Assessment of soil erosion in a small watershed covered by loess

Loose sediments like loess are easily erodable especially on hillslopes used for agriculture. Erosion contributes to the sedimentation and pollution of lakes such threatening quasi-natural ecosystems. On the other hand soil erosion damages fertile soils.The aim of the present paper is the assessment of soil and nutrient loss in a tributary catchment of Lake Balaton, including geoecological aspects of the lake ecosystem and of the slopes mantled by loess.The USLE is applied for small topological units, for the so called erotops. Rainfall simulation experiments were applied for the determination of the erodibility of soils. The calculation is based on a new, GIS aided method. Control measurements have been going on for four years at a gauging station to check how much sediment and water actually leaves the catchment.Results of sediment yield measurements were compared with the results obtained by the application of USLE for the whole catchment. According to this comparison only 2% leaves the catchment so that redeposition processes within the catchment are very important whereas the contribution of soil erosion to the eutrophication of the lake is not very significant in the small tributaries in the northern part of Lake Balaton catchment.     

Tectono‐sedimentary evolution of the northern Iranian Plateau: insights from middle–late Miocene foreland‐basin deposits

Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia–Eurasia collision zone offer the unique possibility to study middle–late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long‐term evolution of the Iranian Plateau, including the regional spatio‐temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle–late Miocene crustal shortening and thickening processes led to the growth of a basement‐cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland‐basin (Great Pari Basin) to the east between 16.5 and 10.7 Ma. By 10.7 Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement‐cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle‐flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran.     

Natural arsenic in Triassic rocks: A source of drinking-water contamination in Bavaria, Germany

 The aquifer system of the Upper Triassic Keuper Sandstone, an important source of drinking water in northern Bavaria, is affected by elevated arsenic concentrations. Within the study area of 8000 km², no evidence exists for any artificial source of arsenic. Data from about 500 deep water wells show that in approximately 160 wells arsenic concentrations are 10–150 μg/L. The regional distribution of arsenic in the groundwater shows that elevated arsenic concentrations are probably related to specific lithofacies of the aquifers that contain more sediments of terrestrial origin. Geochemical measurements on samples from four selected well cores show that arsenic has accumulated in the rocks. This indigenous arsenic is the source of arsenic in the groundwater of certain facies of the middle unit of the Keuper Sandstone. Received, June 1998 / Revised, January 1999, May 1999 / Accepted, June 1999     

Sediment dynamics and geohazards off Uruguay and the de la Plata River region (northern Argentina and Uruguay)

The continental margin off Uruguay and northern Argentina is characterized by high fluvial input by the de la Plata River and a complex oceanographic regime. Here we present first results from RV Meteor Cruise M78/3 of May?CJuly 2009, which overall aimed at investigating sediment transport processes from the coast to the deep sea by means of hydroacoustic and seismic mapping, as well as coring using conventional tools and the new MARUM seafloor drill rig (MeBo). Various mechanisms of sediment instabilities were identified based on geophysical and core data, documenting particularly the continental slope offshore Uruguay to be locus of submarine landsliding. Individual landslides are relatively small with volumes <2km³. Gravitational downslope sediment transport also occurs through the prominent Mar del Plata Canyon and several smaller canyons. The canyons originate at a midslope position, and the absence of buried upslope continuations strongly suggests upslope erosion as main process for canyon evolution. Many other morphological features (e.g., slope-parallel scarps with scour geometries) and abundant contourites in a 35-m-long MeBo core reveal that sediment transport and erosion are controlled predominantly by strong contour currents. Despite numerous landslide events, their geohazard potential is considered to be relatively small, because of their small volumes and their occurrence at relatively deep water depths of more than 1,500?m.     

Modelling gaseous and stellar kinematics in the disc galaxies NGC 772, 3898 and 7782

We present V -band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, 3898 and 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allows us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects.
NGC 772 and 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (| r |≲8 arcsec) of NGC 3898, where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter.     

Kinematics of Gas and Stars Along the Hubble Sequence

We present a comparison between the ionized gas and stellar kinematics for a sample of five early-to-intermediate disc galaxies. We measured the major axis V and σ radial profiles for both gas and stars, and the h ₃ and h ₄ radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their bulges and discs. In order to investigate the differences between the velocity fields of the sample galaxies we adopted the self-consistent dynamical model by Pignatelli and Galletta (1999), which takes into account the asymmetric drift effects, the projection effects along the line of sight and the non-Gaussian shape of the line profiles due to the presence of different components with distinct dynamical behaviour. We find for the stellar component a sizeable asymmetric drift effect in the inner regions of all the sample galaxies, as results from comparing their stellar rotation curves with the circular velocity predicted by the models. The galaxy sample is not wide enough to draw general conclusions. However, we have found a possible correlation between the presence of slowly rising gas rotation curves and the ratio of the bulge/disc half-luminosity radii, while there is no obvious correlation with the key parameter represented by the morphological classification, namely the bulge/disc luminosity ratio. Systems with a diffuse, dynamically hot component (bulge or lens) with a scale length comparable to that of the disc are characterized by slowly rising gas rotation curves. On the other hand, in systems with a small bulge the gas follows almost circular motions, regardless of the luminosity of the bulge itself. We noticed a similar behaviour also in the gas and stellar kinematics of the two early-type spiral galaxies modelled by Corsini et al.(1998). This revised version was published online in July 2006 with corrections to the Cover Date.     

Focused subaerial erosion during ridge subduction: impact on the geomorphology in south‐central Peru

Data obtained from low‐temperature thermochronometers such as apatite fission‐track and (U‐Th)/He are combined with morphometric information extracted from digital elevation models. This combination shows several geomorphological effects that are caused by the migration of the Nazca Ridge along the Peruvian Coastal margin. Offshore, the depth of the deep‐sea trench decreases by ～1500 m where the Nazca Ridge collides with the continental South American Plate. Onshore the ridge causes an uplift of at least 800 m in the Coastal Cordillera. This uplift results in a westward shift of the coastline thereby focusing and increasing erosion in the uplifted areas. At the trailing edge, the shelf subsides and the coastline retreats eastwards, producing at least part of the indentation observed between Paita and Pisco. The Ridge acts therefore like a wave uplifting the Andean margin as it traverses inland and southwards leaving a clear fingerprint on the topographic evolution of the Peruvian coastal margin.     

NGC 3521: Stellar Counter-Rotation Induced by a Bar Component

The spiral galaxy NGC 3521 exhibits apparently normal kinematic properties of gas and stars along its major axis. However, the analysis of the LOSVD reveals strong asymmetries. A decomposition of the LOSVD data with a two-Gaussian component model shows two counter-rotating stellar components. The observed kinematic decoupling is interpreted as a projection effect induced by the presence of a bar component seen almost end on. The bar produces locally a greater concentration of retrograde stellar orbits but this does not relate to a specific counter-rotating population. The signatures of the bar are identified in the velocity field derived from long-slit spectra obtained along the major, minor and 45° intermediate axes and from R-band surface photometry. This revised version was published online in July 2006 with corrections to the Cover Date.