Tracing Anthropogenic Impacts in an Urban Environment: Ostracod Evidence From Lake Müggelsee and Other Water Bodies of Berlin, Germany

Rapid urbanization and industrialization have left a persistent imprint on freshwater ecosystems, particularly in metropolitan regions where lakes act as both sinks and archives of anthropogenic pollution. The present study investigates the potential of ostracods as proxies of anthropogenic impacts by studying several surface water sites for an actualistic calibration and by applying a multi-proxy approach to a short core from lake Müggelsee for testing ostracod performance in paleoenvironmental reconstruction of pollution history.

The 26 surface water sites investigated are situated in the east, center and west of the city and reflect different kinds and degrees of anthropogenic impacts. Water types sampled comprise lakes, ponds, rivers and artificial canals. Almost all samples contain ostracods, proving their general availability for analyses in these contexts. One exception is the artificial, concrete covered canals with high turbulence caused by currents and whirling due to ship traffic, where fine-grained sediments and ostracods are broadly lacking. Opportunistic species tolerating oxygen deficiency dominate within the ostracod fauna. The other fossils the >125 µm size fraction are primarily molluscs.

Müggelsee is the largest lake within the Berlin urban region and is fed and drained by the river Spree entering the Berlin area here. The 70 cm long sediment core B25-MS1, taken from Müggelsee in 2025, allows us to study ostracods through time. The core records transitions from massive black muds to laminated black-greenish muds and surficial blackish muds, reflecting varying redox conditions linked to changing organic matter contents. The ostracod assemblages are dominated by candonids, Darwinula stevensoni, Limnocytherina sanctipatricii and Physocypria kraepelini . Their distribution shows marked stratigraphic shifts: The lowermost section below 56 cm sediment depth is characterised by taxa typical for a dense cover of submerged macrophytes. Afterwards and up to the limit between the black and the black-greenish mud at 22 cm, phytal species decrease in proportion, but cold-water taxa are still abundant pointing to a moderate pollution level and cooler conditions probably associated with the end of the Little Ice Age. The black-greenish mud between 22 cm and 7 cm yields the highest ostracod densities and a maximum of Neglecandona neglecta pointing to high organic pollution. Phytal ostracods decrease considerably with the vanishing of submerged macrophytes due to plankton blooms during the second half of the 20^th century when not properly treated and increasing sewage water outfalls caused rising trophic conditions in water bodies in and around Berlin. The last phase shows similar ostracod distributions as before the maximum pollution but phytal taxa do not recover and Darwinula stevensoni becomes even more abundant.

Overall, our study shows the potential of ostracod data from water body sediments to reveal increasing anthropogenic impact in the vicinity of Berlin, corresponding to phases of city’s industrial development, post-war and 1990s changes in wastewater management, and modern water quality status. Müggelsee thus exemplifies how urban freshwater archives record the Great Acceleration in local ecological systems. These findings provide crucial baselines for restoration strategies in alignment with the EU Biodiversity Strategy for 2030 and the EU Water Framework Directive.