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It’s been more than 30 years since Lake Erie was known as a “dead lake,” but portions of it are dying again.
In the 1970s, there were so many nutrients in the water – mainly in the form of phosphorus – that algae would grow like crazy. When the algae died off, its decay used up the oxygen in the water, suffocating marine life.
About the same time, states started banning phosphorus in laundry detergents, and the water quality lab at Heidelberg College in Tiffin, Ohio, started collecting water samples from the Maumee River.
An automatic sampler at Waterville, Ohio, just upstream from Toledo, takes about 400 samples a year for analysis.
“We’ve been doing this for about 30 years,” said Peter Richards, the senior research scientist at the National Center for Water Quality Research at Heidelberg. “This is a huge amount of information – we’ve got probably 10 to 50 times as much as anybody else has to look at.”
And what do those data tell them?
From 1975 to 1995, the amount of dissolved phosphorus in the water dropped about 80 percent. But then, just a year after the detergent industry voluntarily stopped using phosphorus, the level started going up again.
“Now it’s almost back to the same level it was in 1975,” Richards said.
By 2001, dead zones were forming again in Lake Erie, and once again no one knows why.
Unlike many scientists, however, Richards is in more of a position to offer theories, since he has three times as many years of data to back him up.
Richards said it appears that more farmers are fertilizing in the fall rather than in spring, which gives more time for the nutrients to run off the field before they can be used up by the crops.
Some are also fertilizing less often but using more of it, he said. If a field regularly rotates between corn, soybeans and winter wheat, many farmers will now fertilize for all three years in one pass.
“That means only one field in three is getting fertilizer in a particular year, but it’s getting three times as much,” Richards said. “Whether that all comes out in the wash, we don’t know.”
It also appears that more fertilizer is being put on the surface rather than injected into the soil, making it vulnerable to being washed away.
There’s another theory as well: Farmers apply the amount of phosphorus needed to feed a large crop, but when less crop is produced, not all of the phosphorus is used up. Over the years, the amount of phosphorus in the soil keeps increasing – making more available to be washed into rivers and eventually Lake Erie.
Are those changes causing the dead zones?
“We don’t know,” Richards said. “We’re trying to evaluate the linkages between what’s going on in the lake and what we’re seeing in the watersheds.”
dstockman@jg.net
