IWRA Proceedings

AbstractThe island province (5684 km2) of Prince Edward Island (Canada) relies completely on a productive but highly vulnerable fractured red-bed sandstone aquifer for drinking water. Availability of potable water is constrained by brackish to saline waters in coastal regions, water balance considerations and nitrate contamination, particularly in watersheds with intense agricultural activity. The population of the Province is 140,000 and the economy is dominated by agriculture, with 40% of the land base under cultivation. Slightly more than half of the population resides in rural settings, and rely on private wells, with the remaining population served by small municipal water supply systems. Municipal water is chlorinated, but there are no water treatment plants in the traditional sense. Domestic water supplies typically receive no treatment, although the use of point-treatment devices is increasing in regions of declining water quality. The question we aimed at addressing here is what will the economic consequences of climate change on water supply infrastructure? We have performed an inventory of the current water supply systems, estimated what will be the rate of change for groundwater nitrate levels under various climate scenarios and evaluated the remediation costs for contaminated supply systems under the present-day equipment market. Water supply infrastructure island wide is estimated at 65 million$ (Can), and anticipated replacement costs are perhaps two to three times this value. Contamination of groundwater by nitrate affects 5% of domestic wells across the Province, and more than 10% of wells in intensively cultivated watersheds. To date, the main burden of contamination has fallen on private well owners, with potential annual costs for remediation of 200,000$Can to 400,000$. Three of 12 municipal water-supply systems have been impacted by elevated nitrate levels, however it has been possible to relocate or reconstruct supply wells to reduce nitrate levels at modest costs. Well field protection programs may reduce these risks, but with the Province’s small land base, competition between agricultural productivity and the need to protect water quality poses difficult challenges. Should municipal water treatment be required the costs of producing potable water for distribution could be expected to double. Predictions from numerical modelling suggest that under current land use practices, nitrate levels may increase on average by 11% by the year 2050, and when potential adaptations to climate change by the agricultural sector are considered, nitrate levels could increase in some intensively cultivated watersheds by as much as 30%. This increase in mean nitrate levels could be expected to result in nearly doubling the proportion of wells exceeding the nitrate guideline. In addition, discharge of nitrate-rich groundwater contributes significantly to the nutrient loading of coastal estuaries resulting in increased eutrophication, with direct consequences for the economically important aquaculture sector. These predicted increases in groundwater-nitrate concentrations would have a significant impact on the number of wells exceeding acceptable levels, with far reaching economic consequences for homeowners and municipalities with small water utilities. These economic, ecological and public health consequences of climate change highlight the need for aggressive action to control nitrate leaching to groundwater.