densities, the fallow deer (Dama dama) and the chamois (Rupicapra rupicapra) more localized. Moreover, the
red deer (Cervus elaphus) has a sporadic presence along the boundaries of the region. Wolves reached the
Ligurian Apennines in the late 1980s (the first illegally killed wolf was found in 1990) and the Ligurian Alps in
the late 1990s (the first illegally killed wolf was found in 1997). The most recent research estimated the
presence of minimum five wolf packs by non-invasive genetic sampling [3].
Using data collected through a monitoring project carried out between 2007-2014 [3], we delineated wolf range
using the sampled wolf genotypes by a fixed kernel estimator. We considered all claimed and verified cases of
wolf predation upon wild ungulates recorded during 2007-2016, reporting the preyed species and possibly
some related information (sex, age, proportion of consumption). Around each kill site we defined a buffer
corresponding to the potential hunting area of wolves. We used a width of 13 km, corresponding to the average
travel distance of wolves during the night to go from dens or resting sites to hunting sites in Italy [4]. We
compared the plots where kill sites were recorded and an equal number of random plots within the estimated
wolf range. We formulated a habitat suitability model following an approach presence vs. availability by binary
logistic regression analysis (BLRA, forward stepwise method); we tested the hypothesis that wolf choice of kill
sites is influenced by the morphology and the land use of the area. In each plot, we measured from the Corine
Land Cover III level and the Digital Elevation Models (DEM) the environmental variables used as covariates:
four slope classes (range between 0° and >60°), road density, path density, forests (broad-leaved, coniferous,
and mixed forests), urban and cultivated areas, scrublands, open areas (pastures and grasslands), and bare
ground (rocks and areas with little or no vegetation cover). We considered even two-way interactions between
covariates. We tested the model performance by the percentage of correct classifications of original cases,
Nagelkerke’s R2, and receiver operating characteristic (ROC) curve analysis.
We identified 74 distinct wolf genotypes, corresponding to 189 non-invasive DNA samples (98% faeces, 1%
urines and 1% hairs), collected in the study area from 2007 to 2014. Wolf range had a total extent of 5068 km2.
We mapped and digitized 62 wolf kill sites; among the preyed wild ungulates, we identified 23 roe deer, 18
fallow deer, 16 wild boars, and 5 chamois (Fig. 1). BLRA showed a negative effect of the road density, the
urban areas, the mixed forests, and the medium slopes (20-40°), a positive effect of steep slopes (>60°), open
areas, and bare ground, the latter without statistical significance (Tab. 1). The logistic model explained 56.4%
of the variance of the response variable and correctly classified 78.2% of original cases, 82.3% of kill sites and
74.2% of control ones. The area under the ROC curve was significantly greater than that of a model that
randomly classifies the cases (AUC=0.883±0.029; P<0.001).
Wolves kill sites in Liguria were steep, open habitats (pastures and grasslands) far from roads and urban areas.
Wolves tend to avoid areas with high road and human settlement densities, as they may be barriers to wolf
movements and a cause of direct mortality both from vehicle collisions and illegal killing. Moreover, human
disturbance associated with roads and urban areas may deter or interfere with wolves when attempting to kill
prey, or afterward during carcass consumption. Wolves seemed to select steep slopes, probably because they
may find a suitable habitat in terms of advantage during hunting activities. We found that hiding-cover levels
were lower at kill sites than at random sites. Indeed, dense cover can affect the prey capacity to exploit refuges,
thus enhance its chances of escaping an attack, and can increase the chance of detection the predator,
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because of its noisier approach. From the predator point of view, in open habitats prey were easier to locate
and catch. Wild ungulates mainly use open habitats during the night as feeding areas, because of the higher
quality resources, and more closed habitats during the day, with less forage but a higher degree of shelter. Wild
ungulates have to face a constant trade-off between the choice of better food patches and predation risk. This
trade-off is mediated by the vigilance behaviour, which requires exclusive visual attention to scan the
environment, thereby interrupting or slowing down foraging activity. Wolves usually take advantage of this
wavering behaviour to start the rush. Moreover, wolves are mainly active from dawn to dusk and this is
probably closely related to their hunting pattern, which matches with the activity patterns of wild ungulates.
