Floods and Droughts Shorten River Food Chains

A new study headed by Arizona State University shows that human and climate change influences on river flow are impacting fish, shortening the length of river food chains by eliminating some of its members.  The study looked at 36 rivers across the U.S., including several in the Southwest—the Colorado, Salt, Gila, and Owens rivers. When variability in river flow increased, food chain length decreased, either due to the elimination of top predator fish or the disappearance of the fish typically preyed upon by the top predators.  Both floods and droughts reduced food chain length, but acted differently. Floods typically wiped out the intermediate fish, causing predators to eat lower on the food chain, whereas droughts simply reduced the number of top predator fish, due to low oxygen levels and warmer water temperatures that occur with lower water levels.

Although this study indicates that human regulation of river flows through dams has significant ecological impacts downstream, it also suggests that we have the ability to control flow to benefit downstream ecosystems. And, as climate change will increase the likelihood of extreme hydrologic events like droughts and floods, it gives us an indication of how fish will fare in a future, warmer world.  Here in the Southwest, the impact could be twice as great, as increased extreme rain events and flooding will occur in a mean climate that is projected to be much drier.