A single law to describe atmospheric nitrogen bulk deposition versus rainfall amount: Inputs at the Seine river watershed scale

Atmospheric nitrogen species (NH^sub 4^-N and (NO^sub 3^+NO^sub 2^)-N) were determined in weekly samples of atmospheric bulk deposition (dry plus wet), collected in France at seven sites over the course of a year. Rural, semi-rural and industrialised-urban sites were chosen in the Seine river watershed from the Seine estuary to upstream from Paris. Mean NH^sub 4^-N concentrations varied from 0.7 to 1.7 mg L^sup -1^. Mean (NO^sub 3^+NO^sub 2^)-N concentrations were approximately 0.5 mg L^sup -1^ for all sites except Paris (0.7 mg L^sup -1^), which has a local impact on the fallout contamination from urban emissions. The relation between concentration and rainfall amount obeys a power law, in the form of y = ax^sup b^. When the nitrogen sources are very local, this relationship turns into a dilution law. Annual atmospheric nitrogen deposition (NH^sub 4^-N+(NO^sub 3^+NO^sub 2^)-N) was calculated and varied from 7.8 kg ha^sup -1^ yr^sup -1^ in the neighbourhood of a rural town to 17.3 kg ha^sup -1^ yr^sup -1^ in a very industrialised harbour. 58% of the atmospheric nitrogen deposition occurred during 'spring + summer' period. The total nitrogen atmospheric input to the Seine estuary, via direct deposition + indirect input via the watershed, was estimated to about 5% of the total nitrogen load within the Seine river basin.[PUBLICATION ABSTRACT]