Effects of flow reduction and biodiversity decline on periphyton characteristics and carbon cycling

TROMBONI, FLAVIA; CAROLINA JÁTIVA-GUZMÁN; ALAIN MAASRI; SUSANA BERNAL; ALEXANDER H. FRANK; JOHANNES A.C. BARTH; MARLENE DORDONI; SONJA C. JÄHNIG; SUDEEP CHANDRA; CARINA SEITZ; HANS-PETER GROSSART

Berlin

Congreso; 36th Congress of the International Society of Limnology; 2022

International Society of Limnology and Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) of the Forschungsverbund Berlin e.V.

Climate change induces changes in riverine flow that affects biodiversity and stream functioning. In this work, we disentangle the effects of both low flow and presence of macroinvertebrates on periphyton characteristics. We grew periphyton on tiles placed in 8 identical experimental flow channels at the German Environment Agency (UBA, Berlin), as part of the EU Horizon project Aquacosm-Plus. We tested for the effects of two flow velocities: a normal flow of 0.25 m/s and an extreme low flow of 0.05 m/s. The effect of primary consumers was tested by placing a diverse macroinvertebrate community from a nearby stream in four of the channels. Periphyton tiles exposed to the different treatments were placed in sealed-flow chambers to measure primary production (GPP), ecosystem respiration (ER), and dissolved oxygen isotope ratios (expressed in ‰ as δ18ODO). Moreover, we measured organic matter (AFDM), chlorophyll-a, and taxonomic biodiversity. Flow reduction (i) decreased GPP and increased ER resulting in a more heterotrophic biofilm, and (ii) led to more positive δ18ODOsignals (i.e more enriched in 18O). These changes potentially alter biofilm isotopic composition. The presence of macroinvertebrates contributed to a decrease in AFDM but shifted biofilm composition, so it was dominated by autotrophic production. Moreover, the presence of macroinvertebrates partially buffered the effect of low flow on periphyton metabolic activity. Our results suggest that extreme low flow impact stream functioning, and that a diverse macroinvertebrate community could contribute to increase the resilience of freshwater ecosystems to these changing climate effects.