The site of the Hydrogeochemical Observatory of the Environment (OHGE) is the Strengbach watershed (80 ha), located in the commune of Aubure (60 km southwest of Strasbourg). It is in a mid-altitude mountainous area (between 880 and 1,150 m) in the Vosges massif with steep slopes (from 10° to 30°). More than 80% of the vegetation cover is made of managed forests (80% spruce and 20% beech) growing on a Hercynian acidic granite substratum. The trees have shown signs of forest dieback since the 1980s. The soils range from acid brown soils mainly on the north-facing slope to podzolic ochre soils. The climate is temperate oceanic with an average annual temperature of 6°C and an average rainfall of 1,400 mm/year (including 1 to 3 months of snow). The average water level at the outlet is 800 mm/year. Interannual variations are important and vary by a factor of two between dry and wet years. Four springs used for drinking water are located on this site. Major floods can occur at the end of winter when the snowpack melts or can be due to summer thunderstorms. The low-water period is between late summer and mid-autumn.