Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

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

12.05.2014

New method -- the first physics-based look at the net effect of nitrate removal in the Mississippi network -- shows the filtering system operating at max capacity

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.

Map, Mississippi River Network

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.

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."

J.B. Bird | Eurek Alert!
Further information:
http://www.utexas.edu/

Further reports about: Geosciences Groundwater River Texas USGS compounds downstream farmland filtration Systems method nitrate surface water

More articles from Earth Sciences:

nachricht For a rare prairie orchid, science is making climate change local
12.02.2016 | USDA Forest Service - Northern Research Station

nachricht NASA sees Tropical Cyclone Winston form
12.02.2016 | NASA/Goddard Space Flight Center

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Production of an AIDS vaccine in algae

Today, plants and microorganisms are heavily used for the production of medicinal products. The production of biopharmaceuticals in plants, also referred to as “Molecular Pharming”, represents a continuously growing field of plant biotechnology. Preferred host organisms include yeast and crop plants, such as maize and potato – plants with high demands. With the help of a special algal strain, the research team of Prof. Ralph Bock at the Max Planck Institute of Molecular Plant Physiology in Potsdam strives to develop a more efficient and resource-saving system for the production of medicines and vaccines. They tested its practicality by synthesizing a component of a potential AIDS vaccine.

The use of plants and microorganisms to produce pharmaceuticals is nothing new. In 1982, bacteria were genetically modified to produce human insulin, a drug...

Im Focus: The most accurate optical single-ion clock worldwide

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock which attains an accuracy which had only been predicted theoretically so far. Their optical ytterbium clock achieved a relative systematic measurement uncertainty of 3 E-18. The results have been published in the current issue of the scientific journal "Physical Review Letters".

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock...

Im Focus: Goodbye ground control: autonomous nanosatellites

The University of Würzburg has two new space projects in the pipeline which are concerned with the observation of planets and autonomous fault correction aboard satellites. The German Federal Ministry of Economic Affairs and Energy funds the projects with around 1.6 million euros.

Detecting tornadoes that sweep across Mars. Discovering meteors that fall to Earth. Investigating strange lightning that flashes from Earth's atmosphere into...

Im Focus: Flow phenomena on solid surfaces: Physicists highlight key role played by boundary layer velocity

Physicists from Saarland University and the ESPCI in Paris have shown how liquids on solid surfaces can be made to slide over the surface a bit like a bobsleigh on ice. The key is to apply a coating at the boundary between the liquid and the surface that induces the liquid to slip. This results in an increase in the average flow velocity of the liquid and its throughput. This was demonstrated by studying the behaviour of droplets on surfaces with different coatings as they evolved into the equilibrium state. The results could prove useful in optimizing industrial processes, such as the extrusion of plastics.

The study has been published in the respected academic journal PNAS (Proceedings of the National Academy of Sciences of the United States of America).

Im Focus: New study: How stable is the West Antarctic Ice Sheet?

Exceeding critical temperature limits in the Southern Ocean may cause the collapse of ice sheets and a sharp rise in sea levels

A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Symposium on Climate Change Adaptation in Africa 2016

12.02.2016 | Event News

Travel grants available: Meet the world’s most proficient mathematicians and computer scientists

09.02.2016 | Event News

AKL’16: Experience Laser Technology Live in Europe´s Largest Laser Application Center!

02.02.2016 | Event News

 
Latest News

LIGO confirms RIT's breakthrough prediction of gravitational waves

12.02.2016 | Physics and Astronomy

Gene switch may repair DNA and prevent cancer

12.02.2016 | Life Sciences

Using 'Pacemakers' in spinal cord injuries

12.02.2016 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>