Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A river ran through it

18.10.2010
Nature and humans leaving mark on rivers and streams, affecting aquatic food webs

Rivers and streams supply the lifeblood to ecosystems across the globe, providing water for drinking and irrigation for humans as well as a wide array of life forms from single-celled organisms up to the fish humans eat.


A now dry Colorado River delta branches into the Baja/Sonoran Desert near the Sea of Cortez. Credit: Pete McBride


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 John Sabo, a biologist at 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 affected rivers have dried and no longer run, while others have seen increases in the variability of flows due to storm floods.

The result is that humans and nature 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 do it in different ways," said Sabo.

Sabo is the lead author of a paper reporting results of a study of 36 rivers in this week's issue of the journal Science.

"The length of food chains is a crucial determinate of the functioning of ecosystems," says Alan Tessier, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research.

"Ecologists have long sought to explain why food chain length varies among different ecosystems. This study provides a quantitative answer to that question for stream ecosystems, and provides critical evidence for the importance of flow variation."

High flows "take out the middle men in the food web, making fish [the top predator] feed lower in the food chain," said Sabo. "Droughts completely knock out the top predator."

"The result is a simpler food web, but the effects we see for low flows are more catastrophic for fish--and are long-lasting."

Sabo and co-authors--Jacques Finlay, University of Minnesota, St. Paul; Theodore Kennedy, U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, Ariz.; and David Post, Yale University, New Haven, Conn.--suggest that the fate of large-bodied fishes should be more carefully factored into the management of water use, especially as growing human populations and climate change affect water availability.

The researchers studied rivers and streams in the U.S. ranging in size from the Mississippi and Colorado Rivers, down to small tributaries.

The rivers provide water to large cities like New York City, Minneapolis, Phoenix, Las Vegas and Los Angeles.

The study employed naturally occurring stable isotopes of the element nitrogen to measure how top-predators were faring in the food chain.

Nitrogen provides an indicator as it bioaccumulates, increasing by 3.4 parts per million with each link in the food chain.

"Floods simplify the food web by taking out some of the intermediate players so the big fish begin to eat lower on the chain," Sabo said.

"With droughts, it's completely different: droughts eliminate the top predator altogether because many fish can't tolerate the low oxygen and high temperatures that result when a stream starts drying out."

He added that climate change will play a growing role in coming years.

"Climate is giving us a new set of operating terms to work with," Sabo said. "We will experience overall drying and greater weather variability, both of which will shorten river food chains.

There will be drying in some regions, particularly along the equator, and increased flow in some rivers, primarily at higher latitudes, scientists believe.

"We will see more variability because there will be change in the seasonality of storms," said Sabo. "Ocean currents are changing, and the way the ocean blows storms our way is going to be different."

The human effect on rivers and streams, and the food chain they support, is closely tied to land-use change, such as water diversion and regulation of flows due to dams.

Sabo outlined a classic scenario that humans face during drought years.

As drought takes hold, the need for water for irrigation and agriculture increases and leads to a draw-down of natural river flows.

The effects downstream can be devastating.

"We would not have guessed that the infrequent drought that results would have a big effect on a stream, but our results show that it does," Sabo said.

"Some streams affected by drying five to ten years ago are still missing large-bodied fishes, compared with same-sized streams that never dried.

"Food webs can recover sooner after a flood, in roughly a year, but it takes far longer to recover in the case of drying or drought."

The study hints that competing users of a river's water--for agricultural production and recreational uses like fishing--need to work out amenable uses of rivers and streams that not only look to the immediate future, but also project long-term effects.

"The question becomes: can you have fish and tomatoes on the same table?" Sabo asked.

"They compete for the same resources, and society depends on both: agriculture for grain, fruits, vegetables, and fish for protein, particularly in the developing world.

"Humans may need to make hard decisions about how to allocate water so that we grow the right food, but still leave enough in rivers to sustain fish populations."

Cheryl Dybas | EurekAlert!
Further information:
http://www.nsf.gov

Further reports about: Rivers Sabo Science TV fish population floods food chain single-celled organism

More articles from Ecology, The Environment and Conservation:

nachricht How fires are changing the tundra’s face
12.12.2017 | Gesellschaft für Ökologie e.V.

nachricht Using drones to estimate crop damage by wild boars
12.12.2017 | Gesellschaft für Ökologie e.V.

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

A whole-body approach to understanding chemosensory cells

13.12.2017 | Health and Medicine

Water without windows: Capturing water vapor inside an electron microscope

13.12.2017 | Physics and Astronomy

Cellular Self-Digestion Process Triggers Autoimmune Disease

13.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>