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Nitrate on a Slow Decline: Watershed Water Quality Response during Two Decades of Tallgrass Prairie Ecosystem Reconstruction in Iowa
Journal article   Open access   Peer reviewed

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

Mark D. Tomer, Keith E. Schilling and Kevin J. Cole
Journal of environmental quality, Vol.48(3), pp.579-585
05/01/2019
DOI: 10.2134/jeq2018.07.0258
PMID: 31180425
url
https://doi.org/10.2134/jeq2018.07.0258View
Published (Version of record) Open Access

Abstract

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.
Environmental Sciences Environmental Sciences & Ecology Life Sciences & Biomedicine Science & Technology

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