Synchronous trends in N-NO3 export from N-saturated river catchments in relation to climate

Publication Type:

Journal Article


Rogora M.


Biogeochemistry, Volume 86, p.251-268 (2007)


Climate, Nitrate, Nitrogen saturation, Northern Italy, Trend, Water chemistry


Long term trends (1978–2005) of N–NO3 concentrations in river water were investigated for 10 rivers draining forested catchments in Piedmont, North-Western Italy, and Canton Ticino, Switzerland. All the river catchments come into the category of the medium-high stage of N saturation (levels 2–3 of the Stoddard’s classification). The seasonal signal in N–NO3 concentrations and its changes in time over the course of the study period was also evaluated. Single trends were analysed for significance and magnitude; statistical techniques for the detection of common trends were then applied to identify a common pattern in the N–NO3 time series. Both the increasing NO3 levels and the limited seasonal pattern in recent years indicate an aggrading level of N saturation in time. Synchronous trends of N–NO3 export were found for 8 rivers. The main common trend was used to test relationships with: (i) temperature, (ii) precipitation, and (iii) N deposition.
Step-changes in the data series were also assessed, and the main points of change are discussed in relation to meteorological factors and response to the N saturation status. Temperature proved to be the main factor affecting the temporal pattern of N–NO3 concentrations: warm periods were usually followed by an N–NO3 increase in river water due to enhanced mineralisation and nitrification in soil.