Modeling Riverine N₂O Sources, Fates, and Emission Factors in a Typical River Network of Eastern China

Abstract

Estimates of riverine N 2 O emission contain great uncertainty because of the lack of quantitative knowledge concerning riverine N 2 O sources and fates. Using a 3.5-year record of monthly N 2 O measurements from the Yongan River network of eastern China, we developed a mass-balance model to address the riverine N 2 O source and sink processes. We achieved reasonable model efficacies (R 2 = 0.44−0.84, Nash−Sutcliffe coefficients = 0.40−0.80) across three tributaries and the entire river system. Estimated riverine N 2 O loads originated from groundwater (38−88%), surface runoff (3−26%), and in-stream production (4−48%). Estimated in-stream losses via atmospheric release + complete denitrification accounted for 76, 95, 25, and 89% of riverine N 2 O fate for the agricultural, residential, forest, and entire river system, respectively. Considering limited complete denitrification, the model estimated an upperbound riverine N 2 O emission rate of 2.65 ton N 2 O−N km −2 year −1 for the entire river system. Riverine N 2 O emission estimates were of comparable magnitude to those estimated with a power-law scaling model. Riverine N 2 O emissions using the IPCC default emission factor (0.26%) overestimated emissions by 3−15 times, whereas the dissolved N 2 O concentration-based emission factor overestimated or underestimated emissions. This study highlights the importance of combining comprehensive information on N 2 O sources and fates to achieve accurate riverine N 2 O emission estimates.

N2O Emissions from Aquatic Ecosystems: A Review

“…where C N2O−N (mg•L −1 ) and C NO3−N (mg•L −1 ) are concentrations measured in the water. Uncertainty may be introduced when using EF-based estimation [42] because it ignores potential differences in spatial and temporal N delivery efficiency [90], and multiple sources of input may result in the supersaturation of N 2 O [7,78,95,96]. Moreover, N 2 O in aquatic ecosystems is mainly produced and consumed through nitrification and denitrification pathways, but the EF-based method does not take into account that these processes may differ significantly under different conditions in diverse waters [68,97].…”

High-Resolution Estimates of N2O Emissions from Inland Waters and Wetlands in China

“…The second approach is process-based modeling, which allows for spatially explicit estimates. For instance, the global estimates of N 2 O emissions from inland waters were carried out using the riverine N 2 O mass-balance model, and the global environment-dynamic global nutrient model . However, process-based modeling of N 2 O emissions from African lakes was significantly higher than the data-driven estimates .…”

Propionibacterium freudenreichii-Assisted Approach Reduces N2O Emission and Improves Denitrification via Promoting Substrate Uptake and Metabolism

“…Microbial denitrification plays an important role in the global nitrogen cycle and is also a well-known method to remove nitrate from the water environment to prevent waterbody eutrophication or groundwater pollution. , Denitrifying microorganisms usually use organic matter (carbon source) as an electron donor and nitrate as an electron acceptor to gradually reduce nitrate to nitrite, nitric oxide, nitrous oxide (N 2 O), and finally nitrogen gas . However, incomplete denitrification occurs frequently, that is, NO 3 – is only reduced to NO 2 – or N 2 O instead of N 2 , leading to the accumulation of nitrogenous intermediates and low denitrification performance. ,, In particular, N 2 O emission in the process of denitrification has aroused widespread concern because it is a potential greenhouse gas with a global warming potential of about 300 times that of carbon dioxide, which may lead to stratospheric ozone depletion and climate change . Therefore, to decrease the N 2 O emission and improve biodenitrification performance, several strategies, such as the addition of external carbon sources, trace elements, and redox mediators or the control of the pH value, have been studied previously, but the improper chemical dosage might lead to deterioration of the water quality and secondary pollution of the environment. − …”

“…2,4,5 In particular, N 2 O emission in the process of denitrification has aroused widespread concern because it is a potential greenhouse gas with a global warming potential of about 300 times that of carbon dioxide, which may lead to stratospheric ozone depletion and climate change. 6 Therefore, to decrease the N 2 O emission and improve biodenitrification performance, several strategies, such as the addition of external carbon sources, trace elements, and redox mediators or the control of the pH value, have been studied previously, but the improper chemical dosage might lead to deterioration of the water quality and secondary pollution of the environment. 7−9 Biodenitrification begins with substrate uptake, followed by nitrate metabolism driven by reducing power (nicotinamide adenine dinucleotide, NADH) produced from the carbon source, such as glucose, a commonly used carbon source of denitrifying microorganisms.…”