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Paper No. 82-14
Presentation Time: 5:05 PM

REGIONAL-SCALE GROUNDWATER FLOW AND POTENTIAL CONTAMINANT TRANSPORT PATHWAYS INTO A NATURAL HARBOUR


CRADDOCK, Raymond, Civil and Resource Engineering, Dalhousie University, 5217 Morris St, PO Box 15000, Halifax, NS B3J1B6, Canada, KURYLYK, Barret L., Department of Civil and Resource Engineering and Centre for Water Resources Studies, Dalhousie University, 1360 Barrington Street, P.O. Box 1500, Halifax, ON B3H 4R2, Canada, MOHAMMED, Aaron A., Department of Civil and Resource Engineering and Centre for Water Resources Studies, Dalhousie University, Halifax, NS B3J 1B6, Canada, KENNEDY, Gavin, Energy and Mines, Province of Nova Scotia, 1701 Hollis Street, Halifax, NS B3J 2T9, Canada, JAMIESON, Rob, Department of Civil and Resource Engineering and Centre for Water Resources Studies, Dalhousie University, 1360 Barrington Street, P.O. Box 1500, Halifax, NS B3H 4R2, Canada and KEIZER, Jonathan, Environmental Services, Stantec Inc., 845 Prospect Street, Fredericton, NB E3B2T7, Canada

Groundwater-bourne contamination to coastal waters is a growing risk in the Maritimes region. Groundwater contaminants can enter the marine environment directly as submarine groundwater discharge (SGD), or indirectly as groundwater-derived baseflow discharged through surface watercourses. In this study, the effects of direct and indirect groundwater discharge on nitrate and bacterial contamination of a natural harbour were assessed on a regional scale.

The Mabou Harbour watershed in Cape Breton Island, Nova Scotia has a strong agricultural industry along with a history of persistent microbial contamination. Shoreline and flood-plain piezometers were continuously monitored to analyze temporal patterns in groundwater-surface water interactions. 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 watershed. Model results, complemented by field data, yield important insights into the regional-scale groundwater flow and transport dynamics to surface waterbodies. Results demonstrate how factors such as residence time, groundwater depth, and advective flowpaths influence the risk of contamination to the harbour on a catchment scale. Although direct groundwater discharge only accounts for 8% the of total catchment discharge and residence times are substantially longer than discharge to the deeply incised fluvial valleys, SGD may disproportionately contribute to the influx of nitrate. The relatively deeper flowpaths associated with SGD bypass the natural attenuation zones associated with flow through riparian zones. Conversely, the higher hydraulic gradients and permeability of the alluvial materials found in the fluvial valleys substantially reduce residence times to within the survival limits of certain microorganisms, such that groundwater-borne microbial contamination via indirect groundwater discharge is plausible. As natural harbours are commonplace for rural agricultural communities in coastal regions, these results are applicable to similar environments and will help improve land-use planning in coastal watersheds.

Session No. 82

T98. Groundwater-Surface Water Interactions Under Climate and Anthropogenic Change
Tuesday, 27 October 2020: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol 52, No. 6
doi: 10.1130/abs/2020AM-354169
© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.
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