Wednesday, July 13, 2005

Dissolved Oxygen Levels are Low off New Rochelle

Dissolved oxygen levels in the bottom waters (54 feet deep) near Execution Rocks are at 1.6 milligrams per liter this morning, which is very low.

In 2003 and 2004, DO concentrations didn’t drop that low until mid- to late-August, but then they dropped even lower, to below 1 milligram per liter. In 2002, concentrations dropped below 2 in late July and then were bad throughout August. In 2001, concentration didn’t go below 2 until mid to late August and never went lower. Here are the Connecticut DEP's hypoxia maps.

Execution Rocks, off New Rochelle, is just one dot on the map. A bit further east, about three miles off Greenwich, DO concentrations are 4.1 milligrams per liter, which is fine. DEP should be posting its hypoxia maps soon, which will tell us if the Execution Rocks reading is an isolated low spot or if a general hypoxia is settling in.

Dissolved oxygen concentrations fall every summer. With the Long Island Sound cleanup well under way, the annual questions are: how low will they fall and how big of an area will be affected. There have been no catastrophic fish kills on the Sound since the late 1980s but the last two or three summers have been surprisingly bad in terms of water quality and temporary habitat loss. What will happen this summer, obviously, remains to be seen.


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