Hidden losses in Berlin’s municipal water supply

A new study led by researchers at the Museum für Naturkunde Berlin shows that Berlin’s dragonfly populations have declined by more than half since 1963, whilst populations of frogs, toads and newts have fallen by over three-quarters since 1981. For the first time, decades of Berlin monitoring data were analysed using the internationally recognised ‘Living Planet Index’ (LPI) – the indicator normally used by the WWF to measure global wildlife populations. The study also involved Berlin-based experts Falk Petzold and Klaus-Detlef Kühnel, who coordinate the data series. The study, which was carried out as part of the project „Understanding Diversity – Exploring and Experiencing Nature“, funded by the Senate Department for Mobility, Transport, Climate Protection and the Environment, was published in the journal *Global Change Biology Communications*.

Two groups of animals, one shared fate

Dragonflies and amphibians lead a dual life: as larvae in water, and as adults on land. It is precisely this dependence on two habitats that makes them so vulnerable. For the study, the researchers analysed two extensive, previously unpublished datasets: the Berlin Dragonfly Database, containing almost 24,000 observations dating back to 1850, and the Berlin Amphibian Dataset, comprising over 16,000 records dating back to 1970, compiled by nature conservation organisations and specialist societies. The analysis included 16 bodies of water that had been surveyed regularly and in a comparable manner over several decades: from forest lakes in Grunewald to bog waters in Köpenick and ponds in Marienfelde and Tegel.

The result is clear: between 1963 and 2023, dragonfly populations declined by an average of 51 per cent. Among amphibians, the decline was even more pronounced, at 76 per cent between 1981 and 2022.

„Given the general trend of species decline, it is unfortunately no surprise that both groups are in decline. What is remarkable, however, is how much more severely the amphibians are affected,“ says Silvia Keinath, lead author of the study and a researcher at the Museum für Naturkunde Berlin. „Frogs, toads and newts are significantly less mobile than dragonflies and are therefore particularly vulnerable when migration routes between spawning grounds and terrestrial habitats are disrupted by roads, development or small bodies of water drying up.“ Dragonflies, on the other hand, being good flyers, can more easily colonise new bodies of water, but they too remain vulnerable to changes such as ponds drying up too early and the loss of suitable habitats.

A new perspective on urban biodiversity

The Living Planet Index aggregates the trends in many individual populations into a single trend value – similar to a stock market index, which reflects not the absolute number of animals but the average change in their populations. This makes it possible to visualise how the populations of different species are changing over long periods, even when the underlying data has been collected in a patchy and inconsistent manner.

Dry ponds as a warning sign

One reason for the observed declines could, quite literally, be on our doorstep: When cross-referencing with recent reports on small water bodies in Berlin, the team found that 36 of the water bodies originally studied have since dried up completely, partly as a result of falling groundwater levels and a lack of rainfall. Such permanently lost water bodies could no longer be included in the calculation of the index at all, as there was no longer a continuous time series available. The actual losses are therefore likely to be even higher than the study indicates.

Urban nature requires long-term monitoring

The study forms part of the Museum für Naturkunde Berlin’s growing commitment to researching and conserving Berlin’s urban nature. As recently as 2024, a team from the museum calculated that around 16 per cent of all species once native to Berlin have already disappeared completely since the year 1700. The current study complements this picture with a much finer temporal resolution: it shows not only which species are disappearing, but also how their populations have developed over decades – long before a species vanishes entirely from the city.

„Our findings are a tool,“ says Keinath. „They show that population trends can be meaningfully recorded even at the level of a single city. Provided, that is, that there is continuous, well-documented long-term data and that this is made available for analysis. Such data has so far been rare in Berlin because there is no structured, long-term biodiversity monitoring in place.“ The Museum für Naturkunde Berlin is committed to establishing such a monitoring programme in collaboration with nature conservation organisations, citizen scientists and the city – also as a contribution to the State of Berlin’s ‘Berlin Strategy for Biological Diversity 2030+’.

Publication:

Keinath, S., Griesbaum, F., Sommerwerk, N., Petzold, F., Kühnel, K.-D., & Freyhof, J. (2026). Long-term population declines of habitat-shifting species in urban waters: A Living Planet Index approach for Berlin, Germany. Global Change Biology Communications 1(3), e70039. https://doi.org/10.1002/gcb4.70039