LAKE ERIE

Expert discusses phosphorus at Great Lakes Symposium

Jon Stinchcomb
Reporter

TOLEDO - Researchers have been continuing to narrow down not only the primary chemical culprit leading to Lake Erie’s growing issue of harmful algal blooms, but also exactly how and when it causes the problem so efforts can better be made to combat it.

Laura Johnson, director of the National Center for Water Quality Research at Heidelberg University, discusses where Lake Erie's phosphorus pollution is coming from at the Toledo Zoo's Great Lakes Symposium.

Laura Johnson studies the issue of dissolved phosphorus runoff as the Director of the National Center for Water Quality Research at Heidelberg University.

She was among a panel of experts at the Toledo Zoo’s first Great Lakes Symposium on Wednesday where she discussed her research.

Johnson noted that algal blooms are not new to Lake Erie, and have in fact been dealt with before and successfully managed.

In the 1970s, blooms developed due to urban and industrial point-source runoff. By the 1980s and in through the ‘90s, regulations on phosphorus effectively and steadily reduced the total load drained into the lake. However, in recent years the harmful algal blooms reappeared and were worse than ever.

Point sources are a single, identifiable sources of pollution, such as a drain pipe. Non-point sources cover a much wider area and are harder to attribute to single contributors.

“We said, ‘Ok well, it seems like we have a pretty good handle on these point sources of phosphorus,’” Johnson said. “But now the rest of the phosphorus is mostly the non-point sources, the stuff that comes from land runoff. So we should be concerned about that.”

What they found was, with the total load of phosphorus remaining relatively stable, the more precise cause of the problem went previously unseen: dissolved phosphorus.

Dissolved phosphorus, in contrast to the particulate form attached to sediment, is far more bioavailable for algae to feed on.

Comparing individual watersheds’ dissolved phosphorus discharge levels within the Western Lake Erie Basin showed that those with higher percentages or agricultural land were the larger contributors.

“We can look (at the data) and say this is clearly coming off of the land,” she said. “That’s why we point to that as a concern.”

Still, even with the pinpointing of dissolved phosphorus as a more significant factor, total annual measures of how much of it was being discharged into the lake were fairly consistent over the last five years.

It could not account for why a bloom spiked in 2011, then dropped considerably the next year. Johnson noted that both years had almost the same total load of dissolved phosphorus, 570 to 614.

Further study of the data found that the strongest indicator of spikes in dissolved phosphorus that could eventually lead to major blooms were significant rain events occurring from the months of March through July, when the concentrations of dissolved phosphorus are at their highest.

“It’s how dense that phosphorus is,” Johnson said. “It’s the concentration that really matters, rather than the load.”

Johnson also pointed to a study that found farms are only losing about 1 percent of the phosphorus put down and are using the recommended levels.

“It really points to that a lot of farms are leaking a little bit of phosphorus,” she said. “It gave us the idea that maybe it’s in the wrong place, rather than at the wrong amount.”

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