Hundreds of Millions of Dollars Have Been Spent But Conditions in Long Island Sound Have Not Improved
So how are we doing? The Connecticut DEP put together a handful of interesting graphs illustrating water quality trends over the last 17 years and made them available recently. I think they show that if you judge by the worst conditions – that is, dissolved oxygen concentrations below 2 milligrams per liter – the Sound is getting better, or at least it’s not getting worse.
But if you judge by the goal of having as little as possible of the Sound fall below 3.5 milligrams per liter, conditions are getting worse.
Here’s the first graph (you can click on them to make them bigger):
It shows the number of square miles of the Sound in which dissolved oxygen fell below 3.5 milligrams per liter each summer since 1991. There have been some really bad years – 1994, 1995 and 2003, for example – but the trend is clearly up. Two of the five worst years were 2007 and 2006, and both were well over the median (286, in 1998).
What, on the other hand, happened in 1997, when only 51 square miles were affected? Possibly an August hurricane to mix things up?
This graph shows how long hypoxia lasted, when it started and when it ended. Conditions were clearly better in the mid 1990s through 2000 than they have been in recent years.
The first two graphs use 3.5 milligrams of oxygen per liter of water as a standard. Dave Simpson and his fellow researchers at the Connecticut DEP have figured out than when dissolved oxygen concentrations are between 3 and 3.9 milligrams per liter, the biomass of fish living in the deepest part of the Sound is reduced by 4 percent (compared to when conditions are optimal). What is biomass? I think it basically means the total weight of all the fish they catch during their standardized research trawls.
When dissolved oxygen is between 2 and 2.9 milligrams per liter, biomass is reduced by 41 percent. When it’s between 1 and 1.9, biomass is reduced by 82 percent – in other words, the amount of fish is only 18 percent of what it should be. And when DO falls below 1, the reduction is 100 percent. So the reason for wanting dissolved oxygen to be 3 or higher is obvious, as is the reason for not wanting it to drop too low.
Here are two graphs that show the number of square miles with DO below 1 and below 2. I’m not sure what to make of them, except to say that conditions were bad in 2003 but have gotten better since.