Artificial substrates buried in stream sediments at the karst/floodplain interface were used to examine the spatial and temporal variations of the stygobite Amphipods Niphargus rhenorhodanensis (two stations in France) and Pseudoniphargus sp (one station in Morocco) populations. One station («Verna», France) was supplied by karst water. The other two stations («Pissoir», France and «Grotte du Chameau», Morocco) were supplied by both karst and surface waters. The dynamics of the populations was
found to depend on several interacting factors: spates, geological characteristics, location of the sediment in relation to karstic water supplies and depth within the sediment.