中国湿地甲烷排放对二氧化碳吸收的抵消效应及机制

Offset effect and mechanism of methane emissions to carbon dioxide uptake in China’s wetlands

摘要

【目的】准确量化并提升湿地对大气二氧化碳（CO₂）的吸收能力是应对全球气候变暖的重要举措之一。然而，湿地吸收 CO₂ 的同时也会排放另外一种全球增温潜势更大的温室气体甲烷（CH₄）。系统厘清不同时间尺度、不同湿地类型 CH₄ 年排放量对 CO₂ 年吸收量的抵消效应，有助于避免对湿地碳汇功能的“单一碳汇”误判，从而科学认知其综合气候效应。【方法】本研究利用整合分析方法，系统收集并整理了我国内陆湿地和滨海湿地共计 141 个站点全年监测的生态系统净 CO₂ 交换量（NEE）数据，以及 41 个站点全年 CH₄ 排放量数据，采用 Bootstrap 重采样法计算不同环境条件（如湿地类型、地理位置）下年平均 NEE 和 CH₄ 通量、NEE 与 CH₄ 净辐射平衡以及 CH₄ 排放对 NEE 的抵消效应。【结果】研究结果表明：（1）湿地类型上，所有湿地均表现为大气 CO₂ 的汇（负通量代表汇，负值越小表示汇越强），年 NEE 值排序为滨海红树林湿地（–29 672（–32 228 ~ –27 391）kg/hm²） < 滨海草本湿地（–12 029（–15 078 ~ –9 173）kg/hm²） < 内陆草本湿地（–8 819（–10 786 ~ –6 941）kg/hm²） < 富营养泥炭地（–5 006（–6 520 ~ –3 480）kg/hm²） < 贫营养泥炭地（–4 745（–7 136 ~ –2 452）kg/hm²）；所有湿地均表现为大气 CH₄ 的源，年 CH₄ 排放量则表现为富营养泥炭地（437（385 ~ 483）kg/hm²）、内陆草本湿地（319（228 ~ 404）kg/hm²）显著高于滨海草本湿地（120（75 ~ 165）kg/hm²）、贫营养泥炭地（91（74 ~ 113）kg/hm²）及滨海红树林湿地（87（53 ~ 126）kg/hm²）（数值表示为平均值及其95% 置信区间，下同）。（2）地理位置上，滨海湿地的年NEE（–19 719（–22 420 ~ –16 940）kg/hm²）显著低于内陆湿地（–6 215（–7 384 ~ –5 052）kg/hm²）；而滨海湿地的年 CH₄ 排放量（96（63 ~ 130）kg/hm²）约为内陆湿地（282（222 ~ 345）kg/hm²）的三分之一。（3）气候带上，亚热带湿地的年 NEE（–24 992（–27 590 ~ –22 428）kg/hm²）显著低于温带湿地（–6 237（–7 372 ~ –5 147）kg/hm²），而温带湿地的年 CH₄ 排放量（390（323 ~ 449）kg/hm²）显著高于亚热带湿地（109（86 ~ 133）kg/hm²）。（4）植被功能群上，以森林植物（–29 672（–32 198 ~ –27 434）kg/hm²）或禾本科植物（–11 646（–14 052 ~ –9 396）kg/hm²）为主的湿地，其年 NEE 显著低于以藓类（–7 036（–10 564 ~ –3 350）kg/hm²）或莎草科植物（–4 954（–6 103 ~ –3 800）kg/hm²）为主的湿地，但年 CH₄ 排放量则是莎草科植物（410（337 ~ 471）kg/hm²）为主的湿地最高，其次是以禾本科植物（259（175 ~ 347）kg/hm²）为主的湿地，而以藓类（90（72 ~ 115）kg/hm²）和森林植物（87（53 ~ 127）kg/hm²）为主的湿地最低。此外，本研究也表明中国自然湿地中年 CO₂ 吸收量和 CH₄ 排放量随纬度递增、经度呈抛物线变化趋势。环境因子对年 CO₂ 吸收量和 CH₄ 排放量影响存在差异，年 CO₂ 吸收量随年平均气温（MAT）、降水量（MAP）等 7 项指标增加均线性增加，而年 CH₄ 排放量随 MAT、MAP、盐度线性降低，随地下水位深度呈抛物线变化且水位在地表以下 20 cm 至接近地表的 0 cm 范围内达排放峰值，随土壤有机碳含量（SOC）的增加而呈对数递增趋势。在 20 ~ 500 年不同时间尺度上，年 CO₂ 吸收量和 CH₄ 排放量的净辐射平衡均随经度先降后升高且均随 MAT、MAP、土壤温度、地下水位深度增加而线性降低，增温效应随之减弱。【结论】就净辐射平衡时间动态变化而言，在 20 ~ 100 年尺度上，CH₄ 排放可完全抵消内陆湿地、部分抵消滨海湿地的 CO₂ 吸收；而在 500 年尺度上，CH₄ 排放仅能部分抵消内陆湿地的 CO₂ 吸收，对滨海湿地 CO₂ 吸收的抵消作用则微乎其微。因此，从长期视角来看，我国内陆湿地和滨海湿地均是持续性的含碳温室气体的净汇，且单位面积尺度上滨海湿地在应对气候变化方面的效果优于内陆湿地。

