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TEMPERATURE EFFECTS ON STREAM ECOSYSTEM FUNCTIONING ACROSS SEASONS: INSIGHTS FROM A TEMPERATE THERMAL SPRING IN THE VOSGES MOUNTAINS

During the last decades, the effects of temperature on stream ecosystem functioning have received considerable attention. However, because several biotic or abiotic (e.g. latitudinal, seasonal) factors often co-vary with natural temperature gradients, disentangling the effect of temperature from the influence of confounding factors in field studies remains a challenge. To overcome this limitation, we used a non-volcanic thermal spring that flows out at 21°C all year round and progressively cools downstream, resulting in a moderate negative temperature gradient. We studied microbial decomposition of alder leaf-litter and benthic biofilm production for 28 days, in spring and winter, at 4 sites along this gradient. Results showed contrasting patterns between leaf-litter decomposition and primary production. Surprisingly, increasing temperature hampered decomposition in spring, whereas winter decomposition rates were invariably low along the temperature gradient. Conversely, primary production increased with temperature at both seasons, although this concentration was lower in winter. These results suggest some discrepancies in the temperature-dependence of these two fundamental ecosystem processes. Temperature rise could thus lead to shifts in the balance between carbon fixation and mineralization in stream ecosystems with strong consequences on carbon cycles at the global scale.

Alice Gossiaux (Primary Presenter/Author), LIEC, Univ. Lorraine, France, alice.gossiaux@univ-lorraine.fr;


Pascal Poupin (Co-Presenter/Co-Author), LIEC, Univ. Lorraine, France, pascal.poupin@univ-lorraine.fr;


Jérémy Jabiol (Co-Presenter/Co-Author), LIEC, Univ. Lorraine, France, jeremy.jabiol@univ-lorraine.fr;


Eric Chauvet (Co-Presenter/Co-Author), EcoLab, CNRS, France, eric.chauvet@univ-tlse3.fr;


François Guérold (Co-Presenter/Co-Author), LIEC, Univ. Lorraine, France, francois.guerold@univ-lorraine.fr;