Stream metabolism is a key biogeochemical process in river networks, synthesising the balance between gross primary production (GPP) and ecosystem respiration (ER). Globally, more rivers and streams are drying due to climate change and water abstraction for human uses and this can alter the organic carbon residence time, leading to decoupled ER and terrestrial organic matter supply. While the consequences of drying on CO2 emissions have been recently quantified, its effects on stream metabolism are still poorly studied. We addressed the short- and long-term effects of drying on stream metabolism by monitoring oxygen dynamics at 20 reaches across a drying river network, including perennial (PR) and non-perennial reaches (NPR) for one year. We also calculated several climatic, land use variables and characterized and local abiotic conditions, and biofilm and sediment communities at five sampling dates. ER was significantly higher in NPR than in PR reaches demonstrating in-situ the effects of drying on stream metabolism. When analyzing the long-term drivers of ER and GPP, we found a direct positive effect of drying on ER and a negative effect on GPP. Drying also altered microbial community composition, with algal communities from NPRs being different from those in PRs. In the short-term, the amount of C emitted during rewetting events was positively related to the duration of precedent non-flow period. Our results show that drying had an important effect on stream metabolism both in the short and long term, and supports the need of including NPRs in global estimates of stream metabolism.

Continued advancements in environmental DNA (eDNA) research have made it possible to access intraspecific variation from eDNA samples, opening new opportunities to expand non-invasive genetic studies of wild animal populations. However, the use of eDNA samples for individual genotyping, as typically performed in non-invasive genetics, still remained unachieved. We present the first successful individual genotyping of eDNA obtained from snow tracks of three large carnivores: brown bear (Ursus arctos), European lynx (Lynx lynx) and wolf (Canis lupus). DNA was extracted using a protocol for isolating water eDNA and genotyped using amplicon sequencing of short tandem repeats (STR) and, for brown bear, a sex marker, on a high-throughput sequencing platform. Individual genotypes were obtained for all species, but genotyping performance differed among samples and species. Multilocus genotyping success for individual identification was higher for brown bear samples (6 over 7), than for wolf (7 over 10) and lynx (4 over 9) samples. The sex marker was genotyped in 5 out of 7 brown bear samples. Results for three species show that reliable individual genotyping, including sex identification, is now possible from eDNA in snow tracks, underlining its vast potential to complement the non-invasive genetic methods used for wildlife. To fully leverage the application of snow track eDNA, improved understanding of the ideal species- and site-specific sampling conditions, as well as laboratory methods promoting genotyping success are needed. This will also inform efforts to retrieve and type nuclear DNA from other eDNA samples, thereby advancing eDNA–based individual and population level studies.