Original paper

The protection potential of soils and post-Jurassic covers against nitrate seepage (Southern Franconian Jura, Germany)

Zielhofer, Christoph

Abstract

The mid-mountain plateau of the Southern Franconian Jura exhibits base rocks of bedded and massive Upper Jurassic (Malm) carbonate rocks. These only provide a low protection potential against nitrate seepage. Hence, post-Jurassic covers may play an important role for a sustainable fresh water protection. Extensive tracer analyses in the Southern Franconian Jura offer the opportunity to investigate nitrate outputs on the basis on karst spring catchments. Hydrochemical analyses of spring waters can be correlated with known geomorphic, sedimentological and pedological features of vadose zones within the karst spring catchments. According to geomorphological and pedological criteria, the Southern Franconian Jura is characterised by four landscape types which reveal different protection potentials against nitrate seepage. Within the uncovered zone of the Franconian Jura the karst spring waters exhibit enhanced nitrate contents if the rate of agrarian land use is also enhanced in the catchments. This can be especially observed in the zone of bedded limestones (mean NO3 content: 38.5 mg/l). By contrast, the NO3 contents within the springs of the Tertiary Cover (Miocene) clearly reveal lower mean values (24.3 mg/l) indicating enhanced protection potential of the thick soils and Upper Fresh Water Molasse covers against nitrate seepage.