Presence of nitrous oxide hotspots in the coastal upwelling area off central Chile: an analysis of temporal variability based on ten years of a biogeochemical time series

Abstract

Seasonal and inter-annual variabilities of biogeochemical variables, including nitrous oxide (N 2 O), an important climate active gas, were analyzed during monthly observations between 2002 and 2012 at an ocean Time-Series station in the coastal upwelling area off central Chile (36°30.8′; 73°15′).Oxygen, N 2 O, nutrients and chlorophyll-a (Chl-a) showed clear seasonal variability associated with upwelling favorable winds (spring-summer) and also inter-annual variability, which in the case of N 2 O was clearly observed during the occurrence of N 2 O hotspots with saturation levels of up to 4849%. These hotspots consistently took place during the upwelling-favorable periods in 2004, 2006, 2008, 2010 and 2011, below the mixed layer (15-50 m depth) in waters with hypoxia and some − NO 2 accumulation. The N 2 O hotspots displayed excesses of N 2 O (ΔN 2 O) three times higher than the average monthly anomalies (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). Estimated relationships of ΔN 2 O versus apparent oxygen utilization (AOU), and ΔN 2 O versus − NO , 3 suggest that aerobic ammonium oxidation (AAO) and partial denitrification are the processes responsible for high N 2 O accumulation in subsurface water. Chl-a levels were reasonably correlated with the presence of the N 2 O hotspots, suggesting that microbial activities fuelled by high availability of organic matters lead to high N 2 O production. As a result, this causes a substantial N 2 O efflux into the atmosphere of up to 260 μmol m −2 d −1 . The N 2 O hotspots are transient events or hot moments, which may occur more frequently than they are observed. If so, this upwelling area is producing and emitting greater than expected amounts of N 2 O and is therefore an important N 2 O source that should be considered in the global atmospheric N 2 O balance. OPEN ACCESS RECEIVED

Air pollution and risk of hospitalization for epilepsy: the role of farm use of nitrogen fertilizers and emissions of the agricultural air pollutant, nitrous oxide

“…We have previously highlighted clinical case reports 13 , as well as several animal studies 14,15,16 , which indicated the role of N 2 O exposure in reducing epileptiform seizure activity 17 , while withdrawal from the drug has been shown to induce seizure-like activity 14,15,16 . Our novel environmental N 2 O-mediated hypothesis of neurodevelopmental impairment is supported by recent evidence indicating N 2 O hotspots in central Chile, given the following statement from the work: "…in our study area (off central Chile), they have ΔN 2 O three times higher than the average monthly ΔN 2 O… the increased N 2 O production seemed to be caused by the addition of anthropogenic NO 3 -associated with strong river runoff and a subsequent reduction to N 2 O (i.e., partial denitrification) 18 . " However, the aforementioned analyses by Cakmak et al…”

“…Consistent with the future goals identified by Chilean health and government officials 5 , we attempt to qualify the prior work by these research groups by performing regression analyses using a state-based total of farm use of anthropogenic nitrogen fertilizer, which is thought to be the major environmental contributor to N 2 O emissions 18,19 . While we attempt to document prior associations, by Cakmak et al 2 and others, between certain air pollution exposures and hospitalization for epilepsy for years 2001 to 2005, we also wish to test our hypothesis that increasing use of anthropogenic nitrogen-based fertilizers in agriculture (the most recognized causal environmental contributor to N 2 O emissions) may be significantly and negatively associated with hospitalization for epilepsy.…”

Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru

“…In areas where highly oxygen-deficient waters extended over the continental shelf, extreme accumulation of N 2 O has been found before in the Arabian Sea (Naqvi et al, 2010(Naqvi et al, ., 2006 and off Chile (Farías et al, 2015) and has been explained by rapid changes in the environmental conditions: Naqvi et al (2000) explained the extreme N 2 O accumulation over the Indian shelf with the response of denitrifying enzymes to transient oxygen depletion. N 2 O thus accumulated when waters reached suboxic conditions.…”

Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem

“…Likewise, the relative contribution to ammonium oxidation, quantified by the ammonia monooxygenase subunit A gene (Molina et al, 2010), and dark carbon assimilation rates (Farías et al, 2009), showed that archaea had a greater potential activity relative to the homologous bacteria in the system. Also, the Thaumarchaeota are mainly associated with the oxycline (Belmar et al, 2017), where N 2 O hotspots are frequently observed (Cornejo and Farías, 2012;Farías et al, 2015), further suggesting their possible participation in N 2 O production in this layer, particularly as the isotopic signature suggests ammonium oxidation by archaea is a major precursor of N 2 O in the ocean (Santoro et al, 2011). To reconcile the inhibitor results with all other evidence, we speculate that GC7, as a growth inhibitor of archaea, might not affect archaeal metabolism in short-term incubations, thus masking the relative importance of this domain for AO during this study.…”