Submarine groundwater discharge (SGWD): an unseen yet potentially important coastal phenomenon in Canada

Abstract

Both terrestrial and fresh or marine forces drive underground fluid flows in the coastal zone. Hydraulic gradients on land result in groundwater seepage near shore and may contribute to flows from confined aquifers further out on the shelf. The terrestrial and oceanic forces overlap spatially, so measured fluid advection through coastal sediments may be a result of composite forcing. ''Subsurface/submarine groundwater discharge'' (SGWD) can be defined as any and all flow of water on continental margins from the seabed to the coast, regardless of fluid composition or driving force. SGWD is typically characterized by low specific flow rates, making detection and quantification difficult. However, because such flows occur over very large areas, the total flux is significant. Discharging fluids, whether derived from land or composed of re-circulated seawater, will react with sediment components. These reactions may substantially increase the concentrations of nutrients, carbon, and metals in the fluids. These fluids are thus a source of biogeochemically important constituents to the coast. Terrestrially derived fluids represent a pathway for the flux of new material to the coast. This may result in diffuse pollution in areas where the discharge of contaminated groundwater occurs. This review presents an historical context of SGWD studies, defines the process in a form that is consistent with our current understanding of the driving forces as well as our assessment techniques, and reviews the estimated global fluxes and biogeochemical implications. This review concludes that, to fully characterize marine geochemical budgets, one must give due consideration to SGWD. New methodologies, technologies, and modeling approaches are required to discriminate among the various forces that drive SGWD, pollutants to evaluate these fluxes more precisely to Canadian coast.

Arctic terrestrial hydrology: A synthesis of processes, regional effects, and research challenges

“…Climate model agreement on runoff changes is also particularly limited for Arctic basins [ Bring and Destouni , ; Törnqvist et al ., ]. Along the coast, information shortages combine to yield great uncertainty both in surface flows, which are poorly monitored for many smaller rivers, and the interaction between groundwater, surface water, permafrost, and seawater [ Bobba et al ., ; see also Carmack et al ., ]. To address these knowledge gaps in river fluxes, some proposed strategies to improve monitoring may help [e.g., Karlsson et al ., ; Azcárate et al ., ; McClelland et al ., ], as will a continuation of the Sustaining Arctic Observation Networks process.…”

“…An explicit focus on the hydrological interactions between land and sea across all of the coastal interface, and not just through rivers, would help overbridge disciplinary boundaries and expand knowledge on a relatively understudied part of the Arctic freshwater system. Also, our understanding of marsh hydrology, including hydrodynamics and hydroecology of the Arctic coastal zone, is limited [ Overduin et al ., ], as well as our knowledge of submarine groundwater discharge and the forming of salt‐fresh aquifers in coastal zones [ Bobba et al ., ]. Groundwater models of varying complexity [e.g., Danielescu et al ., ; Mazi et al ., ], potentially coupled to hydrological and oceanographic models, should be applied to Arctic conditions to increase understanding of the coastal zone.…”

Freshwater and its role in the Arctic Marine System: Sources, disposition, storage, export, and physical and biogeochemical consequences in the Arctic and global oceans

“…Increased precipitation will, in turn, support Arctic greening, thus altering drainage basin hydrology [ Bhatt et al ., ]. Groundwater discharges are likely to increase, but little systematic analysis has been carried out [see Bobba et al ., ]. While the fluvial flux of sediments to the Arctic Ocean are low, only about 1% of the global flux, owing to the low precipitation, thin weathering crust, low temperatures, and underlying permafrost, a model‐based analysis by Gordeev [] suggests that for every 2°C of atmospheric warming a 30% increase in sediment flux will occur, and for every 20% increase in water discharge a 10% increase in sediment flux could follow.…”