Iowa's lakes among filthiest in the world

By PERRY BEEMAN
March 6, 2001

A first-of-its-kind study of Iowa's 132 lakes shows they are among the most fertilizer-polluted waters on Earth.

"We suspected Iowa has some of the most nutrient-rich water in the world, and this proves it," Iowa State University researcher John Downing said Monday. He plots the state's waters at the upper reaches of a worldwide chart.

Downing's conclusion is based on three rounds of samples from each of Iowa's 132 lakes, all taken last summer. The samples show heavy concentrations of nitrates and phosphorus, two common ingredients in farm and yard runoff.

The tests confirm past studies that suggested Iowa's lakes were paying a price for fertilizer use. The runoff feeds algae, which grows thick and chokes off bottom plants. Fish struggle to find food. The algae can also produce foul odors, discouraging recreation. Lakes die when they are overrun with algae.

Downing's finding is even more significant considering 2000 was relatively dry. Readings can jump in wetter years, he said.

Downing and ISU colleague Joy Ramstack warned that the study represents only the beginning of five years' worth of sampling at Iowa's 132 major recreational lakes. "It's a snapshot," Downing said of the initial tests.

Downing presented his study at a three-day water-quality conference at ISU. He said Iowa's lakes have some of the world's highest levels of algae-popping nitrogen and phosphorus. Biologists call those elements "nutrients" because they feed plant growth, including algae.

The samples showed that levels of health-threatening nitrates seemed to have risen slightly in the past 15 years. Phosphorus levels could be dropping, based on the first-year results.

Nitrates tended to be higher in lakes near crop fields and lower when pastures were nearby, Downing said.

The tests do not pinpoint the origin of the nitrogen and phosphorus, both of which also occur naturally. Nitrates can come from human or animal waste, decaying plants, lightning and rain, as well as from crop and lawn fertilizers. Phosphorus also comes from human and animal waste, occurs naturally in rich soils and can come from fertilizers.

Both elements, especially nitrogen, play a role in removing oxygen from a large area in the Gulf of Mexico from spring to fall, disrupting one of the world's richest shrimp-fishing areas.

Farm group officials have said their members try to cut soil erosion and use only as much fertilizer as needed. But soil runoff continues to be Iowa's biggest water-quality problem, Downing said.

"Most of the lakes are not terribly clear," he said.

Scientists said the five-year project will help farmers and homeowners learn more about how they can keep Iowa's waterways clean.

Mary Skopec of the Iowa Department of Natural Resources said an expanded network of river-sampling stations shows that phosphorus levels appear to have dropped over the past 15 years. However, more than half the stations recorded levels above proposed federal standards.