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This article in JEQ

  1. Vol. 43 No. 3, p. 1071-1080
    Received: Nov 21, 2013
    Published: June 24, 2014

    * Corresponding author(s): mbeutel@wsu.edu
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Phosphorus Removal in a Surface-Flow Constructed Wetland Treating Agricultural Runoff

  1. Marc W. Beutel *a,
  2. Matthew R. Morganb,
  3. Jonathan J. Erlenmeyera and
  4. Elaine S. Brouillardb
  1. a Dep. of Civil and Environmental Engineering, Washington State Univ., 101 Sloan Hall, Pullman, WA 99164
    b Roza-Sunnyside Board of Joint Control, 120 S. 11th St., Sunnyside, WA 98944. Assigned to Antonio Delgado
    b Roza-Sunnyside Board of Joint Control, 120 S. 11th St., Sunnyside, WA 98944


Agricultural runoff is a leading source of phosphorus (P) pollution to lakes and streams. The objective of this study was to evaluate P removal dynamics in a constructed treatment wetland (CTW) treating agricultural irrigation return flows. The CTW included a sedimentation basin (SB) followed by two surface-flow wetlands in parallel. Typical retention times and total P (TP) loading were 1.4 d and 50 to 110 g m−2 yr−1 P, respectively, for the SB and 5 to 6 d and 4 to 10 g m−2 yr−1 P, respectively, for wetlands. On the basis of this multiyear study, concentration removal efficiency in the SB averaged 21% for TP and 32% for reactive phosphorus (RP). Concentration removal efficiency in wetlands averaged 37 and 43% for TP and 22 and 33% for RP. Areal first-order removal rates for TP averaged 22 and 31 m yr−1 in wetlands. Total P removal in wetlands exhibited a strong seasonal pattern, with minimum removal in the summer when high temperatures likely enhanced P release from decaying plant biomass. The performance of the CTW was stochastic, with removal unpredictably poorer in some years in part as a result of muskrat bioturbation and plant harvesting. In years before muskrat impacts, concentration removal efficiencies in wetlands were 50% for TP and 65% for RP.

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