Farms producing grain in the Great Plains of Nebraska, Kansas, Colorado, and Texas account for roughly 17% of all the grain produced throughout the world, with water used to irrigate these crops coming from the High Plains Aquifer, the largest groundwater source in the country. New research has revealed that 50 years of groundwater extraction has caused long sections of rivers to dry up, to the detriment of large-stream Fish populations.

The scientists caution that unless groundwater pumping is curtailed, these aquatic habitats will shrink even further, together with the fish they support.

Considering that 90% of all water used by humans globally is used for crop irrigation, the results of this study have widespread implications for other watersheds all across the world, particularly in areas where aquifers are running dry.

According to co-author, Kurt Fausch, a professor at Colorado State University, the results of the study are concerning. Earlier field studies and modeling conducted by Jeff Falke, assistant professor at the University of Alaska Fairbanks and a past student of CSU, show that the Arikaree River to the east of Colorado, which used to flow for around 70 miles, is expected to be reduced to just one-half mile by 2045.

"You have this train wreck where we're drying up streams to feed a growing human population of more than 7 billion people," said Fausch, who describes the scenario as a "wicked problem," that has no good solution. "More water is pumped out every year than trickles back down into the aquifer from rain and snow," he said. "We are basically drying out the Great Plains."

Over the last 60-70 years, around 100 trillion gallons of water — equivalent of the volume of water in Lake Erie — has been pumped from the aquifer, and practically none of the water extracted feeds back into the underground aquifer.

"This pumping has dried up long segments of many streams and small rivers in the region," Fausch said. From 1950 to 2010, a total of 350 miles of stream dried up in the large area the team studied in eastern Colorado, southwestern Nebraska and northwestern Kansas. "Our models project that another 180 miles of stream will dry up by 2060," Fausch said.

Its not just the loss of water that is concerning, fish populations are also taking a knock. Fish that are dependent upon habitat that is only found in rivers and larger streams in the region are being replaced by species that are able to survive in the smaller streams that remain, said Fausch. Whole populations of fish species are being lost from rivers within that region, as the habitat that supports their existence disappears.

To illustrate this point, only 9 of the 16 indigenous fish species that used to inhabit the Arikaree River are left. Seven species, including catfish, suckers and small minnows, have completely disappeared. However, because these fish species are not currently endangered, there are no regulations in place to protect their habitats.

The negative effect of groundwater extraction will not only affect fish in these rivers, but also the farmers themselves, as well as the places that depend on or benefit from water in these rivers, which without water, could disappear too.

"If they lose the river, they'll not only lose fishes, but they'll also lose water for their cattle, and cottonwoods that provide shade," Fausch explained. "They also lose the grass that grows in the riparian zone, which is critical forage for cattle in summer. Some of that's your livelihood, but it's also the place you go for picnics, and to hunt deer and turkeys. If you lose the river, you lose a major feature of what that landscape is."

But despite the sombre findings, Fausch says that some progress is being made to address the issue. Meters have been installed on wells to monitor the amount of water farmers pump from the aquifer to ensure they stick to within the quotas allocated to them. By the same token, farmers continue to experiment with new technologies that will enable them to maximize crop yield and minimize water usage, as pumping water from underground aquifers incurs a cost for electricity usage. Cutting costs obviously increases profits, so it is in their interests to optimize water usage. However, Fausch cautions that this doesn't imply that levels of aquifers that feed into streams are no longer dropping, but rather they are dropping more slowly than they were in the past.

So what are the options? One alternative may be for farmers to transition to growing dryland crops — crops that depend on rainfall only — rather than crops that require pumping water for irrigation. But the problem here is that annual crop yields can vary widely depending on how much rain is received during the year. Another option is for farmers to switch to more economical water-wise irrigation methods, such as drip irrigation as soon as they are locally available.

Fausch, who has spent his entire career studying rivers, grows wistful as he contemplates the fate of these rivers.

"When we lose these rivers, we will lose them for our lifetime, our children's lifetime, and our grandchildren's lifetime," he said.

Even if we stopped all pumping tomorrow, it would take a very long time — probably 100 years, possibly more — for the aquifer to refill and rivers to start flowing again, said Fausch, providing some perspective.

Journal Reference

Joshuah S. Perkin et al, Groundwater declines are linked to changes in Great Plains stream fish assemblages, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1618936114