Friday, September 08, 2006

Water Quality In The Sound This Summer: Average to Better Than Average (Although Average Is Still Pretty Bad)

The Connecticut Department of Environmental Protection has recalculated its hypoxia data from early August, and it turns out that conditions in Long Island Sound were not as unusually bad as they seemed. In fact they were about average compared to similar periods in other years (which is still bad, but it could have been worse).

The area of the Sound with dissolved oxygen concentrations below 3 milligrams per liter was about 199 square miles (the total area of the Sound is about 1,300 square miles), which is 1.07 times bigger than the average area from 1991 through 2005.

The DEP sent out the correction yesterday afternoon, along with an analysis of mid-August data, which showed that water quality improved in the middle of the month, and in fact was better than during any similar period from 2002 through 2005. Here’s what the report said:

A total of 250 km2 [96 miles] were found to have DO concentrations less than the CT Water Quality criteria minimum threshold of 3.5 mg/L. A total of 132 km2 [51 miles] were found to have DO concentrations less than 3.0 mg/L.

And the area with the worst hypoxia – DO’s below 2 milligrams per liter – was smaller than in any year since at least 2002. Here are the number of square miles below 2 ppm: 2002 – 55.6. 2003 – 185.7. 2004 – 61.7. 2005 – 95. 2006 – 17.6.

The report also says:

Current conditions have improved from the [early August] survey (August 1-7, 2006) with no stations showing severe hypoxia (DO<0.99 mg/L), and are better than conditions observed during the August hypoxia surveys conducted between 2002 and 2005 …. Thermal stratification is diminishing with a maximum difference in the bottom and surface water of three degrees. The areal extent of hypoxia (DO <3 mg/L) documented during this survey was 3.65 times smaller than the average areal extent of 483 km2 from 1991-2005.

Why? The weather, probably. Winds speeds ranged from 8 miles per hour to 24 miles per hour (wind whips up the waves and injects oxygen into the water). And the days were cooler, with high temperatures in the low 80s (presumably this cools off the water a bit, which makes it capable of holding more oxygen).

So keeping in mind that average water quality condition on the Sound are bad (that's why we're spending so much money to try to improve them), this year was average to better than average.

The DEP hypoxia maps are all here.


Blogger Sam said...

If I may comment, a statistical running average is often a better measure than looking at "instantaneous" data. This is an attempt to flatten out the vagaries of changing weather conditions which well, change each and every year.

An example: in particulate matter air monitoring, it used to be that a few days of an exceedance (a bad air day) could trigger a violation of the standards. This is known as the "hair trigger" method.

Using a staistical, time-weighted method over each year and then combined with several years tell much more about the trends and magnitude of the problem, and whether things are working over the long haul.

I hope that makes sense without going into the math.

On a separate note, Dr. Jeff Masters has noted that El Nino is starting to form, which could have a profound effect on out winter weather. he last time El Nino formed this time of year was about 1950.

You'll have to catch it fast because he's watching the hurricanes every day.

3:58 PM  

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