The processing of organic matter in freshwater ecosystems is crucial for integrating terrestrial plant material into aquatic food webs, with many systems depending on allochthonous inputs. In a study published in Oikos (https://doi.org/10.1111/oik.10774) we investigated how the population density of native and non-native amphipods (Gammarus fossarum and Gammarus roeselii) affects leaf litter processing, revealing a negative density-dependent relationship in both laboratory and field experiments. Interspecific competition confirmed functional redundancy between the species and showed that processing rates plateau at defined breakpoints, which reflect minimal metabolic needs. The findings emphasize the importance of accounting for nonlinear density-dependencies and breakpoints in aquatic ecosystem models, as population density significantly impacts ecosystem functions.

Biodiversity monitoring in groundwater ecosystems is lagging behind due to limited taxonomic knowledge and methodological challenges. Also, terrestrial land use changes strongly affect groundwater ecosystems, but the extent and impact on groundwater communities are poorly understood. Our recent work led by Mara Knüsel resolved some of these issues.

In a first study of Swiss groundwater macroinvertebrates published in Subterranean Biology (https://doi.org/10.3897/subtbiol.49.132515) we found that while obligate groundwater species (such as groundwater amphipods) showed no seasonal abundance patterns, other species exhibited pronounced seasonality in detection rates. The results emphasize the need for tailored, extensive sampling strategies and careful consideration of detection probability and sampling effort in groundwater fauna monitoring programs.

In a second study of Swiss groundwater amphipods published in Ecological Applications (https://doi.org/10.1002/eap.3040) we revealed a direct correlation between surrounding land use intensity, nitrate levels (a proxy for water quality), and amphipod presence, with higher forest cover supporting more amphipods. These effects were most pronounced within a 400–1000 m radius around sampling sites, exceeding current groundwater protection zone sizes, highlighting the need for broader, ecosystem-based approaches to groundwater management.

As part of Mara Knüsel’s impressive PhD work, we publisehd a paper in Ecography that explores how Late Pleistocene glaciation influenced the diversity and distribution of 36 groundwater amphipod species in the Alpine and peri-Alpine regions. It is based on a massive citizen science approach in collaboration with drinking water providers. The analysis, based on data from over 1,000 systematic sampling sites across Switzerland, reveals a significant impact of the Last Glacial Maximum (LGM) ice extent on the current distribution of groundwater amphipods. The findings highlight a pronounced species turnover and distinct spatial envelopes of species occurrences in zones that were formerly ice-covered, ice-free, or transitional.

The genus Niphargus, the most diverse subterranean amphipod genus in the western Palearctic, shows many cryptic species and homoplasy, necessitating molecular methods for understanding its evolution. In a new study, published in Contributions to Zoology, we used DNA-based taxonomy and traditional morphotaxonomy to study Niphargus bihorensis Schellenberg, 1940, from the Western Alps and Carpathians. The type material from Bihor County, Romania, revealed a cryptic species, N. absconditus n. sp., in the same area. Furthermore, we describe the Alpine populations as a new species, N. tizianoi n. sp. Our phylogenetic analyses suggest the N. bihorensis species complex is part of a well-supported clade with species ranging from Switzerland to Iran.

We published a study of 99 small Swiss streams in Aqua & Gas which reveals that most of these streams have significant ecological deficits, limiting their ability to serve as habitats for animals. In over 70% of the streams studied, pesticide-sensitive insect larvae and other small animals are partially missing. Statistical analyses show that these aquatic organisms are particularly affected when the stream bed structure and morphology have been altered or when the catchment area has a high proportion of agricultural land.