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Tiny creatures indicate river’s health

By Brad Haire
University of Georgia

The tiny creatures that thrive in the Savannah River’s flood plain and the fish that feed on them can tell a lot about the river’s health, says a University of Georgia entomologist, and may help regulators better manage it.

A healthy river has a natural pulse, one that creates a flood plain when water flows over its banks during heavy rainfall, says Darold Batzer, a research entomologist with the UGA College of Agricultural and Environmental Sciences.

He studies water-dwelling invertebrates, or animals without backbones like fly and mosquito larvae and microscopic crustaceans. Invertebrates feed on the plant matter and are closer to the beginning of the food chain. This makes them an important link to a healthy animal population.

“The main river is tied to what happens in the flood plains,” he said. “Much of the energy for the fish comes from the flood plain. You break that connection and you can negatively impact the river.”

For a half century, the Savannah River’s flow has been controlled by a series of dams handled by the U.S. Army Corps of Engineers. This control has restricted the river’s natural flooding, or its pulse. And conservation groups are concerned, he said.

In cooperation with The Nature Conservancy, the corps now wants to manage the flow to improve the health of the river and the things that live in and around it.

“Some people think floods need to be controlled,” Batzer said. “But in many ways they are what make Southeastern rivers tick.”

With funding from TNC and the U.S. Geological Survey, Batzer has studied the invertebrates and fish in the river’s flood plain. Over the past three years, the corps has carried out new flow scenarios to mimic the river’s natural pulse in an effort to restore ecosystems.

To get an idea of what a less-regulated, more natural flood plain should be like, Batzer has studied the Altamaha River for the past six years. By knowing how many and what species of invertebrates and fish are in the Altamaha flood plain, regulators will know better what the Savannah flood plain should be like.

The Altamaha has one big flood, or pulse, at least once a year if there is no drought, he said. It’s having one right now. The water flows over the banks and remains for a few weeks filling swamps for a few months. Smaller pulses can reconnect the swamps throughout the year.

Batzer has set collection sites throughout both plains. He and his team use core samples and nets to collect the invertebrates and mild electric shock to collect the fish.

The Altamaha’s flood plain is much more dynamic than Savannah’s plain, he said. It contains hundreds of species of invertebrates and dozens of fish.

Creatures like the dytiscid beetles and fingernail clams are easily found in the Altamaha plain, but not in the Savannah plain. But mosquito larvae are more common on the Savannah plain, he said. With little to no flooding, the fish in the Savannah River can’t get to the larvae and eat them in the rain-fed pools created on the flood plain there.

It’s too early to know if the corps’ new efforts on the Savannah River are working, he said. “It will take many years to detect a recovery of the system.”

The Savannah River runs the border between Georgia and South Carolina and is about 350 miles long. The Altamaha River starts around Hazlehurst, Ga., in southeast Georgia and runs 140 miles south to the Atlantic Ocean.

(Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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