Thin Skin Beneath Streams Can Power Large Improvements in Water Quality plus 1 more

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Title: USGS Newsroom

Thin Skin Beneath Streams Can Power Large Improvements in Water Quality plus 1 more

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Thin Skin Beneath Streams Can Power Large Improvements in Water Quality

Posted: 11 Dec 2013 01:27 PM PST

Recent U.S. Geological Survey research has found that natural biochemical processes in water moving back and forth between a stream and its underlying sediment were significant in removing nitrate from streams in the Illinois River basin, one of the world’s most intensively farmed regions.

The USGS study in a nitrogen-polluted stream found that the flow of streamwater through a very thin zone of sediment enhances chemical reactions that decrease nitrate delivery to coastal areas where nitrogen fuels formation of hypoxic "dead zones."  

"One of the thorniest issues in the overall quality of our Nation's waters is relatively high levels of nitrates and other nutrients in many of our streams and rivers,” said Lori Caramanian, Department of the Interior Deputy Assistant Secretary for Water and Science. "A better understanding of the natural processes that reduce nutrients in our streams and rivers will help us mange our waterways in a more effective manner." 

Beneath all streams and rivers is a shallow layer of sediment that is permeated by water exchange across the sediment surface. This boundary between the world of earth and water in streams is referred to by scientists as the "hyporheic" zone, from Greek words meaning "under the flow." The hyporheic zone can be thought of as the stream's "skin," since it serves vital functions such as the removal of dissolved and particulate contaminants being transported by the stream.

Previous research has established under laboratory conditions that hyporheic flow should be critical to sparking reactions that improve stream water quality, but field studies have generally been unable to reveal the contribution of hyporheic flow to decreasing the flow of contaminants to sensitive downstream waters.

This field study determined that a very thin skin, a mere four centimeters (1.6 in.) of sediment, was effective in removing nitrate from streams of the Illinois River basin during late summer. The crucial investigative approach was labeling in-stream nitrate with an isotopic tracer that could be followed at very fine scales in the sediment and simultaneously tracked for kilometers downstream.

The study scientists found that hyporheic flow increased nitrate removal by renewing the supply of dissolved organic carbon and nitrate to specialized bacteria in the sediment that performed denitrification, a reaction that converts dissolved nitrate to gaseous nitrogen and so removes nitrate permanently from flowing water. 

The top four centimeters of sediment had the greatest abundance of denitrifying bacteria, in addition to the highest levels of hyporheic flow. Sediment properties in this thin layer were also conducive to the formation of oxygen-free micro zones that are required for the reaction to take place.

"USGS hydrologic research is focused on, among other things, improving our understanding of the biochemical processes at work in our waterways so that we can provide policy makers with information that will lead to better informed decisions." observed Jerad Bales, USGS Acting Associate Director for Water. "This work is an excellent example of how science is critically important for effectively addressing the one of the important environmental issues of our time."

Stream restoration is a billion dollar industry in the U.S., although its water quality benefits are not widely proven. Most restoration structures are designed in a manner that creates relatively deep hyporheic flow, which adds, this study demonstrated, only minimally to additional hyporheic flow and nitrogen removal in comparison to shallow hyporheic flow operating alone.

The study suggests how restoration structures might be modified to protect naturally functioning hyporheic zones and how hyporheic flow could be increased in order to stimulate greater removal of stream nitrate by denitrification.

These findings have immediate importance to the U.S. Environmental Protection Agency’s ongoing effort to evaluate federal jurisdiction in headwater streams, ponds, and wetlands where processes such as hyporheic flow may positively influence water quality and deliver additional benefits to downstream ecological health and recreational values of rivers and estuaries.  

The study was published in the October 2013 edition of Water Resources Research. The findings were presented December 11 at the fall meeting of the American Geophysical Union.

Learn more

• USGS Water Quality Watch
• Nitrate in the Mississippi River and its tributaries

The hyporheic zone, from Greek words meaning “under the flow,” lies under the streambed and serves as the “skin” of the stream.

Chelton Receives 2013 Pecora Award for Achievements in Ocean Remote Sensing

Posted: 11 Dec 2013 11:00 AM PST

The Department of the Interior's U.S. Geological Survey (USGS) and NASA presented the 2013 William T. Pecora Award for achievement in Earth remote sensing to Dudley B. Chelton, distinguished professor of Earth, Ocean, and Atmospheric Sciences at Oregon State University, Corvallis.

Chelton was recognized for his contributions to ocean remote-sensing science, education, and applications. The award was presented Wednesday by Suzette Kimball, USGS acting director, and Michael Freilich, director of the Earth Science Division in NASA's Science Mission Directorate, at the American Geophysical Union meeting in San Francisco. 

The Department of the Interior and NASA present the Pecora Awards to honor outstanding contributions in the field of remote sensing and its application to understanding Earth. The award was established in 1974 to honor the memory of William T. Pecora, former USGS director and Interior undersecretary. Pecora was influential in the establishment of the Landsat satellite program, which created a continuous, 40-plus-year record of Earth's land areas. 

"Every year the Pecora Award signifies the very high value that both the USGS and NASA place in observing Earth from space," said Kimball. "As our natural resources around the world continue to be stressed by a growing population and changing climate, it is more critical than ever that we have an objective, comprehensive view of the changes happening to our planet." 

Chelton is a pioneer in the oceanographic use of satellite data to explore the role of the ocean in the Earth's climate system. His work has led to new hypotheses in ocean studies and has inspired many follow-up investigations by the ocean remote-sensing community, increasing the practice and appreciation of ocean remote-sensing.

"Throughout his career, Dudley has been known for developing statistical methods to analyze existing satellite data while preparing for the next generation of remote-sensing instruments," said Freilich.

After receiving a Ph.D. in physics from the University of Colorado, Boulder, he moved to NASA's Jet Propulsion Laboratory in 1980 to analyze newly available data from Seasat. His 1981 paper in Nature demonstrated the ability of satellite instruments to make global observations of the ocean. Chelton moved to Oregon State University in 1983 where he established an ocean remote-sensing program that has grown into national prominence.

The comprehensive understanding of the technical and statistical aspects of ocean remote-sensing serves as the foundation of Chelton's major scientific discoveries. For over thirty years, he has led efforts to improve satellite-derived measurements of the four primary ocean variables that can be sensed remotely: sea surface height, surface winds, sea surface temperature, and ocean surface biological productivity.

Chelton is a Fellow of the American Geophysical Union and the American Meteorological Society and received a NASA Public Service Medal. Many of his 110 papers and book chapters have become standard references in his field.

Learn more

• William T. Pecora Award
• USGS Landsat
• NASA Landsat