Modellierung des organismischen Response in Buhnenfeldern der mittleren Elbe-Determinierende Umweltfaktoren des Makrozoobenthos der Elbe

In order to develop a mathematical model which reflects the abundance of benthic species in groyne fields of the river Elbe in relation to the mayor abiotic variables of its living space, the following steps have been taken: - The benthos was sampled and the corresponding abiotic parameters were measured. - Correlation analysis of benthic species and abiotic parameters was carried out. - The main and determining abiotic parameters were identified and a mathematical approach based on RDA (redundancy analysis) was made describing the abundance of some benthic species in dependence to abiotic parameters. - The plausibility of the resulting model was determined by comparison with the relevant literature. - Mayor environmental deficiencies of the existing groyne fields were identified and distinctive features were determined to optimize ecologically sound groyne fields. - Upon these findings new groyne types were introduced into the model, the hydrological and morphological abiotic conditions were simulated, and the resulting distribution of some species was modelled and graphically displayed in GIS. The surveyed parts of the river Elbe are characterized by their poor composition of benthic species. The soft-substrates are mainly colonized by Chironomidae and Oligochaeta up to 600.000 individuals per square meter. The quantity of other taxa and individuals is quite low. The hard-substrate is sparsely colonized, the dominating taxa are Chironomidae. The multivariate analysis of the fauna and the abiotic factors by means of the RDA determines the dependencies of the benthic fauna on the main variables time, discharge velocity and substrate (in descending importance). The response characteristics of some species (especially Limnodrilus hoffmeisteri, Propappus volki and Robackia demeijerei) proved to be pronounced and could be assigned to these factors. These findings have been determined on a high level of significance and were confirmed by the literature. The polynomial set up on the basis of RDA, representing the relationship between taxa abundance and abiotic parameters, as well as the abiotic data calculated by application of a mathematical hydraulic model of the project partner were integrated into the project database. The database served as interface and control unit for the modelling of scenarios of the taxa behaviour. The simulation results were visualized in Arcview GIS. The method developed is a tool easy to handle and to prognosticate changes in the fauna as a consequence to changes in the hydro- and morphological conditions of the River Elbe. A list of demands was compiled to optimize the ecological function of groyne fields, which should take tasks formerly assigned to the main stream. Modified groyne types were designed in order to change the conditions in the groyne fields in the required way, and were integrated in the model. The resulting morpho- and hydrodynamic conditions were computed by means of the hydraulic model of the project partner, and the effects were visualized exemplary with two species in three groyne field associations. The simulation of the groyne modifications demonstrated a higher habitat diversity which resulted in an improved patchiness by the tested species. It turned out that each river section has to be investigated individually in order to consider the local conditions in every part of the groyne fields. The presented modelling enables decision-makers to investigate various solutions of bank conserving measures incorporating the requirements of the ecology and the economy with different scales. Generally a reconstruction of the semiterrestric river zones, especially of its groyne fields would be particularly desirable, but also the ecologically sound rehabilitation of the river itself and its meadows should be aimed at. A sustainable design should rather be subordinated to short term economic profit and, besides the aesthetic and ecological gains, would include economic advantages as rivers with comparatively natural shape hardly will need maintenance by hydraulic engineering (Bohle & Engel-Methfessel 1993). The authors even wrote in 1993 that it would be desirable "to consider more extensively the function of rivers in a natural environment, particularly since the defects arising from an exclusively technically oriented river management, will turn out to permanent and also economic constraints?. That is even more of relevance to the present situation under the impression of the flood disaster at Elbe and Oder with its negative impacts on economy and people.