Nonlinear pattern and algal dual-impact in N2O emission with increasing trophic levels in shallow lakes

Distinctive Microbial Processes and Controlling Factors Related to Indirect N2O Emission from Agricultural and Urban Rivers in Taihu Watershed

“…Dissolved N 2 O concentrations and N 2 O flux were measured using the headspace equilibrium technique and floating chamber method, respectively, as previously reported . Details of sampling, N 2 O measurements, and dissolved N 2 O saturation calculations can be found in the Supporting Information.…”

“…Recently, regional and global estimations of freshwater N 2 O fluxes have presumed that N 2 O emissions increase linearly with increased dissolved inorganic nitrogen loading . Hence, the Intergovernmental Panel on Climate Change (IPCC) used dissolved nitrate and the indirect emission factor (EF 5r ) to estimate the dissolved N 2 O concentration in surface water (i.e., N 2 O–N = NO 3 – –N × EF 5r ) for riverine N 2 O emission estimation. , This IPCC method is convenient for regional and global N 2 O emission estimation as dissolved NO 3 – –N concentration data are more commonly available than N 2 O data. However, the default EF 5r value (0.0026) given by IPCC in 2019 may skew the estimations of riverine N 2 O fluxes with different land use types. , In fact, the EF 5r of freshwater ecosystems remains unspecified, especially for agricultural and urban rivers. ,, The IPCC have refined EF 5r from 0.0075 (1998) to 0.0025 (2006) and to 0.0026 (2019) .…”

“…Hence, the Intergovernmental Panel on Climate Change (IPCC) used dissolved nitrate and the indirect emission factor (EF 5r ) to estimate the dissolved N 2 O concentration in surface water (i.e., N 2 O–N = NO 3 – –N × EF 5r ) for riverine N 2 O emission estimation. , This IPCC method is convenient for regional and global N 2 O emission estimation as dissolved NO 3 – –N concentration data are more commonly available than N 2 O data. However, the default EF 5r value (0.0026) given by IPCC in 2019 may skew the estimations of riverine N 2 O fluxes with different land use types. , In fact, the EF 5r of freshwater ecosystems remains unspecified, especially for agricultural and urban rivers. ,, The IPCC have refined EF 5r from 0.0075 (1998) to 0.0025 (2006) and to 0.0026 (2019) . Hence, many studies have estimated the EF 5r (EF 5r‑e ) with different landscapes using field-measured dissolved N 2 O and NO 3 – –N concentrations and provide EF 5r‑e for the refinement of the default EF 5r value or the establishment of a regionally-specific EF 5r . ,, Previous studies that investigated the IPCC’s predictions concluded that they only accounted for about 76% of the measured N 2 O emissions in urban rivers .…”

“…Nitrification, nitrifier denitrification, incomplete denitrification, and dissimilatory nitrate reduction to ammonium are the main processes resulting in N 2 O production . Among them, incomplete denitrification is commonly assumed to be the dominant N 2 O generating pathway in lotic environments and is governed by a variety of physicochemical factors. , Nitrate concentration and organic carbon-to-nitrate ratio are the two main factors that affect N 2 O production and consumption, respectively. Nitrate is the substrate and organic carbon serves as an electron donor for denitrification.…”

“…Hence, high organic carbon-to-nitrate ratios can ensure complete denitrification and consequently reduce N 2 O production . In addition, trophic state, suspended solids, algae accumulation and decomposition, temperature, dissolved oxygen (DO) concentration, pH, and many other environmental factors have been reported to significantly affect N 2 O emissions in inland rivers. ,,, Together, the influences of these environmental factors on N 2 O production are very complex and interconnected. The lack of understanding how N 2 O is produced and consumed by microbial processes in different inland rivers makes it difficult to correctly evaluate the N 2 O emissions and assess the importance of inland rivers in the global N 2 O budget.…”