Effect of Mitigation on U.S. Water Quality Draft, April 10, 2020
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Brent Boehlert 1,2,* , Kenneth M. Strzepek 3 , Steven C. Chapra 2 , Charles Fant 3 , Yohannes
Gebretsadik
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, Megan Lickley
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, Richard Swanson
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, Alyssa McCluskey
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, James E. Neumann
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Jeremy Martinich
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1. Industrial Economics, Inc., Cambridge, Massachusetts, USA
2. Tufts University, Medford, Massachusetts, USA
3. Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
4. University of Colorado, Boulder, Colorado, USA
5. U.S. Environmental Protection Agency (EPA), Washington, D.C., USA
* Corresponding author, phone: (617) 354-0074, fax: (617) 354-0463, bboehlert@indecon.com
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1.
INTRODUCTION
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This supplement presents a set of graphics that demonstrate the responsiveness of the
QUALIDAD parsimonious water quality model to (1) loading under constant flow and temperature conditions, and (2) loading of a single constituent at a time given constant flow and time-varying temperature conditions over a single year. Each graphic presents results for a single representative basin with a main channel that is 100 kilometers in length, where loadings occur as a distributed nonpoint source over the length of the river, and the presented concentrations of each constituent occur at the basin outlet. The constituents in each figure include river temperature, particulate organic carbon (Part org C), dissolved organic carbon (Dis org C), organic nitrogen (Org
N), river flow, ammonia, nitrate, organic phosphorus (Org P), photosynthetically active radiation
(PAR), inorganic phosphorus (Inorg P), phytoplankton (Phyto), and dissolved oxygen (DO). In
Section 2, carbon and DO are measured in grams per cubic meter (g/m 3 ), and all other constituents

Effect of Mitigation on U.S. Water Quality Draft, April 10, 2020
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2.
RESULTS UNDER CONSTANT LOADINGS, FLOWS AND TEMPERATURES
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Figure S1 shows the set of constituents evaluated within QUALIDAD, and the effect of introducing a constant loading of each constituent under constant temperature and river flow conditions
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37 and flow, each constituent reaches a steady state concentration within approximately four days. In the
38 case of DO, there is an initial spike toward saturation as reaeration occurs, and then levels fall slightly as
39 the concentration of dissolved organic carbon increases in the basin.
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Figure S1: Water quality constituent concentrations at steady state temperatures and flows, and constant nonpoint source loadings
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RESULTS WITH ONE LOADING AT A TIME UNDER VARIED TEMPERATURES
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Figures S2 through S6 present the effect of adding constant nonpoint source loading of one constituent to the representative basin under time-varying temperature and PAR conditions, while
46 loadings of all other constituents remain at zero. Each graphic presents hourly constituent concentrations
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Effect of Mitigation on U.S. Water Quality Draft, April 10, 2020
47 over a one-year period. Figure S2 shows loadings of particulate organic carbon transformed into
48 dissolved organic carbon, which then causes slight reductions of DO from full saturation. Note that on
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DO level. Figure S3 shows the significant effect that a larger loading of dissolved organic carbon has on
51 DO levels, and Figure S4 shows an organic nitrogen loading, its breakdown into ammonia, which is
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53 subsequently broken down into nitrate. Due to the low levels of organic nitrogen introduced (measured in
μg/m 3 ), the resulting effect on DO levels is minimal. The transformation of organic phosphorus loadings
54 to dissolved phosphorus are shown in Figure S5; as with introduction of organic nitrogen, the too little
55 phosphorus is introduced to have a significant effect on DO. Lastly, Figure S6 shows the complex effects
56 of introducing constant levels of phytoplankton to the basin. As can be seen, phytoplankton death
57 introduces organic carbon, nitrogen, and phosphorus to the system, but again at low enough
58 concentrations to have a minimal effect on DO.
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Figure S2: Constituent concentrations when constant nonpoint source loadings of particulate organic carbon are applied
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Figure S3: Constituent concentrations when constant nonpoint source loadings of dissolved organic carbon are applied
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Figure S4: Constituent concentrations when constant nonpoint source loadings of organic nitrogen are applied
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Figure S5: Constituent concentrations when constant nonpoint source loadings of organic phosphorus are applied
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Figure S6: Constituent concentrations when constant nonpoint source loadings of phytoplankton are applied
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