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Tech Prof Publishes River Research in ‘Nature Geoscience’

SOCORRO, N.M. October 28, 2015 – New assistant professor of hydrology Dr. Jesus Gomez-Velez is the author of a new study in the journal Nature Geoscience. His research was conducted while he was a post-doc with the USGS in Texas.

Working throughout the Mississippi River basin, Gomez-Velez collaborated with colleagues from the University of Texas at Austin to establish the river’s potential to decrease its load of nitrate and identified how certain basic river management practices could increase that potential. 

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Dr. Jesus Gomez-Velez (left) at work in the Animas River.

 

 
 

For the complete Nature Geoscience article, click here. 

Gomez-Velez is a two-time graduate of Tech, having earned his master’s in 2008 and his Ph.D. in 2014. He won the Founders Award at the 2014 commencement, an award that is given to the graduate student who made an outstanding contribution to the university over the previous year. Another co-author is Dr. M. Bayani Cardenas, an associate professor at the University of Texas who earned his Ph.D. at New Mexico Tech in hydrology in 2006.

"Increasing nitrogen concentrations, mostly due to the runoff of agricultural fertilizers, in the world's major rivers have led to over-fertilization of waters downstream, diminishing their commercial and recreational values,” said William Werkheiser, USGS associate director for water. “Understanding the natural potential of rivers themselves to remove nitrogen from the water, and boosting that potential, is a promising avenue to help mitigate the problem." 

Beneath all streams and rivers is a shallow layer of sediment that is permeated by water exchange across the sediment surface. This thin region in the sediment beneath and to the side of the stream is referred to by scientists as the "hyporheic" zone, from Greek words meaning "under the flow." 

"We’ve found in previous studies,” Gomez-Velez said, “that the flow of stream water through this thin zone of sediment enhances chemical reactions by microbes that perform denitrification, a reaction that removes nitrogen from the aquatic system by converting it to nitrogen gas.” 

The research team determined that, throughout the Mississippi River network, vertical hyporheic exchange (with sediments directly beneath streams and rivers) has denitrification potential that far exceeds lateral hyporheic exchange with bank sediments.

"Rivers with more vertical exchange are more efficient at denitrification, as long as the contact time with sediment is matched with a reaction time of several hours," said co-author Jud Harvey, the USGS team leader for the study.  

The study findings suggest that managing rivers to help avoid the sealing of streambeds with fine sediments, which decreases hyporheic flow, would help exploit the valuable natural capability of rivers to improve their own water quality. Other river management and restoration practices that protect permeable river bedforms could also boost efficiency, such as reducing fine sediment runoff to rivers. 

However, typical river channel restoration strategies that realign channels to increase meandering would not be as effective, because a comparatively small amount of water and river nitrate are processed through river banks compared with river beds. Although not yet tested in the model, allowing natural flooding over river banks onto floodplains may also be an effective means of processing large amounts of river water to remove nitrogen before it reaches sensitive coastal waters. 

– NMT –