24 Feb 2022
24 Feb 2022
Status: this preprint is currently under review for the journal HESS.

Intertidal spring discharge to a coastal ecosystem and impacts of climate change on future groundwater temperature: A multi-method investigation

Jason KarisAllen1, Aaron Mohammed1,2, Joseph Tamborski3, Rob Jamieson1, Serban Danielescu4,5, and Barret Kurylyk1 Jason KarisAllen et al.
  • 1Department of Civil and Resource Engineering and Centre for Water Resources Studies, Dalhousie University, Halifax, B3H 4R2, Canada
  • 2Department of Earth and Planetary Sciences, McGill University, Montreal, H3A 0E8, Canada
  • 3Department of Ocean and Earth Sciences, Old Dominion University, Norfolk, VA, 23529, USA
  • 4Water Science and Technology Directorate, Environment and Climate Change Canada, Burlington, ON L7S 1A1, Canada
  • 5Agriculture and Agri-Food Canada, Fredericton Research and Development Centre, Fredericton, New Brunswick E3B 4Z7, Canada

Abstract. In inland settings, groundwater discharge is known to thermally modulate receiving surface water bodies and provide localized thermal refuges; however, the thermal influence of intertidal springs on coastal waters and the thermal sensitivity of these springs to climate change are not well studied. We addressed this knowledge gap with a field- and model-based study of a threatened coastal lagoon ecosystem in south-eastern Canada. We paired in-situ thermal and hydrologic monitoring with analyses of drone-based thermal imagery to estimate the discharge to the lagoon from intertidal springs and groundwater-dominated streams in summer 2020. Results, which were generally supported by independent radon-based groundwater discharge estimates, revealed that the combined summertime spring inflows (0.047 m3 s-1) were comparable to the combined stream inflows (0.050 m3 s-1). Heat flux analyses indicated that the net advection for the streams and springs were also comparable to each other but were two orders of magnitude less than the downwelling shortwave radiation across the lagoon. Although the lagoon-scale thermal effects of groundwater inflows were small compared to atmospheric forcing, spring discharge dominated heat transfer at a local scale, creating pronounced cold-water plumes along the shoreline.

A numerical model was used to investigate seasonal and multi-decadal groundwater temperature patterns to relate measured spring temperatures to their respective aquifer source depths, and to consider long-term groundwater warming. Based on the different climate scenarios used for 2020 to 2100 (5-year averaged air temperature increase up to 4.32 °C), modelled 5-year averaged subsurface temperatures increased 0.08 to 2.23 °C in shallow groundwater (4.2 m depth) and 0.32 to 1.42 °C in the deeper portion of the aquifer (13.9 m), indicating the depth-dependency of warming. This study presents the first analysis of the thermal sensitivity of groundwater-dependent coastal ecosystems to climate change and indicates that coastal ecosystem management should consider the potential impacts of groundwater warming.

Jason KarisAllen et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-49', Anonymous Referee #1, 15 Apr 2022 reply

Jason KarisAllen et al.

Data sets

Dataset for KarisAllen et al. (2022, HESSD) Jason J. KarisAllen, Aaron A. Mohammed, Joseph J. Tamborski, Rob C. Jamieson, Serban Danielescu, Barret L. Kurylyk

Jason KarisAllen et al.


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Short summary
We used a combination of aerial, thermal, hydrologic, and radionuclide monitoring to investigate inter-tidal springs flowing into a coastal lagoon with a threatened ecosystem. Field data highlight the critical hydrologic and thermal role of these springs in the nearshore zone, and modeling results reveal that the groundwater springs will likely warm substantially in the coming decades due to climate change. Springs sourced from shallower zones in the aquifer will warm first.