The Importance of Organic Content to Fractal Floc Properties in Estuarine Surface Waters: Insights From Video, LISST, and Pump Sampling

To better understand the nature of flocs of varying organic content in estuarine surface waters, Laser in situ Scattering and Transmissometry, video settling, and pump sampling were deployed in the York River estuary. A new in situ method was developed to simultaneously solve the floc fractal dimension (F), primary particle size (d p ), and primary particle density (ρ p ) by fitting a simple fractal model to observations of effective floc density (∆ρ) as a function of floc diameter (d f ), while ensuring that the integrated particle size distribution was consistent with measurements of bulk apparent density (ρ a ). When fractal fits were statistically justified, application of the above methods showed the bulk fraction of organic matter (f org ) to be well correlated to multiple floc properties. As f org increased, d p and ρ a also increased, while ρ p , total suspended solids (TSS), and median floc size decreased. Notably for microflocs, neither F nor ∆ρ was significantly related to either f org or TSS. This indicates that organic matter may partially displace water content within microflocs without fundamentally changing the flocs’ inorganic structure. When pooling multiple samples, a marked decrease in F was seen at the transition to macroflocs, and most strongly for high f org cases. This suggested that settling velocities \u3e_ ~1 mm/s may produce turbulent stresses that tend to tear macroflocs apart. This study also found that when the fractal theory held, ρ p had a near 1:1 correlation with the bulk dry density of filtered TSS, implying that primary particles are tightly bound aggregates of combined mineral and organic component

Prescribing practices for intravenous aminoglycosides in UK cystic fibrosis clinics: a questionnaire survey

Background: Intravenous aminoglycoside antibiotics are widely used to treat pulmonary infection with Pseudomonas aeruginosa in individuals with cystic fibrosis (CF). Over the last decade evidence has accumulated showing that the choice of aminoglycoside and the dosing regimen may help reduce adverse effects such as nephrotoxicity. Methods: We undertook an online survey to determine current practice in UK CF Centres. Results: We received a response from 35/48 (73%) centres. A once daily regimen was used in 30/35 (86%) centres. Around one third had stopped using gentamicin in the last 10 years. In most cases respondents reported changing practice in response to new evidence or evidence based guidelines. Obstacles to introducing evidence based practice were identified both at the level of the CF Centre and the hospital trust. Conclusions: A once daily aminoglycoside regimen is now used in the majority of UK CF Centres. Tobramycin is first line and many centres have stopped using gentamicin. Obstacles to evidence based practice remain in a minority of centres

Sediment Resuspension Due to Near-Bed Turbulent Effects: A Deep Sea Case Study on the Northwest Continental Slope of Western Australia

Sediment transport equations often consider a mean velocity threshold for the initiation of sediment motion and resuspension, ignoring event‐based turbulent bursting processes. However, laboratory experiments have suggested that near‐bed sediment resuspension is influenced by intermittent turbulent coherent structures. In the field, accessibility constraints for deployment of easily operated equipment has largely prevented further identification and understanding of such processes, which may contribute to resuspension in the marine environment. Field experiments were conducted on the Northwest Slope, Australia, under conditions where the mean current velocities were below the estimated and measured time‐averaged critical velocity to investigate the relationship between near‐bed turbulent coherent structures and sediment resuspension. Results indicate that sediment resuspension occur even when velocities are below the estimated and measured mean critical values. The majority of turbulent sediment flux is due to ejection and sweep events, with lesser contributions from up‐acceleration and down‐deceleration (vertical flow) events. Spectral and quadrant analysis indicated the anisotropic and intermittent nature of Reynolds stresses, and wavelet transform revealed a group of turbulent bursting sequences associated with sediment resuspension. These observations, in flow conditions where resuspension was not expected to occur based on mean threshold concepts, reveal that intermittent turbulent events control sediment resuspension rather a single time‐averaged critical velocity. This highlights the need of considering turbulence as a significant factor in sediment resuspension and should be further investigated for inclusion into future sediment transport modeling

High riverine CO2 emissions at the permafrost boundary of Western Siberia

Acknowledgements: The study was part of the JPI Climate initiative, financially supported by VR (the Swedish Research Council) grant no. 325-2014-6898 to J.K. Additional funding from RNF (RSCF) grant no. 18-17-00237, RFBR grant no. 17-55-16008 and RF Federal Target Program RFMEFI58717X0036 ‘Kolmogorov’ to O.S.P. and S.N.K. as well as NERC grant no. NE/M019896/1 to C.S. is acknowledged. The authors thank A. Sorochinskiy and A. Lim for assistance in the field, as well as M. Myrstener, M. Klaus and S. Monteux for advice on data analysis. L. Kovaleva is acknowledged for artwork.Peer reviewedPostprin

International evidence-based medicine survey of the veterinary profession: information sources used by veterinarians

Veterinarians are encouraged to use evidence to inform their practice, but it is unknown what resources (e.g. journals, electronic sources) are accessed by them globally. Understanding the key places veterinarians seek information can inform where new clinically relevant evidence should most effectively be placed. An international survey was conducted to gain understanding of how veterinary information is accessed by veterinarians worldwide. There were 2137 useable responses to the questionnaire from veterinarians in 78 countries. The majority of respondents (n = 1835/2137, 85.9%) undertook clinical work and worked in a high income country (n = 1576/1762, 89.4%). Respondents heard about the survey via national veterinary organisations or regulatory bodies (31.5%), online veterinary forums and websites (22.7%), regional, discipline-based or international veterinary organisations (22.7%) or by direct invitation from the researchers or via friends, colleagues or social media (7.6%). Clinicians and non-clinicians reportedly used journals most commonly (65.8%, n = 1207/1835; 75.6%, n = 216/286) followed by electronic resources (58.7%, n = 1077/1835; 55.9%, n = 160/286), respectively. Respondents listed a total of 518 journals and 567 electronic sources that they read. Differences in veterinarian preference for resources in developed, and developing countries, were found. The nominated journals most read were the Journal of the American Veterinary Medical Association (12.7% of nominations) for clinicians and the Veterinary Record (5.7%) for non-clinicians. The most accessed electronic resource reported was the Veterinary Information Network (25.6%) for clinicians and PubMed (7.4%) for non-clinicians. In conclusion, a wide array of journals and electronic resources appear to be accessed by veterinarians worldwide. Veterinary organisations appear to play an important role in global communication and outreach to veterinarians and consideration should be given to how these channels could be best utilised for effective dissemination of key research findings

Particle Size Distribution Controls the Threshold Between Net Sediment Erosion and Deposition in Suspended Load Dominated Flows

The central problem of describing most environmental and industrial flows is predicting when material is entrained into, or deposited from, suspension. The threshold between erosional and depositional flow has previously been modeled in terms of the volumetric amount of material transported in suspension. Here a new model of the threshold is proposed, which incorporates (i) volumetric and particle size limits on a flow's ability to transport material in suspension, (ii) particle size distribution effects, and (iii) a new particle entrainment function, where erosion is defined in terms of the power used to lift mass from the bed. While current suspended load transport models commonly use a single characteristic particle size, the model developed herein demonstrates that particle size distribution is a critical control on the threshold between erosional and depositional flow. The new model offers an order of magnitude, or better, improvement in predicting the erosional‐depositional threshold and significantly outperforms existing particle‐laden flow models