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M.S. Thesis Defense - Jenna McCoy

Nitrate Removal via Plant Uptake and Denitrification from Floating Treatment Wetlands under Aerated and Unaerated Conditions: Field and Laboratory Results

9:00 am – 10:00 am
Hardin Hall Room: 901 South
3310 Holdrege St
Lincoln NE 68583
Additional Info: HARH
Virtual Location: Zoom
Target Audiences:
Steve Comfort,
Eutrophic conditions often become prevalent in urban and stormwater retention ponds following years of external nutrient loads. In 2020, a novel biological and chemical treatment was initiated to remove accumulated nutrients from an urban retention pond (Densmore Pond, Lincoln, NE) that had severe algae and weed growth. Our approach included installing two 37 m2 (6.1 m x 6.1 m) floating treatment wetlands (FTWs) and two airlift pumps that contained slow-release lanthanum composites. The floating treatment wetlands promoted microbial denitrification and plant uptake of nitrogen and phosphorus, while the airlift pumps slowly released lanthanum to the water column over the growing season to reduce soluble reactive phosphorus. Four seasons of field sampling (2020-2023) showed median NO3-N concentrations were reduced from 23 µg L-1 in 2020 to 1.3 µg L-1 in 2023, while PO4-P decreased from 42 µg L-1 to 19 µg L-1. The reduction in N and P from the water column coincided with less algae, weeds, and pond muck (sediment), and greater dissolved oxygen concentrations and water clarity. To quantify the sustainability of this bio-chemical approach, this study focused on measuring nitrate removal rates from the FTWs. By enclosing quarter sections of the field-scale FTWs (3.05 x 3.05 m) inside vinyl pool liners in the pond, nitrate removal rates were measured by spiking nitrate into the enclosed root zone and then measuring nitrate loss under aerated and unaerated conditions. Results showed that NO3-N removal rates were roughly three-fold greater under unaerated (1485 mg NO3-N/d) versus aerated conditions (515 mg NO3-N/d). Extrapolating these removal rates to mass (kg) of nitrate-N removed, we estimate the two the full-sized FTWs installed in the Densmore Pond could remove between 0.64 to 1.82 kg of NO3-N over a growing season (May-September, 153 d), with removal mass dependent on dissolved oxygen concentrations beneath the FTWs. Complementary laboratory mesocosm experiments using similar treatments to field experiments will also be presented.

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This event originated in SNR Seminars & Discussions.