Investigating key drivers of N2O emissions in heterogeneous riparian sediments: Reactive transport modeling and statistical analysis

Pei Li; Corey D Wallace; Jeffrey T McGarr; Farzad Moeini; Zhenxue Dai; Mohamad Reza Soltanian

doi:10.1016/j.scitotenv.2023.166930

Investigating key drivers of N₂O emissions in heterogeneous riparian sediments: Reactive transport modeling and statistical analysis

Sci Total Environ. 2023 Dec 20:905:166930. doi: 10.1016/j.scitotenv.2023.166930. Epub 2023 Sep 11.

Authors

Pei Li¹, Corey D Wallace², Jeffrey T McGarr³, Farzad Moeini³, Zhenxue Dai⁴, Mohamad Reza Soltanian⁵

Affiliations

¹ Department of Geosciences, University of Cincinnati, Cincinnati, OH 45221, United States. Electronic address: lip6@ucmail.uc.edu.
² Geosyntec Consultants, Columbus, OH 43085, United States.
³ Department of Geosciences, University of Cincinnati, Cincinnati, OH 45221, United States.
⁴ College of Construction Engineering, Jilin University, Changchun, Jilin 130026, China.
⁵ Department of Geosciences, University of Cincinnati, Cincinnati, OH 45221, United States; Department of Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221, United States. Electronic address: soltanma@ucmail.uc.edu.

PMID: 37704143
DOI: 10.1016/j.scitotenv.2023.166930

Abstract

Nitrous oxide (N₂O) is a potent greenhouse gas that also contributes to ozone depletion. Recent studies have identified river corridors as significant sources of N₂O emissions. Surface water-groundwater (hyporheic) interactions along river corridors induce flow and reactive nitrogen transport through riparian sediments, thereby generating N₂O. Despite the prevalence of these processes, the controlling influence of physical and geochemical parameters on N₂O emissions from coupled aerobic and anaerobic reactive transport processes in heterogeneous riparian sediments is not yet fully understood. This study presents an integrated framework that combines a flow and multi-component reactive transport model (RTM) with an uncertainty quantification and sensitivity analysis tool to determine which physical and geochemical parameters have the greatest impact on N₂O emissions from riparian sediments. The framework involves the development of thousands of RTMs, followed by global sensitivity and responsive surface analyses. Results indicate that characterizing the denitrification reaction rate constant and permeability of intermediate-permeability sediments (e.g., sandy gravel) are crucial in describing coupled nitrification-denitrification reactions and the magnitude of N₂O emissions. This study provides valuable insights into the factors that influence N₂O emissions from riparian sediments and can help in developing strategies to control N₂O emissions from river corridors.

Keywords: Heterogeneous riparian sediments; Monte Carlo simulation; Nitrous oxide; Reactive transport model (RTM); Sensitivity analysis; Uncertainty analysis.