Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)

Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the 1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m⁻² d⁻¹) decreasing seaward (22–37 mmol C m⁻² d⁻¹). A significant decrease of NIT was observed with regard to previous investigations although this process still represents up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time in the estuary with values ranging from −300 to 165 mmol C m⁻² d⁻¹. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published benthic metabolic rates. A NEP of −39±8 mmol C m⁻² d⁻¹ was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m⁻² d⁻¹) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear.     

Using a genetic algorithm for 3-D inversion of gravity data in Fuerteventura (Canary Islands)

The use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the non-linearity inherent in such applications. We have implemented a genetic algorithm to efficiently invert a set of gravity data. Employing several fixed density contrasts, this algorithm determines the geometry of the sources of the anomaly gravity field in a 3-D context. The genetic algorithms, based on Darwins theory of evolution, seek the optimum solution from an initial population of models, working with a set of parameters by means of modifications in successive iterations or generations. This searching method traditionally consists of three operators (selection, crossover and mutation) acting on each generation, but we have added a further one, which smoothes the obtained models. In this way, we have designed an efficient inversion gravity method, confirmed by both a synthetic example and a real data set from the island of Fuerteventura. In the latter case, we identify crustal structures related to the origin and evolution of the island. The results show a clear correlation between the sources of gravity field in the model and the three volcanic complexes recognized in Fuerteventura by other geological studies.     

A gravimetric 3D Global inversion for cavity detection1

A gravimetric survey, covering a site 200 m square, was carried out in order to locate karstic cavities. After eliminating the regional trend using a polynomial fit, the residual is modelled by least-squares prediction. Correlated signals for several wavelengths are detected. The inversion of these anomalies is performed by a global 3D adjustment using spherical bodies as models. The adjustment is repeated in order to obtain a stable configuration. The results show the probable presence of a system of cavities and galleries. Data collected from boreholes and the subsequent appearance of sink-holes are consistent with the results.     

Conditions governing the use of approximations for the Saint-Vénant equations for shallow surface water flow

The solutions of the Saint-Vénant equations are compared with those of the kinematic, diffusion and gravity wave approximations, for a range of constant Froudé and kinematic wave numbers, with two different lower boundary conditions: (1) critical flow; and (2) zero depth gradient. For each lower boundary condition, zones are defined in the F₀,k-field in which either kinematic, diffusion or gravity wave solutions may be used to approximate the full Saint-Vénant solutions.     

Effect of Krein signatures on the stability of relative equilibria

We consider the linear stability of the equilibrium points of the generic rotating potentials U(r), U(r, ), U(r, and U(r, , . The stability analysis is performed using the concept of Krein's signature. This signature is calculated for all eigenvalues of the above potentials. Thereby, the Lagrangian points of the restricted three-body problem and the synchronous satellites of oblate and prolate planets are also studied. We find also the new positions of the eigenvalues for perturbations of the original L ₄ and L ₅ points of Mars, Jupiter, Saturn, Uranus and Neptune. Finally, we study the problem with the mass ratio µ close to the critical value and the stability of geostationary satellites perturbed by the Moon.     

Determination of the long period tidal waves in the GGP superconducting gravity data

Several results about the long period (LP) tidal waves are obtained by the analysis of series of superconducting gravity data, provided by the Global Geodynamics Project (GGP). The most important result is the determination of a single group called LPMF, composed by all LP tides but representing accurately the parameters of the M_f wave. As the LP tidal generating potential is vanishing at latitudes ±35°15′52″ we cannot determine accurate tidal amplitude factors for the stations located between ±40° and ±30°. However, it is still possible to obtain tidal residual vectors and compare them with oceanic tidal loading computations. For 15 stations the NAO99 oceanic model is giving a coherent picture. For nine stations with M_f amplitude larger than 3 μgal (1 μgal = 10 nm s⁻²) a global analysis is obtained by introducing the loading effect of the ocean directly in the observation equations. The mean amplitude factor obtained for LPMF is larger than expected from the models and there is a significant phase lag, showing the imperfection of the tidal oceanic models for M_f. Other new result is the first separate estimation of the parameters of the LP tides, generated by the tidal potential of third degree, dominated by a Lunar declinational monthly wave, called here 3M_md. Due to their small amplitudes (under 1 μgal) these waves are practically hidden by the noise. Nevertheless, the quality of the data and the flexibility of the VAV analysis method [Venedikov, A.P., Arnoso, J., Vieira, R., 2001. Program VAV/2000 for tidal analysis of unequally spaced data with irregular drift and colored noise. J. Geodetic Soc. Jpn. 47 (1), 281–286; Venedikov, A.P., Arnoso, J., Vieira, R., 2003. VAV: a program for tidal data processing. Comput. Geosci. 29, 487–502.] allow getting significant results, in agreement with the theory of the Earth deformation by the tidal potential of third degree.     

