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- Title
Denitrification and DNRA in Urban Accidental Wetlands in Phoenix, Arizona.
- Authors
Handler, Amalia M.; Suchy, Amanda K.; Grimm, Nancy B.
- Abstract
Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) both require low oxygen and high organic carbon conditions common in wetland ecosystems. Denitrification permanently removes nitrogen from the ecosystem as a gas while DNRA recycles nitrogen within the ecosystem via production of ammonium. The relative prevalence of denitrification versus DNRA has implications for the fate of nitrate in ecosystems. Unplanned and unmanaged urban accidental wetlands in the Salt River channel near downtown Phoenix, Arizona, USA receive high nitrate relative to non‐urban wetlands and have a high capacity for denitrification, but unknown capacity for DNRA. We conducted in‐situ push‐pull tests with isotopically labeled nitrate to measure denitrification and DNRA rates in three of the dominant vegetative patch types in these urban accidental wetlands. DNRA accounted for between 2% and 40% of nitrate reduction (DNRA plus denitrification) with the highest rates measured in patches of Ludwigia peploides compared to Typha spp. and non‐vegetated patches. The wetland patches were similar with respect to dissolved organic carbon concentration but may have differed in carbon lability or strength of reducing conditions due to a combination of litter decomposition and oxygen supply via diffusion and aerenchyma. The ratio of DNRA to denitrification was negatively correlated with nitrate concentration, indicating that DNRA may become a more important pathway for nitrate attenuation at low nitrate concentration. Although DNRA was generally lower than denitrification, this pathway was an important component of nitrate attenuation within certain patches in these unmanaged urban accidental wetlands. Plain Language Summary: Urban waterways commonly have higher nitrogen concentrations relative to non‐urban systems, which can damage ecosystems. Wetlands support microbes that can carry out denitrification, which removes a deleterious form of nitrogen, and dissimilatory nitrate reduction to ammonium (DNRA), transforming to a less mobile but still potentially deleterious form of nitrogen, thus recycling the nitrogen in the system. We measured these two transformations in urban accidental wetlands in Phoenix, Arizona, USA. We found DNRA was ubiquitous and could account for as much as 40% of the combined rates. Both denitrification and DNRA were higher in places covered by certain plant species than in other wetland areas. These plants may create conditions more favorable for microbes because the plant produces substances that are easily consumed by the microbes or because they regulate oxygen conditions through roots. Overall, we found that DNRA was a small yet substantial pathway for nitrogen recycling in these urban wetland ecosystems. Key Points: Dissimilatory nitrate reduction to ammonium (DNRA) accounted for up to 40% of nitrate reduction (DNRA plus denitrification) in the urban accidental wetlands in Phoenix, Arizona, USADNRA rates differed among wetland patches with unique plant species and these differences were not driven by dissolved organic carbonPerennial accidental wetlands have a high capacity to attenuate nitrate loading through both DNRA and denitrification
- Subjects
DENITRIFICATION; NITROGEN removal (Sewage purification); ECOSYSTEMS; AMMONIUM; WETLANDS
- Publication
Journal of Geophysical Research. Biogeosciences, 2022, Vol 127, Issue 2, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2021JG006552