A Variable Mesh Spacing for Large-Eddy Simulation Models in the Convective Boundary Layer

A variable vertical mesh spacing for large-eddy simulation (LES) models in a convective boundary layer (CBL) is proposed. The argument is based on the fact that in the vertical direction the turbulence near the surface in a CBL is inhomogeneous and therefore the subfilter-scale effects depend on the relative location between the spectral peak of the vertical velocity and the filter cut-off wavelength. From the physical point of view, this lack of homogeneity makes the vertical mesh spacing the principal length scale and, as a consequence, the LES filter cut-off wavenumber is expressed in terms of this characteristic length scale. Assuming that the inertial subrange initial frequency is equal to the LES filter cut-off frequency and employing fitting expressions that describe the observed convective turbulent energy one-dimensional spectra, it is feasible to derive a relation to calculate the variable vertical mesh spacing. The incorporation of this variable vertical grid within a LES model shows that both the mean quantities (and their gradients) and the turbulent statistics quantities are well described near to the ground level, where the LES predictions are known to be a challenging task.     

Seasonal Variability and Estuary–Shelf Interactions in Circulation Dynamics of a River-dominated Estuary

The long-term response of circulation processes to external forcing has been quantified for the Columbia River estuary using in situ data from an existing coastal observatory. Circulation patterns were determined from four Acoustic Doppler Profilers (ADP) and several conductivity–temperature sensors placed in the two main channels. Because of the very strong river discharge, baroclinic processes play a crucial role in the circulation dynamics, and the interaction of the tidal and subtidal baroclinic pressure gradients plays a major role in structuring the velocity field. The input of river flow and the resulting low-frequency flow dynamics in the two channels are quite distinct. Current and salinity data were analyzed on two time scales—subtidal (or residual) and tidal (both diurnal and semidiurnal components). The residual currents in both channels usually showed a classical two-layer baroclinic circulation system with inflow at the bottom and outflow near the surface. However, this two-layer system is transient and breaks down under strong discharge and tidal conditions because of enhanced vertical mixing. Influence of shelf winds on estuarine processes was also observed via the interactions with upwelling and downwelling processes and coastal plume transport. The transient nature of residual inflow affects the long-term transport characteristics of the estuary. Effects of vertical mixing could also be seen at the tidal time scale. Tidal velocities were separated into their diurnal and semidiurnal components using continuous wavelet transforms to account for the nonstationary nature of velocity amplitudes. The vertical structure of velocity amplitudes were considerably altered by baroclinic gradients. This was particularly true for the diurnal components, where tidal asymmetry led to stronger tidal velocities near the bottom.     

Strength Properties of Sandy Soil–Cement Admixtures

Soil stabilization with cement is a good solution for the construction of subgrades for roadway and railway lines, especially under the platforms and mostly in transition zones between embankments and rigid structures, where the mechanical properties of supporting soils are very influential. These solutions are especially attractive in line works where other ground improvement techniques are extensive and, therefore, very expensive. On the other hand, the economic and environmental costs of such works should be optimized with good balances between excavation and embankment volumes. For this purpose, the improvement of locally available soils can bring great advantages, avoiding a great amount in borrowing appropriate material, as well as the need of disposing huge volumes in deposits. This paper focus on the characteristics of two soils, Osorio sand and Botucatu residual sandstone, which can be converted to well acceptable materials for this purpose, if stabilized with cement. The study of soil stabilization with cement relies on the quantification of the influence of percentage of cement and porosity adopted in the admixing process for different state and stress conditions. This influence will be evaluated from the analysis of unconfined compression strength (UCS or q _u ) test results. This experimental framework will enable a good definition of mechanical parameters used in design of foundations and subgrades of railways platforms and for their execution quality control.     

Unique episodic groundwater recharge event in a South American sedimentary aquifer and its long-term impact on baseflow

The anomalous entrance of water into groundwater systems can affect storage throughout long periods and normally relies on infrequent and irregular pulses of groundwater recharge defined by the term episodic recharge. Recently there was a groundwater recharge of large magnitude with unknown circumstances in the Caiuá aquifer. This unique event was explored in detail here and allowed to better understand the occurrence of such events in humid subtropical climates in South America. For this study, groundwater monitoring daily data from the Integrated Groundwater Monitoring Network was used combined with a specific yield obtained from geophysical wireline logging to obtain groundwater recharge rates. To improve the investigation, we also used a baseflow separation method to obtain the groundwater contribution into local rivers. The groundwater storage variations were also assessed by remote sensing with the GRACE data. Results showed the importance of high soil moisture storage on the occurrence of large episodic recharge events. We estimated that the groundwater recharger volumes derived from 1 year that included the unique episodic recharge observed (total of 866 mm for April 2015–March 2016) were comparable with the sum of 7 years of groundwater recharge (total of 867 mm). Atypical rainfall in winter periods were responsible for the increase in soil moisture that explained that unique event. GRACE-based GWS showed concordance detecting the occurrence of the unique episodic recharge. However, the variation in terms of volumes obtained by GRACE does not represent the behaviour observed in the aquifer by the WTF method. The results also indicated that changes in aquifer storage caused by episodic recharge events directly affect low flows in rivers over long periods. The main knowledge gap addressed here relates to exploring a unique episodic recharge event quite rare to observe with its long-term impacts on hydroclimatic variability over a humid subtropical portion of the Caiuá aquifer.     

