Nitrate input from fertilizers is one of the main sources for water pollution in Europe.
Especially in areas where groundwater is used as drinking water resource, exceeding the EU
groundwater threshold value of 50 mg/L for nitrate is problematic. Nitrate removal processes
like denitrification can lower the nitrate concentrations in groundwater naturally, however,
only under favorable conditions, such as low oxygen concentrations and presence of electron
donors. The aim of this study was to analyse spatial patterns and temporal development of
nitrate pollution at groundwater monitoring sites in Bavaria. Furthermore conditions for
nitrate removal via denitrification were assessed. We analysed groundwater chemistry data
for the period 2007-2017 from 604 monitoring sites of the Bavarian monitoring network. This
network comprises groundwater monitoring wells mostly in the uppermost aquifer and
natural springs as well as sites operated by drinking water suppliers. Nitrate concentrations
varied widely across Bavaria, with 8,5 % of the groundwater exceeding the threshold value of
50 mg/L nitrate. Especially the districts Lower Bavaria, Middle Franconia and Lower Franconia
showed a higher portion of polluted sites. Regarding the statistical trend analysis the majority
of the monitoring sites (78,5 %) did not exhibit a significant temporal trend; 16,4 % of all sites
showed a significant falling trend whereas 5,1 % had significant rising concentrations.
Favorable conditions for nitrate degradation via denitrification could be identified at 135 sites.
Overall, nitrate concentrations have remained quite stable over the period 2007-2017 at many
sites in Bavaria, indicating only a slow progress with respect to improving the groundwater
quality. Although some sites with favorable conditions for nitrate removal could be identified,
most of the aquifers have oxidizing conditions and therefore, do not provide conditions for
natural nitrate removal.