The modeled and observed response of Lake Spokane hypolimnetic dissolved oxygen concentrations to phosphorus inputs

Michael T. Brett*, Suvi K. Ahopelto, Hunter K. Brown, Barton E. Brynestad, Titus W. Butcher, Emily E. Coba, Christina A. Curtis, Jebessa T. Dara, Kallie B. Doeden, Kevin R. Evans, Lu Fan, Josh D. Finley, Noah J. Garguilo, Senait M. Gebreeyesus, Marissa K. Goodman, Kenneth W. Gray, Crystal Grinnell, Kathryn L. Gross, Brian R.E. Hite, Andrew J. JonesPhilip T. Kenyon, Angela M. Klock, Raji E. Koshy, Amanda M. Lawler, Man Lu, Luke Martinkosky, Jeremy R. Miller-Schulze, Quyen T.N. Nguyen, Elizabeth R. Runde, Joanie M. Stultz, Songlin Wang, Francesca P. White, Corey H. Wilson, Andrea S. Wong, Shirley Y. Wu, Peter G. Wurden, Tessora R. Young, George B. Arhonditsis

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)


Lake Spokane, a reservoir in eastern Washington State, was previously hypereutrophic due to phosphorus discharges from the City of Spokane wastewater treatment plant (WWTP). This reservoir subsequently recovered to a meso-oligotrophic state after implementation of advanced phosphorus removal. The present study tested whether the mechanistic Lake Spokane water quality (WQ) model realistically represents the sensitivity of this reservoir's hypolimnetic oxygen concentrations to phosphorus inputs. We compared the observed relationship between the mean summer input total phosphorus concentration (TPIN) and the minimum volume weighted hypolimnetic dissolved oxygen concentration (DOMIN) to model values for conditions ranging from hypereutrophic to oligotrophic. Prior to advanced phosphorus removal, TPIN and DOMIN averaged 86 ± 37 (SD) µg/L and 1.4 ± 1.3 mg/L, respectively. Currently (2010–2014), these values average 14 ± 3 µg/L and 6.5 ± 0.8 mg/L, respectively. By contrast, the model's DOMIN response for similar TPIN concentrations was much less pronounced, with hypereutrophic and contemporary DOMIN averaging 3.8 ± 0.4 and 4.7 ± 0.04 mg/L, respectively. The model also has a structural DO deficit (saturated DO − DOMIN) of 5.3 mg/L that was evident when all TP inputs to the reservoir were set to zero. Similarly, when all WWTP effluent sources were set to TPEFF = 0 µg/L, the reservoir epilimnetic TP concentrations were ≈8 µg/L higher than the Spokane River inputs. The water quality model indicates that even if effluent phosphorus concentrations are reduced to zero, the dissolved oxygen goals for Lake Spokane cannot be met.

Original languageEnglish
Pages (from-to)246-258
Number of pages13
JournalLake and Reservoir Management
Issue number3
Publication statusPublished - 2 Jul 2016
MoE publication typeA1 Journal article-refereed


  • CE-QUAL-W2
  • eutrophication
  • hypolimnetic oxygen
  • Lake Spokane
  • phosphorus
  • wastewater treatment plant effluents


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