Microplastics as a chronostratigraphic indicator in the sediments of the Urft reservoir

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Fluvial systems in Central Europe, but also worldwide, have been subject to rapid change in recent decades to centuries. Changes in land use but also climatic changes have led to drastic alterations in the sediment balance and runoff patterns. However, for the identification and quantification of geomorphological changes in recent decades, suitable geochronological markers are essential. These markers are important either to quantify changes in the spatial and the temporal domain but also to disentangle natural and anthropogenic geomorphological processes. In this context, the occurrence of plastics or microplastics in sediments has been intensively discussed for several years. Microplastics are purely anthropogenic and have been used on a massive scale worldwide since about 1950. However, so far there are only a few studies that consistently applied this concept. Therefore, this project investigates the extent to which microplastics can be used as chronostratigraphic markers in fluvial sediments.The sediments of the Urft reservoir offer an excellent opportunity to test microplastics as a chronostratigraphic marker. The Urft dam was built in 1905. The resulting lake has a length of 12 km and a maximum volume of 45.5 million km³. In November 2020, it was almost completely drained for maintenance work. In cooperation with the Eifel-Rur Water Board, the reservoir sediments were intensively sampled. The detailed spatial recording of the sediment body was carried out by means of drone survey. A total of 10 cores with a length of up to 4 m were obtained. For one of the cores, a chronology of the sediments was established based on caesium-137. The first occurrence of caesium-137, which marks the beginning of worldwide nuclear weapons testing from 1952, is found at a depth of 240 cm. This makes it possible to determine the lower limit of microplastics in the sediments over several cores and to classify them precisely in time.In a further step, the different polymers are examined in more detail. Since different types of polymers were developed at various times, they were also introduced into the environment at different times. The investigations at the Urft will now show whether differences in the time of entry are reflected in the sediments and whether plastic can thus also be used for precise dating after the year 1950.The aim of the project is to record microplastics in the sediments of the Urft reservoir in detail, both spatially and temporally, and thus to provide new impulses for the use of plastics as an independent dating method in geomorphological-sedimentological research.