The identifiability of parameters in a water quality model of the Biebrza River, Poland

The identifiability of model parameters of a steady state water quality model of the Biebrza River and the resulting variation in model results was examined by applying the Monte Carlo method which combines calibration, identifiability analysis, uncertainty analysis, and sensitivity analysis. The water quality model simulates the steady state concentration profiles of chloride, phosphate, ammonium, and nitrate as a function of distance along a river. The water quality model with the best combination of parameter values simulates the observed concentrations very well. However, the range of possible modelled concentrations obtained for other more or less equally eligible combinations of parameter values is rather wide. This range in model outcomes reflects possible errors in the model parameters. Discrepancies between the range in model outcomes and the validation data set are only caused by errors in model structure, or (measurement) errors in boundary conditions or input variables. In this sense the validation procedure is a test of model capability, where the effects of calibration errors are filtered out. It is concluded that, despite some slight deviations between model outcome and observations, the model is successful in simulating the spatial pattern of nutrient concentrations in the Biebrza River.     

Numerical Studies with a Regional Atmospheric Climate Model Based on Changes in the Roughness Length for Momentum and Heat Over Antarctica

A regional atmospheric climate model is used toexamine the effect of changes in the roughnesslengths of momentum (_z0m) and heat (_z0h)on the structure of the lower atmosphere and on thesurface energy fluxes over Antarctica. Fourexperiments were carried out in which _z0mand/or _z0h were altered with respect to acontrol experiment. The changes consisted of (1) alowering of _z0m from a field aggregated froma vegetation map with an orographic correction basedon the European Centre for Medium-Range WeatherForecasts _z0m field, to a constant value of10^-3 m; and (2) a lowering of _z0h from a valueequal to _z0m to a constant value of 10^-3 mor a value dependent on the wind speed via a surfacerenewal model. A reduction of _z0m results in theexpected increase in near-surface wind speed. It alsoresults in an increase in the depth of the layer in whichsouth-easterly near-surface winds prevail, and in adecrease in the strength of the large-scale flow overthe continent, in particular in summer. In theescarpment region a decrease of _z0m is foundto result in too high wind speeds. Surface temperatureson average decrease while atmospheric temperaturesincrease, resulting in an increase of near-surfacestatic stability. Changes in roughness lengths donot significantly change the temperature profiles.The surface fluxes, on average found reduced, aremodelled best by using the _z0h based on thesurface renewal method.     

Space-time mapping of soil salinity using probabilistic bayesian maximum entropy

The mapping of saline soils is the first task before any reclamation effort. Reclamation is based on the knowledge of soil salinity in space and how it evolves with time. Soil salinity is traditionally determined by soil sampling and laboratory analysis. Recently, it became possible to complement these hard data with soft secondary data made available using field sensors like electrode probes. In this study, we had two data sets. The first includes measurements of field salinity (EC_a) at 413 locations and 19 time instants. The second, which is a subset of the first (13 to 20 locations), contains, in addition to EC_a, salinity determined in the laboratory (EC_2.5). Based on a procedure of cross-validation, we compared the prediction performance in the space-time domain of 3 methods: kriging using either only hard data (HK) or hard and mid interval soft data (HMIK), and Bayesian maximum entropy (BME) using probabilistic soft data. We found that BME was less biased, more accurate and giving estimates, which were better correlated with the observed values than the two kriging techniques. In addition, BME allowed one to delineate with better detail saline from non-saline areas.     

Use of microtremor measurement for assessing site effects in Northern Belgium – interpretation of the observed intensity during the MS = 5.0 June 11 1938 earthquake

