Groundwater nitrate concentration evolution under climate change and agricultural adaptation scenarios: Prince Edward Island, Canada

Daniel Paradis,Martine M Savard,Harold Vigneault,Budong Qian,René Lefebvre,Jean-Marc Ballard

doi:10.5194/esd-7-183-2016

Abstract

Abstract. 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.

Highlights

Significant increases in groundwater nitrate concentration ([NO3]) are caused largely by sewage leaks, wastewater treatment without denitrification, improper management of wastewater effluents and overuse of fertilizers and/or animal waste
The novelty of this study is to provide a quantitative comparison of climate change effects and agricultural adaptation impacts on the future evolution of [NO3], taking into account potential changes in groundwater recharge and nitrate leached
On the basis of the previous calibration results, it is assumed that the FEFLOW model provides a good representation of groundwater flow conditions and nitrate transport in the Prince Edward Island (PEI) aquifer system as well as of present-day [NO3] in drinking water

Summary

Introduction

Significant increases in groundwater nitrate concentration ([NO3]) are caused largely by sewage leaks, wastewater treatment without denitrification, improper management of wastewater effluents and overuse of fertilizers and/or animal waste. These nitrate sources are responsible for the contamination of numerous aquifers, especially in those areas where groundwater is replenished directly from the surface over large areas. Nitrate contamination is often associated with anthropogenic activities at ground surface, such as the fertilization of agricultural crops. Remediation is difficult, the prevention of contamination is the primary strategy used for water quality management (Ghiglieri et al, 2009). D. Paradis et al.: Groundwater nitrate concentration evolution under climate change: Prince Edward Island

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