Evaluation of nitrate distribution and matrix storage effects in a dual permeability fractured bedrock aquifer with heterogeneous hydrochemistry

Abstract

There is growing concern in Prince Edward Island as groundwater nitrate concentrations in the bedrock aquifer have increased since the mid-1980s due to intensive agriculture, with associated ecological impacts evidenced by surface water eutrophication. While, agricultural beneficial management practices have been implemented, subsurface heterogeneity and matrix diffusion processes appears to be limiting their effectiveness. The objective of this study was to quantify nitrate concentrations in lower K zones and hydrogeochemical influence on concentration via porewater analysis of discrete samples from cores, and application of multi-level systems for high-resolution spatial and temporal monitoring of hydraulic head and hydrochemistry. Results show elevated nitrate persists in the shallow subsurface, suggesting minimal denitrification due to lack of electron donors / oxygenated conditions and matrix storage effects. Such data improves conceptual models of nitrate migration and fate in sedimentary bedrock aquifers to allow adjustments to agricultural practices that can meet source water protection goals.