Abstract

[Objective] Maximizing carbon dioxide (CO₂) uptake in wetlands is part of the global effort to combat climate warming. Yet, the simultaneously emitted potent greenhouse gas methane (CH₄) from wetlands may counterbalance their CO₂ uptake potentially. Studying the offset effect of annual CH₄ emissions to annual CO₂ uptake across different time scales and across different types of wetlands can avoid the misjudgment of “single carbon sink”, is conducive to fully understanding the carbon sink function of wetlands. [Method] In this study, using the meta-analysis method, 141 years of data on net ecosystem CO₂ exchange (NEE) and 41 years of data on CH₄ fluxes were collated from different types of natural wetlands in China, including inland peatlands, marshes, coastal marshes, and mangroves. The Bootstrap resampling method was used to estimate annual mean NEE and CH₄ fluxes, the net radiative balance between NEE and CH₄, and the offsetting effect of CH₄ emissions to NEE across various environmental conditions (e.g., wetland types and geographic locations). [Result] We find that, in terms of wetland types, all wetlands function as net sinks for atmospheric CO₂ (negative flux represents sink and a smaller negative value indicates a stronger sink), and annual NEE increased following the order of coastal mangroves (–29 672 (–32 228 ~ –27 391) kg/ha), coastal marshes (–12 029 (–15 078 ~ –9 173) kg/ha), inland marshes (–8 819 (–10 786 ~ –6 941) kg/ha), fens (–5 006 (–6 520 ~ –3 480) kg/ha), and peatland bogs (–4 745 (–7 136 ~ –2 452) kg/ha), while all wetlands function as net sources for atmospheric CH₄, and annual CH₄ emission rates were significant greater from peatland fens (437 (385 ~ 483) kg/ha) and inland marshes (319 (228 ~ 404) kg/ha) than those from coastal marshes (120 (75 ~ 165) kg/ha), peatland bogs (91 (74 ~ 113) kg/ha) and coastal mangroves (87 (53 ~ 126) kg/ha) (data is indicated as mean with 95% confidence interval, the same below). For the wetland location, annual NEE of coastal wetlands (–19 719 (–22 420 ~ –16 940) kg/ha) is significantly lower than inland wetlands (–6 215 (–7 384 ~ –5 052) kg/ha) while annual CH₄ emission rate from coastal wetlands (96 (63 ~ 130) kg/ha) is approximately one-third of inland wetlands (282 (222 ~ 345) kg/ha). With regard to the climate zone, subtropical wetlands (–24 992 (–27 590 ~ –22 428) kg/ha) showed significantly lower annual NEE than temperate wetlands (–6 237 (–7 372 ~ –5 147) kg/ha), while annual CH₄ emissions are significant greater for temperate wetlands (390 (323 ~ 449) kg/ha) than subtropical wetlands (109 (86 ~ 133) kg/ha). Considering the plant functional group, wetlands dominated by the forest (–29 672 (–32 198 ~ –27 434) kg/ha) or graminoid species (–11 646 (–14 052 ~ –9 396) kg/ha) showed significantly lower annual NEE than wetlands dominated by moss (–7 036 (–10 564 ~ –3 350) kg/ha) or sedge species (–4 954 (–6 103 ~ –3 800) kg/ha), while annual CH₄ emissions is greatest in wetlands dominated by sedge species (410 (337 ~ 471) kg/ha), followed