The ichthyofauna and migration permeability of the River Otava

The River Otava (a tributary of the River Vltava, Elbe drainage area) belonged in the past to the known rivers where Salmo salar were immigrating to spawn. On the Otava stream, in total 33 transverse steps of various types were built, which constitute mostly insurmountable barriers to fish migration

The first record of the black bullhead (Ameiurus melas) in the Třeboň district, Czech Republic

In the Czech Republic, the occurrence of the Black bullhead, Ameiurus melas (Rafinesque, 1820) was recorded for the first time. The species occurs in some of the fishponds in the environs of Lomnice nad Lužnicí, southern Bohemia. The species was introduced unintentionally as an admixture to carp stocking material from Croatia in 2003. In the autumn of 2005, the occurrence was observed of adults as well as yearling fry, indicating that natural reproduction had taken place in some of the ponds. The water from the fishpond system is released into the Lužnice River so that there is a possibility of the species spreading over natural habitats of the river mentioned. The occurrence of this species in the fishponds in southern Bohemia tends to confirm the fact that transports of stocking fish, above all, carp but other species as well, present a real risk of unintentional introductions of non-native species and an important way of their subsequent dispersal

Structural setting of the Čertovka landslide (Ústí nad Labem, Czech Republic) analysed by morphostructural analysis and electrical resistivity tomography

The Čertovka landslide at Vaňov south of Ústí nad Labem, Czech Republic, is developed in a steep slope of the Labe River Valley (LRV). A major episode of landsliding occurred in the first months of 1995, and the slope at Vaňov has been subjected to geological and geomorphological investigation since then. This paper presents structural setting of the Čertovka landslide based on the latest geological survey, detailed geomorphological mapping, morphostructural analysis and results of electrical resistivity tomography. The landslide was found to be initiated at the boundary between Late Eocene to Oligocene basaltic lavas above and volcaniclastics below, with bedding dipping against the slope (anaclinal slope). The underlying volcaniclastics show tendency to argillization and have a much lower rock strength, which acts as an important factor of slope instability at the site. The Čertovka landslide is a complex slope deformation consisting of several landslides and flowslides, with boulder streams merging into a boulder accumulation further downslope. The headscarp area of the landslide developed at one of the structural levels built by basaltic lavas and forming step-like morphology of the valley slope. The headscarp coincides with the course of a regional E–W-striking Vaňov Fault which underwent multiple tectonic history and is associated with a dense fracture system including smooth slickensides on the headscarp. Structural observations combined with detailed knowledge of the anatomy of the landslide based on airborne data, surface data and geophysical data permitted to conclude on structural controls of landsliding and predict future evolution of the slope deformation. Future landsliding will be initiated at structural levels of basaltic rocks, with the headscarps developed along fractures parallel to the Vaňov Fault. The probable gradual retreat of headscarps at the individual structural levels along the slope profile denotes a retrogressive landslide style

Acceleration of late pleistocene activity of a central European fault driven by ice loading

We studied the southern part of the NW-SE trending Sudetic Marginal fault (SMF), situated at the northeastern limit of the Bohemian Massif in central Europe, to assess its Quaternary activity. Eighteen trenches and thirty-four electric resistivity profiles were performed at Bílá Voda to study the fault zone and 3-dimensional distribution of a beheaded alluvial fan on the NE side of the fault. We interpret a small drainage, located about 29–45 m to the SE of the fan apex, as the only plausible source channel implying a similar amount of left-lateral offset. The alluvial fan deposits’ radiometric ages range between about 24 and 63 ka, but postglacial deposits younger than 11 ka are not displaced, indicating that all motion occurred in the late Pleistocene. The site lies ∼150 km south of the late Pleistocene Weichselian maximum (∼20 ka) ice sheet front. We model the effects of the ice load on lithospheric flexure and resolved fault stresses, and show that slip on the SMF was promoted by the presence of the ice sheet, resulting in a late Pleistocene slip rate of ∼1.1+2.3/−0.6 mm/yr. As the most favorable time for glacial loading-induced slip would be during the glacial maximum between about 24 and 12 ka, it is doubtful that the slip rate remained constant during the entire period of activity, and if most slip occurred during this period, the short-term rate may have been even higher. Considering that the modern maximum principal stress (σ1) is oriented nearly parallel to the Sudetic Marginal fault (NNW-SSE) and is thus unfavorable for fault motion, our observations suggest that the likelihood of continued motion and earthquake production is much lower in the absence of an ice sheet