High Spatial‐Resolution Monitoring to Investigate Nitrate Export and Its Drivers in a Mesoscale River Catchment Along an Anthropogenic Land‐Cover Gradient

Nitrate monitoring is commonly conducted with low-spatial resolution, only at the outlet or a small number of selected locations. As result, information about spatial variations in nitrate export and its drivers scarce. In this study, we present results high-spatial resolution between 2012 2017 65 sub-catchments an Alpine mesoscale river catchment characterized by land-use gradient. We combined stable isotope techniques Bayesian mixing models geostatistical methods to investigate main drivers, namely, microbial N turnover processes, land use hydrological conditions. investigated sub-catchments, mean values NO3− concentrations signatures (δ15NNO3 δ18ONO3) varied from 2.6 26.7 mg L−1, −1.3‰ 13.1‰, −0.4‰ 10.1‰, respectively. was important driver for export. Very strong positive correlations were found percentages agricultural cover δ15NNO3, concentration, Mean proportional contributions sources spatially seasonally, followed patterns. The contribution manure sewage much higher catchments high percentage urban comparing forested sub-catchments. Specific loads strongly correlated specific discharge moderately concentrations. concentration analysis suggest that external stored accumulated soil storage pools. Nitrification reduced nitrogen species those pools plays most role N-dynamics Erlauf catchment. Consequently, nitrification source except dominated use. catchment, denitrification minor controlling on regional scale.