Eutrophication and hypoxia in four streams discharging in Guanabara Bay, RJ, Brazil, a case study

Four streams in the city of São Gonçalo, were sampled to evaluate their potential as sources of nutrients to Guanabara Bay aiming to contribute with the government program to decrease the levels of pollution in this area. Imbuaçu, Guaxindiba, Marimbondo and Brandoas streams were sampled in 2007, 2008 and 2009. The streams revealed to be hipereutrophic with severe limitation of primary production by nitrogen, as shown by the N/P molar ratio. Phosphate levels were abnormally high varying between 4.35 and 130.82 μM, whereas nitrate and nitrite ranged from 0.06 to 54.05 μM and from 0.28 to 19.23 μM, respectively. The streams also presented severe hypoxia and anoxia, with oxygen values varying from non-detected to 3.72 ml l⁻¹. Heavy loads of particulate suspended material were recorded in the studied streams, ranging between 6.00 and 400.00 mg l⁻¹. The streams were considered inexorable sources of nutrients, enhancing the severe eutrophication process in Guanabara Bay.     

Effects of ultraviolet radiation on the abundance,diversity and activity of bacterioneuston and bacterioplankton: insights from microcosm studies

The effects of ultraviolet-B (0.4 W m⁻²) radiation on the abundance, diversity and heterotrophic metabolism of bacterioneuston and bacterioplankton communities from Ria de Aveiro (Portugal) were assessed and compared to those of freshwater communities from Lake Vela (Portugal) in microcosm experiments. Exposure to 9 h of artificial ultraviolet radiation (UVR) led to 24–33% reduction in bacterial abundance and up to a 70% decrease in bacterial diversity. Maximum extracellular enzyme activity and monomer incorporation rates were reduced by 16–90% and 80–100%, respectively. Recovery of bacterial activity during post-UV dark incubations ranged from 10 to 100% for extracellular enzyme activity and 40% for monomer incorporation rates. In general, the heterotrophic activity of bacterioneuston was more inhibited by UVR than that of bacterioplankton. However, DGGE profiles revealed greater UVR-induced reductions in the diversity of bacterioplankton compared to bacterioneuston. The similarity between bacterioneuston and bacterioplankton communities in samples collected at early morning was lower than at noon (pre-exposed communities) and increased upon experimental irradiation, possibly indicating selection for UV-resistant bacteria. The observation that UV exposure resulted in enhanced reduction of bacterioneuston activity, but a lower reduction in bacterial diversity accompanied by enhanced dark recovery potential compared to bacterioplankton, indicates re-directioning of bacterioneuston metabolism towards stress defence/recovery strategies rather than the sustained heterotrophic metabolism. Our results indicate that UVR can significantly decrease the abundance, diversity and activity of bacteria inhabiting the surface and sub-surface layers of freshwater and estuarine systems with potentially important impacts on the biogeochemical cycles in these environments.     

Electrodialytic treatment of sewage sludge: influence on microbiological community

This study aimed to evaluate the changes in microbiological communities present in sewage sludge (SS) when subjected to an electric field. The establishment of these relations is important to design and optimize an electrotechnology that not only promotes a direct degradation of the emerging organic contaminants, through electrodegradation, but also stimulates their biodegradation. Different current intensities were used continuously or by steps, in a two compartment electrodialytic (ED) cell. Samples collected between May and July of 2015 were analysed, prior to ED treatment, and the 35 Taxa identified were divided in 12 groups. Initial samples, collected on May, were mainly constituted by stalked ciliates (86%), followed by shelled amoebae (8%), whereas the samples collected between June and July presented higher number of shelled amoebae, between 52 and 92%. Epistylis, Vorticella and Arcella gibbosa were the most frequent protozoa identified. Samples richness (R) was between 7 and 14, Simpson’s biodiversity index (D) between 0.45 and 0.69, and evenness between 0.42 and 0.65. At the end of the ED experiments, a decrease in the number of identified Taxa and individuals was observed and, consequently, SS biodiversity also decreased. This decline was more pronounced in the ED experiments conducted with currents above 50 mA (0.10 mA cm^?2). In terms of abundance, the final SS was mainly constituted by shelled amoebae that showed to be the most resistant to the conditions within the ED cell. The obtained results showed that the studied conditions within the ED cell were not appropriate to the microbiological communities, which influenced the final SS quality.     

Experimental evaluation of rectangular reinforced concrete column behaviour under biaxial cyclic loading

The cyclic behaviour of reinforced concrete columns has been the subject of many experimental studies in recent years. However, most of these studies have focused on the unidirectional loading of columns with square cross‐sections under constant axial loading conditions. In the present study, four types of full‐scale quadrangular building columns were tested under different types of loading, including uniaxial and biaxial loading conditions. The first two specimens of each column type were independently cyclically tested in the strong and weak directions. Bidirectional tests using different loading paths were performed on the other column specimens. All columns were tested under constant axial loading conditions. In this paper, the experimental results are presented, and the global behaviour of tested columns is discussed, particularly focusing on the stiffness and strength degradation because of the increasing cyclic demand. Finally, the deformation‐based performance limits proposed in Part 3 of Eurocode 8 were calculated and compared with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd.