Scientists Says Sediment Biggest Water Problem

Other Factors Encourage Algae Growth besides Sewer Plant Discharges, Research Shows

Friday, Apr 2, 2004

By Scott F. Davis

NW Arkansas Morning News

ROGERS -- The primary cause of dirty water in Northwest Arkansas streams may be the dirt in the water, instead of sewer plant discharges or phosphorus from poultry litter spread on pastures.

University of Arkansas scientists studying the impact of wastewater treatment plants in the Illinois River basin have found sedimentation to be more of a problem than they expected.

These preliminary findings point to the importance of following new federal storm-water rules and best management practices to reduce the amount of soil erosion during and after rainfall, said Martin Maner, chief of the water quality division of the Arkansas Department of Environmental Quality.

"Sediment is a grossly underrated impairment ... Sediment is everything" Marty Matlock, an associate professor of biological and agricultural engineering at the university, told utility officials last week at the northwest district meeting of the Arkansas Water and Waterworks Association in Rogers.

Matlock said he believes sediment is the leading cause of impairment in the Illinois River watershed.

He said, however, this is not yet the conclusion of the U.S. Environmental Protection Agency, which funded the study to determine the impact of discharge from wastewater treatment plants on the Illinois and Kings rivers and their tributaries.

The preliminary findings of the draft report are being reviewed by state and federal agencies and several changes are expected.

Sedimentation has long been recognized as a water quality problem. It's the leading cause of streams being added to EPA's national list of impaired streams.

Matlock said scientists on this project knew sedimentation was a problem but were surprised to find the problem so widespread.

Scientists and students took water samples and examined habitat and ecosystems of 16 sites along the Illinois and Kings rivers and tributaries. These include places above and below sewage treatment plant discharges from Springdale, Rogers and Prairie Grove, he said.

He said pristine sites -- along the upper Flint and Spavinaw creeks -- were studied to provide background data and also are affected by sedimentation.

Storm-water Controls

Maner is not surprised to hear the main problem appears to be sediment, rather than nutrients. EPA funded the study after the Department of Environmental Quality objected to adding Osage Creek to its impaired-water list.

Maner said his review of the study showed some isolated areas where streams are harmed by the sewage plants, but the bigger problem is sediment.

"That's what I've been crying for years," Maner said.

Unsurfaced county roads, construction activities with inappropriate control features and eroding stream banks are major sources of sediment that storm water washes into streams, Maner said.

Northwest Arkansas cities have combined their efforts in a regional approach to educate developers, construction company officials and others about following best management practices required under new federal storm-water rules that states will enforce. Sessions on the rules already have been presented to city leaders and construction industry officials, and more are planned.

Jeff Hawkins, executive director of the Northwest Arkansas Regional Planning Commission, said it makes sense for local cities to take a regional approach in addressing this issue.

Light Is Limiting Factor

Nutrient and sediment levels in the water aren't the only factors affecting streams.

The water quality deal worked out with the state of Oklahoma last year focused mainly on reducing phosphorus, because high levels of this nutrient promote excessive algae bloom, cause the water to look green and can lead to taste and odor problems when treating drinking water.

Matlock is not sure that simply reducing nutrient levels in streams will prevent algae bloom.

The streams in this region are so nutrient-rich that light becomes the limiting factor, he said. Additional light can increase algae growth.

Matlock said the scientists found sites upstream from sewer plants where algae growth was a bigger problem than downstream, because of the loss of the canopy in riparian areas along the upstream areas.

Matlock is not suggesting sewer plants do not affect streams, because he says they clearly do. The canopy provided by the trees alongside the streams and the condition of the riparian areas along the streams, however, are also important, he said.

Most of the canopy remains intact along Northwest Arkansas stream banks, but in Oklahoma where the river widens, much of the tree cover along stream banks is gone. Matlock said this is one reason Oklahoma has more of a problem with algae bloom.

He said that, if more trees are removed in riparian areas along Northwest Arkansas streams, the algae here will flourish, making streams appear much more polluted.

One of the biggest impacts of sewer treatment plants is the amount of water they add to the streams. During certain times of the year, the sewer plant flows may actually be beneficial, Matlock said.

Scientists estimate that 75 percent of the visible flow in the Illinois River at the end of August comes from Northwest Arkansas' wastewater treatment plants, Matlock said.

Matlock said the Illinois River would probably not have enough water to float canoes late in the summer, if not for the flows from the cities.