Is it relevant the order of occurrence of stressors for the maintenance of river biofilm functions? Results for short-term experiments

ORTIZ RIVERO JAVIER; GULTEMIRIAN MARÍA DE LOURDES; FREIA ANNA; SABATER SERGI

Simposio; 13th Symposium for European Freshwater Sciences; 2023

Freshwater ecosystems are exposed to multiple stressors from anthropogenic activities such as agriculture, livestock, or industry that affect aquatic organisms to multiple stressors, and the occurrence of these differs in their order of occurrence as well as in their intensity. We investigated whether the order of occurrence, contrasting their simultaneous and sequential appearance and intensity affected on the response of epilithic biofilms, which respond rapidly to disturbances and play an essential role in several relevant processes in river ecosystems. For this purpose, we conducted a 2 separate 96-hour experiments using glass microcosms to respectively evaluate the effect of a mixture of pesticides (stressor 1) and hydric stress (stressor 2), and of a mixture of pesticides (stressor 1) and increase of temperature (stressor 2). Pesticides had negative effect on biofilm functions and the combination with other stressors can result in a synergistic or antagonistic effects, the order of co-occurrence of each stressor remains poorly studied. We studied the response of biofilm communities in basal fluorescence, photosynthetic efficiency, phosphorus uptake and extracellular enzyme activities, as well as on chlorophyll-a, 18S rRNA, and 16S rRNA. Our results showed how the order of stressors has a direct impact on microbial communities, where a differential effect was observed depending on whether the pesticide mixture was incorporated the first or in the last 48 hours of the experiment. Similarly, we determined that the impact of most harmful stressor (pesticides) will be compensated by the less stressful stressor, producing an antagonistic effect in the same functions.