Contaminant mixtures and their impact on nitrate removal in wetlands: A mesocosm study

Authors: Nottingham Byers, Emily; MESSER, T - University Of Kentucky; Miller, Daniel; BARTON, C - University Of Kentucky; UNRINE, J - University Of Kentucky; AGOURIDIS, C - University Of Kentucky

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2025
Publication Date: 4/26/2025
Citation: Nottingham Byers, E.R., Messer, T.L., Miller, D.N., Barton, C., Unrine, J., Agouridis, C. 2025. Contaminant mixtures and their impact on nitrate removal in wetlands: A mesocosm study. Journal of Environmental Management. 383. Article 125518. https://doi.org/10.1016/j.jenvman.2025.125518.
DOI: https://doi.org/10.1016/j.jenvman.2025.125518

Interpretive Summary: Constructed wetlands are effective treatment systems for nutrients, particularly nitrogen. However, nitrogen is not the only contaminant of concern in the environment. This study found that floating treatment wetlands have high removal potential for both nitrogen and other emerging contaminants (caffeine, PFOS, glyphosate, atrazine, and imidacloprid), but it's treatment efficiency was significantly impacted by seasonal shifts in plant growth and temperature. Free-water surface wetlands performed better earlier in the growing season and exhibited more consistent treatment performance. Sulfate was the only contaminant study with limited removal in both wetland designs. These findings improve our understanding of water treatment for contaminant mixtures and their impact on nitrate removal, guiding treatment wetland design for both policymakers (e.g., TMDL limits, design standards) and professionals.

Technical Abstract: Wetland treatment systems are used extensively across the world to mitigate surface runoff. While wetland treatment for nitrogen (N) mitigation has been comprehensively studied, a knowledge gap remains regarding implications of other contaminants such as pesticides and pharmaceuticals on N reduction. This study sought to fill that gap by determining the impact imidacloprid, caffeine, perfluorooctane sulfonic acid (PFOS), atrazine, glyphosate, and sulfate (SO42-) have on nitrate-N (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. The rate of NO3-N removal was inhibited by individual contaminants in both designs 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 presence of contaminant type and mixtures. The FWSs outperformed the FTWs earlier in the growing season (May-June) when the water temperatures were lower, while the FTWs outperformed the FWSs when the plants reached maturity (July-September). Both designs also observed significant removal of contaminants with 28 to 89%, 63 to 70%, >90%, and >92% removal for PFOS, caffeine, glyphosate, and atrazine, respectively. Sulfate saw limited removal (-9.3 – 57.9%). These findings improve our understanding of water treatment for contaminant mixtures and their impact on NO3-N removal, guiding treatment wetland design.