The influence of tidal action on porewater nitrate concentration and dynamics in intertidal sediments of the Sado estuary

The change in porewater nitrate (NO₂ ^? + NO₃ ^?) concentrations during exposure of intertidal sediment was studied at a fixed location in the Sado estuary, southwest Portugal, in November 1994. In order to follow nitrate concentration and dynamics from pre-ebb to post flood, during the day, high vertical resolution profiles (0.2 cm) were studied. As a complement, in February 1995, potential nitrification rates in the sediment were measured by laboratory incubations, with high vertical resolution (0.2 cm) up to 3 cm depth. Oxygen penetration was measured with polarographic mini-electrodes. The sediment’s texture as well as the organic matter composition in carbon and nitrogen were studied in deeper (30 cm) cores. In February 1993,²¹⁰Pb activity depth profiles were measured in a core sampled at the beginning of exposure, in order to evaluate the possibility of nonlocal particle exchange. C:N ratios and²¹⁰Pb activity profiles show evidence of nonlocal exchange of solid phase particles between the surface and deeper sediment, most likely due to macrofaunal activity. As a consequence, fresh organic matter is brought from the surface to 7–9 cm depth, causing enhancement of nutrient concentrations. Results of this study suggest nitrate dynamics in intertidal sediments of the Sado estuary are strongly influenced by tidal action. Periodic submersion and exposure allow for the diversification of pathways of oxygen supply to the sediment. Tidal stress at the sediment-water interface during the arrival (flooding) and departure (exposure) of the tidal front at the site has an important bearing on the effective depth of the nitrification zone. A denitrification rate of 2.16 μmol N dm^?5 h^?1 was measured directly from the nitrate inventory in the 1.5–6 cm depth layer. The schematic model of N cycling in these sediments suggests that 20% of the N pool is denitrified during exposure, and that this process is limited by O₂ availability for nitrification.     

Impact of a Saturation-Dependent Dissipation Source Function on Operational Hindcasts of Wind-Waves in the Australian Region

The impact of a modified parametric form of the dissipation source function S ds on the skill of an operational spectral wind-wave model is investigated. Numerical experiments are made with a version of the WAM model presently used operationally by the Australian Bureau of Meteorology to produce sea-state forecasts within the Australian region. Performances of wave hindcasts obtained using several alternative forms of this newly proposed dissipation source function are compared to those produced with forms of S ds commonly used operationally. A new ad hoc technique to compare modelled and observed wave spectra is introduced to assess the quality of calculated one-dimensional frequency spectra.

Our results indicate that wave model performance in terms of integral spectral parameters, such as the significant wave height H s , may benefit from improved parameterisations of the dissipation source term S ds . On the other hand, we also found that model performance was relatively poor in terms of predictions of the one-dimensional frequency spectrum, regardless of the chosen form of S ds . These results suggest that further refinements of the dissipation source term are strongly dependent on improved parametrisations of the nonlinear interactions source term S nl .     

Impact of climate and hydrology on juvenile fish recruitment towards estuarine nursery grounds in the context of climate change

Larvae of various coastal fish undergo immigration from spawning grounds towards estuarine nurseries. Several environmental factors can have an important impact on survival at this stage making it crucial for recruitment. Generalized linear models were applied in order to investigate the relation between river drainage, sea surface temperature (SST), NAO index and the North-South wind component intensity, over the two months prior to the estuarine colonization peak, and the densities of Platichthys flesus, Dicentrarchus labrax, Diplodus vulgaris and Diplodus bellottii in the nursery grounds based on a discontinuous historical dataset (from 1978 to 2006), for the Tagus estuary. The relation between SST over the 12 months prior to the estuarine colonization peak and fish densities in the nurseries was also investigated, as it integrates the periods of spawning stock maturation, spawning and larval immigration. While SST over the prior 12 months was negatively correlated with the abundance of P. flesus, it was positively correlated with the abundance of D. bellottii. Abundance of D. vulgaris was positively correlated with SST in the two months prior to the estuarine colonization peak, while the abundance of D. labrax was positively correlated with river drainage. The relations between SST and the abundance of P. flesus, a cold-water species with declining densities, and the subtropical species D. bellottii and D. vulgaris, which are increasing in abundance, are indicative of species abundance alterations related to climate warming. Dicentrarchus labrax will probably also be affected by climate change because of lowered precipitation and consequently river drainage.     

On a question of A. Wintner about Jacobi coordinates in the three-body problem

In his work on the elimination of the nodes in the Three-Body Problem, Jacobi considered a certain straight line (defined below, in the Introduction) which lies always within the invariable plane. Here we settle the question of Wintner on the classification of all motions for which this line fails to exist.     

Volcanic-sedimentary features in the Serra Geral Fm., Paraná Basin,southern Brazil: Examples of dynamic lava-sediment interactions in an arid setting

The formation of volcanic–sedimentary interaction features in extreme arid environments is not a commonly described process. Specifically the occurrence of dynamically mixed sediments and juvenile igneous clasts as peperites, for water has been considered one major important factor in the processes of magma dismantling and mingling with unconsolidated sediment to form such deposits. The study area, located in south Brazil, shows a sequence of lava flows and intertrapic sandstone layers from the Paraná Basin, associated with the formation of clastic dykes, flow striations, peperite and ‘peperite-like’ breccias. Four processes are suggested for the genesis of the peperites: (a) fragmentation of the flow front and base; (b) sand injection; (c) dune collapse; (d) magma cascade downhill. The continued flow of a lava, while its outer crust is already cooling, causes it to break, especially in the front and base, fragments falling in the sand and getting mixed with it, generating the flow front ‘peperite-like’ breccia. The weight of the lava flow associated to shear stress at the base cause sand to be injected inwards the flow, forming injection clastic dykes in the cooled parts and injection peperite in the more plastic portions. The lava flow may partially erode the dune, causing the dune to collapse and forming the collapse ‘peperite-like’ breccia. The shear stress at the base of a flowing lava striates the unconsolidated sand, forming the flow striations. The sand that migrates over a cooled, jointed lava flow may get caught in the cavities and joints, forming the filling clastic dykes. These deposits are analogous to those found in the Etendeka, NW Namibia, and show that sediment–lava interactions in arid settings are widespread throughout the Paraná-Etendeka province during the onset of flood volcanism.     

