Abstract

Constructed wetlands are used extensively to mitigate surface runoff. While wetland treatment for nitrogen (N) has been comprehensively studied, a knowledge gap remains regarding the implications of other contaminants (e.g., pesticides, pharmaceuticals) on nitrate-N (NO₃-N) removal. This study sought to fill that gap by determining the impact imidacloprid, caffeine, perfluorooctane sulfonic acid (PFOS), atrazine, glyphosate, and sulfate (SO₄²⁻) have on NO₃-N removal rates. The contaminants were determined based on their occurrence across Kentucky surface waters in urban (imidacloprid, caffeine, and PFOS) and rural (atrazine, glyphosate, and SO₄²⁻) environments. Two constructed wetland designs, floating treatment wetlands (FTWs), and free-water surface wetlands (FWSs), were evaluated along with planted and un-planted controls, equating to 24 mesocosms. Individual contaminants in both designs inhibited the rate of NO₃-N removal, while the presence of the contaminants in their mixtures decreased N removal rates in FWSs compared to FTWs. However, by the end of each trial, 72–99 % of the NO₃-N was removed despite the wetland design or the presence of contaminant(s). The FWSs outperformed the FTWs earlier in the growing season (May–June) when the water temperatures were colder, while the FTWs outperformed the FWSs when the plants reached maturity (July–September). Both FTWs and FWSs observed significant removal of contaminants with 28–89 %, 63–70 %, >90 %, and >92 % removal for PFOS, caffeine, glyphosate, and atrazine, respectively. Limited removal of SO₄²⁻ was observed (≤57.9 %). These findings improve our understanding of water treatment for contaminant mixtures and their impact on NO₃-N removal, guiding treatment wetland design and placement.

Authors

Emily N Byers, Tiffany L Messer, Daniel N Miller, Christopher Barton, Jason Unrine, Carmen Agouridis