From March to the end of August 2026, the University of Barcelona (UB) / MAiMA team, Spanish partner of the NPP-SOL project, carried out the final experimental phase of the project at the Spanish case study (Ejea de los Caballeros, Zaragoza). This involved various field activities at the Constructed Wetland (CW) of the Lerma basin, including maintenance tasks (removal of excess vegetation and cleaning of the CW entry, calibration of sensors, etc.), a series of biostimulation cycles (intermittent and continuous flow), sampling campaigns for chemical and multi-isotopic analyses, and pumping tests.
Overall, the integrated interpretation of results from the different biostimulation strategies adopted at Lerma CW along the whole project showed increased efficiency of denitrification compared with natural conditions, with removal of the inlet nitrate varying from 20 to 100%. Harmful denitrification intermediate products such as nitrite or ammonium were always negligible at the outlet, reinforcing the treatment safety. The Lerma Gully CW proved to be an effective nature-based solution for nitrate pollution mitigation from agricultural runoff.
Still, when comparing the nitrate removal in the CW with the nitrogen circulating in the Lerma Gully, results indicate that the CW alone does not allow nitrate levels to be reduced below the threshold for consumption. Given the extremely high amount of nitrate circulating through the Lerma Gully, it would be crucial to strengthen the implementation of best management practices aimed at limiting fertilizer application in agricultural fields.
NPP-SOL is part of the PRIMA Programme supported by the European Union.