by graminoid species (259 (175 ~ 347) kg/ha) and lowest in wetlands dominated by moss (90 (72 ~ 115) kg/ha) and forest species (87 (53 ~ 127) kg/ha). Moreover, annual CO₂ uptake rates were significantly decreased and CH₄ emission rates were significantly increased with the increasing latitudes from 20°N to 55°N while exhibited parabolic trend with longitudes across natural wetlands in China. There exist distinct differences in the impacts of environmental factors on annual CO₂ uptake rates and CH₄ emission rates. Annual CO₂ uptake rates exhibit a linear increase with the increase of seven indicators, including mean annual temperature (MAT) and mean annual precipitation (MAP). In contrast, annual CH₄ emissions decrease linearly with MAT, MAP, and salinity; display a parabolic variation with water table depth (WTD), peaking within the range of 20 cm below the soil surface to 0 cm of soil surface; and show a logarithmic increasing trend with the increase of soil organic carbon (SOC) content. Across time scales spanning from 20 to 500 years, the net radiation balance of CO₂ uptake rates and CH₄ emission rates first decreases and then increases with longitude, while both linearly decline with the increase of MAT, MAP, soil temperature (T_s), and WTD, accompanied by a corresponding weakening of the warming effect. [Conclusion] In conclusion, from the perspective of temporal variations of net radiative forcing, the positive radiative forcing of annual CH₄ emissions can completely and partially offset the negative radiative forcing of annual CO₂ uptake from inland and coastal wetlands, respectively, over 20- to 100-yr timeframes, while partially and marginally offset CO₂ uptake from inland and coastal wetlands, respectively, over 500-yr timeframe. Therefore, inland and coastal wetlands function as persistently C-based net greenhouse gas sinks from the long-term perspective and the latter is more effective natural climate solutions than the former on a per-unit-area basis.

关键词

滨海湿地 / 内陆湿地 / 甲烷 / 生态系统净 CO₂ 交换量 / 抵消效应

Key words

coastal wetland / inland wetland / methane / net ecosystem exchange of CO₂ / offset

参考文献

[1] Fawzy S, Osman A I, Doran J, et al. Strategies for mitigation of climate change: a review [J].Environmental Chemistry Letters, 2020, 18(6): 2069-2094.

[2] Aurela M, Laurila T, Tuovinen J P. Annual CO₂ balance of a subarctic Fen in northern Europe: importance of the wintertime efflux [J].Journal of Geophysical Research: Atmospheres, 2002, 107(D21): ACH17−1-ACH17−12.

[3] Mitsch W J, Bernal B, Nahlik A M, et al. Wetlands, carbon, and climate change [J].Landscape Ecology, 2013, 28(4): 583-597.

[4] Helbig M, Chasmer L E, Desai A R, et al. Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest—wetland landscape [J].Global Change Biology, 2017, 23(8):3231-3248.

[5] Yao H, Peng H J, Hong B, et al. Environmental controls on multi—scale dynamics of net carbon dioxide exchange from an alpine peatland on the eastern Qinghai—Tibet Plateau [J].Frontiers in Plant Science, 2022, 12: 791343.

