Environmental determinants of bacterial activity and faunal assemblages inalluvial riverbank aquifers

Groundwater quality can be strongly influenced by the source of the water t hrough the contributions of oxygen, organic, and inorganic materials. Micro bial characteristics (abundance and activity) and faunal distribution were examined in groundwater collected from two aquifers that are characterized by different water sources. For both aquifers, water samples were collected from three wells at different depths, three times in the year. The two aqu ifers showed contrasting characteristics concerning hydrodynamic variables, carbon content and presence of electron acceptors (oxygen and nitrate). At the local scale, spatial variations were low compared to seasonal changes. The combination of five variables (aquifer transmissivity, temperature, ox ygen, dissolved organic carbon (DOC), and percentage of biodegradable DOC ( BDOC)) accounted for 57 % of the variability in bacterial activity (express ed as the percentage of Electron Transport System active bacteria). The bes t multivariate linear regression model of faunal abundance accounted for 52 % of the variability with 5 significant variables (aquifer transmissivity, oxygen, DOC, redox, and pH). At the regional scale, the different water so urces have consequences on spatial variations of chemical and biological wa ter quality.