University of Louisville graduate student Allison Smith is collecting something nearly invisible from the Ohio River. Zooplankton.
“Zooplankton are small invertebrates. People would be most familiar with them as the food fish eat. So the zooplankton eat the primary producers, the algae, then they’re eaten by fish and pretty much everything else. So they’re an important link in that food web,” Smith says.
A web, Smith says, that could be threatened by climate change. Smith says an invasive species of zooplankton that’s recently moved into the Ohio may fare better than the natives in the warmer temperatures she’s observing. So she’s running an experiment to find out. She’ll put them in tanks together and simulate life in the river, in the lab.
“I’m going to have three incubators at different temperatures, ranging from about 25 degrees up to about 32 degrees. These are temperatures that are typically seen in tropical systems. But we’re detecting those temperatures here, in a temperate region, frequently.”
The idea is to see which organism wins the competition for resources at which temperature. Smith thinks the invasive species will most likely be better able to adapt in the warmer temperatures. If her hypothesis proves true, she says the consequences could be dramatic.
“Let me give you just one example. Another thing that’s unique about this invasive species is that it has defensive mechanisms to prevent it from getting eaten. So it has this huge helmet on its head, a long pointy tail. So, that means that they are less likely to get eaten by fish,” says Smith.
That’s why this invasive species, Daphnia lumholtzi, could have a big advantage in the Ohio.
Now, if lumholtzi is able to competitively displace native species who don’t have those defense mechanisms, fish will be having to rely on Daphnia lumholtzi, which they are able to eat less effectively. So if we change that community structure, and we start replacing it with species that are less palatable to fish, that could impact how many fish are able to survive and grow to adulthood, which then impacts so many other things, and we have these cascading effects up the food web.”
Smith is contributing to a small but growing body of research into how climate change could affect freshwater systems. But scientists want to know more so that they can start offering up suggestions to local decision-makers for how to deal with the impacts. The U.S. Geological Survey’s director of water science for Indiana and Kentucky, Bill Guertal, says we still lack some pretty basic data: trends in river temperatures.
“And we are working on that right now, with Fish and Wildlife, trying to look at what data we have available, and I have not seen the results come back on that information yet,” Guertal said.
Guertal says he’s hoping for government funding to help his researchers answer one of his top questions about the Ohio.
”If you’re going to assume that things are going to generally get warmer, what’s that going to do to native fish species, and then potentially, what that could do to invasive species, or a shift in the pattern of where the fish are, and will that cause you problems?”
Guertal is a hydrologist by training, and he says he’s also looking into how changes in precipitation caused by global warming could affect river levels on the Ohio and, ultimately, navigation, and even the availability of drinking water. Guertal says his research is aimed at helping people adapt to climate change. But Environmental Defense Fund conservation scientist Stacy Small says there may be ways to mitigate the effects of climate change on the river by restoring riparian, or river bank, environments.
“As riparian vegetation has been stripped from river banks over the last century, water temperatures do increase, the water is exposed to more sunlight. Riparian vegetation provides important shade that cools water temperatures. That’s really important for fish, that’s really important for the whole aquatic ecosystem,” says Small.
Small says the Ohio River’s industrial water fronts have swept away some of that vital vegetation and left fish with less refuge from warmer temperatures. She advocates reclaiming those water fronts with trees and grasses.
“They have actually, in the face of climate change, a lot more value, if restored to a natural state,” says Small.
Cities along the Ohio have begun to reclaim some sections of waterfront, which could do more than simply offer shade to fish. Replanted river banks could help absorb flooding if the region sees more precipitation.