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101.
The Burdekin delta floodplain, north Queensland, is highly modified for agricultural purposes. Riparian condition is very poor and exotic aquatic weeds dominate waterways. Historically, most streams and lagoons were highly seasonal, but those now used for the delivery of irrigation water maintain elevated flows and increased turbidity and nutrient loading. These factors have aided exotic weed growth and many major lagoons are covered by dense water hyacinth (Eichhornia crassipes) mats which greatly reduce dissolved oxygen levels, one of the most important water quality variables for aquatic fauna. Mechanical harvesting of water hyacinth from several of these lagoons resulted in rapid and substantial increases in dissolved oxygen saturation, and improved suitability of the habitat to support fish species. Decrease in dissolved oxygen as water passes sequentially through weed-infested lagoons, justified the approach of harvesting upstream lagoons first, however, the channels that connect these lagoons remain weed-infested and are still impacting upon downstream oxygen levels. 相似文献
102.
Paleogeography of the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB) from Eocene to Pliocene 总被引:1,自引:1,他引:0
Jean-Pierre Berger Bettina Reichenbacher Damien Becker Matthias Grimm Kirsten Grimm Laurent Picot Andrea Storni Claudius Pirkenseer Christian Derer Andreas Schaefer 《International Journal of Earth Sciences》2005,94(4):697-710
Twenty paleogeographic maps are presented for Middle Eocene (Lutetian) to Late Pliocene times according to the stratigraphical data given in the companion paper by Berger et al. this volume. Following a first lacustrine-continental sedimentation during the Middle Eocene, two and locally three Rupelian transgressive events were identified with the first corresponding with the Early Rupelian Middle Pechelbronn beds and the second and third with the Late Rupelian Serie Grise (Fischschiefer and equivalents). During the Early Rupelian (Middle Pechelbronn beds), a connection between North Sea and URG is clearly demonstrated, but a general connection between North Sea, URG and Paratethys, via the Alpine sea, is proposed, but not proved, during the late Rupelian. Whereas in the southern URG, a major hiatus spans Early Aquitanian to Pliocene times, Early and Middle Miocene marine, brackish and freshwater facies occur in the northern URG and in the Molasse Basin (OMM, OSM); however, no marine connections between these basins could be demonstrated during this time. After the deposition of the molasse series, a very complex drainage pattern developed during the Late Miocene and Pliocene, with a clear connection to the Bresse Graben during the Piacenzian (Sundgau gravels). During the Late Miocene, Pliocene and Quaternary sedimentation persisted in the northern URG with hardly any interruptions. The present drainage pattern of the Rhine river (from Alpine area to the lower Rhine Embayment) was not established before the Early Pleistocene. 相似文献
103.
The boron isotope-pH technique is founded on a theoretical model of carbonate δ11B variation with pH that assumes that the boron isotopic composition of carbonates mirrors the boron isotopic composition of borate in solution (δ11Bcarb = δ11Bborate). Knowledge of the fractionation factor for isotope exchange between boric acid and borate in solution (α4-3), the equilibrium constant for the dissociation of boric acid (pKB*), as well as the isotopic composition of boron in seawater (δ11Bsw) are required parameters of the model.The available data suggests that both the value of α4-3 and the history of δ11Bsw are poorly constrained. However, if one assumes that δ11Bcarb = δ11Bborate, an empirical value for α4-3 can be estimated from the results of inorganic carbonate precipitation experiments. This exercise yields an α4-3 value of ∼0.974 in accordance with recent theoretical estimates, but substantially deviates from the theoretical value of 0.981 often used to estimate paleo-ocean pH. Re-evaluation of ocean pH using an α4-3 value of 0.974 and published foraminiferal δ11B values for the Cenozoic yield pH estimates that are relatively invariant, but unrealistically high (∼8.4-8.6). Uncertainty increases as foraminiferal ‘vital effects’ are considered and different models for secular changes in seawater δ11B are applied.The inability to capture realistic ocean pH possibly reflects on our understanding of the isotopic relationship between carbonate and borate, as well as the mechanism of boron incorporation in carbonates. Given the current understanding of boron systematics, pH values estimated using this technique have considerable uncertainty, particularly when reconstructions exceed the residence time of boron in the ocean. 相似文献
104.
