Denitrification, anammox, and dissimilatory nitrate reduction to ammonium across a mosaic of estuarine benthic habitats

Abstract

Estuaries play a key role in moderating the flow of nitrogen (N) to marine ecosystems. However, the magnitude of this N removal can vary dramatically both within and between estuaries due to the benthic habitats present. Here, we compare denitrification, coupled nitrification–denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) across a mosaic of benthic habitats in the subtropical Noosa River Estuary, Australia. Using 15N tracer techniques and passive pore‐water samplers, we show that coupled nitrification–denitrification was the dominant pathway for N2 production across all habitats, with higher rates in vegetated habitats (10–70 μmol N m−2 h−1) compared to bare sediments (0.9–2 μmol N m−2 h−1). Unusual pore‐water profiles in the macroalgal sediments suggest the presence of sulfur‐driven anoxic nitrification of NH4+ to NO3− and N2. A benthic N budget showed that combined denitrification and coupled nitrification–denitrification accounted approximately 96% of the N2 production, while DNRA accounted for 9% of total NO3− reduction pathways in the Noosa River Estuary. The macroalgae habitat contributed 76% of total N removal via N2 production and 65% of N retention via DNRA, despite accounting for only 25% of the total surface area. We show a strong relationship between seagrass and macroalgae area and N2 production (r2 = 0.8; p < 0.01), and as such, the capacity to mitigate reactive N loads in estuaries may decrease with the large‐scale loss of seagrass and other vegetated habitats.

Benthic nitrogen cycling in the deep ocean of the Kuroshio Extension region

“…The relative contribution of denitrification and anammox to total nitrogen loss, which affects the nitrogen budget, varies in different marine environments. Therefore, it has gained much attention over the last two decades (Devol, 2015;Chen et al, 2021). However, compared to marginal seas, studies on deep-ocean sediment are still scarce.…”

Copper Contamination Affects the Biogeochemical Cycling of Nitrogen in Freshwater Sediment Mesocosms

“…Many of the aforementioned studies on the effects of Cu on N-cycling microorganisms have been carried out in laboratory incubations, where the delicate sediment redox gradients are disrupted, which limits their applicability to in situ environments. This is particularly challenging for investigating the effects of copper on N cycling in sediments, where different biogeochemical processes often exist in distinct strata [32,33]. On the other hand, while replicated outdoor mesocosms with spiked metal concentrations can overcome some of the limitations associated with laboratory-based tests and improve the representation of natural conditions, they are expensive to establish and maintain, and deliberate contamination of river sediments can arguably attract negative publicity, especially when cultural values are associated with the purity of water resources [34].…”

Denitrification and DNRA in Urban Accidental Wetlands in Phoenix, Arizona

“…These plant species occupy distinct zones in the wetland that may compartmentalize denitrification capacity (Suchy et al., 2019). The effect of vegetation cover type on DNRA has been scarcely explored in wetland ecosystems (Chen et al., 2021; Hoffman et al., 2019; Zhang et al., 2017).…”