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The Illinois and Upper Mississippi Rivers are changing. Here's how

The Illinois River as seen from the shoreline in East Peoria.
Tim Shelley
The Illinois River as seen from the shoreline in East Peoria.

There's more water flowing through the Illinois and upper Mississippi rivers now than in the past few decades.

That's one of the key takeawaysfrom a recent report on ecological trends in the river systems. It's part of a study monitoring long-term changes in the rivers over the past three decades.

Kathi Jo Jankowski is a research ecologist with the U.S. Geological Survey, which collaborated on the report with the U.S. Army Corps of Engineers Rock Island District.

She said the increase in discharge means researchers are noticing more water, more of the time in the river channels. That means higher averages, and higher minimum and maximum water flows.

"As river scientists, we like to describe discharge of the volume of water as the master variable in a river system, because it really controls everything else that's happening," Jankowski said. "It carries sediment from the watershed into the river, it carries nutrients. It also can erode the banks that affects where we have habitat. That can affect the shoreline forests. So it's a really important finding that we are seeing increasing."

The reasons why discharge is increasing in the Illinois and upper Mississippi rivers isn't as clear. Jankowski said while this study didn't specifically investigate the causes, the trends are generally attributed to three factors: climate change, land usage like construction and farming in watersheds, and engineered structures like levees and dams altering water flow.

"It's a complex combination of these things, and it's probably more some in some areas than others. But there's other studies that are trying to really dig into that question," Jankowski said.

Another big ecological change over the past three decades is the widespread proliferation of invasive copi, formerly known as Asian carp. Jankowski said they now make up to half of the Illinois River's total biomass.

Copi are outcompeting native fish for the same food, leading to a decline in native species' populations. That in turn has led to a decline in recreational and commercial fishing on the river.

Jankowski said invasive species are also making inroads into floodplain forests. Native plant species are being negatively impacted, in part by changes in watershed flooding attributed to locks and dams.

"As those die off, those gaps get filled in by invasive species, like red canary grass and Japanese hops. So invasive species are also not only impacting the river itself, but also the forests," she said.

Jankowski said forests are an integral part of the river system, serving as a wildlife habitat and a "filter" for the river itself, particularly during flood events.

Sedimentation is also affecting river health. Large rain events wash sediment and soil from erosion downstream. That can reduce sunlight penetration into the water, limiting the growth of the plants and algae which underpins the river ecosystem. Backwater lake habitats are also filled in by accumulating sedimentation over time.

Jankowski said the data gathered through the study provides focus for conservation and restoration work.

"This report is a is the fruit of a long term partnership of many people in many agencies. And so I think it's really a testament to people's ability to partner together and have a focus on improving and restoring the health of the Mississippi River, which is such an important river system for this whole entire region," she said.

Tim is the News Director at WCBU Peoria Public Radio.