Located in South West of Brittany, western France, the elementary catchments of Kerbernez are underlain by old bedrock and is characterised by a oceanic, humid and temperate climate and by an intensive agriculture. In every catchment, the hydrology is controlled by a shallow aquifer made of the unconsolidated weathered bedrock. The water table in the aquifer is close to the soil surface in bottom land areas of catchment. During storm event, surface runoff occurs mainly over the saturated soils of bottom lands. The Environmental Research Observatory (ERO) AgrHyS focuses on the response times of changing Agro-Hydro-Systems (defined as a catchment influenced by agricultural activity) for hydro-chemical fluxes.