Three-dimensional buoyancy-driven flow along a fractured boundary

We describe the steady motion of a buoyant fluid migrating through a porous layer along a plane, inclined boundary from a localized well. We first describe the transition from an approximately radially spreading current near the source, to a flow which runs upslope, as it spreads in the cross-slope direction. Using the model, we predict the maximum injection rate for which, near the source, the flow does not fully flood the porous layer. We then account for the presence of a fracture on the boundary through which some of the flow can drain upwards, and calculate how the current is partitioned between the fraction that drains and the remainder which continues running upslope. The fraction that drains increases with the permeability of the fracture and also with the distance from the source, as the flow slows and has more time to drain. We introduce new scalings and some asymptotic solutions to describe both the flow near the fracture and the three-dimensional surface of the injected fluid as it spreads upslope. We extend the model to the case of multiple fractures, so that the current eventually drains away as it flows over successive fractures. We calculate the shape of the region that is invaded by the buoyant fluid and we show that this flow, draining through a series of discrete fractures, may be approximated by a flow that continuously drains through its upper boundary. The effective small uniform permeability of this upper boundary is given by \textbackslash{k}_{b} \textbackslashapprox \textbackslashint \textbackslashnolimits {k}_{f} \textbackslashhspace{0.167em} \textbackslashmathrm{d} x/ {D}_{F} \textbackslash, where \textbackslash\textbackslashint \textbackslashnolimits {k}_{f} \textbackslashhspace{0.167em} \textbackslashmathrm{d} x\textbackslash is the integral of permeability across the width of the fracture and \textbackslash{D}_{F} \textbackslash is the inter-fracture spacing. Finally, we discuss the relevance of the work for CO2 sequestration and we compare some simple predictions of the plume shape, volume and volume flux derived from our model with data from the Sleipner project, Norway for the plume of CO2 which developed in Horizon 1

Buoyancy-driven dispersion in a layered porous rock

AbstractWe investigate the longitudinal dispersion of a passive tracer by a gravity-driven flow in a porous medium consisting of a series of independent horizontal layers connected to a constant pressure source. We show that in a formation of given vertical extent, the total flux is only weakly dependent on the number of layers, and is very similar to that in a single layer of the same total depth. However, although the flow speed in each layer is approximately uniform, the speed gradually increases with layer depth. As a result, if a pulse of tracer is released in the flow it will migrate more rapidly through the lower layers, leading to longitudinal dispersion of the tracer. Eventually, the location of the tracer in the different layers may become separated in space so that a sufficiently distant observation well would detect a series of discrete pulses of tracer rather than the original coherent input, as would occur in a single permeable layer. For a constant pressure source, at long times, the standard deviation of the longitudinal distribution of tracer asymptotes to a fraction of order 0.1 of the position of the centre of mass, depending on the number of layers and the overpressure of the source.This is the author accepted manuscript. The final version is available from CUP via http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9556173&fileId=S0022112014007447

Maximum sustainable yield from interacting fish stocks in an uncertain world: two policy choices and underlying trade-offs

The case of fisheries management illustrates how the inherent structural instability of ecosystems can have deep-running policy implications. We contrast ten types of management plans to achieve maximum sustainable yields (MSY) from multiple stocks and compare their effectiveness based on a management strategy evaluation (MSE) that uses complex food webs in its operating model. Plans that target specific stock sizes ($B_{\text{MSY}}$) consistently led to higher yields than plans targeting specific fishing pressures ($F_{\text{MSY}}$). A new self-optimising control rule, introduced here for its robustness to structural instability, led to intermediate yields. Most plans outperformed single-species management plans with pressure targets set without considering multispecies interactions. However, more refined plans to "maximise the yield from each stock separately", in the sense of a Nash equilibrium, produced total yields comparable to plans aiming to maximise total harvested biomass, and were more robust to structural instability. Our analyses highlight trade-offs between yields, amenability to negotiations, pressures on biodiversity, and continuity with current approaches in the European context. Based on these results, we recommend directions for developments of EU fisheries policy.Comment: 21 pages, 1 figure, 2 tables, plus supplementary material (substantial textual revision of v5

Exposure of individual harbour seals (Phoca vitulina) and waters surrounding protected habitats to acoustic deterrent noise from aquaculture

