Does the efficiency of grazer introduction to restore and preserve the hydraulic performance of infiltration basins depend on the physical and biological characteristics of the infiltration media?

Groundwater constitutes the principal source of drinking water in Europe but the increase of urbanized impervious surfaces reduced the natural recharge of aquifers. To bypass this problem, infiltration systems have been largely developed for groundwater recharge. Nevertheless, the hydraulic performance of these systems is often altered by physical and biological clogging. The present study aimed to experimentally quantify the impact of a grazer (Viviparus viviparus) on hydraulic conductivity of three infiltration basins differentially clogged by benthic algal mat. The influence of the gastropod was also measured on the physical (proportion of silt and clay particles) and biological (algal biomass, bacteria abundance, total organic carbon, gross photosynthetic and hydrolytic activities) of the top layer of the infiltration media. We expected that grazers would have the highest influence on hydraulic performance of basin presenting the highest algal biomass. Our results showed that: (i) the grazers had a positive influence on hydraulic conductivity in the three basins; (ii) these positive effects were not significantly influenced by the initial conditions (algal biomass) in the three basins; and (iii) the impact of the grazers on hydraulic conductivity was not restricted to the removal of biofilm biomass by trophic action but may be also associated with bioturbation activities (pelletization and sediment reworking of the top sediment layer). While management practices developed to improve hydraulic performance of infiltration basins mainly focus on costly and non-environmentally friendly actions (e.g. mechanical sediment scraping), this study highlights the opportunity to consider alternative ecological solutions using the trophic and/or the bioturbation activities of animals.