Diel feeding, daily food consumption and the predatory impact of whitemouth croaker (Micropogonias furnieri) in an estuarine environment

Diel feeding pattern and food consumption of whitemouth croaker (Micropogonias furnieri) were examined and related to seasonal variations in an estuarine environment. To determine diel feeding pattern whitemouth croaker were collected from the Patos Lagoon Estuary over 24 h (～3‐h intervals) and their stomach contents were examined. Food consumption of whitemouth croaker was determined from evacuation rates estimated experimentally and in the field. The results suggested that whitemouth croaker in the Patos Lagoon estuary feed all day long. However, whitemouth croaker showed higher feeding intensity and food consumption during daylight hours when the water transparency increased than in others when water transparency was low. Thus, whitemouth croaker seemed to intensify their feeding when they could see their prey. Daily food consumption was between 0.9 and 5.3% of body wet weight (these being the lowest and highest consumption rates during the winter and summer, respectively). The maximum predation impact of whitemouth croaker on their preferential prey, the tanaid Kalliapseudes schubartii, was 27indiv·m^?2·day^?1. The results suggested that the changes in water transparency seem to affect the diel feeding pattern and food consumption of whitemouth croaker. This could have important consequences for fish growth.     

Accurate seabed modeling using finite difference methods

Finite difference is the most widely used method for seismic wavefield modeling. However, most finite-difference implementations discretize the Earth model over a fixed grid interval. This can lead to irregular model geometries being represented by ‘staircase’ discretization, and potentially causes mispositioning of interfaces within the media. This misrepresentation is a major disadvantage to finite difference methods, especially if there exist strong and sharp contrasts in the physical properties along an interface. The discretization of undulated seabed bathymetry is a common example of such misrepresentation of the physical properties in finite-difference grids, as the seabed is often a particularly sharp interface owing to the rapid and considerable change in material properties between fluid seawater and solid rock. There are two issues typically involved with seabed modeling using finite difference methods: firstly, the travel times of reflections from the seabed are inaccurate as a consequence of its spatial mispositioning; secondly, artificial diffractions are generated by the staircase representation of dipping seabed bathymetry. In this paper, we propose a new method that provides a solution to these two issues by positioning sharp interfaces at fractional grid locations. To achieve this, the velocity model is first sampled in a model grid that allows the center of the seabed to be positioned at grid points, before being interpolated vertically onto a regular modeling grid using the windowed sinc function. This procedure allows undulated seabed bathymetry to be represented with improved accuracy during modeling. Numerical tests demonstrate that this method generates reflections with accurate travel times and effectively suppresses artificial diffractions.     

A Multistep Methodology for Building a Stochastic Model of Gold Grades in the Disseminated and Complex Deposit of Casas Novas in Alentejo,Southern Portugal

This paper proposes a multistep approach for creating a 3D stochastic model of gold grades in a complex disseminated auriferous deposit located in the Alentejo region, southern Portugal. The approach involves the following steps: (i) the creation of a 3D low‐resolution vector object model of two geological domains that better discriminate gold grades; (ii) the definition of three intervals for gold grades (low, intermediate, and high values); (iii) the estimation of the probability of each grid block belonging to each interval constrained by the geological domains; (iv) the calculation of local conditional cumulative distribution functions (CCDFs) of gold grades, for each block, taking into account the geological domains and the borehole data; and finally (v) the simulation of images of gold grades. The results demonstrate the usefulness and accuracy of the proposed procedure, as they are in compliance with the conceptual model, the distribution laws are conditioned by the geological domains, and the transition of grades between domains is continuous.     

El Niño influence on streamflow forecasting

Stochastic models are often fitted to historical data in order to produce streamflow scenarios. These scenarios are used as input data for simulation/optimization models that support operational decisions for water resource systems. The streamflow scenarios are sampled from probability distributions conditioned on the available information, such as recent streamflow data. In this paper we introduce a procedure for further conditioning the probability distributions by considering the recent measurements of climatic variables, such as sea temperatures, that are used to describe the occurrence of El Ni?o. We adopt an auto-regressive model and use the “El Ni?o information” to refine the parameter estimation process for each time step. The corresponding methodology is tested for the monthly energy time series, “inflowing” to the power plants of Colombia. This is a linear combination of streamflow values for the 18 most important rivers of the country.