A reversal in NO3 trends for lakes and rivers in Northern Italy: towards a recovery from N saturation?

Long-term studies on the chemistry of atmospheric deposition and surface waters have been performed in North-Western Italy since the 1970s. Deposition of inorganic N in this area is around 20-25 kg N ha-1 y-1, and has remained fairly constant in the last 30 years. This huge flux of N caused N-saturation of terrestrial catchments and increasing levels of NO3 in rivers and lakes. Recently, monitoring data for both rivers and lakes showed a reversal in NO3 Methods/Approach trends: concentrations started to decrease, with a change-point around 2003-2004 at several sites. This change was widespread, affecting both high altitude lakes in the Alps and subalpine lakes and rivers. Atmospheric input of N also showed a recent change, with a slight tendency to decrease, mainly due to the limited precipitation amount occurred between 2003 and 2009. Surface water may be responding to these changing N input, but possible climate change effects, as a higher N uptake in soil and water under a warmer climate, should also be taken into account.