[6] Bansal S, Post van der Burg M, Fern R R, et al. Large increases in methane emissions expected from North America’s largest wetland complex [J].Science Advances, 2023, 9(9): eade1112.

[7] Delwiche K B, Knox S H, Malhotra A, et al. FLUXNET—CH₄: a global, multi—ecosystem dataset and analysis of methane seasonality from freshwater wetlands [J].Earth System Science Data, 2021, 13(7): 3607-3689.

[8] Peng H J, Chi J S, Yao H, et al. Methane emissions offset net carbon dioxide uptake from an alpine peatland on the eastern Qinghai—Tibetan Plateau [J].Journal of Geophysical Research: Atmospheres, 2021, 126(19): e2021JD034671.

[9] Liu J G, Zhou Y L, Valach A, et al. Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half [J].Global Change Biology, 2020, 26(9): 4998-5016.

[10] Lan X, Thoning K, Dlugokencky E. Trends in globally—averaged CH₄, N₂O, and SF₆ determined from NOAA Global Monitoring Laboratory measurements [EB/OL].2023 [2025−10−19].https://gml.noaa.gov/ccgg/trends_ch4/.

[11] Voosen P. Global alarm system watches for methane [J].Science, 2023, 379: 528.

[12] Forster P. The Earth’s energy budget, climate feedbacks, and climate sensitivity [R] // Masson—Delmotte V, Zhai P, Pirani A,et al. Climate change 2021—the physical science basis: contribution of working group I to thesixth assessment report of the Intergovernmental panel on climate change. Cambridge: Cambridge University Press, 2021.

[13] Lehner B, Döll P. Development and validation of a global database of lakes, reservoirs and wetlands [J].Journal of Hydrology, 2004, 296(1−4): 1-22.

[14] Mao D H, Wang Z M, Du B J, et al. National wetland mapping in China: a new product resulting from object—based and hierarchical classification of Landsat 8 OLI images [J].ISPRS Journal of Photogrammetry and Remote Sensing, 2020, 164: 11-25.

[15] Meng W Q, He M X, Hu B B, et al. Status of wetlands in China: a review of extent, degradation, issues and recommendations for improvement [J].Ocean & Coastal Management, 2017, 146: 50-59.

[16] Lund M, Lafleur P M, Roulet N T, et al. Variability in exchange of CO₂ across 12 northern peatland and tundra sites [J].Global Change Biology, 2010, 16(9): 2436-2448.

[17] Lu W Z, Xiao J F, Liu F, et al. Contrasting ecosystem CO₂ fluxes of inland and coastal wetlands: a meta—analysis of eddy covariance data [J].Global Change Biology, 2017, 23(3): 1180-1198.

[18] Ma L, Gan D Z, Li Z, et al. Magnitudes, patterns, controls and mitigation potentials of net ecosystem carbon balances across wetlands in China [J].Geoderma, 2025, 458: 117332.

[19] Fan B X, Peng H J, Ran J C, et al. Environmental and microbial regulation of multi—temporal scale methane flux dynamics in a shallow karst lake [J].Water Research, 2026, 294: 125511.

[20] Zhao X S, Fan X W, Griffis T J, et al. Three gorges dam operations affect the carbon dioxide budget of a large downstream connected lake [J].Geophysical Research Letters, 2023, 50(12): e2022GL102697.

[21] 邱吉丽, 张弥, 蒲旖旎, 等. 涡度相关观测的太湖 CH₄ 通量数据插补方法评价 [J].应用生态学报, 2022, 33(10): 2785-2795.

[22] Qiu J L, Zhang M, Pu Y N, et al. Evaluation of gap—filling methods for CH₄ flux data based on eddy covariance method in the Lake Taihu, China [J].Chinese Journal of Applied Ecology, 2022, 33(10): 2785-2795.

[23] Du Q, Liu H Z, Liu Y, et al. Factors controlling evaporation and the CO₂ flux over an open water lake in southwest of China on multiple temporal scales [J].International Journal of Climatology, 2018, 38(13): 4723-4739.

