Irrigation as a disturbance for interstitial crustacean communities in a French Pyrenean alluvial aquifer

Abstract

While the impacts of groundwater contamination on interstitial invertebrate communities are well studied, very few work have examined other potential disturbance resulting from agricultural practices. In the present study, the interstitial crustacean fauna was studied in an alluvial aquifer characterized by intensive cereal irrigation, to test the influence of groundwater extraction on the assemblage characteristics (abundance, diversity, persistence, species distribution patterns). Micro- and macrocrustaceans were sampled at 4 seasons in 15 wells with contrasted groundwater use (cereal irrigation / domestic use / no groundwater use) scattered over a 250 km2 alluvial floodplain. The aquifer harbored diverse assemblages dominated numerically and specifically by cyclopoids. Total abundance, diversity expressed using species richness or Shannon index, overall persistence in species composition did not vary between stations whether micro- or macrocrustaceans were considered. Yet, marked differences in the cyclopoids assemblages composition were found in relation to groundwater utilization. Disturbed irrigation wells were dominated by epigean species, while hypogean species were mainly found in less impacted domestic wells. In contrast, amphipods/isopods did not exhibit particular assemblages composition between irrigation, domestic or abandoned wells. The differential responses between micro- / macrocrustaceans, epigean / hypogean species emphasized that levels of disturbance are strongly taxondependent. At the scale of the aquifer, these results suggest that groundwater extraction resulting from intensive irrigation has to be considered as a potential disturbance for the interstitial communities.