Groundwater-Surface Water Interactions in the Mabou Harbour Drainage Basin and Potential for Harbour Contamination

Abstract

Groundwater-borne contamination to coastal waters is a growing risk in the Canadian Maritimes region. Groundwater contaminants can enter the marine environment directly as submarine groundwater discharge, or indirectly as groundwater-derived baseflow discharged through surface watercourses. In this study, the spatial patterns of groundwater-surface water interactions (GSIs) and the effects of direct and indirect groundwater discharge on nitrate and bacterial contamination of Mabou Harbour (located in Cape Breton Island) were assessed on a regional scale. Shoreline and floodplain piezometers were continuously monitored to analyze temporal patterns in GSIs. Hydrograph analysis and evaluation of thermal regimes were used to assess the GSIs between the major rivers. Seepage meters were deployed to constrain direct submarine groundwater discharge fluxes. A 3D groundwater flow model was constructed using MODFLOW-NWT and calibrated to historic static well water levels in addition to the baseflow of major rivers in the drainage basin.