[24] 展鹏飞, 仝川. 甲烷排放部分抵消湿地生态系统碳汇功能: 全球数据分析 [J].应用生态学报, 2023, 34(11): 2958-2968.

[25] Zhan P F, Tong C. Methane emissions partially offset carbon sink function in global wetlands: an analysis based on global data [J].Chinese Journal of Applied Ecology, 2023, 34(11): 2958-2968.

[26] 罗玲, 王宗明, 毛德华, 等. 沼泽湿地主要类型英文词汇内涵及辨析 [J].生态学杂志, 2016, 35(3): 834-842. Luo L,

[27] Wang Z M, Mao D H, et al. Connotation and differentiation of terminology on main kinds of wetlands in English [J].Chinese Journal of Ecology, 2016, 35(3): 834-842.

[28] 胡楠, 范玉龙, 丁圣彦, 等. 陆地生态系统植物功能群研究进展 [J].生态学报, 2008, 28(7): 3302-3311.

[29] Hu N, Fan Y L, Ding S Y, et al. Progress in researches on plant functional groups of terrestrial ecosystems [J].Acta Ecologica Sinica, 2008, 28(7): 3302-3311.

[30] Neubauer S C, Megonigal J P. Moving beyond global warming potentials to quantify the climatic role of ecosystems [J].Ecosystems, 2015, 18(6): 1000-1013.

[31] Ma L, Zhu G F, Chen B L, et al. A globally robust relationship between water table decline, subsidence rate, and carbon release from peatlands [J].Communications Earth & Environment, 2022, 3: 254.

[32] Deshmukh C S, Susanto A P, Nardi N, et al. Net greenhouse gas balance of fibre wood plantation on peat in Indonesia [J].Nature, 2023, 616: 740-746.

[33] Evans C D, Peacock M, Baird A J, et al. Overriding water table control on managed peatland greenhouse gas emissions [J].Nature, 2021, 593: 548-552.

[34] Reithmaier G M S, Cabral A, Akhand A, et al. Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes [J].Nature Communications, 2023, 14: 8196.

[35] Gan D Z, Zhang Z L, Li H N, et al. Ditch emissions partially offset global reductions in methane emissions from peatland drainage [J].Communications Earth & Environment, 2024, 5: 640.

[36] Le Mer J, Roger P. Production, oxidation, emission and consumption of methane by soils: a review [J].European Journal of Soil Biology, 2001, 37(1): 25-50.

[37] Capooci M, Seyfferth A L, Tobias C, et al. High methane concentrations in tidal salt marsh soils: where does the methane go? [J].Global Change Biology, 2024, 30(1): e17050.

[38] Al—Haj A N, Fulweiler R W. A synthesis of methane emissions from shallow vegetated coastal ecosystems [J].Global Change Biology, 2020, 26(5): 2988-3005.

[39] Poffenbarger H J, Needelman B A, Megonigal J P. Salinity influence on methane emissions from tidal marshes [J].Wetlands, 2011, 31(5): 831-842.

[40] Page S E, Baird A J. Peatlands and global change: response and resilience [J].Annual Review of Environment and Resources, 2016, 41: 35-57.

[41] Kuwae T, Watanabe A, Yoshihara S, et al. Implementation of blue carbon offset crediting for seagrass meadows, macroalgal beds, and macroalgae farming in Japan [J].Marine Policy, 2022, 138: 104996.

[42] Murray B C, Pendleton L, Jenkins W A, et al. Green payments for blue carbon: economic incentives for protecting threatened coastal habitats: NI R 11—04 [R]. Durham, North Carolina: Nicholas Institute for Environmental Policy Solutions, Duke University,2011.

基金资助

甘肃省基础研究计划−软科学专项项目(26JRZA155)

甘肃省重点人才项目(2026RCXM008)

国家自然科学基金项目(32471767、32241035)