| The study of the twenty-five largest rivers of Brittany showed that nitrate concentrations are positively correlated with river flow, in 90 % of the cases. The hydrogeological characteristics of the watersheds had an influence on these relationships. In this respect, river basins characterized by prevalent surficial water runoff exhibited higher correlation coefficients and lower lag times between river flow sequences and nitrate concentrations. The multi-year trend in riverine nitrate concentrations indicated a fourfold increase over 30 years. Nevertheless, 80% of rivers exhibited a recent decrease in nitrate concentrations, independent of inter-annual river flow fluctuations. The highest annual rates of nitrate decrease corresponded to river basins for... |
