Nitrate (N-NO3) concentration in groundwater, the sole source of
potable water in Prince Edward Island (PEI, Canada), currently exceeds the
10 mg L−1 (N-NO3) health threshold for drinking water in 6 % of
domestic wells. Increasing climatic and socio-economic pressures on PEI
agriculture may further deteriorate groundwater quality. This study assesses
how groundwater nitrate concentration could evolve due to the forecasted
climate change and its related potential changes in agricultural practices.
For this purpose, a tridimensional numerical groundwater flow and mass
transport model was developed for the aquifer system of the entire Island
(5660 km2). A number of different groundwater flow and mass transport
simulations were made to evaluate the potential impact of the projected
climate change and agricultural adaptation. According to the simulations for
year 2050, N-NO3 concentration would increase due to two main causes:
(1) the progressive attainment of steady-state conditions related to
present-day nitrogen loadings, and (2) the increase in nitrogen loadings due
to changes in agricultural practices provoked by future climatic conditions.
The combined effects of equilibration with loadings, climate and
agricultural adaptation would lead to a 25 to 32 % increase in N-NO3
concentration over the Island aquifer system. The change in groundwater
recharge regime induced by climate change (with current agricultural
practices) would only contribute 0 to 6 % of that increase for the various
climate scenarios. Moreover, simulated trends in groundwater N-NO3
concentration suggest that an increased number of domestic wells (more than
doubling) would exceed the nitrate drinking water criteria. This study
underlines the need to develop and apply better agricultural management
practices to ensure sustainability of long-term groundwater resources. The
simulations also show that observable benefits from positive changes in
agricultural practices would be delayed in time due to the slow dynamics of
nitrate transport within the aquifer system
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