Spatial distribution and uncertainties of nitrogen budgets for agriculture in the Tagus river basin in Portugal – Implications for effectiveness of mitigation measures

The present study describes a methodology to quantify the gross soil nitrogen balance (SNB) for agricultural land use in the Tagus Nitrate Vulnerable Zone (TVZ) between 1989 and 2016, including effects of implementation of the EC Nitrates Directive (ND, 91/676/EEC) since 2004. The study uses decadal information from National Agricultural Census at parish level and is supported by a Geographical Information System (GIS). The average SNB of the TVZ decreased significantly (p