Author: Roman Alther

Leaf litter processing by amphipods under laboratory and natural conditions is density-dependent

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Figure 4 from the study, showing the litter processing rates relative to amphipod density (a) and amphipod biomass (b) in the two-species treatment including G. fossarum and G. roeselii.

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.

Improving methods for groundwater fauna monitoring

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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.

Figure 1 from our land use study published in Ecological Applications (https://doi.org/10.1002/eap.3040), showing our sampling design across the Swiss plateau.

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.

Environmental DNA and participatory science to map groundwater fauna

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Figure 1 from https://doi.org/10.1038/s41598-023-44908-8

In our most recent study, published in Scientific Reports (https://doi.org/10.1038/s41598-023-44908-8), we used participatory science and environmental DNA (eDNA) metabarcoding to investigate groundwater amphipods and to capture a broader picture of the groundwater community, including microorganisms. Combining both methods revealed co-occurring amphipod species and their correlation with overall groundwater biodiversity, enhancing our understanding of subterranean ecosystems. In conclusion, we propose two novel methods for studying groundwater organisms, which can be applied independently or, more effectively, in combination. These approaches offer valuable tools for addressing uncharted aspects of subterranean biology.

Environmental DNA in groundwater

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Through close cooperation with local waterproviders in the Töss catchment area, we were able to detect a diverse groundwater fauna. The corresponding publication has just been published in Molecular Ecology (https://doi.org/10.1111/mec.16955). In contrast to earlier studies, we did not have to use nets and actually catch the organisms, but were able to detect them on the basis of DNA traces in water samples. We were able to show that the diversity of groundwater fauna differs depending on whether the samples were taken from agricultural or forested sites. However, it is not yet possible to make a statement about the cause or to do a water quality assessment. Eawag has published a news article on the publication. Many thanks also to the FOEN, the SVGW and Eawag for their financial support of the research project.

An insight into foodwebs of alpine streams

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WindRiverRange_Stream

Finally, the latest paper I was involved during my Masters got released: “A note on the trophic structure of alpine streams in the Wind River Mountains, Wyoming, USA” in Fundamental & Applied Limnology. The results suggest a glacial carbon signature in stream foodwebs close to the glacier. Further a longitudinal shift in carbon sources was observed in these streams, from a glacial to an instream source and finally to a allochthonous source when moving along the system. Thanks again to the whole team. Riding to the remote sites and sampling was great fun and an exciting adventure.