[en] Highlights: • In the Couette laminar flow the D. magna filtration increases linearly with shear. • Turbulent flow completely inhibits D. magna filtration. • Turbulent regime restricts D. magna swimming capacity. • D. magna filtration is predicted to increase with the third power of the body length. Daphnia are filter feeder organisms that prey on small particles suspended in the water column. Since Daphnia individuals can feed on wastewater particles, they have been recently proposed as potential organisms for tertiary wastewater treatment. However, analysing the effects of hydrodynamics on Daphnia individuals has scarcely been studied. This study focuses then, on quantifying the filtration and swimming velocities of D. magna individuals under different hydrodynamic conditions. Both D. magna filtration and movement responded differently if the flow was laminar or if it was turbulent. In a laminar-dominated flow regime Daphnia filtration was enhanced up to 2.6 times that of a steady flow, but in the turbulent-dominated flow regime D. magna filtration was inhibited. In the laminar flow regime D. magna individuals moved freely in all directions, whereas in the turbulent flow regime they were driven by the streamlines of the flow. A model based on Daphnia-particle encountering revealed that the filtration efficiency in the laminar regime was driven by the length of the D. magna individuals and the shear rate imposed by the system.

[en] Highlights: • The filtration capacity of D. magna is enhanced in sheared flows. • High MP concentrations lead to a reduction in D. magna filtration capacity. • The amount of exposure time to MP reduces the filtration capacity of D. magna. -- Abstract: There is consensus on the need to study the potential impact microplastics (MP) have on freshwater planktonic organisms. It is not yet fully understood how MP enter the aquatic food web or the effect they have on all the trophic levels. As a result of the potential for MP to accumulate throughout food webs, there is increasing interest in evaluating their fate in a variety of environmental conditions. This study investigated the variability in the ingestion of MP to food ratios and the exposed time of MP to Daphnia magna in non-sheared and sheared conditions. The sheared environment provided Daphnia magna with the conditions for optimal filtering capacity. Regardless of the ratios of MP concentration to food concentration (MP:Food), the filtration capacity of the Daphnia magna was enhanced in the sheared experiments. In both the sheared and non-sheared experiments, filtration capacity decreased when the ratios of MP to food concentration and the exposure times to MP were increased. Mortality was mainly enhanced in the non-sheared conditions at higher MP concentrations and exposure times to MP. No mortality was found in the sheared conditions for the exposure times studied. Therefore, in aquatic systems that undergo constant low sheared conditions, Daphnia magna can survive longer when exposed to MP than in calm conditions, provided food concentrations do not limit their capacity to filter.

[en] Highlights: • A minimum seagrass patch size is needed for successful canopy restoration • The response of seagrass patches depends on wave velocity and canopy density. • Under low velocities seagrasses do not interact with waves, but attenuate seabed TKE. • Under moderate to high wave velocities seagrasses interact with waves producing TKE. For the past two centuries coastal zones have been suffering seagrass loss resulting in a network of vegetated patches which are barely interconnected and which may compromise the ecological services provided by the canopy. To optimize management efforts for successful restoration strategies, questions need to be addressed about what appropriate canopy architectural considerations are required under certain hydrodynamic conditions. In this study, a set of laboratory experiments were conducted in which hydrodynamic conditions, plant densities and vegetated patch lengths were varied to determine minimum patch lengths for successful management strategies. Based on the TKE production, this study finds two possible canopy behaviours of seagrasses under oscillating flows: one where plants do not interact with the flow and the other where they interact with waves and produce TKE. A threshold from the first to second behaviour occurs for ${\left[C_{D-\mathit{Patch}}\frac{n{d}^2}{2\left(1-\mathrm{\varphi }\right)}\right]}^{\frac{1}{3}}{U}_w$ = 2, where C_D is the drag of the vegetated patch, n is the number of stems per m², d is the stem diameter and ϕ is the solid plant fraction. Therefore, high canopy densities, large patches of vegetation or moderate wave velocities will produce plant-wave interaction, whereas low canopy densities, small vegetation patches or slow wave velocities will produce a behaviour akin to the non-vegetated cases.

[en] Aquatic plants, turbulence and sediment fluxes interact with each other in a complex, non-linear fashion. While most studies have considered turbulence as being generated primarily by mean flow, it can, however, also be generated by the action of the wind or by the night cooling convection at the surface of the water column. Here, we study turbulent interaction with vegetation and the effects it has on sediment suspension, in the absence of mean flow. In a water tank containing a base layer of sediment, turbulence was generated by oscillating a grid with the main objective being to determine the differences in sediment resuspension in sediment beds over a wide range of consolidation times (1 h–3 days), for a set of model canopies with different structural characteristics: density and flexibility, and for three types of sediment beds. The greater the consolidation time was, the lower the sediment resuspension. For bed consolidation times below 6 h, the concentration of resuspended sediment was approximately constant and had no dependence on turbulence intensity. However, for higher bed consolidation times, between 6 and 3 days, the resuspension of the sediment beds increased with turbulence intensity (defined in terms of turbulent kinetic energy; TKE hereafter). The TKE within the sparse flexible canopies was higher than that in the sparse rigid canopies, while within the dense flexible canopies it was below that of the rigid canopies. Therefore, the sediment resuspension in the sparse flexible canopies was greater than that of the sparse rigid canopies. In contrast, the sediment resuspension in the dense flexible canopies was lower than that of the dense rigid canopies. Using different sediment types, the results of the study indicate that sediments with greater concentrations of small particles (muddy beds) have higher concentrations of resuspended sediment than sediment beds that are composed of larger particle sizes (sandy beds).

[en] The aim of this study was to analyse the reasons for not starting or for early of radiotherapy at the Radiation Oncology Department. All radiotherapy treatments from March 2010 to February 2012 were included. Early withdrawals from treatment those that never started recorded. Clinical, demographic and dosimetric variables were also noted. From a total of 3250 patients treated and reviewed, 121 (4%) did not start or complete the planned treatment. Of those, 63 (52%) did not receive any radiotherapy fraction and 58 (48%) did not complete the course, 74% were male and 26% were female. The mean age was 67 ± 13 years. The most common primary tumour was lung (28%), followed by rectum (16%). The aim of treatment was 62% radical and 38% palliative, 44% of patients had metastases; the most common metastatic site was bone, followed by brain. In 38% of cases (46 patients) radiotherapy was administered concomitantly with chemotherapy (10 cases (22%) were rectal cancers). The most common reason for not beginning or for early withdrawal of treatment was clinical progression (58/121, 48%). Of those, 43% died (52/121), 35 of them because of the progression of the disease and 17 from other causes. Incomplete treatment regimens were due to toxicity (12/121 (10%), of which 10 patients underwent concomitant chemotherapy for rectal cancer). The number of patients who did not complete their course of treatment is low, which shows good judgement in indications and patient selection. The most common reason for incomplete treatments was clinical progression. Rectal cancer treated with concomitant chemotherapy was the most frequent reason of the interruption of radiotherapy for toxicity