Influence of stormwater infiltration systems on the structure and the activities of groundwater biofilms: Are the effects restricted to rainy periods?

Stormwater infiltration systems (SIS) have been set up to collect and infiltrate urban stormwater runoff in order reduce flooding artificially recharge aquifers. Such practices produce environmental changes shallow groundwater ecosystems like an increase organic matter concentrations that could drive structure functions of microbial communities. Previous works suggested SIS influence physico-chemistry during either rainy dry period but no study has examined the impact on microorganisms both periods. This aimed fill this gap by assessing impacts quality parameters three with vadose zone thickness < 3 m two contrasting meteorological conditions (rainy/dry periods). Physicochemical (dissolved carbon nutrient concentrations) variables (biomass, dehydrogenase hydrolytic activities, bacterial community structure) were assessed SIS-impacted non-SIS-impacted zones aquifers for SIS. Using clay beads incubated aquifer biofilm, we show increased richness diversity biofilms not period. In contrast, significant differences dissolved concentrations, biofilm biomass structures (Bray-Curtis distances, relative abundances main orders) measured between comparable These results suggest structural indicators probably controlled long-term effects nutrients whereas activities temporally stimulated infiltrations decoupling functional responses suggests highly reactive fluxes associated events.