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Nitrate on a Slow Decline: Watershed Water Quality Response during Two Decades of Tallgrass Prairie Ecosystem Reconstruction in Iowa
Author(s) -
Tomer Mark D.,
Schilling Keith E.,
Cole Kevin J.
Publication year - 2019
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2018.07.0258
Subject(s) - watershed , environmental science , streamflow , hydrology (agriculture) , water quality , ecosystem , land cover , flooding (psychology) , climate change , land use , geography , ecology , drainage basin , geology , psychology , cartography , geotechnical engineering , machine learning , computer science , psychotherapist , biology
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 NO 3 –N losses that accompanied this change in land cover to a 20‐yr record. Annual flow‐weighted NO 3 –N concentrations declined by 0.15 mg NO 3 –N L −1 yr −1 , which was not significantly different from the rate of 0.07 mg NO 3 –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 NO 3 –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. Core Ideas Nitrate in streamflow draining a prairie reconstruction was tracked for 20 yr. Nitrate loss decreased with time, at a slow rate of only 0.15 mg NO 3 –N L −1 yr −1 . Even with substantial land use change, water quality response may take decades.