Impoverished streams

EurekAlert: Rivers and streams supply the lifeblood of ecosystems across the globe, providing water for drinking and irrigation for humans as well as a wide array of life forms in rivers and streams from single-celled organisms all the way up to the fish humans eat. But humans and nature itself are making it tough on rivers to continue in their central role to support fish species, according to new research by a team of scientists including one from Arizona State University.

Globally, rivers and streams are being drained due to human use and climate change. These and other human impacts alter the natural variability of river flows. Some impacted rivers have dried and no longer run, while still others have actually seen increases in the variability of flows due to storm floods. The end result is that these two forces are conspiring to shorten food chains, particularly by eliminating top predators like many large-bodied fish.

"Floods and droughts shorten the food chain but they accomplish this in different ways," said John Sabo, an Arizona State University associate professor in the School of Life Sciences. Sabo is the lead author of the paper, "The Role of Discharge Variation in Scaling of Drainage Area and Food Chain Length in Rivers," which appeared Oct. 15, 2010, in Science Express, the online, early publication venue for the journal Science.

"High flows take out the middle men in the food web making fish (the top predator) feed lower in the food chain; droughts completely knock out the top predator. The end result in either case is a simpler food web, but the effects we see for low flows are more catastrophic for fish, and much more long lasting," said Sabo, who studies ecology, evolution and environmental sciences….

Dniester river near Ţipova, Rezina County, Moldova, photographer unknown, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license