Forecasting and Mass Transport Modelling of Nitrates in the Esposende–Vila Do Conde Nitrate Vulnerable Zone (Portugal)

Abstract

Esposende–Vila do Conde, a nitrate-vulnerable zone, in the littoral north of Portugal, is contaminated by nitrates of an agricultural origin. Measures have been implemented to reduce that contamination. The effectiveness of the measures was evaluated, predicting the time required for the groundwater body reach the quality standard, i.e., less than 50 mg/L for dissolved nitrates. Two methodologies were used, groundwater flow and nitrates transport modelling, and predictive analysis of time series. The transient simulation of nitrate transport shows that the minimization measures imposed in the NVZ are being effective. However, the persistence of concentrations above 50 mg/L in some areas is notorious even in the next 24 years. The forecasting points out to a recovery period of ten years if current agricultural practices are maintained. The prediction of NO₃ concentration based on forecasting methodology may not be applicable in the long run because it is a punctual analysis, not taking into consideration the contaminant dispersion dependent on the aquifer characteristics.