Present and future thermal regimes of intertidal groundwater springs in a threatened coastal ecosystem

Abstract. In inland settings, groundwater discharge thermally modulates receiving surface water bodies and provides localized thermal refuges; however, the influence of intertidal springs on coastal waters their sensitivity to climate change are not well studied. We addressed this knowledge gap with a field- model-based study threatened lagoon ecosystem in southeastern Canada. paired analyses drone-based imagery situ hydrologic monitoring estimate from groundwater-dominated streams summer 2020. Results, which were generally supported by independent radon-based estimates, revealed that combined summertime spring inflows (0.047 m3 s?1) comparable stream (0.050 s?1). Net advection values for also each other but 2 orders magnitude less than downwelling shortwave radiation across lagoon. Although lagoon-scale effects small compared atmospheric forcing, dominated heat transfer at local scale, creating pronounced cold-water plumes along shoreline. A numerical model was used interpret measured temperature data investigate seasonal multi-decadal patterns. Modelled temperatures relate respective aquifer source depths, while simulations forced historic projected assess long-term warming. Based 2020–2100 scenarios (for 5-year-averaged air increased up 4.32?), modelled subsurface 0.08–2.23? shallow (4.2 m depth) 0.32–1.42? deeper portion (13.9 m), indicating depth dependency This presents first analysis groundwater-dependent ecosystems indicates management should consider potential impacts