Distinctive Microbial Processes and Controlling Factors Related to Indirect N<sub>2</sub>O Emission from Agricultural and Urban Rivers in Taihu Watershed

Gao

et al. 2022

Environ. Sci. Technol.

Nitrous oxide (N 2 O) emissions from lakes exhibit significant spatiotemporal heterogeneity, and quantitative identification of the different N 2 O production processes is greatly limited, causing the role of nitrification to be undervalued or ignored in models of a lake's N 2 O emissions. Here, the contributions of nitrification and denitrification to N 2 O production were quantitatively assessed in the eutrophic Lake Taihu using molecular biology and isotope mapping techniques. The N 2 O fluxes ranged from −41.48 to 28.84 μmol m −2 d −1 in the lake, with lower N 2 O concentrations being observed in spring and summer and significantly higher N 2 O emissions being observed in autumn and winter. The 15 N site preference and relevant isotopic evidence demonstrated that denitrification contributed approximately 90% of the lake's gross N 2 O production during summer and autumn, 27−83% of which was simultaneously eliminated via N 2 O reduction. Surprisingly, nitrification seemed to act as a key process promoting N 2 O production and contributing to the lake as a source of N 2 O emissions. A combination of N 2 O isotopocule-based approaches and molecular techniques can be used to determine the precise characteristics of microbial N 2 O production and consumption in eutrophic lakes. The results of this study provide a basis for accurately assessing N 2 O emissions from lakes at the regional and global scales.

Section: Key Processes Related To N 2 O Emissionssupporting

confidence: 92%

Section: Discussionmentioning

confidence: 72%

Nitrification Regulates the Spatiotemporal Variability of N₂O Emissions in a Eutrophic Lake

Liang

Gao

et al. 2022

Environ. Sci. Technol.

“…For both the incubations with C and S additions, δ 15 N β and δ 15 N α -N 2 O covaried at a ratio near 1, which might be due to the similarity of enzymes. A previous study gave an excellent example linking N 2 O flux with microbial populations . Isotope analysis is another powerful tool providing information on biogeochemistry and microbiology.…”

Section: Discussionmentioning

confidence: 99%

“…A previous study gave an excellent example linking N 2 O flux with microbial populations. 76 Isotope analysis is another powerful tool providing information on biogeochemistry and microbiology. The unchanged δ 15 N β -N 2 O could be applied to field research to identify the biotic contribution of iron to N 2 O production.…”

Section: Discussionmentioning

confidence: 99%

Influence of Electron Donors (Fe, C, S) on N₂O Production during Nitrate Reduction in Lake Sediments: Evidence from Isotopes and Functional Genes

Pang

et al. 2022

ACS EST Water

Nitrate reduction is a major source of nitrous oxide (N 2 O), which is a potent greenhouse gas and an ozone-depleting agent. Microbial nitrate reduction could be driven by organic carbon, sulfur, and iron oxidation. However, the biochemical mechanisms of N 2 O production driven by C, S, and Fe are poorly understood, and the contributions of these electron donors to N 2 O production are hard to discern. Here, we incubated lake sediments with glucose, sulfide, and iron(II) and measured N 2 O isotopes associated with each incubation. δ 15 N α -N 2 O and δ 15 N β -N 2 O (N α and N β , respectively, indicate central and terminal N atoms in the N 2 O molecule, N β -N α -O) covaried with a ratio near 1 in the incubations with glucose and sulfide. Surprisingly, unchanged δ 15 N β -N 2 O values were observed during iron(II)-driven microbial denitrification in both short-term and long-term incubations. Such an unchanged δ 15 N β -N 2 O pattern did not show during chemodenitrification. Based on metagenomic analysis, the nitric oxide reductase receiving electrons from quinols (qNorB) had a higher contribution to N 2 O production in the incubations with iron than with other electron donors. The difference in the reductases might explain different δ 15 N β -N 2 O versus δ 15 N α -N 2 O patterns. Our findings suggested that the unchanged δ 15 N β -N 2 O values could possibly be used as an indicator for iron(II)-driven microbial N 2 O production in field research and help to distinguish abiotic and biotic roles of iron in nitrogen cycling.

“…Currently, a number of in situ measurements have been conducted to determine EF 5r values across different land use types and climate zones (Hama‐Aziz et al, 2017; Tian et al, 2019; Wang et al, 2018; Zhang et al, 2020). Furthermore, previous efforts have been made to explore the spatiotemporal pattern of variations in EF 5r values and the relationships between EF 5r values and environmental variables (Cooper et al, 2017; Hu et al, 2016; Qin et al, 2019; Song et al, 2022; Yan et al, 2022), such as physicochemical (dissolved organic carbon, dissolved inorganic nitrogen, water temperature, pH, etc. ), geographic (land cover, climate zones, etc.…”

Section: Introductionmentioning

confidence: 99%

Indirect nitrous oxide emission factors of fluvial networks can be predicted by dissolved organic carbon and nitrate from local to global scales

Zhang

et al. 2022

Global Change Biology

Streams and rivers are important sources of nitrous oxide (N 2 O), a powerful greenhouse gas. Estimating global riverine N 2 O emissions is critical for the assessment of anthropogenic N 2 O emission inventories. The indirect N 2 O emission factor (EF 5r ) model, one of the bottom-up approaches, adopts a fixed EF 5r value to estimate riverine N 2 O emissions based on IPCC methodology. However, the estimates have considerable uncertainty due to the large spatiotemporal variations in EF 5r values. Factors regulating EF 5r are poorly understood at the global scale. Here, we combine 4-year in situ observations across rivers of different land use types in China, with a global metaanalysis over six continents, to explore the spatiotemporal variations and controls on EF 5r values. Our results show that the EF 5r values in China and other regions with high N loads are lower than those for regions with lower N loads. Although the global mean EF 5r value is comparable to the IPCC default value, the global EF 5r values are highly skewed with large variations, indicating that adopting region-specific EF 5r values rather than revising the fixed default value is more appropriate for the estimation of regional and global riverine N 2 O emissions. The ratio of dissolved organic carbon to nitrate (DOC/NO 3 − ) and NO 3 − concentration are identified as the dominant predictors of region-specific EF 5r values at both regional and global scales because stoichiometry and nutrients strictly regulate denitrification and N 2 O production efficiency in rivers. A multiple linear regression model using DOC/NO 3 − and NO 3 − is proposed to predict region-specific EF 5r values. The good fit of the model associated with easily obtained water quality variables allows its widespread application. This study fills a key knowledge gap in predicting region-specific EF 5r values at the global scale and provides a pathway to estimate global riverine N 2 O emissions more accurately based on IPCC methodology. K E Y W O R D S dissolved organic carbon, EF 5r , greenhouse gas, nitrogen cycle, nitrous oxide, river, urban rivers, water quality | 7271 WANG et al.