Do bacteria and nutrients control faunal assemblages in alluvial aquifers?

Bacterial abundance and activity were studied at the scale of a regional aq uifer. The focus was on spatial and temporal distribution patterns in relat ionship with groundwater quality and with potential food resources for meio - and macrofauna. Six wells located along an agricultural/urban gradient we re sampled at three dates. The physical and chemical characteristics of the ground water showed few differences among wells except for nitrate content which was higher in the agricultural area. Metal contents in water and sed iments indicated a chronic metal contamination of this aquifer. Abundances of bacteria in the water (total and ETS-active bacteria) were homogeneous t hroughout the aquifer but varied over time. These variations were correlate d with DOC content. The faunal abundances varied according to wells and dat es, and correlated with total number of ETS-active bacteria. At all samplin g dates assemblages were dominated by the same taxa: oligochaetes in the no rthern part of the aquifer and niphargid amphipods in the southern part of the aquifer.