To provide quantitative information on site effects in the northern part of Belgium, forty-seven H/V microtremor measurements were performed with 5 second seismometers over an area of about 15.000 km². Most of the results show a northward regular increase of the fundamental period in agreement with the augmentation of the Mesozoic and Cainozoic soft sedimentsthickness from a few meters 40 km south of Brussels to 900 m at the Netherlands-Belgium border. The measured resonance frequency values wereconsistent with theoretical computations performed at different sites onthe basis of existing information and shallow seismic experiments. At oneparticular site (Uccle) where borehole data were available, microtremor measurements using an array of four seismological stations with differentapertures allowed to obtain the low frequency part of the Rayleigh wave dispersion curve, extending the range covered by the analysis of surfacewaves artificially generated. The Vs profile derived from the surface waveinversion corroborates the 1 Hz natural frequency of the site. Comparison of these results with the macroseismic information concerning the M_S = 5.0 1938 earthquake which occurred 50 km west of Brussels,confirmed the hypothesis that the geological structure of the Brabant massifis likely to control damage distribution during such an earthquake. Comparisonbetween the intensity map of the 1938 earthquake and the resonance period ofsediments obtained by our microtremor study shows a clear relation betweenthe two parameters. During the 1938 earthquake, site effects played a prominent role due to the dimension of the source whose corner frequency wasabout 1 Hz.     

Rhenium and chalcophile elements in basaltic glasses from Ko’olau and Moloka’i volcanoes: Magmatic outgassing and composition of the Hawaiian plume

The behavior of chalcophile metals in volcanic environments is important for a variety of economic and environmental applications, and for understanding large-scale processes such as crustal recycling into the mantle. In order to better define the behavior of chalcophile metals in ocean island volcanoes, we measured the concentrations of Re, Cd, Bi, Cu, Pb, Zn, Pt, S, and a suite of major elements and lithophile trace elements in moderately evolved (6-7% MgO) tholeiitic glasses from Ko’olau and Moloka’i volcanoes. Correlated variations in the Re, Cd, and S contents of these glasses are consistent with loss of these elements as volatile species during magmatic outgassing. Bismuth also shows a good correlation with S in the Ko’olau glasses, but undegassed glasses from Moloka’i have unexpectedly low Bi contents. Rhenium appears to have been more volatile than either Cd or Bi in these magmas.Undegassed glasses with 880-1400 ppm S have 1.2-1.5 ppb Re and 130-145 ppb Cd. In contrast, outgassed melts with low S (<200 ppm) are depleted in these elements by factors of 2-5. Key ratios such as Re/Yb and Cu/Re are fractionated significantly from mantle values. Copper, Pb, and Pt contents of these glasses show no correlation with S, ruling out segregation of an immiscible magmatic sulfide phase as the cause of these variations. Undegassed Hawaiian tholeiites have Re/Yb ratios significantly higher than those of MORB, and extend to values greater than that of the primitive mantle. Loss of Re during outgassing of ocean island volcanoes, may help resolve the apparent paradox of low Re/Os ratios in ocean island basalts with radiogenic Os isotopic compositions. Plume source regions with Re/Yb ratios greater than that of the primitive mantle may provide at least a partial solution to the “missing Re” problem in which one or more reservoirs with high Re/Yb are required to balance the low Re/Yb of MORB.Lithophile trace element compositions of most Ko’olau and Moloka’i tholeiites are consistent with variable degrees of melting of fertile mantle peridotite. However, light rare earth element (LREE)-enriched glasses have trace element compositions more consistent with a garnet-rich source having a distinctive trace element composition. This provides additional evidence for a unique source component possibly related to recycled oceanic crust contributing to Ko’olau tholeiites.     

Découverte d'un diatrème de kimberlite diamantifère à Séguéla en Côte-d'Ivoire

The Séguéla area in Ivory Coast is known for its diamond-bearing field related to dykes of kimberlite and lamproite. These dykes, devoid of any deformation and metamorphism, crosscut the Birimian formations. Their N 170° orientation is controlled by the tectonized contact between the Archean and the Paleoproterozoic shields of the West-African craton. Discovery of a diatreme, with its pipe breccias and well-preserved maar sediments, below the present-day colluvia, attests for the probable recent geological age (Cretaceous?) of the kimberlitic activity. To cite this article: A. Pouclet et al., C. R. Geoscience 336 (2004).     

