Nitrate levels in Iowa rise with rain, but improve from 2013

This summer's nitrate pulse in Iowa rivers and streams was less severe than last year's, according to water quality experts.

'This year's peaks were not as high as last year's, and the high levels did not last as long,” said Stephen Kalkhoff, supervisor of the Water Quality and Environmental Health Unit of the U.S. Geological Survey Iowa Water Science Center.

Even so, nitrate concentrations in Iowa rivers frequently exceeded the Environmental Protection Agency's safe drinking water standard of 10 parts per million, said Susan Heathcote, water programs manager for the Iowa Environmental Council.

On June 25, for example, about 10 days into an exceptionally rainy period in Iowa, 12 of the 16 continuously monitored USGS gauges in the state registered nitrate concentrations ranging from 10.4 ppm on the North Raccoon River at Jefferson to 19.9 on Prairie Creek at Otho.

The reading that day on the Cedar River at Palo, the nearest gauge to Cedar Rapids, was 11.15.

Kalkhoff said this year's nitrate levels were not expected to match those recorded last year, when protracted heavy spring rains flushed out nitrate fertilizer left unused in farm fields during the 2012 drought.

Nitrate concentrations actually are decreasing during periods of normal and below-normal stream flow, according to Kalkhoff.

Unfortunately, heavy late spring and early summer rains, which flush water-soluble nitrates from the soil and wash away phosphorous clinging to soil particles, have fueled increasingly common nutrient pulses that threaten health and the environment.

Besides degrading Iowa waters, nitrogen and phosphorous pollution stimulates the growth of algae in the Gulf of Mexico, causing an extensive dead zone when the decomposing algae uses up oxygen otherwise available to aquatic animals.

Scientists are expecting an average hypoxic or 'dead zone” in the Gulf of Mexico this year, covering an area ranging from 4,633 to 5,708 square miles.

Readings from the continuously monitored gauge on the Cedar River at Palo illustrate how this year and last year compare in nitrate concentration and load.

During that same three-month period last year, more than 1,000 tons of nitrate passed the Palo gauge on 18 days, with a peak load of 1,900 tons on June 1. This year the nitrate load at Palo topped the 1,000-ton mark on eight days, with the peak load of 1,620 tons occurring June 24.

Similar results were recorded on gauges on two Cedar River tributaries monitored by Marty St. Clair, a professor of chemical and environmental studies at Coe College in Cedar Rapids.

On Lime Creek, which flows into the Cedar in Benton County, nitrate concentrations peaked above 20 ppm in late May last year and at 18 ppm in early July this year.

The peak nitrate concentration on Indian Creek, which enters the Cedar in Linn County, was slightly higher this year than last, according to Sinclair's data, although the duration above the 10 ppm safe drinking water standard was longer last year than this year for the two creeks.

Drinking water

'The nitrate pulse is back again this year,” though concentrations are not as high as last year on the Des Moines and Raccoon rivers, the two main sources for the Des Moines Water Works, according to Bill Stowe, its CEO and general manager.

Last year the facility spent more than $500,000 to operate its denitrification units. This year they have not been needed, although they might have been had the plant not tapped water from sources other than the two rivers, according to Stowe.

Stowe said it's clear the state's nutrient reduction strategy, which relies on farmers voluntarily adopting conservation practices to reduce levels of nitrogen and phosphorus fertilizer washing off farm fields into streams, 'is not working when three-fourths of the monitoring sites show higher-than-permissible levels of nitrates.”

Cedar Rapids does not treat water for nitrates because its source water, drawn from wells much deeper than the bed of the Cedar River, comes into the plant below the EPA safe drinking water standard.

Even so, city testing shows nitrate spikes that coincide with the April through June pulses, said Steve Hershner, the city's utilities director.

'We are worried about nitrates in our source water. We know what conservation practices work to reduce runoff, and we need more of them upstream in our watershed,” he said.