Fate of nitrate during groundwater recharge in a fractured karst aquifer in Southwest Germany

Abstract Over the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability nitrate (NO 3 − ) contamination, yet nitrogen (N) turnover processes within recharge area are still poorly understood. This study investigated role of karstified in NO transfer by combining isotopic analysis nitrite 2 with time series data hydraulic heads specific electrical conductivity from monitoring wells a karstic spring Germany. A large spatial variability concentrations (0.1–0.8 mM) was observed, which cannot be explained solely agricultural land use. Natural-abundance N O isotope measurements (δ 15 δ 18 O) confirm that derives mainly manure or fertilizer applications. Fractional elimination denitrification is indicated relatively N- O-NO values, elevated (0.05–0.14 mM), N-NO values were systematically lower than corresponding . Hydraulic chemical response patterns suggest rain events result displacement water transient storage compartments such as epikarst fissure network phreatic zone. Although levels groundwaters close saturation, local might promoted microoxic anoxic niches formed ferrous iron-bearing carbonate rock formations. The results revealed (temporarily) saturated networks zone may play an important during aquifers.