Flusskorridore und Auenstrukturen im schweizerischen Mittelland (nördliches Alpenvorland) | River corridors and alluvial structures in Central Switzerland (northern sub-alpine area)
Long-term spatial variation of river channel distribution in this alluvial valley zone is described for two examples by analysing historical maps covering a period of over 300 years. Such a time series enables the identification of the occupied river corridor or «Pendelband». Two river sections in northern Switzerland were chosen, one of the Aare river and one of the Reuss river to analyse the spatial evolution of the river channels over time, as well as alluvial structures. Knowledge of the river corridor as an historical reference give us an important guideline when developing appropriate regional measures for river restoration projects.
RIVERINE LANDSCAPES: BIODIVERSITY PATTERNS, DISTURBANCE REGIMES, AND AQUATIC CONSERVATION
Abstract The term riverine landscape implies a holistic geomorphic perspective of the extensive interconnected series of biotopes and environmental gradients that, with their biotic communities, constitute fluvial systems. Natural disturbance regimes maintain multiple interactive pathways (connectivity) across the riverine landscape. Disturbance and environmental gradients, acting in concert, result in a positive feedback between connectivity and spatio-temporal heterogeneity that leads to the broadscale patterns and processes responsible for high levels of biodiversity. Anthropogenic impacts such as flow regulation, channelization, and bank stabilization, by (1) disrupting natural disturbance regimes, (2) truncating environmental gradients, and (3) severing interactive pathways, eliminate upstream-downstream linkages and isolate river channels from riparian/floodplain systems and contiguous groundwater aquifers. These alterations interfere with successional trajectories, habitat diversification, migratory pathways and other processes, thereby reducing biodiversity. Ecosystem management is necessary to maintain or restore biodiversity at a landscape scale. To be effective, conservation efforts should be based on a solid conceptual foundation and a holistic understanding of natural river ecosystems. Such background knowledge is necessary to re-establish environmental gradients, to reconnect interactive pathways, and to reconstitute some semblance of the natural dynamics responsible for high levels of biodiversity. The challenge for the future lies in protecting the ecological integrity and biodiversity of aquatic systems in the face of increasing pressures on our freshwater resources. This will require integrating sound scientific principles with management perspectives that recognize floodplains and groundwaters as integral components of rivers and that are based on sustaining, rather than suppressing, environmental heterogeneity.
Behavior of Aquifers Concerning Contaminants: Differential Permeability and Importance of the Different Purification Processes
Contaminants in transit through groundwater systems cross different types of rocks, each one with different water-bearing characteristics. It is imperative to understand the behavior of different aquifers (porous or karstic) concerning contaminants and the relative functions and mechanisms of major processes in a given system before planning remedial measures. From the surface systems to groundwater four main types of filter can be considered. They intervene most often simultaneously and the interactions are very strong. The activities of the different filters lead us to the concept of permeability, which varies according to the efficiency of the filter, ranging from the most impermeable porous aquifers to karstic aquifers. Among major processes we have chosen to consider three groups: retention, selfpurification and dilution and to discuss their importance and their rate of change. We focus more specifically on the problem in karstic systems. An example concerning nitrate profiles in a French karstic system is given, showing an increase of nitrate concentration in the epikarstic zone due to the impact of agriculture. Very few studies on karstic system contamination are mentioned because the processes controlling contaminant cycling inside the karst are as yet not very well understood.