Featured Research

from universities, journals, and other organizations

Hydrologists find Mississippi River network's buffering system for nitrates is overwhelmed

Date:
May 11, 2014
Source:
University of Texas at Austin
Summary:
A new method of measuring surface water-ground water interaction along the length of the Mississippi River suggests the nitrates causing the Gulf of Mexico dead zone can not be controlled through existing natural filtration systems. The research provides valuable information for water quality efforts, including tracking of nitrogen fertilizers that flow through the river network into the gulf.

The map shows the fractional amount of surface water that is likely to enter the hyporheic zone, where it can undergo filtration. Orange and red represent areas experiencing a lower fraction of water entering the hyporheic zone. Dark blue areas approach 100 percent likelihood water will enter the zone.
Credit: Kiel and Cardenas, Jackson School of Geosciences, The University of Texas at Austin.

A new method of measuring the interaction of surface water and groundwater along the length of the Mississippi River network adds fresh evidence that the network's natural ability to chemically filter out nitrates is being overwhelmed.

Related Articles


The research by hydrogeologists at The University of Texas at Austin, which appears in the May 11 edition of the journal Nature Geoscience, shows for the first time that virtually every drop of water coursing through 311,000 miles (500,000 kilometers) of waterways in the Mississippi River network goes through a natural filtering process as it flows to the Gulf of Mexico.

The analysis found that 99.6 percent of the water in the network passes through filtering sediment along the banks of creeks, streams and rivers.

Such a high level of chemical filtration might sound positive, but the unfortunate implication is that the river's natural filtration systems for nitrates appear to be operating at or very close to full capacity. While further research is needed, this would make it unlikely that natural systems can accommodate the high levels of nitrates that have made their way from farmland and other sources into the river network's waterways.

As a result of its filtration systems being overwhelmed, the river system operates less as a buffer and more as a conveyor belt, transporting nitrates to the Gulf of Mexico. The amount of nitrates flowing into the gulf from the Mississippi has already created the world's second biggest dead zone, an oxygen-depleted area where fish and other aquatic life can't survive.

The research, conducted by Bayani Cardenas, associate professor of hydrogeology, and Brian Kiel, a Ph.D. candidate in geology at the university's Jackson School of Geosciences, provides valuable information to those who manage water quality efforts, including the tracking of nitrogen fertilizers used to grow crops in the Midwest, in the Mississippi River network.

"There's been a lot of work to understand surface-groundwater exchange," said Aaron Packman, a professor in the Department of Civil and Environmental Engineering at Northwestern University. "This is the first work putting together a physics-based estimate on the scale of one of these big rivers, looking at the net effect of nitrate removal in big river systems."

The Mississippi River network includes the Ohio River watershed on the east and the Missouri River watershed in the west as well as the Mississippi watershed in the middle.

Using detailed, ground-level data from the United States Geological Survey (USGS) and Environmental Protection Agency, Cardenas and Kiel analyzed the waterways for sinuosity (how much they bend and curve); the texture of the materials along the waterways; the time spent in the sediment (known as the hyporheic zone); and the rate at which the water flows through the sediment.

The sediment operates as a chemical filter in that microbes in the sand, gravel and mud gobble up compounds such as oxygen and nitrates from the water before the water discharges back into the stream. The more time the water spends in sediment, the more some of these compounds are transformed to potentially more environmentally benign forms.

One compound, nitrate, is a major component of inorganic fertilizers that has helped make the area encompassed by the Mississippi River network the biggest producer of corn, soybeans, wheat, cattle and hogs, in the United States.

But too much nitrogen robs water of oxygen, resulting in algal blooms and dead zones.

While the biggest source of nitrates in the Mississippi River network are industrial fertilizers, nitrates also come from animal manure, urban areas, wastewater treatment and other sources, according to USGS.

Cardenas and Kiel found that despite an image of water flowing freely downstream, nearly each drop gets caught up within the bank at one time or another. But not much of the water -- only 24 percent -- lingers long enough for nitrate to be chemically extracted.

The "residence times" when water entered the hyporheic zones ranged from less than an hour in the river system's headwaters to more than a month in larger, meandering channels. A previous, unrelated study of hyporheic zones found that a residence time of about seven hours is required to extract nitrogen from the water.

Cardenas said the research provides a large-scale, holistic view of the river network's natural buffering mechanism and how it is failing to operate effectively.

"Clearly for all this nitrate to make it downstream tells us that this system is very overwhelmed," Cardenas said.

The new model, he added, can be a first step to enable a wider analysis of the river system.

When a river system gets totally overwhelmed, "You lose the chemical functions, the chemical buffering," said Cardenas. "I don't know whether we're there already, but we are one big step closer to the answer now."

###


Story Source:

The above story is based on materials provided by University of Texas at Austin. Note: Materials may be edited for content and length.


Journal Reference:

  1. Brian A. Kiel, M. Bayani Cardenas. Lateral hyporheic exchange throughout the Mississippi River network. Nature Geoscience, 2014; DOI: 10.1038/ngeo2157

Cite This Page:

University of Texas at Austin. "Hydrologists find Mississippi River network's buffering system for nitrates is overwhelmed." ScienceDaily. ScienceDaily, 11 May 2014. <www.sciencedaily.com/releases/2014/05/140511165509.htm>.
University of Texas at Austin. (2014, May 11). Hydrologists find Mississippi River network's buffering system for nitrates is overwhelmed. ScienceDaily. Retrieved December 18, 2014 from www.sciencedaily.com/releases/2014/05/140511165509.htm
University of Texas at Austin. "Hydrologists find Mississippi River network's buffering system for nitrates is overwhelmed." ScienceDaily. www.sciencedaily.com/releases/2014/05/140511165509.htm (accessed December 18, 2014).

Share This


More From ScienceDaily



More Earth & Climate News

Thursday, December 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Ivory Trade Boom Swamps Law Efforts

Ivory Trade Boom Swamps Law Efforts

Reuters - Business Video Online (Dec. 17, 2014) Demand for ivory has claimed the lives of tens of thousands of African elephants and now a conservation report says the illegal trade is overwhelming efforts to enforce the law. Amy Pollock reports. Video provided by Reuters
Powered by NewsLook.com
Indictments in West Virginia Chemical Spill Case

Indictments in West Virginia Chemical Spill Case

AP (Dec. 17, 2014) A grand jury indicted four former executives of Freedom Industries, the company at the center of the Jan. 9, 2014 chemical spill in Charleston, West Virginia. The spill contaminated the Elk River and the water supply of 300,000 people. (Dec. 17) Video provided by AP
Powered by NewsLook.com
Uphill Battle to Tackle Indonesian Shark Fishing

Uphill Battle to Tackle Indonesian Shark Fishing

AFP (Dec. 17, 2014) Sharks are hauled ashore every day at a busy market on the central Indonesian island of Lombok, the hub of a booming trade that provides a livelihood for local fishermen but is increasingly alarming environmentalists. Duration: 00:42 Video provided by AFP
Powered by NewsLook.com
France's Sauternes Wine Threatened by New Train Line

France's Sauternes Wine Threatened by New Train Line

AFP (Dec. 16, 2014) Winemakers in southwestern France's Bordeaux are concerned about a proposed high speed train line that could affect the microclimate required for the region's sweet wine. Duration: 01:06 Video provided by AFP
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