T82 Groundwater-Surface Water Interactions Under Climate and Anthropogenic Change

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

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

Paper number: T82-16
Program: Technical Sessions
Time: 5:05 PM – 5:15 PM

Authors

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-354169

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