This work was funded by the European Social Fund and Scottish Funding Council as part of Developing Scotland's Workforce in the Scotland 2014–2020 European Structural and Investment Fund Programme. NDM and AF were funded by the Centre for Environment, Fisheries and Aquaculture Science (Cefas). Funding for the seal tagging was provided by the Scottish Government to the Sea Mammal Research Unit (SMRU) as part of the Marine Mammal Scientific Support Program MMSS/002/15, with additional resources from the Natural Environment Research Council (grant numbers NE/J004251/1 and SMRU1001).1. Pinniped depredation at aquaculture sites is a globally recognized problem. To mitigate depredation, the aquaculture sector uses acoustic deterrent devices (ADDs) as a non-lethal alternative to shooting pinnipeds interacting with caged finfish. However, it is unclear whether sound emissions from ADDs have the potential to also impact non-target pinnipeds at spatial scales relevant to populations. 2. Global Positioning System (GPS) tracking data from seven harbour seals tagged in a non-aquaculture context, on the west coast of Scotland, in 2017 were combined with modelled maps of ADD noise to quantify sound exposure and estimate the potential for auditory impairment. The acoustic model applied an energy flux approach across the main frequency range of ADDs (2–40 kHz). Predictions of temporary and permanent auditory threshold shifts were made using seal location data and published noise exposure criteria. The acoustic exposure of waters (10-km buffers) surrounding protected habitats (i.e. designated haul outs and Special Areas of Conservation (SACs)) on the west coast of Scotland was also assessed. 3. All tagged seals and waters surrounding 51 of 56 protected sites were predicted to be exposed to ADD noise exceeding median ambient sound levels. Temporary auditory impairment was predicted to occur in one of the seven tagged harbour seals and across 1.7% of waters surrounding protected habitats over a 24-hour period, when assuming a 100% ADD duty cycle. 4. Although the predicted risk of auditory impairment appears to be relatively low, these findings suggest that harbour seals inhabiting inshore waters off western Scotland are routinely exposed to ADD noise that exceeds median ambient sound levels. This chronic exposure risks negative consequences for individual harbour seals among the wider population in this region. The use of ADDs to mitigate pinniped depredation should be carefully considered to reduce unintended habitat-wide impacts on non-target species, including pinnipeds that are not specifically interacting with aquaculture.Publisher PDFPeer reviewe

Auditory impairment from acoustic seal deterrents predicted for harbour porpoises in a marine protected area

Management interventions to reduce human–wildlife conflict can have unintended consequences for non-target species. Acoustic deterrent devices (ADDs) are used globally by the aquaculture sector. However, the potential for these sound emissions to impact non-target species, such as cetaceans, has not yet been quantified at population relevant spatial scales. To better understand the extent of potential impacts on cetaceans, such as harbour porpoises, we used acoustic modelling to investigate levels of ADD noise throughout the west coast of Scotland and across a Special Area of Conservation (SAC) for this species. Using an energy-flux acoustic propagation model and data on aquaculture sites known to be using ADDs, we predicted the spatial extent of ADD noise on the Scottish west coast from 1 February 2017 to 31 January 2018. Noise maps were produced to determine the risk of auditory impairment for harbour porpoises under a range of scenarios which assumed single or multiple ADDs and simultaneous use across all sites. The acoustic propagation model performed well when tested against field measurements up to 5 km, with 98% of sound exposure level (SEL) predictions within ±10% of the measurements. Predictions of SELs over a 24-hr period suggested extensive temporary hearing loss zones (median radius: ~28 km) for harbour porpoises around aquaculture sites. Assuming a single device at each site, 23% of the harbour porpoise SAC was predicted to be exposed to ADD noise sufficient to induce a temporary threshold shift, and under the worst-case scenario (multiple, continuously running devices per site with an aggregate duty cycle of 100%), levels exceeding permanent threshold shift could reach 0.9% of the SAC. Policy implications. This study highlights the potential for ‘collateral damage’ from interventions such as acoustic deterrent devices (ADDs) which are intended to reduce human–wildlife conflicts with pinnipeds but may affect the long-term health and habitat use of non-target species. This is especially true for harbour porpoises which are protected under the EU and UK Habitats Regulations. The aquaculture industry, policymakers and regulators in countries where ADDs are used should consider these findings when attempting to mitigate pinniped depredation