The International Laser Ranging Service and its support for IGGOS

The International Laser Ranging Service (ILRS) was established in September 1998 as a service within the IAG to support programs in geodetic, geophysical, and lunar research activities and to provide data products to the International Earth Rotation Service (IERS) in support of its prime objectives. Now in operation for 5 years, the ILRS develops: (1) the standards and specifications necessary for product consistency and (2) the priorities and tracking strategies required to maximize network efficiency. The service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientific, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost effectiveness of its data products. The ILRS works with: (1) the global network to improve station performance; (2) new satellite missions in the design and building of retroreflector targets to maximize data quality and quantity and (3) science programs to optimize scientific data yield. The ILRS Central Bureau maintains a comprehensive web site as the primary vehicle for the distribution of information within the ILRS community. The site, which can be accessed at: http://ilrs.gsfc.nasa.gov is also available at mirrored sites at the Communications Research Laboratory (CRL) in Tokyo and the European Data Center (EDC) in Munich.During the last 2 years, the ILRS has addressed very important challenges: (1) data from the field stations are now submitted hourly and made available immediately through the data centers for access by the user community; (2) tracking on low satellites has been significantly improved through the sub-daily issue of predictions, drag functions, and the real-time exchange of time biases; (3) analysis products are now submitted in SINEX format for compatibility with the other space geodesy techniques; (4) the Analysis Working Group is heavily engaged in Pilot Projects as it works toward an ILRS “standard” global solution and (5) SLR has significantly increased its participation in the International Terrestrial Reference Frame (ITRF) activity, which is important to the success of IGGOS.     

From water to tillage erosion dominated landform evolution

While water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land, there is growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land. In this study, we examined soil redistribution rates and patterns for an agricultural field in the Belgian loess belt. ¹³⁷Cs derived soil erosion rates have been confronted with historical patterns of soil erosion based on soil profile truncation. This allowed an assessment of historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant geomorphic process. The results clearly show that an important shift in the relative contribution of tillage and water erosion to total soil redistribution on agricultural land has occurred during recent decades. Historical soil redistribution is dominated by high losses on steep midslope positions and concavities as a result of water erosion, leading to landscape incision and steepening of the topography. In contrast, contemporary soil redistribution is dominated by high losses on convex upperslopes and infilling of slope and valley concavities as a result of tillage, resulting in topographic flattening. This shift must be attributed to the increased mechanization of agriculture during recent decades. This study shows that the typical topographical dependency of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile evolution.     

Stochastic Modelling of the Impact of Flood Protection Measures Along the River Waal in the Netherlands

River flooding is a problem of international interest. In the past few years many countries suffered from severe floods. A large part of the Netherlands is below sea level and river levels. The Dutch flood defences along the river Rhine are designed for water levels with a probability of exceedance of 1/1250 per year. These water levels are computed with a hydrodynamic model using a deterministic bed level and a deterministic design discharge. Traditionally, the safety against flooding in the Netherlands is obtained by building and reinforcing dikes. Recently, a new policy was proposed to cope with increasing design discharges in the Rhine and Meuse rivers. This policy is known as the Room for the River (RfR) policy, in which a reduction of flood levels is achieved by measures creating space for the river, such as dike replacement, side channels and floodplain lowering. As compared with dike reinforcement, these measures may have a stronger impact on flow and sediment transport fields, probably leading to stronger morphological effects. As a result of the latter the flood conveyance capacity may decrease over time. An a priori judgement of safety against flooding on the basis of an increased conveyance capacity of the river can be quite misleading. Therefore, the determination of design water levels using a fixed-bed hydrodynamic model may not be justified and the use of a mobile-bed approach may be more appropriate. This problem is addressed in this paper, using a case study of the river Waal (one of the Rhine branches in the Netherlands). The morphological response of the river Waal to a flood protection measure (floodplain lowering in combination with summer levee removal) is analysed. The effect of this measure is subject to various sources of uncertainty. Monte Carlo simulations are applied to calculate the impact of uncertainties in the river discharge on the bed levels. The impact of the “uncertain” morphological response on design flood level predictions is analysed for three phenomena, viz. the impact of the spatial morphological variation over years, the impact of the seasonal morphological variation and the impact of the morphological variability around bifurcation points. The impact of seasonal morphological variations turns out to be negligible, but the other two phenomena appear to have each an appreciable impact (order of magnitude 0.05–0.1 m) on the computed design water levels. We have to note however, that other sources of uncertainty (e.g. uncertainty in hydraulic roughness predictor), which may be of influence, are not taken into consideration. In fact, the present investigation is limited to the sensitivity of the design water levels to uncertainties in the predicted bed level.     

Polymorphic phase transition in Superhydrous Phase B

We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200°C (LT) and 1400°C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to −180°C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.