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- Title
Hydro‐Biogeochemical Controls on Nitrate Removal: Insights From Artificial Emergent Vegetation Experiments in a Recirculating Flume Mesocosm.
- Authors
Waterman, B. R.; Hansen, A. T.
- Abstract
Environments with aquatic vegetation can mitigate excess nitrogen (N) loads to downstream waters. However, complex interactions between multiple hydro‐biogeochemical processes control N removal within these environments and thus complicate implementation of aquatic vegetation as a management solution. Here, we conducted controlled experiments using a canopy of artificial rigid emergent vegetation in a recirculating flume mesocosm to quantify differences in rates of mass transport and nitrate (NO3−N) removal between the open channel‐canopy interface across a range in nominal water velocities. We found NO3−N removal rates were 86% greater with the canopy present compared to no canopy control experiments and were always greatest at intermediate velocity (6 cms−1). With the canopy present, a hydrodynamically distinct mixing layer formed at the open channel‐canopy interface, and resources, such as carbon (C), CN ratios, and dissolved oxygen, differed between open channel and vegetated canopy. The dimensionless Damköhler (Da) number indicated NO3−N removal rates were reaction limited (Da << 1) for all canopy experiments, yet across all velocities NO3−N removal was more reaction limited in the open channel than the canopy due to higher rates of mixing and less contact time with reactive surfaces. We found significant relationships between NO3−N removal rates and Da with hydrodynamic metrics (mixing zone width and Reynolds number, respectively), suggesting that NO3−N removal in the presence of rigid vegetation can be enhanced by manipulating flow conditions. These findings demonstrate that rigid emergent vegetation‐open channel interfaces create conditions conducive for NO3−N removal and with effective management can improve overall water quality. Plain Language Summary: Persistent excess nitrate (NO3−N) in surface waters is a major threat to water quality. Environments with aquatic plants, like wetlands, vegetated ditches or streams, can improve water quality by removing NO3−N from water ways, yet reasons for increased removal capacity, especially under different flow conditions, are unclear. Using a controlled, yet realistic experimental set up, we investigated how flow conditions impact rates of mass transport and NO3−N removal near model canopies of rigid emergent aquatic vegetation. We found that the rate NO3−N is removed from the water is greater when the model vegetation is present, but regardless NO3−N removal rates were greatest at intermediate velocity. When the canopy was present, the transport of water and resources occurred much faster than the removal of NO3−N. We observed predictive relationships between flow conditions with removal rates and the ratio of mass transport to NO3−N removal rate which can be useful for predicting or increasing NO3−N removal in real environments. Our findings show the transformative role rigid aquatic vegetation can have in improving water quality within flowing waters, offering a promising pathway for sustainable water management. Key Points: Nitrate removal rates were 86% higher with the artificial canopy present than the no canopy control experimentsMaximum nitrate removal occurred at intermediate velocity (6 cms−1) for both the canopy and no canopy control experimentsMixing, induced by the canopy‐open water interface, enhanced open channel nitrate removal rates
- Subjects
VEGETATION management; WATER quality; REYNOLDS number; WATER supply; WATER management
- Publication
Water Resources Research, 2024, Vol 60, Issue 8, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2023WR036995