9 / 2024-07-29 17:17:53
In-situ On-line Monitoring of Greenhouse Gases Emitted from Seaweed Bed in the Lagoon of Dongsha Atoll, South China Sea and Their Seasonal and Diurnal Variation Trends
Dongsha Atoll, seaweeds in lagoon, greenhouse gases (GHGs), in-situ monitoring, seasonal and diurnal variation, global warming potential
Session 24 - Estuaries and coastal environments stress - Observations and modelling
Abstract Accepted
Chung-Shin Yuan / Institute of Environmental Engineering; National Sun Yat-sen University
Po-Hsuan Yen / Institute of Environmental Engineering, National Sun Yat-sen University, Kaohsiung
Yu-Lun Tseng / Institute of Environmental Engineering, National Sun Yat-sen University, Kaohsiung
Chin-Chang Hung / Department of Oceanography and Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung
Ker-Yea Soong / Department of Oceanography and Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung
This study developed an on-line greenhouse gases (GHGs) sampling/monitoring system to investigate the seasonal and diurnal aviation of GHGs emitted from seaweeds at the Dongsha Atoll in South China Sea (CSC). The system was designed on the basis of non-dispersive infrared (NDIR) absorption to continuously measure GHGs emissions. The emissions of three GHG species (CO2, CH4, and N2O) were simultaneously monitored over the lagoon surface at the Dongsha Atoll in the summer and winter of 2021-2022, which were then converted to the vertical emission/uptake fluxes of GHGs. During the monitoring periods, the emissions of CO2, CH4, and N2O were in the ranges of 297.9-493.4, 2.7-5.7, and 1.3-9.5 ppm, respectively. In terms of seasonal variation, the GHG emissions in summer were higher than those in winter. Additionally, a significant diurnal variation of CO2 emissions was observed with lower daytime CO2 emissions than nighttime. High solar radiation in the daytime enhanced the uptake of CO2 by seaweeds via photosynthesis, and also accelerated the microbial activities in sea water and sea bed. Both effects caused the decrease of CO2 emissions. An opposite diurnal trend was observed for CH4 and N2O emissions. The production and emissions of CH4 and N2O correlated highly with the temperatures of seawater.  High temperature in the daytime facilitates microbial decomposition of organic matter in seawater and on sea bed. Biomass debris on the sea bed stimulated methanogenic bacteria to generate CH4. The production of N2O were attributed from nitrification and denitrification processes. Although the concentrations of GHG emissions from seaweeds were ordered as CO2>CH4>N2O, N2O has the highest impact on global warming potential.