An unusual (but not abnormal) event—an overturn (also called a ventilation) of bottom waters—happened in the Upper Pond of Narrow River on Saturday, November 16, 2024. The resulting hydrogen sulfide (rotten egg) smell was strongest near Upper Pond in North Kingston but has been noticed as far away as the Walgreen’s on Boston Neck Road. A cloudy or milky hue clouded the waters of Upper Pond.
The overturn was discovered early Saturday morning by GSO Marine Research Specialist II Laura Reed and her husband, Howard, who went to Upper Pond for fishing, but ended up helping GSO Alum Coordinator and Narrow River Preservation Association (NRPA) President Veronica Berounsky, Ph.D.’90, take water column profiles with MERL’s YSI sonde and take water samples. Dave Borkman, M.S.’00, Ph.D.’02, took phytoplankton samples to count and identify. The team confirmed low oxygen (about 0.45 mg O2/L), and salinity (about 22 o/oo), and temperature (about 11ºC)—values that were mostly constant throughout the water column. There were normal oxygen values in Lower Pond that started at about 7 mg O2/L near the surface.
The bottom waters in the deep ponds of Narrow River — also called the Pettasquamscutt Estuary — are naturally anoxic (without oxygen). Overturns occur in the deep ponds of Narrow River when there are certain weather conditions. This overturn occurred because the very dry fall meant less freshwater entering Upper Pond via Gilbert Stuart Stream and King Tides bringing in more seawater from Rhode Island Sound. Seawater is colder, saltier and more dense, so when it flows into Upper Pond it sinks to the bottom and pushes the bottom water to the surface where winds help mix the water. So the anoxic bottom waters come to the surface and, when they come in contact with air, sulfur precipitates out, which makes the water look milky and smell like rotten eggs. These conditions may last for hours or up to weeks. As of last Thursday evening, despite the almost one inch of rain, the overturn water persisted.
Check out the Narrow River Preservation Association webpage for more details, maps, and photos. If you want to go take a look yourself, you can see Upper Pond from parts of Gilbert Stuart Road or you can walk into the King Benson Preserve and get close to the water.
Alex Kuffner, science writer for the Providence Journal published this article online about overturn. Also, there was coverage on Nov. 21, 2024, on the 5:30 p.m. WPRI news (channel 12). Both stories include wonderful drone footage by GSO Professor Emeritus Steve Carey, Ph.D. ’83.