Featured Research

from universities, journals, and other organizations

River Plants May Play Major Role In Health Of Ocean Coastal Waters

Date:
February 5, 2008
Source:
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering
Summary:
Aquatic plants in rivers and streams may play a major role in the health of large areas of ocean coastal waters. A new article describes the physics of water flow around aquatic plants. It may be used to guide restoration work in rivers, wetlands and coastal zones by helping ecologists determine appropriate vegetation patch length and planting density.

Blue dye swirls in a vortex along the horizontal boundary of a submerged canopy in Nepf’s lab. As the vortices pass over a canopy, they cause the plants to wave, a phenomenon named monami (Japanese for “waving water weed”). The vortices push water into the canopy and pull it back out again.
Credit: Marco Ghisalberti

Recent research at MIT’s Department of Civil and Environmental Engineering suggests how aquatic plants in rivers and streams may play a major role in the health of large areas of ocean coastal waters.

This work describes the physics of water flow around aquatic plants and demonstrates the importance of basic research to environmental engineering. This new understanding can be used to guide restoration work in rivers, wetlands and coastal zones by helping ecologists determine the vegetation patch length and planting density necessary to damp storm surge, lower nutrient levels, or promote sediment accumulation and make the new patch stable against erosion.

Professor Heidi Nepf is principle investigator on the research.* Brian White, a former graduate student at MIT who is now an assistant professor at the University of North Carolina, is co-author with Nepf of the JFM paper. Marco Ghisalberti, a postdoctoral associate at the University of Western Australia, worked with Nepf on some aspects of this research when he was an MIT graduate student. This work was supported by grants from the National Science Foundation.

Traditionally people have removed vegetation growing along rivers to speed the passage of waters and prevent flooding. But in recent years that practice has changed. Ecologists now advocate replanting, because vegetation provides important habitat.  In addition, aquatic plants and the microbial populations they support remove excess nutrients from the water.  The removal of too many plants contributes to nutrient overload in rivers, which can subsequently lead to coastal dead zones—oxygen-deprived areas of coastal water where nothing can survive. One well-documented dead zone in the Gulf of Mexico, fed by nutrient pollution from the Mississippi River, grows to be as large as the state of New Jersey every summer.

Nepf’s work—which describes how water flows into and through a plant canopy, and how long it remains within the canopy—can be used to find the right balance between canopy and flow in a river.

Vegetation generates resistance to flow, so the velocity within a canopy is much less than the velocity above it. This spatial gradient of velocity, or shear, produces a coherent swirl of water motion, called a vortex. Using scaled physical models, Nepf and Ghisalberti described the dynamic nature of these vortices and developed predictive models for canopy flushing that fit available field observations. The team showed that vortices control the flushing of canopies by controlling the exchange of fluid between the canopy and overflowing water. Similar vortices also form at the edge of a vegetated channel, setting the exchange between the channel and the vegetation.

The structure and density of the canopy controls the extent to which flow is reduced in the canopy and also the water-renewal time, which ranges from minutes to hours for typical submerged canopies. These timescales are comparable to those measured in much-studied underground hyporheic zones, suggesting that channel vegetation could play a role similar to these zones in nutrient retention. In dense canopies, the larger vortices cannot penetrate the full canopy height. Water renewal in the lower canopy is controlled by much smaller turbulence generated by individual stems and branches.

“We now understand more precisely how water moves through and around aquatic canopies, and know that the vortices control the water renewal and momentum exchange,” said Nepf. “Knowing the timescale over which water is renewed in a bed, and knowing the degree to which currents are reduced within the beds help researchers determine how the size and shape of a canopy will impact stream restoration.”

*This research appeared in the Dec. 25 issue of the Journal of Fluid Mechanics.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. Note: Materials may be edited for content and length.


Cite This Page:

Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. "River Plants May Play Major Role In Health Of Ocean Coastal Waters." ScienceDaily. ScienceDaily, 5 February 2008. <www.sciencedaily.com/releases/2008/01/080129162245.htm>.
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. (2008, February 5). River Plants May Play Major Role In Health Of Ocean Coastal Waters. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2008/01/080129162245.htm
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. "River Plants May Play Major Role In Health Of Ocean Coastal Waters." ScienceDaily. www.sciencedaily.com/releases/2008/01/080129162245.htm (accessed October 2, 2014).

Share This



More Earth & Climate News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: 12 More Bodies Found on Japan Volcano

Raw: 12 More Bodies Found on Japan Volcano

AP (Oct. 1, 2014) — A dozen more bodies were found Wednesday as Japanese rescuers resumed efforts to find survivors and retrieve bodies of those trapped by Mount Ontake's eruption. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Cultural Learning In Wild Chimps Observed For The First Time

Cultural Learning In Wild Chimps Observed For The First Time

Newsy (Oct. 1, 2014) — Cultural transmission — the passing of knowledge from one animal to another — has been caught on camera with chimps teaching other chimps. Video provided by Newsy
Powered by NewsLook.com
Raw: Trapped Scientist Rescued from Cave in Peru

Raw: Trapped Scientist Rescued from Cave in Peru

AP (Oct. 1, 2014) — A Spanish scientist, who spent 12 days trapped about 1300 feet underground in a cave in Peru's remote Amazon region, was rescued on Tuesday. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Media, Industry Groups React To Calif. Plastic Bag Ban

Media, Industry Groups React To Calif. Plastic Bag Ban

Newsy (Sep. 30, 2014) — California is the first state in the country to ban single-use plastic bags in grocery, liquor and convenience stores. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins