This work focuses on the behavior of the stable Mg and Si isotope compositions of the largest Arctic river, the Yenisey River and 28 of its major and minor tributaries during the spring flood period. Samples were collected along a 1500 km latitudinal profile covering a wide range of permafrost, lithology, and vegetation. Despite significant contrasts in the main physico-geographical, climate, and lithological parameters of the watersheds, the isotope composition of both dissolved Mg and Si was found to be only weakly influenced by the degree of the permafrost coverage, type of vegetation (forest vs. tundra), and lithology (granites, basalts, carbonates or terrigenous rocks). This observation is generally consistent with the lack of chemical uptake of Mg and Si by soil mineral formation and vegetation during the early spring. The radiogenic Sr isotope composition of the Yenisey and its tributaries varied within a narrow range (0.708 ≤ 87 Sr/ 86 Sr ≤ 0.711) reflecting the dominance of Phanerozoic rock weathering and/or atmospheric deposition on these compositions. The Mg and Si isotopic compositions of riverine samples reflect two main processes with distinct isotopic signatures. First, isotopically heavier Mg (δ 26 Mg =-1.0 ± 0.2 ‰) and isotopically lighter Si (δ 30 Si = 1.0 ± 0.25 ‰) are added to the waters by river suspended matter dissolution and leaching from vegetation biomass/topsoil litter. Second, isotopically lighter Mg (δ 26 Mg =-1.5 to-1.75 ‰) and isotopically heavier Si (δ 30 Si = 1.75 to 2.0 ‰) are delivered to the Yenisey's tributaries from deep underground water feeding the rivers via taliks. This lighter Mg and heavier Si isotopic composition is interpreted to originate from Precambrian dolomite dissolution and aluminosilicate dissolution coupled with authigenic mineral precipitation, respectively, in deep underground water reservoirs. Taking account of the isotopic composition evolution over the course of the year established earlier on mono-lithological watersheds of the Yenisey basin, the average annual isotopic signatures of the Yenisey river arriving to the Arctic Ocean are estimated to be δ 26 Mg =-1.58±0.30 ‰ and δ 30 Si =+1.60±0.25 ‰. As the Yenisey is the largest river feeding the Arctic Ocean and as it

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The drainage systems of several tunnels in Austria are heavily clogged with calcite precipitates. Cleaning and water conditioning are cost-intensive for the operating company. The results of the case study Koralm tunnel show that the dissolved calcium in the drainage solutions derives from the ground water and especially from the dissolution of portlandite at the shotcrete. Accordingly, the drainage solutions are often strongly alkaline and as sufficient supersaturation with respect to calcite is reached, calcite precipitates. The carbonate in the calcite sinter is obtained from the ground water or from the absorption of atmospheric CO 2 . Extensive chemical, mineralogical, and isotopic analyses as well as hydrogeochemical modelling permit to decipher the effective parameters in order to develop recommendations for retaliatory action. In-situ experiments in the Koralm tunnel simulate the conditions for the designed drainage system, which should provide an appropriate evaluation of the sinter formation in the drainage and the application of inhibitors. Sinter formation will be reduced by using tailored construction materials. Koralmtunnel als Fallbeispiel für Versinterungen in Dränage-systemen -Ablagerungsmechanismen und GegenmaßnahmenIn den Dränagesystemen mehrer Tunnel in Österreich werden enorme Mengen an Kalzit abgelagert. Die Reinigung und Wasserkonditionierung sind für den Betreiber mit erheblichen Kosten verbunden. In dieser Arbeit konnte anhand der Fallstudie Koralmtunnel gezeigt werden, dass das gelöste Kalzium in dem Dränage-wasser aus dem Bergwasser selbst und insbesondere aus der Auflösung von Portlandit im Spritzbeton bereitgestellt wird. Die so erhaltenen Lösungen sind häufig stark alkalisch. Hierdurch kommt es zu einer Übersättigung an Kalzit, wodurch in weiterer Folge die Abscheidung von Kalzit eingeleitet werden kann. Das Karbonat im Kalksinter kann entweder aus dem Grundwasser oder aus der Absorption von atmosphärischem CO 2 erhalten werden. Durch umfangreiche chemische, mineralogische und isotopenchemische Analysen sowie hydrogeochemische Modellierungen wurden die jeweils wirksamen Faktoren identifiziert, um auf deren Basis Ansätze für Gegenmaßnahmen entwickeln zu können. In-situ-Experimente im Koralmtunnel simulieren die Bedingungen in der geplanten Dränage. Hierüber soll eine Beurteilung der Versinterungen im Dränagesystem und der Anwendung von Inhibitoren ermöglicht werden. Versinterungen werden auch durch den Einsatz maßge-schneiderter Baustoffe verringert werden. IntroductionThe formation of carbonate sinter is a natural phenomenon as well as a challenge in the fields of engineering [3] [4]. Carbonate precipitation in drainage systems may cause serious problems due to the reduction of the cross section of drainage tubes (Figure 1) and the pollution of receiving streams by suspended carbonates and ongoing sinter formation.The Koralm tunnel will be the longest tunnel in Austria and special effort is given to minimize costs for maintenance action such as cleaning of the drainage system and wat...

Scaling of tunnel drainage systems comprises complex reaction mechanisms, which are essentially caused by the interaction of water with cement-based materials and the atmosphere. The resulting precipitation of CaCO 3 in the drainage is an economically highly challenging task for tunnel operators with respect to maintenance and cleaning action. Hydrochemical modelling is used to decipher reaction mechanisms and thus to provide quantifications, which are required to develop monitoring tools, like in-situ alert systems, and prevention strategies, like application of loweluting shotcrete and inhibitors.