The characteristics of dissolved CH4 in the Langhe Bay of the Danjiangkou Reservoir in summer
MENG Jiang-huai1, XIAO Shang-bin1,2, KANG Man-chun1,2, LIU Jia1,2, JI Dao-bin1,2, LONG Liang-hong1,2, ZHU Yi-fan3, FU Chen-le1, HAN Yan-xing1
1. College of Water Conservancy and Environment, China Three Gorges University, Yichang 443002, China; 2. Hubei Field Observation and Scientific Research Stations for Water Ecosystem in the Three Gorges Reservoir, Yichang 443002, China; 3. Central Southern China Electric Power Design Institute Co., Ltd. of China Power Engineering Consulting Group, Wuhan 430071, China
摘要 This study focuses on the dissolved CH4 concentration (CCH4), CH4 diffusive flux at the water-air interface (FCH4) and the physicochemical properties of the water body in Danjiangkou Reservoir. Using high-resolution equipment (FaRAGE), a two-day monitoring campaign was conducted from August 20th to 22nd, 2023 in the Langhe Bay, including continuous monitoring at a certain site and vertical profile monitoring at multiple sites. The results showed that the surface CCH4 and FCH4 in the reservoir bay exhibited significant spatial variability, with mean values of (0.54±0.16) μmol/L and (89.35±27.23) μg/(m2·h), respectively, and FCH4 was comparable to other water source reservoirs but generally lower than non-water-source reservoirs. Vertically, CCH4 was stratified with low levels in the surface water and high levels in the bottom water. Temporally, the nocturnal surface CCH4 and FCH4 were higher than those during the day. The results of the structural equation model indicated that spatial variations of surface CCH4 in the reservoir bay could be attributed to pH with an explanation degree of 39.17%. Vertically, water temperature and dissolved oxygen (DO) mainly drove CCH4, explaining 56.14% and 35.25% of the variance of CCH4, respectively, while 52.32% of variance of diurnal CCH4 resulted dominantly from DO. Water quality in the reservoir bay was classified as the oligotrophic status based on the comprehensive trophic level index (TLI(Σ)), and TLI(Σ) of the surface water gradually decreased longitudinally from site LH00 to LH05, with an average of (47.36±8.28). Vertically, TLI(Σ) (the mean was less than 50) was lower in the middle layer than both at the surface and bottom layers of the water column. There was no significant positive correlation between CCH4 and TLI(Σ) in the Danjiangkou Reservoir, which was different from the findings in other studies. The mesotrophic water in source reservoirs reduced the risk of algal blooms, and thereby maintained the water quality and low CH4 emissions; however, evaluating CH4 emissions using TLI(Σ) was not suitable for mesotrophic reservoirs.
Key words：Danjiangkou Reservoir；dissolved CH4；comprehensive trophic level index；dissolved oxygen；pH value
Abstract：This study focuses on the dissolved CH4 concentration (CCH4), CH4 diffusive flux at the water-air interface (FCH4) and the physicochemical properties of the water body in Danjiangkou Reservoir. Using high-resolution equipment (FaRAGE), a two-day monitoring campaign was conducted from August 20th to 22nd, 2023 in the Langhe Bay, including continuous monitoring at a certain site and vertical profile monitoring at multiple sites. The results showed that the surface CCH4 and FCH4 in the reservoir bay exhibited significant spatial variability, with mean values of (0.54±0.16) μmol/L and (89.35±27.23) μg/(m2·h), respectively, and FCH4 was comparable to other water source reservoirs but generally lower than non-water-source reservoirs. Vertically, CCH4 was stratified with low levels in the surface water and high levels in the bottom water. Temporally, the nocturnal surface CCH4 and FCH4 were higher than those during the day. The results of the structural equation model indicated that spatial variations of surface CCH4 in the reservoir bay could be attributed to pH with an explanation degree of 39.17%. Vertically, water temperature and dissolved oxygen (DO) mainly drove CCH4, explaining 56.14% and 35.25% of the variance of CCH4, respectively, while 52.32% of variance of diurnal CCH4 resulted dominantly from DO. Water quality in the reservoir bay was classified as the oligotrophic status based on the comprehensive trophic level index (TLI(Σ)), and TLI(Σ) of the surface water gradually decreased longitudinally from site LH00 to LH05, with an average of (47.36±8.28). Vertically, TLI(Σ) (the mean was less than 50) was lower in the middle layer than both at the surface and bottom layers of the water column. There was no significant positive correlation between CCH4 and TLI(Σ) in the Danjiangkou Reservoir, which was different from the findings in other studies. The mesotrophic water in source reservoirs reduced the risk of algal blooms, and thereby maintained the water quality and low CH4 emissions; however, evaluating CH4 emissions using TLI(Σ) was not suitable for mesotrophic reservoirs.
孟江槐, 肖尚斌, 康满春, 刘佳, 纪道斌, 龙良红, 朱怡帆, 付陈乐, 韩燕星. 丹江口水库浪河库湾夏季溶存CH4特征[J]. 中国环境科学, 2024, 44(11): 6302-6312.
MENG Jiang-huai, XIAO Shang-bin, KANG Man-chun, LIU Jia, JI Dao-bin, LONG Liang-hong, ZHU Yi-fan, FU Chen-le, HAN Yan-xing. The characteristics of dissolved CH4 in the Langhe Bay of the Danjiangkou Reservoir in summer. CHINA ENVIRONMENTAL SCIENCECE, 2024, 44(11): 6302-6312.
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Key words：Danjiangkou Reservoir；dissolved CH4；comprehensive trophic level index；dissolved oxygen；pH value
