Assessing the Relative Importance of Nitrogen-Retention Processes in a Large Reservoir Using Time-Series Modeling |
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| Authors: | Elizabeth Hansen Kung-Sik Chan Christopher S Jones Keith Schilling |
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| Institution: | 1.Department of Mathematics,Western Illinois University,Macomb,USA;2.Department of Statistics and Actuarial Science,University of Iowa,Iowa City,USA;3.IIHR—Hydroscience & Engineering,University of Iowa,Iowa City,USA |
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| Abstract: | Nitrogen (N) removal within reservoirs can be substantial, but few studies have reported the relative importance of various N-retention pathways. Assessing N-removal processes in reservoirs is important for quantifying the impacts of reservoirs on downstream water quality. In this study, we used a time-series approach to quantify the relative importance of various N-removal processes in the Saylorville Reservoir in Iowa. Dynamic regression modeling of upstream–downstream changes in key water-quality surrogates (pH, hardness, alkalinity, and suspended solids) and their relation to N concentration changes were used to estimate the relative importances of denitrification, N assimilation by algal uptake, and sedimentation of N on N retention in the reservoir. Assuming that decreasing N concentrations in the reservoir are the sum of these three processes, we estimate that denitrification is the dominant N removal process (60.9 %) followed by algal assimilation (37.9 %) and sedimentation (1.2 %). Our approach represents a new method of establishing the relative importance of N-removal processes in reservoirs and quantifying the impacts of reservoirs on downstream water quality. |
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