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Oct 14, 2008 12:23 PMPublication: The Southampton Press

Fish kill mystery remains unsolved

Oct 14, 2008 12:23 PM

Scientists have ruled out pesticides as the cause of death of thousands of fish in Water Mill’s Mill Pond in September, though what actually caused the fish kill remains a mystery.

On September 22, Dr. Chris Gobler, a researcher at Stony Brook University’s School of Atmospheric and Marine Sciences, began investigating the death of thousands of fish of several species at the pond. Though he had initially suspected that a blue-green algae bloom observed in the pond before the fish kill might have consumed much of the oxygen in the water, asphyxiating the fish, Dr. Gobler later learned that the oxygen levels just after the fish kill were higher than they usually are after a bloom-related fish kill occurs.

At dawn on the morning after the fish kill was reported, the oxygen levels in the pond were 4 milligrams per liter, lower than normal but higher than the level that would have caused the scientists to be concerned.

Dr. Gobler has continued to monitor oxygen levels in the pond, and said this week that they are now between 7 and 12 milligrams per liter, far higher than they were right after the fish kill occurred.

“Oxygen deprivation may have been a contributing factor, but as we look at fish themselves, that’s going to give us the biggest indication [of what actually killed them],” said Dr. Gobler. “We never measured a level of oxygen that was harmful to fish.”

Last week, Dr. Gobler received the first piece of analysis on the fish carcasses. The Suffolk County Health Department had assisted his research group in conducting tests for dozens of hazardous compounds that are commonly found in pesticides. “They all came back negative,” he said.

Three other tests, a histopathological analysis of the major organs of the fish, a test for bacterial infections and parasites, and a cyanotoxin analysis, are also in the works. Dr. Gobler said that the cyanotoxin test might be the most telling, though the results of that test will not be ready for months. The test measures certain toxins that are found in some strains of blue-green algae that are present in the pond and which may have killed the fish, and may have explained why the fish were still dying as the oxygen levels in the pond returned to normal.

“That’s gonna take a while,” he said. “It’s some tricky chemistry.”

And the results of the other two tests won’t be in for weeks, Dr. Gobler said.

“We do know that the low levels of oxygen would be due to the algae bloom. The root cause is getting at what causes the algae blooms,” he added. “They’re caused by the input of nutrients to Mill Pond. What can be done to alleviate these nutrient loads?”

Dr. Gobler added that, while attributing the long-term problems with the pond to road runoff, as many neighbors of the pond have done, would be “nice and simple,” he said that sometimes the best solution is not the simplest one.

“You can see the road runoff. It’s tempting to come to the conclusion that that’s the problem,” he said. “But you have to look at all the input to that system. The groundwater is very rich in nutrients, there’s atmospheric deposition, road runoff, what’s being generated inside the pond from the sediment and long-term storage of nutrients.”

Though Dr. Gobler said that his research group has “not in a robustly quantitative way” monitored the growth of lily pads and other aquatic vegetation that neighbors believe is contributing to the problem, he said that the group, which has been monitoring the pond since 2005, has noticed an increase in plants in the pond. He said that they could also be one source of the increase in nutrients.

Southampton Town Trustee Fred Havemeyer said this week that the Trustees, who oversee the waters in Mill Pond, have hired pond experts from Lycott Environmental and Interscience to do an extensive study of the health of the pond.

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