Elucidation of the dominant factors influencing N2O emission in water-level fluctuation zones in a karst canyon reservoir, southwest China

Sai-Nan Chen; Yongmei Hou; Fu-Jun Yue; Zhifeng Yan; Xiao-Long Liu; Si-Liang Li

doi:10.1016/j.scitotenv.2024.171417

Elucidation of the dominant factors influencing N₂O emission in water-level fluctuation zones in a karst canyon reservoir, southwest China

Sci Total Environ. 2024 May 1:923:171417. doi: 10.1016/j.scitotenv.2024.171417. Epub 2024 Mar 4.

Authors

Sai-Nan Chen¹, Yongmei Hou¹, Fu-Jun Yue², Zhifeng Yan³, Xiao-Long Liu⁴, Si-Liang Li³

Affiliations

¹ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin 300072, China. Electronic address: fujun_yue@tju.edu.cn.
³ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin 300072, China.
⁴ Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China.

PMID: 38447725
DOI: 10.1016/j.scitotenv.2024.171417

Abstract

The water-level fluctuations zones (WLFZs) are crucial transitional interfaces within river-reservoir systems, serving as hotspots for N₂O emission. However, the comprehension of response patterns and mechanisms governing N₂O emission under hydrological fluctuation remains limited, especially in karstic canyon reservoirs, which introduces significant uncertainty to N₂O flux assessments. Soil samples were collected from the WLFZs of the Hongjiadu (HJD) Reservoir along the water flow direction from transition zone (T1 and T2) to lacustrine zone (T3, T4 and T5) at three elevations for each site. These soil columns were used to conduct simulation experiments under various water-filled pore space gradients (WFPSs) to investigate the potential N₂O flux pattern and elucidate the underlying mechanism. Our results showed that nutrient distribution and N₂O flux pattern differed significantly between two zones, with the highest N₂O fluxes in the transition zone sites and lacustrine zone sites were found at 75 % and 95 % WFPS, respectively. Soil nutrient loss in lower elevation areas is influenced by prolonged impoundment durations. The higher N₂O fluxes in the lacustrine zone can be attributed to increased nutrient levels resulting from anthropogenic activities. Furthermore, correlation analysis revealed that soil bulk density significantly impacted N₂O fluxes across all sites, while NO₃^-and SOC facilitated N₂O emissions in T1-T2 and T4-T5, respectively. It was evident that N₂O production primarily contributed to nitrification in the transition zone and was constrained by the mineralization process, whereas denitrification dominated in the lacustrine zone. Notably, the annual N₂O efflux from WLFZs accounted for 27 % of that from the water-air interface in HJD Reservoir, indicating a considerably lower contribution than anticipated. Nevertheless, this study highlights the significance of WLFZs as a vital potential source of N₂O emission, particularly under the influence of anthropogenic activities and high WFPS gradient.

Keywords: Karst reservoir; Lacustrine zone; N(2)O fluxes; Transition zone; Water-level fluctuation zones.