Cold Springs in a Warming Lagoon

Takeaway: Some of the coldest water in a summer lagoon can come from underground springs, but even those hidden cool spots are slowly warming from the top down.When coastal water gets too warm, the difference between stress and survival can come from places we barely see: cold groundwater seeping out of the shore. This episode visits Basin Head lagoon on Prince Edward Island, a shallow Marine Protected Area where a unique form of Irish moss has collapsed and summer water can get hot enough to matter for the whole food web. We unpack how researchers used drone thermal images, field sensors, stream measurements, radon tracing, and heat modeling to find hidden intertidal springs, estimate how much cool water they deliver, and ask whether those cool spots can last in a warming climate.The study shows a useful tension for coastal management: groundwater springs may not cool the entire lagoon much compared with sunlight and weather, but right where they emerge they create sharp cold-water plumes that could function as small thermal refuges. The catch is that groundwater is not frozen in time. Shallow aquifers can warm over decades, and springs fed from shallower depths may lose some of their cooling power sooner than deeper ones.Paper discussed: KarisAllen, J. J., Mohammed, A. A., Tamborski, J. J., Jamieson, R. C., Danielescu, S., and Kurylyk, B. L.: Present and future thermal regimes of intertidal groundwater springs in a threatened coastal ecosystem, Hydrol. Earth Syst. Sci., 26, 4721–4740, 2022, https://doi.org/10.5194/hess-26-4721-2022.Disclosure: This Waterlines episode uses AI-generated voices for the host conversation.