We will present results of the role of denitrification in groundwater nitrate retention in riparian zones at various scales, i.e. from the (hot) spot over the plot to the catchment. The following observations could be deducted. Geomorphology (e.g. buried organic carbon) could be identified as the first important controlling variable, while hydrology was the second important controlling variable for groundwater nitrate retention in riparian zones. Further we introduced a unique methodology, i.e. the use of the natural abundance of 15-N in groundwater nitrate to quantify the relative importance of denitrification versus plant uptake for groundwater nitrate retention in riparian zones. Finally we initiated the development of an ecosystem indicator to identify potential riparian zones for groundwater nitrate retention. Such an indicator could be the ‘holy grail' for applied riparian buffer zone research (policy relevant). In conclusion, we observed that groundwater nitrate retention in riparian zones seems to be largely controlled by the hydrogeomorphology of the river valley, rather than by its vegetation cover. Consequently, the proposed methods to identify the occurrence of ideal hydrogeomorphological settings may contribute to management strategies and the identification of potential areas for the (re-)construction of riparian zones for water pollution control.