Nitrate Removal by Floating Treatment Wetlands Amended with Spent Coffee: A Mesocosm-Scale Evaluation

Abstract

HighlightsA floating treatment wetland design was evaluated for water quality improvements.Nitrate-N removal rates were quantified using spent coffee grounds as a carbon source.Nitrate-N removal rates increased throughout the growing season Abstract. The Midwestern U.S. is vulnerable to eutrophic conditions from high nutrient concentrations. Floating treatment wetlands (FTWs) are an innovative wetland design for nutrient removal from nonpoint sources and provide a unique treatment. The objectives of this project were to quantify nitrate removal in traditional and carbon-amended FTWs planted with Midwestern plant species during the establishment year. Three greenhouse experiments were conducted throughout the growing season using 18 mesocosms. Two vegetation designs were evaluated: rush species ( and ) and diverse species (, , , , , and ). Spent coffee grounds were applied to 9 of the 18 mesocosms as a carbon amendment. Nitrate-N removal increased during the establishment growing season in the FTW systems (Spring: 15.0% to 17.3%, Summer 1: 82.8% to 92.6%, Summer 2: 86.4% to 94.7%). Nitrate-N removal was also impacted by carbon amendments (FTW without amendment: 82.8% to 94.7%, FTW with amendment: 88.4% to 96.1%). Carbon additions were found to enhance denitrifying conditions even in the absence of FTWs (decreased dissolved oxygen, increased available organic carbon). Significant differences in nitrate-N removal were not observed between FTW vegetation designs. This study provides new insight on the impacts of the growing season, plant species, and carbon amendments on FTW nitrate-N removal performance during the establishment year. Keywords: Best management practices, Carbon amendment, Floating treatment wetlands, Nitrogen removal, Spent coffee grounds

Neonicotinoid pesticide and nitrate mixture removal and persistence in floating treatment wetlands

“…Although ORP dropped below 250 after Day 5 in control mesocosms, the presence of DO (4.0-5.1 mg L −1 ) and low C source (1.1-1.8 mg mg L −1 ) availability may account for limited NO 3 -N removal. The preestablishment of the FTWs likely contributed to the higher DOC levels in those treatments compared with the controls and has been observed in other mesocosm treatment wetland studies (Keilhauer et al, 2019;. Plant uptake of N incorporated into the biomass during the 2019 growing season was 90.0 ± 6.82 g m −2 in above-surface biomass and 54.9 ± 3.09 g m −2 in below-surface biomass (Messer et al, 2022).…”

“…Floating treatment wetland mesocosms consisted of 380‐L black Rubbermaid feeding troughs filled with simulated greenhouse water (Figure 1; Supplemental Figure S1). Due to limited greenhouse space, control mesocosms (no FTWs) were 56‐L buckets, as previously used in similar mesocosm experiments (Keilhauer et al., 2019; Messer Burchell, Birgand, et al., 2017; Messer et al., 2022). Floating treatment wetland mats (60 cm by 60 cm) were purchased from Beemats and stocked with 10 native Nebraska wetland plants that were planted in spring 2017 and established until the experiment began in 2019 with periodic fertilizer applications.…”

“…Floating treatment wetland mesocosms consisted of 380-L black Rubbermaid feeding troughs filled with simulated greenhouse water (Figure 1; Supplemental Figure S1). Due to limited greenhouse space, control mesocosms (no FTWs) were 56-L buckets, as previously used in similar mesocosm experiments (Keilhauer et al, 2019;Messer et al, 2022).…”

“…First-order NO 3 -N removal rates were calculated for all mesocosms following both experiments (Benjamin, 2010;Brezonik & Arnold, 2011;Keilhauer et al, 2019;:…”

Wetland Ecosystem Resilience: Protecting and Restoring Valuable Ecosystems

“…Few studies have investigated the impact of floating treatment wetlands for recreational lakes in agricultural regions, specifically to enhance water quality in both urban and agricultural regions. Keilhauer et al (2019) evaluated the resilience of floating treatment wetland design for water quality improvements. Nitrate-N removal rates were quantified for traditional and carbon-amended (spent coffee grounds) floating treatment wetland mesocosms in the Midwestern U.S. using two vegetation designs.…”