Influence of a Xenobiotic Mixture (PCB and TBT) Compared to Single Substances on Swimming Behavior or Reproduction of Daphnia magna

Aroclor 1254, a technical PCB mixture (polychlorinated biphenyls) and TBT (tributyltinchloride) are environmental pollutants that cause a broad spectrum of acute toxic and chronic effects in aquatic animals. In this paper, the sensitivity of Daphnia magna to chronic exposure to mixed xenobiotics was evaluated under laboratory conditions. The results show that xenobiotic mixtures (50 % each of the single compounds) were more toxic than individual xenobiotics alone. By measuring behavioral parameters of animals, it becomes evident that exposure to single xenobiotics significantly affects daphnids: exposure led finally to a rapid decrease in mean swimming activity and also caused changes in preferred swimming depth, with daphnids preferring the upper layers of aquaria. The mixture altered the swimming behavior even more strongly compared to the group stressed by single chemicals. Finally, all daphnids sank to the bottom of the aquaria, still alive, but inactive at the end of the exposure period. In addition, we investigated the reproductive capacity (number of newborn per female and day). PCB did not affect the number of newborn significantly, TBT‐stress led to an evidently decreased number of young daphnids and the xenobiotic mixture decreased reproduction even more. In conclusion, we found significant effects of the single compounds as well as approximately additive (swimming behavior) and synergistic (reproduction) effects of the chemical mixture on daphnids indicating the possibility of dramatic ecological consequences of the occurrence of mixed xenobiotic substances in the aquatic environment.     

Distribution patterns and habitat characterization of Simuliidae (Insecta: Diptera) in a low-order sandstone stream (Weidlingbach, Lower Austria)

A total of 1504 larval and 31 pupal Simuliidae were caught from March 2000 to February 2001 at the Weidlingbach, a fourth order tributary of the Danube near Vienna, Austria, using a modified box sampler (sampling area = 2116 cm²) at 12 sampling stations from source to mouth. From the six species collected, Prosimulium tomosvaryi (Enderlein) and two species of the Simulium ornatum-group (S. trifasciatum Curtis and S. ornatum Meigen) accounted for 97.5% of the total. Based on head width, instars 1–7 were collected in the S. ornatum-group and instars 2–7 in P. tomosvaryi; from two of the remaining species [Simulium (Nevermannia) cryophilum (Rubzov) and S. (N.) vernum Macquart], only pupae were sampled. The S. ornatum-group was most abundant on coarse substrates (median = 55.9 mm) exposed to high water velocity (median = 55.9 cm/s; range = 9–83 cm/s); the latter was also true for P. tomosvaryi although it favoured smaller sediment grain sizes (median = 32.4 mm). Species richness and population density increased from source to mouth. At sampling sites near the source Simuliidae were completely lacking. In headwaters only P. tomosvaryi was present, whereas the S. ornatum-group and Simulium (Simulium) argyreatum Meigen was collected exclusively near the mouth.     

Numerical modeling of cracking pattern’s influence on the dynamic response of thickened tailings disposals: a periodic approach

Copper production is an essential component of the Chilean economy. During the extraction process of copper, large quantities of waste materials (tailings) are produced, which are typically stored in large tailing ponds. Thickened Tailings Disposal (TTD) is an alternative to conventional tailings ponds. In TTD, a considerable amount of water is extracted from the tailings before their deposition. Once a thickened tailings layer is deposited, it loses water and it shrinks, forming a relatively regular structure of tailings blocks with vertical cracks in between, which are then filled up with “fresh” tailings once the new upper layer is deposited. The dynamic response of a representative column of this complex structure made out of tailings blocks with softer material in between was analyzed using a periodic half-space finite element model. The tailings’ behavior was modeled using an elasto-plastic multi-yielding constitutive model, and Chilean earthquake records were used for the seismic analyses. Special attention was given to the liquefaction potential evaluation of TTD.     

Pumping test in a confined aquifer under tidal influence

In a coastal environment, tide-induced head fluctuations can complicate the interpretation of drawdown data from pumping tests. For confined aquifers and sinusoidal tides, the superposition principle can be used to obtain a closed-form solution. After subtracting the net tidal effects, the drawdown data become amenable to the standard analyses. Numerical simulations have shown that the method is reliable when the distance of the monitoring well to the well does not exceed 10% of the distance between the well and the tidal boundary.     

Crop area mapping in West Africa using landscape stratification of MODIS time series and comparison with existing global land products

In Africa, food security early warning systems use satellite-derived data concerning crop conditions and agricultural production. Such systems can be improved if they are provided with a more reliable estimation of the cultivated area at national scale. This paper evaluates the potential of using time series from the MODerate resolution Imaging Spectroradiometer MOD13Q1 (16-day composite of normalized difference vegetation index at 250 m resolution) to extract cultivated areas in the fragmented rural landscapes of Mali. To this end, we first stratified Southern Mali into 13 rural landscapes based on the spatio-temporal variability of NDVI and textural indices, using an object-oriented classification scheme.The accuracy of the resulting map (MODIS_crop) and how it compares with existing coarse-resolution global land products (GLC2000 Africa, GLOBCOVER, MODIS V05 and ECOCLIMAP-II), was then assessed against six crop/non-crop maps derived from SPOT 2.5 m resolution images used as references. For crop areal coverage, the MODIS_crop cultivated map was successful in assessing the overall cultivated area at five out of the six validation sites (less than 6% of the absolute difference), while in terms of crop spatial distribution, the producer accuracy was between 33.1% and 80.8%. This accuracy was linearly correlated with the mean patch size index calculated on the SPOT crop maps (r² = 0.8). Using the Pareto boundary as an accuracy assessment method at the study sites, we showed that (i) 20-40% of the classification crop error was due to the spatial resolution of the MODIS sensor (250 m), and that (ii) compared to MODIS V05, which otherwise performed better than the other existing products, MODIS_crop generally minimized omission-commission errors. A spatial validation of the different products was carried out using SPOT image classifications as reference. In the corresponding error matrices, the fraction of correctly classified pixels for our product was 70%, compared to 58% for MODIS V05, while it ranged between 40% and 51% for the GLC2000, the ECOCLIMAP-II and the GLOBCOVER.     

Observation of the Earth’s nutation by the VLBI: how accurate is the geophysical signal

We compare nutation time series determined by several International VLBI Service for geodesy and astrometry (IVS) analysis centers. These series were made available through the International Earth Rotation and Reference Systems Service (IERS). We adjust the amplitudes of the main nutations, including the free motion associated with the free core nutation (FCN). Then, we discuss the results in terms of physics of the Earth’s interior. We find consistent FCN signals in all of the time series, and we provide corrections to IAU 2000A series for a number of nutation terms with realistic errors. It appears that the analysis configuration or the software packages used by each analysis center introduce an error comparable to the amplitude of the prominent corrections. We show that the inconsistencies between series have significant consequences on our understanding of the Earth’s deep interior, especially for the free inner core resonance: they induce an uncertainty on the FCN period of about 0.5 day, and on the free inner core nutation (FICN) period of more than 1000 days, comparable to the estimated period itself. Though the FCN parameters are not so much affected, a 100 % error shows up for the FICN parameters and prevents from geophysical conclusions.     

First GOCE gravity field models derived by three different approaches

Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10?cm in terms of geoid heights, and 3?mGal in terms of gravity anomalies, globally at a resolution of 100?km (degree/order 200).