Association study between idiopathic male infertility and the MTHFD1 G1958A SNP

Couple infertility is a global health problem and according to the World Health Organization approximately one couple in seven is affected by fertility or subfertility problems. Male infertility in humans has been acknowledged as the cause of couple’s inability to have children in 20-50% of total cases and although there have been much progress in understanding its etiology many of the case are still considered to be idiopathic, arising from an unknown cause. The MTHFD1 G1958A SNP (single nucleotide polymorphism) by altering the structure of the encoded enzyme, a trifunctional enzyme which catalyzes the interconversion of 1-carbon derivatives of tetrahydrofolate could lead to an abnormal folate status, hyperhomocysteinemia and altered DNA synthesis. The folate metabolic pathway is essential for DNA methylation, DNA synthesis, as well as methylation of various other substrates, thus a disruption to this cellular pathway may lead to major pathologic consequences. By means of molecular genetic techniques, respectively PCR-RFLP (Polymerase Chain Reaction - Restriction Fragment Length Polymorphism) we investigated the possible role of MTHFD1 G1958A SNP in the etiology of male infertility by comparing the distribution of this SNP in two groups: a group of 66 men with idiopathic azoospermia or severe oligozoospermia and a control group of 67 healthy men which have at least one child. Statistical analysis was performed by means of chi-square and Fisher’s exact tests. The genotype distribution in the two groups was in agreement with the Hardy-Weinberg Law. We obtained the following genotype stratification: 18 (27.3%) G/G, 27 (40.9%) G/A, 21(31.8%) A/A in the cases group compared to 19(28.4%) G/G, 36(53.7%) G/A, 12(17.9%) A/A in the control group; with a p value of 0.23 (odds ratio: 1.85, Cl 95%: 0.71-4.82) when comparing the mutant homozygous status (A/A) to the normal homozygous status (G/G). Because of the profound social, familial, medical and emotional outcomes that male infertility generates a greater emphasis should be made in understanding its etiology. After performing the first study on a Romanian population, due to the similar distribution of the studied polymorphism in the two groups we can state the MTHFD1 G1958A SNP is not a risk factor for idiopathic male infertility in our study group

Validated shipping noise maps of the Northeast Atlantic

Underwater noise pollution from shipping is globally pervasive and has a range of adverse impacts on species which depend on sound, including marine mammals, sea turtles, fish, and many invertebrates. International bodies including United Nations agencies, the Arctic Council, and the European Union are beginning to address the issue at the policy level, but better evidence is needed to map levels of underwater noise pollution and the potential benefits of management measures such as ship-quieting regulations. Crucially, corroboration of noise maps with field measurements is presently lacking, which undermines confidence in their application to policymaking. We construct a computational model of underwater noise levels in the Northeast Atlantic using Automatic Identification System (AIS) ship-tracking data, wind speed data, and other environmental parameters, and validate this model against field measurements at 4 sites in the North Sea. Overall, model predictions of the median sound level were within ±3 dB for 93% of the field measurements for one-third octave frequency bands in the range 125 Hz-5 kHz. Areas with median noise levels exceeding 120 dB re 1 μPa and 20 dB above modelled natural background sound were predicted to occur in the Dover Strait, the Norwegian trench, near to several major ports, and around offshore infrastructure sites in the North Sea. To our knowledge, this is the first study to quantitatively validate large-scale modelled noise maps with field measurements at multiple sites. Further validation will increase confidence in deeper waters and during winter months. Our results highlight areas where anthropogenic pressure from shipping noise is greatest and will inform the management of shipping noise in the Northeast Atlantic. The good agreement between measurements and model gives confidence that models of shipping noise can be used to inform future policy and management decisions to address shipping noise pollution

Underwater noise modelling for environmental impact assessment

Assessment of underwater noise is increasingly required by regulators of development projects in marine and freshwater habitats, and noise pollution can be a constraining factor in the consenting process. Noise levels arising from the proposed activity are modelled and the potential impact on species of interest within the affected area is then evaluated. Although there is considerable uncertainty in the relationship between noise levels and impacts on aquatic species, the science underlying noise modelling is well understood. Nevertheless, many environmental impact assessments (EIAs) do not reflect best practice, and stakeholders and decision makers in the EIA process are often unfamiliar with the concepts and terminology that are integral to interpreting noise exposure predictions. In this paper, we review the process of underwater noise modelling and explore the factors affecting predictions of noise exposure. Finally, we illustrate the consequences of errors and uncertainties in noise modelling, and discuss future research needs to reduce uncertainty in noise assessments