Nitrate on a Slow Decline: Watershed Water Quality Response during Two Decades of Tallgrass Prairie Ecosystem Reconstruction in Iowa

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Tomer, Mark
Schilling, Keith
Cole, Kevin
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Iowa Nutrient Research Center
The Iowa Nutrient Research Center was established to pursue science-based approaches to evaluating the performance of current and emerging nutrient management practices and providing recommendations on practice implementation and development. Publications in this digital repository are products of INRC-funded research. The INRC is headquartered at Iowa State University and operates in collaboration with the University of Iowa and the University of Northern Iowa. Additional project information is available at:
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College of Agriculture and Life SciencesIowa Nutrient Research Center

The Neal Smith National Wildlife Refuge was established as a tallgrass prairie ecosystem reconstruction in the Walnut Creek watershed (5238 ha), Jasper County, Iowa, with >1200 ha of prairie plantings initiated between 1993 and 2006. This study updates the documented decreases in watershed NO3–N losses that accompanied this change in land cover to a 20-yr record. Annual flow-weighted NO3–N concentrations declined by 0.15 mg NO3–N L−1 yr−1, which was not significantly different from the rate of 0.07 mg NO3–N L−1 yr−1 reported after the first decade of monitoring. There was also evidence (p < 0.1) that prairie reconstruction led to a declining trend in annual watershed water yield, which would have contributed to the trend of decreasing NO3–N loads. However, variability in climate, including 2 yr with significant flooding events followed by a major drought during the second decade of monitoring, challenged any notion that a watershed water quality record will stabilize even >10 yr after a substantial change in land cover, in this naturally drained watershed underlain by fine grained glacial deposits that exhibit multidecadal groundwater transport times. Efforts to document progress toward water quality goals will need to consider dominant flow paths and associated travel times, uncertainty in the effectiveness of management changes, and a changeable climate.


This is an article published as Tomer, Mark D., Keith E. Schilling, and Kevin J. Cole. "Nitrate on a Slow Decline: Watershed Water Quality Response during Two Decades of Tallgrass Prairie Ecosystem Reconstruction in Iowa." Journal of environmental quality 48, no. 3 (2019): 579-585. Posted with permission of INRC.

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