Geochemical and isotopic constraints on groundwater-surface water interactions in a highly anthropized site. The Wolfen/Bitterfeld megasite (Mulde subcatchment, Germany).

The Bitterfeld/Wolfen region is a megasite with multiple contaminant sources from more than a century of industrial activity, which have a considerable impact on the environment. At present, the contaminated groundwater covers an area of about 25km(2) and poses a threat for the surrounding aquifers and the Mulde River. This study focuses on the Schachtgraben, a man-made channel in the Mulde Floodplain that collects the effluents of the industrial area. It aims to characterise the relationship between surface water (channels, rivers) and the groundwater in the shallow Quaternary aquifer. Waters are Ca-SO(4) type with TDS reaching 3.8gL(-1) in the industrial area. Stable isotopes (delta(18)O, delta(2)H) show that two of the rivers are recharged mainly by groundwater that can be divided into two groups. Strontium isotopes ((87)Sr/(86)Sr) designate different geochemical end-members and enable the identification of mixing between natural and anthropogenic surface and groundwater.