High nutrient levels are responsible for the hypoxic conditions in the Gulf of Mexico. Iowa contributes significant nitrate loads to the Mississippi River which then contributes to the formation of an annual hypoxic zone. The primary object of this research was to calculate Iowa’s statewide nitrate load export from 1999-2015. Evaluating the statewide load will provide a means to track the effects of the Iowa Nutrient Reduction Strategy developed in 2012. This research also evaluated nitrate patterns to identify spatial and temporal variables that may be responsible for much of the variability in average nitrate yields and annual nitrate loads. Data from 62 sites within the Iowa Department of Natural Resources (DNR) ambient water quality monitoring network were linearly interpolated from monthly grab samples. Twenty-three of the study sites were main study basins. The remaining watersheds were subbasins within the main basins. The main study basins were used to extrapolate annual statewide load. Percent row crop and water yield were used to predict spatial average annual nitrate yields. Additionally, linear regression modeling using annual water yield was found to best replicate temporal annual nitrate loads. Regional regression equations were formulated using temporal water yield regression equation parameters (slope and intercept) for the 62 subbasins organized by Major Land Resource Area (MLRA). DNR ambient nitrate loads were also compared to nitrate loads from the Iowa Water Quality Information System (IWQIS), a high-resolution water quality sensor network operated by IIHR—Hydroscience and Engineering at the University of Iowa. Nitrate loads between the two networks can vary significantly during April through July. Nutrient load reduction could be more confidently determined with improved statewide load export estimations.
| Identifer | oai:union.ndltd.org:uiowa.edu/oai:ir.uiowa.edu:etd-7455 |
| Date | 15 December 2017 |
| Creators | Nielsen, Jacob Kevin |
| Contributors | Weber, Larry Joseph |
| Publisher | University of Iowa |
| Source Sets | University of Iowa |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | Copyright © 2017 Jacob Kevin Nielsen |
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