Thursday, September 14, 2006

Water Quality Has Rebounded

Long Island Sound was in better shape in late August-early September than it has been in a while. Only one small patch of water, covering 17.3 square km off Port Jefferson, had dissolved oxygen concentrations below 3 milligrams per liter. The entire western end of the Sound – Westchester, Nassau and part of Fairfield counties – had about 5 milligrams per liter of better, which is considered excellent. Since hypoxia (low levels of dissolved oxygen) is a summertime phenomenon, we can assume that the problem is finished for 2006.

The reason September was better, according to the Connecticut DEP, was the cool, rainy weather in late August. That brought water temperatures in the Sound down, and in particular it broke down the stratification that occurs when the deeper waters are cooler than the top waters. That stratification is essential for hypoxia. When it breaks down, the upper and lower layers of water mix, and the waters become infused with dissolved oxygen. Here’s what the DEP’s September Water Quality Sampling Summary says:

Between 25 August and 29 August, rain was abundant throughout the area; Kennedy airport recorded 2.6 inches, Bridgeport recorded 8.05 inches with more than 4 inches falling on 27 August, New Haven recorded 3.87 inches with 3.6 inches falling on the 28th, and Groton recorded 4.96 inches with 2.75 inches falling on 28 August. Rain generally tapered off on 30 and 31 August with only trace amounts being recorded at Kennedy, Bridgeport and Groton. New Haven, however, received 0.27 inches of rain on 30 August. …

Water temperature ranged from 19.6ºC to 22.1ºC. The maximum difference in temperature between the surface and bottom waters was 0.7 ºC (station 22). At sixteen stations the temperature of the bottom water was warmer than the surface water. Of those sixteen stations, ten stations exhibited a difference of 0.1ºC. The remaining six stations (05, 08, 09, 12, 16, 18), all located along the northern shore of the Sound between Stratford and Stamford, CT, exhibited differences between 0.21 and 0.41ºC.

The result was that the area of the Sound affected by hypoxia during this year’s September survey was 28 times smaller than the average September survey from 1991 through 2005.

The September map isn't online yet, but when it is, it will be here. The DEP says an analysis of the whole summer is forthcoming.

It's worth noting, by the way, that the rains that cooled off the Sound also washed enough bacteria into the Sound to close beaches and shellfish beds for days. So it's a mixed blessing.


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