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Geographically Referenced Modelling of the fate of LAS in the stream Itter

For the simulation of spatial concentration patterns of 'down-the-drain'-chemicals mathematical models were coupled with a Geographical Information System (GIS). As an application the detergent chemicals LAS (Linear Alkylbenzenesulfonate) and Boron were simulated in the Itter, a small tributary to the Rhine, which has a length of approximately 20 km. Three municipal sewage treatment plants (STP) serving a total of 182,137 population equivalents are discharged into the Itter. In order to estimate the release of the aforementioned chemicals into the Itter two different model concepts have been implemented and evaluated. In the first concept, the concentration at the mouth of the Itter is calculated based on possible emissions at any location of the catchment area. This approach shows that mainly the connectivity to the STPs and the elimination processes taking place in them influence the predicted concentrations. In the second concept, concentrations in various stretches of the Itter are calculated based on the release via point sources (STPs), taking instream removal into account. A deeper study of the elimination behaviour of LAS with the means of statistical analyses show a high correlation between the half-life of LAS and the water quality parameters TOC and ammonium. Furthermore, Monte Carlo simulations hint that the variability of the measured concentrations near the mouth of the Itter can be explained by variable flows, whereas further upstream unknown factors seem to influence the variability of the concentrations. The models have been calibrated with measured concentrations generated by a monitoring program in 1996 and were compared with measured concentrations from 1997.

This study is closely connected to the research projects GREAT-ER (oneway) and Validation of exposure models and parameters as well as to Frank Koormann's diploma thesis Organische Schadstoffe im Fließgewässernetz Rhein which was finished in January 1997. All these projects are in the context of environmental risk assessment of chemicals.

The german version of the masters thesis as zipped Postscript-File (download) can be downloaded.

To get an idea of the Itter, some pictures which were being taken during the 1997 sampling are shown here.

The study was presented during the poster session of the 8th annual SETAC Europe meeting 1998 in Bordeaux. The whole poster and its elements are stored as JPEG-files on this server.

archived: August 2001 - last modified by the author: May 10, 2001

E-Mail: Carsten.Schulze@usf.Uni-Osnabrueck.DE [ index card (»German) ]

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