Denitrification and DNRA in Urban Accidental Wetlands in Phoenix, Arizona

Abstract

Nitrogen is an essential, often limiting, element for biological growth that can act as a pollutant if present at high concentrations. Excessive nitrogen in highly biologically available forms, especially nitrate (NO 3 − ), is common in urban ecosystems. Urban ecosystems tend to have higher NO 3 − burdens due to higher inputs from fertilizer application (Baker et al., 2001;Law et al., 2004), deposition from fossil fuel combustion (Bettez & Groffman, 2013;Hale et al., 2014), and treatment of sewage (Lauver & Baker, 2000). In addition, urban stormwater infrastructure quickly transports runoff to storm drains that can discharge into water bodies (Baker et al., 2001;Kaye et al., 2006). Whether this high NO 3 − burden causes eutrophication partially depends on the capacity of the aquatic ecosystem to attenuate NO 3 − inputs. Wetland ecosystems can be hotpots for NO 3 − attenuation due to the availability of water, organic matter, and variable oxygen zones (Ehrenfeld, 2000;Mitsch & Gosselink, 2015). These environmental conditions are conducive to NO 3 − attenuation through pathways such as denitrification and dissimilatory NO 3 − reduction to ammonium (NH 4 + ) (DNRA). Indeed, urban wetland ecosystems are thought to

Nitrogen Sinks or Sources? Denitrification and Nitrogen Removal Potential in Riparian Legacy Sediment Terraces Affected by Milldams

“…Unfortunately, our analysis did not include direct measurements of DNRA, which should be performed in the future as it is an understudied, potentially important component of riparian N cycling. Indeed, zones of concentrated ammonium-N have been observed in other riparian systems with similar groundwater hydrodynamics, such as beaver ponds (Duval & Hill, 2006;Lazar et al, 2015;Naiman et al, 1994) and urban "accidental" wetlands (Handler et al, 2022). While many early studies have typically attributed high ammonium-N concentrations to ammonification and suppression of nitrification, there is increasing appreciation of the importance of DNRA as a mechanism for N production in anoxic soils/sediments.…”

Nitrate as an alternative electron acceptor destabilizes the mineral associated organic carbon in moisturized deep soil depths

“…As Figure 3 shows, the soil ammonium concentration did not change significantly ( P > 0.05) between the beginning and end of the incubations, which indicated that dissimilatory nitrate reduction to ammonium (DNRA) was negligible. In addition, study showed that DNRA may be a minimal pathway at high nitrate concentrations ( Handler et al, 2022 ), it is generally believed that low nitrogen and high carbon will tilt the balance to DNRA ( Van Den Berg et al, 2016 ; Pandey et al, 2020 ; Wei et al, 2022 ), the opposite is the high nitrogen and lower carbon contents in this study. Denitrification was the main nitrate reduction pathway, the amount of nitrate consumed (65 μmol N) was significantly larger than the cumulative amount of the N 2 O plus N 2 (31 μmol N) produced by day 98 (Experiment 2).…”