Abstract

Constructed wetlands mitigate nitrogen (N) loads in surface runoff, yet implications of common contaminant “cocktail” mixtures to wetland N removal are relatively unexplored. A ¹⁵N isotopic tracer was used to assess the impact contaminants from urban (imidacloprid, caffeine, and PFOS) and rural (atrazine, glyphosate, and sulfate) environments have on nitrogen (N) pathways in free-water surface wetlands (FWS) and floating treatment wetlands (FTW). Nitrate-N removal rates ranged from 0.20 to 0.68 d^-1and were dependent on the contaminant mixture and wetland design. Of the enriched ¹⁵N, biomass uptake accounted for 36.5 ± 30.7 %, 6.3 ± 4.2 % was denitrified and lost through air-water exchange, and 55.9 ± 24.4 % was assumed to have been denitrified and transmitted through plant tissues or lost due to ebullition (bubbling). The FTWs had increased temporary storage of N while the FWSs had increased permanent removal. In the presence of contaminant mixtures, both designs observed a shift in the NO₃N removal pathway toward increased biomass uptake. Caffeine (59.7 ± 3.6 %), PFOS (65.9 ± 8.8 %), atrazine (92.0 ± 0.6 %), and glyphosate (>89.1 %) were effectively removed from the water with limited removal for SO₄^2- (2.3 ± 12.3 %). Findings elucidate implications to N fate and maintenance required (e.g., biomass harvesting) in two constructed pulse-flow wetlands positioned in urban and rural landscapes while providing a clear understanding of how system design and water quality characteristics impact biogeochemical cycling.

Authors

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