Damien Gagnevin 《Geochimica et cosmochimica acta》2005,69(21):5171
105.
Damien Closson Najib Abou Karaki Musa Jad Hussein Hassan Al-Fugha André Ozer Abdullah Mubarak 《Comptes Rendus Geoscience》2003,335(12):869-879
The Dead Sea shore is affected by major subsidence and sinkholes hazards due to the decrease of the sea level. The frequency of resulting accidents increased during the last four decades. Those phenomena could be at the origin of the catastrophic destruction of a major salt evaporation pond on 22 March 2000. In this paper, we show the main results of eight years of research in gravimetry and radar interferometry devoted to identify potentially hazardous areas, at different scales along the Jordanian Dead Sea coast, from the metric scale (gravimetric approach) to the kilometric one (interferometric approach). To cite this article: D. Closson et al., C. R. Geoscience 335 (2003). 相似文献
106.
Liesbet Jacobs Olivier Dewitte Jean Poesen Damien Delvaux Wim Thiery Matthieu Kervyn 《Landslides》2016,13(3):519-536
With its exceptionally steep topography, wet climate, and active faulting, landslides can be expected to occur in the Rwenzori Mountains. Whether or not this region is prone to landsliding and more generally whether global landslide inventories and hazard assessments are accurate in data-poor regions such as the East African highlands are thus far unclear. In order to address these questions, a first landslide inventory based on archive information is built for the Rwenzori Mountains. In total, 48 landslide and flash flood events, or combinations of these, are found. They caused 56 fatalities and considerable damage to road infrastructure, buildings, and cropland, and rendered over 14,000 persons homeless. These numbers indicate that the Rwenzori Mountains are landslide-prone and that the impact of these events is significant. Although not based on field investigations but on archive data from media reports and laymen accounts, our approach provides a useful complement to global inventories overlooking this region and increases our understanding of the phenomenon in the Rwenzori Mountains. Considering the severe impacts of landslides, the population growth and related anthropogenic interventions, and the likelihood of more intense rainfall conditions, there is an urgent need to invest in research on disaster risk reduction strategies in this region and other similar highland areas of Africa. 相似文献
107.
Marcus Gutjahr Louise Bordier Eric Douville Jesse Farmer Gavin L. Foster Ed C. Hathorne Brbel Hnisch Damien Lemarchand Pascale Louvat Malcolm McCulloch Johanna Noireaux Nicola Pallavicini James W. B. Rae Ilia Rodushkin Philippe Roux Joseph A. Stewart Franois Thil Chen‐Feng You 《Geostandards and Geoanalytical Research》2021,45(1):59-75
Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO2 through Earth’s history. While isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the boron isotopic composition (commonly expressed in δ11B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp‐1 (coral Porites) and JCt‐1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre‐treatment, aimed at removing organic material from carbonate, can influence the resulting δ11B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ11B; and (c) to provide well‐constrained consensus δ11B values for JCp‐1 and JCt‐1. The resultant robust mean and associated robust standard deviation (s*) for un‐oxidised JCp‐1 is 24.36 ± 0.45‰ (2s*), compared with 24.25 ± 0.22‰ (2s*) for the same oxidised material. For un‐oxidised JCt‐1, respective compositions are 16.39 ± 0.60‰ (2s*; un‐oxidised) and 16.24 ± 0.38‰ (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement. 相似文献
108.
We have summed up three recent modellings of Mars' polar motion (Hilton, 1992; Yoder and Standish, 1997; Zhang, 1998) from which we have studied in particular the Chandler wobble (CW) of the planet and expressions of its period TCW. We add a fourth study (Kubo, 1991) which deals with the polar motion on the Earth, but whose the results can easily be applied to Mars. To conpare the different expressions of the period TCW from the authors above, we have chosen common parameters of the planet coming from recent data and we have calculated values of the period corresponding to these parameters after having determined from analytical developments the moments of inertia of the core and of the mantle. We show how the different formula proposed by the authors lead to different values of TCW and we study in particular the contribution of somc parameters such as the core radius, the mass of the core and the Love number of these values. 相似文献
109.