Estimation of potential failure risks in a mine slope using indicator kriging

Indicator kriging has been applied to the study of failure mechanisms in a mine slope in Minas Gerais, Brazil, to estimate potential failure risks in limited areas along this slope. Timbopeba Mine, Vale Company, is an open pit iron mine situated in the Quadrilátero Ferrífero, a very important mining district in Minas Gerais. A slope excavated in quartzite with a maximum height of 200 m at the time of this study, has presented many failure problems involving the sliding of blocks formed by discontinuities. These blocks are of limited size in comparison to the dimensions of the overall slope. They appear along the entire slope, wherever discontinuity orientations have led to the kinematic feasibility of these blocks. Geostatistics permits the estimation of local failure probability distributions associated to these local failures, which would not be possible with traditional statistical models. The geostatistical method employed in this study, indicator kriging, is quite suitable because it is unnecessary to assume a particular global distribution of the phenomena being modeled. The model was used for locating areas with a great tendency for sliding failure, as it considers the local spatial variability of discontinuity orientations. Copyright © 2010 John Wiley & Sons, Ltd.     

How much are the Bolinao-Anda coral reefs worth?

The Total Economic Value of the estimated 200 km² of coral reef area straddling the municipalities of Alaminos, Anda, Bani and Bolinao in Pangasinan, Philippines is estimated to reach US$38 million per year consisting mainly of indirect benefits from shoreline protection. Direct use from fisheries, aquaculture, and tourism was valued at US$6 million based on the coral reef interaction index. Non-use values for coral reef conservation were based on estimates of willingness to pay across the three economic sectors plus the general public as a fourth sector. Results varied across sectors and municipalities although the ranges were not wide, especially for fishers. Fishers’ willingness to pay averaged at US$0.25 per individual per year. Except for aquaculture operators in Bolinao, which yielded willingness to pay values reaching US$3 per individual per year, the range of conservation funding was narrow for the three other municipalities for all sectors. Using binary logistic regression (logit model), differences in willingness to pay among fishers are explained by the age, number of children, and employment status.     

Groundwater overexploitation and soil subsidence monitoring on Recife plain (Brazil)

Facing natural disasters is a priority challenge for cities, exacerbated by increases in urban population and climate change. Improving the resilience of cities is a critical need for the international community and especially for territories exposed to multiple risks, such as Chile. Although disasters are always tragic, the recovery and reconstruction post-disaster may provide a unique opportunity to prevent future suffering, enhancing the resilience of local communities. This paper presents the analysis of two Chilean reconstruction programmes applied in Mehuin and Dichato, after the earthquake and tsunami of 22 May 1960 and 27 February 2010, respectively. In both cases, reconstruction programmes were supported by the Chilean Government, but using different approaches: one focused on providing housing for people injured in the earthquake, while the other also included urban amenities and services. This article proposes an urban morphology analysis framework; in addition, it presents the assessment of the two case studies before and after a disaster, thus evaluating their resilience. By comparing urban morphology resilience pre- and post-disaster, a discussion about the effectiveness of two reconstruction approaches is presented. Finally, conclusions and recommendations to better integrate resilience into urban planning are proposed, with the aim of opening the discussion about how to make cities more resilient to natural disasters.     

Iodine and bromine contents in the Palaeoproterozoic Hotazel iron formation, Transvaal Supergroup, South Africa: A reconnaissance study

A reconnaissance bulk geochemical study was carried out on ten samples from the Palaeoproterozoic Hotazel iron formation, South Africa, with emphasis on iodine and bromine abundances. Very low-absolute contents recorded for both halogens, i.e. 0.08–0.26 μg/g for I and 0.35–1.23 μg/g for Br, indicate that they should largely have been lost during burial diagenesis. Bulk I/Br ratios (0.08–0.50), however, show marginal variation across the selected sample set and broadly resemble those that typify recent marine sediments containing organic matter. The possibility emerges that both elements are organic matter-sourced and may thus provide a potential proxy for the role of biological processes during deposition and diagenesis of Precambrian iron formations.     

The Stellar Content of Active Galaxies

We present the results of a long-slit spectroscopic study of 38 active and four normal galaxies. Stellar absorption features, continuum colours and their radial variations are analysed in an effort to characterize the stellar population in these galaxies and detect the presence of a featureless continuum underlying the starlight spectral component. Spatial variations of the equivalent widths of conspicuous absorption lines and continuum colours are detected in most galaxies. Star-forming rings, in particular, leave clear fingerprints in the equivalent widths and colour profiles. We find that the stellar populations in the inner regions of active galaxies present a variety of characteristics, and cannot be represented by a single starlight template. Dilution of the stellar lines by an underlying featureless continuum is detected in most broad-lined objects, but little or no dilution is found for most of the 20 type 2 Seyferts in the sample. Colour gradients are also ubiquitous. In particular, all but one of the observed Seyfert 2s are redder at the nucleus than in its immediate vicinity. Possible consequences of these findings are briefly outlined.