Overall, the environmental factors of the kill sites identified in this study are consistent with the cursorial hunting
strategy of wolves
Wolves and wild ungulates in the Ligurian Alps (Western Italy): prey selection and spatial-temporal interactions
No full textWe propose the integration of different noninvasive sampling methods to the study of predator-prey interactions. We analyzed the diet of the wolf (Canis lupus) to point out its elective prey and we investigated its spatial and temporal interactions with prey species from December 2012 to November 2014 in the Ligurian Alps (Southern Alps, Italy). In this area, the wolf is the only large predator, and there is a rich wild ungulate community consisting of four species. Our analyses showed that the most consumed species by wolves were the wild boar (Sus scrofa) and the roe deer (Capreolus capreolus). To successfully hunt these species, wolves need to share their spatial range, searching for them in the most suitable habitat types and in the periods of the diel cycle during which they are mainly active. Fallow deer (Dama dama) and chamois (Rupicapra rupicapra) consumption was low, and wolves showed also relatively low overlap with these species. Our results suggest that wolves might be firstly specialized on wild boar predation, as they showed substantial spatial and temporal overlap with this species, and secondly on roe deer predation, especially during the denning season when they probably take advantage of the presence of fawns
Direct replacement of antibodies with molecularly imprinted polymer (MIP) nanoparticles in ELISA - development of a novel assay for vancomycin
No full textA simple and straightforward technique for coating microplate wells with molecularly imprinted polymer nanoparticles (nanoMIPs) to develop ELISA type assays is presented here for the first time. NanoMIPs were synthesized by a solid phase approach with immobilized vancomycin (template) and characterized using Biacore 3000, dynamic light scattering and electron microscopy. Immobilization, blocking and washing conditions were optimized in microplate format. The detection of vancomycin was achieved in competitive binding experiments with a HRP-vancomycin conjugate. The assay was capable of measuring vancomycin in buffer and in blood plasma within the range 0.001-70 nM with a detection limit of 0.0025 nM (2.5 pM). The sensitivity of the assay was three orders of magnitude better than a previously described ELISA based on antibodies. In these experiments nanoMIPs have shown high affinity and minimal interference from blood plasma components. Immobilized nanoMIPs were stored for 1 month at room temperature without any detrimental effects to their binding properties. The high affinity of nanoMIPs and the lack of a requirement for cold chain logistics make them an attractive alternative to traditional antibodies used in ELIS
Niche partitioning between sympatric wild canids: the case of the golden jackal (Canis aureus) and the red fox (Vulpes vulpes) in north-eastern Italy
No full textAbstract Background Two coexisting species with similar ecological requirements avoid or reduce competition by changing the extent of their use of a given resource. Numerous coexistence mechanisms have been proposed, but species interactions can also be aggressive; thus, generally a subordinate species modifies its realized niche to limit the probability of direct encounters with the dominant species. We studied niche partitioning between two sympatric wild canids in north-eastern Italy: the golden jackal and the red fox, which, based on competition theories, have a high potential for competition. We considered four main niche dimensions: space, habitat, time, and diet. Results We investigated three study areas monitoring target species populations from March 2017 to November 2018 using non-invasive monitoring techniques. Red fox presence was ascertained in every study area, while golden jackal presence was not ascertained in one study area, where we collected data regarding wolf presence. Considering the two target species, we observed partial diet partitioning based on prey size, with the golden jackal mainly feeding on wild ungulates and the red fox mainly feeding on small mammals. The two canids had an extensive temporal overlap along the diel cycle, having both predominant crepuscular and nocturnal activity patterns, but marked spatial partitioning and differential use of habitats. The golden jackal proved to be specialist concerning the habitat dimension, while the red fox resulted completely generalist: the former selected less human-modified habitats and avoided intensively cultivated lands, while the latter was present in all habitats, including intensively cultivated lands. Conclusions The observed partitioning might be due partially to some ecological adaptations (e.g. specialist vs. generalist use of resources) and specific behaviours (e.g. cooperative vs. solitary hunting) and partially to the avoidance response of the red fox aimed at reducing the probability of direct encounters with the golden jackal
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