Friday, October 21, 2011

Is Hypoxia in Long Island Sound Improving? It's Hard to Say

Everyone concerned about Long Island Sound wants to know if things are getting better or worse. The answer, of course, is yes.

Except where hypoxia is concerned. Then the answer is: who knows?

Hypoxia is defined as dissolved oxygen concentrations below 3.0 milligrams per liter. The Connecticut DEEP sent out its end-of-the-season hypoxia review the other day and it put 2011 in the context of the last 21 years, since 1991.

Average number of days hypoxia has lasted since 1991 -- 55.
In 2011 -- 54 days
in 2010 -- 40 days
in 2009 -- 45 days

So 2011 was average after a couple of better-than-average years.

Average number of square miles affected by hypoxia since 1991 -- 178
In 2011 -- 130 square miles
in 2010 -- 101 square miles
in 2009 -- 169 square miles

So for three years in a row it’s been better-than-average.

But I’m skeptical of averages because they can be skewed by the extremes. So I looked at the median.

Median number of days hypoxia has lasted since 1991 -- 55 (coincidentally, the same as the average).
in 2011 -- 54
in 2010 -- 40
in 2009 -- 45

Median number of square miles hypoxia has affected since 1991 -- 169.
in 2011 -- 130
in 2010 -- 101
in 2009 -- 169

So two of the last three years were below the median in both categories; and one year was just about at the median.

So it’s possible that things are getting slightly better. But it’s hard to know definitively. The DEEP says the full end-of-season report will be going up on their website. I couldn’t find it but will link to it when it’s up.

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