Study finds karst keeps tight grip on phosphorus
July 1, 2014
- Karst can keep a tighter grip on phosphorus than widely assumed, depends on conditions at each site
- Karst landscapes can slowly re-release retained nutrients over a decade or longer
FAYETTEVILLE, Ark. -- The porous nature of the land that underlies the Ozark Plateau doesn't necessarily mean high-speed transport of phosphorus away from fields on which fertilizer has been spread to nearby streams, according to an article published in the Journal “Environmental Science and Technology.”
Karst landscapes, such as those in the Ozarks, are often seen as highly vulnerable to loss of nutrients such as phosphorus from the surface because of underlying features that can range in size from small fissures to large caves. How fast the phosphorus moves depends on the unique characteristics of each site. In the case of this study, continuous layers of chert -- a silica-rich sedimentary rock -- separate the surface from the underlying limestone karst, slowing the flow of water, and phosphorus into the karst.
The article, “Phosphorus Retention and Remobilization along Hydrological Pathways in Karst Terrain,” published this spring, challenges the assumption that karst landscapes are always highly vulnerable to agricultural phosphorus and other nutrients found in manure and other fertilizers. The study was conducted at the Savoy Beef Farm in northwest Arkansas. Researchers from several university departments have been collaborating on joint research on nutrient flows in the karst at the Savoy farm for many years.
The article’s 10 co-authors include three of the scientists studying the impact of the hog farm in the Buffalo River watershed: Andrew Sharpley, professor, University of Arkansas System Division of Agriculture; John Van Brahana, University of Arkansas emeritus professor of Geosciences in Fulbright College, and Brian Haggard, director of the Arkansas Water Resources Center, part of the Division of Agriculture.
“Our results suggest that karst drainage may, in some cases, provide a greater phosphorus sink than previously considered,” Sharpley said. However, while karst may hold phosphorus more tightly than previously thought, the researchers noted that “the retained phosphorus may become a long-term source -- a decade or more -- of slowly-released ‘legacy’ phosphorus via soil drainage and springs to surface waters.”
The authors said further work would be needed to determine the ecological impacts of the release of these nutrients into receiving streams.
Other authors are Helen Jarvie and Colin Neal, Alan Lawlor, Darren Sleep and Sarah Thacker of the Centre for Ecology & Hydrology in the U.K.; and Tarra Simmons and April Price of the UA’s Division of Agriculture.
The study may be found online at http://pubs.acs.org/doi/abs/10.1021/es405585b.
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By U of A Division of Agriculture
Media Contact: Mary Hightower
Dir. of Communication Services
U of A Division of Agriculture
Cooperative Extension Service