杭州湾沉积物中硫酸盐—甲烷转换带内的碳循环

贺行良; 谭丽菊; 段晓勇; 印萍; 谢永清; 杨磊; 董超; 王江涛

doi:10.16562/j.cnki.0256-1492.2020021401

杭州湾沉积物中硫酸盐—甲烷转换带内的碳循环

贺行良^1,2,3,,
谭丽菊¹,
段晓勇^2,3, ,,
印萍^2,3,
谢永清⁴,
杨磊⁴,
董超⁴,
王江涛¹

1.
中国海洋大学海洋化学理论与工程技术教育部重点实验室，青岛 266100
2.
青岛海洋科学与技术国家实验室海洋矿产资源评价与探测技术功能实验室，青岛 266237
3.
中国地质调查局青岛海洋地质研究所，青岛 266071
4.
浙江省水文地质工程地质大队，宁波 315012

基金项目: 国家地质调查项目“浙江中部海岸带综合地质调查”（DD20190276），“长江口等重点海岸带综合地质调查”（DD20160145）；国家自然科学基金“海洋沉积物中天然气水合物分解释放气体的氧化特性研究”（41406076）；浙江省地质矿产专项资金“浙江省海岸带重点区综合地质调查（嘉兴重点区）”（【省资】2017005）

详细信息

作者简介:
贺行良（1982—），男，高级工程师，主要研究方向为海洋生物地球化学，E-mail：76791772@qq.com

通讯作者:
段晓勇（1987—），男，副研究员，主要研究方向为环境地球化学，E-mail：duan-xy@qq.com

中图分类号: P76
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出版历程
- 收稿日期: 2020-02-13
- 修回日期: 2020-03-16
- 网络出版日期: 2020-05-05
- 刊出日期: 2020-05-31

Carbon cycle within the sulfate-methane transition zone in the marine sediments of Hangzhou Bay

1.
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
2.
Evaluation and Detection Technology Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
3.
Qingdao Institute of Marine Geology, Qingdao 266071, China
4.
Zhejiang Institute of Hydrogeology and Engineering Geology, Ningbo 315012, China

摘要

摘要: 杭州湾海底沉积物中蕴藏着大量的浅层生物气，作为温室气体CH₄的重要载体，研究其甲烷厌氧氧化（AOM）及相关碳循环过程，对正确评估浅层生物气的生态环境效应具有重要的科学意义。通过对YS6孔柱状沉积物孔隙水、顶空气等地球化学参数的测试分析，基于质量平衡和碳同位素质量平衡原理，利用“箱式模型”定量研究了硫酸盐—甲烷转换带（SMTZ）内的碳循环过程。结果表明：SMTZ位于海底约6～8 mbsf沉积层，其内部碳循环过程除了包含有机质的硫酸盐还原（OSR）、AOM和碳酸盐沉淀（CP）反应外，还隐藏存在“AOM生成的溶解无机碳（DIC）”产甲烷反应（CR），反应速率分别为9.14、7.42、4.36、2.72 mmol·m⁻²·a⁻¹，而有机质降解产甲烷反应（ME）未发生。各反应对SMTZ内孔隙水DIC的补充贡献率为OSR＞AOM＞ME，而对DIC的消耗贡献率CP＞CR。深部含甲烷沉积层向上扩散而来的CH₄并不是驱动SMTZ内部SO₄²⁻还原的唯一电子供体，CR和OSR反应亦是导致进入SMTZ内硫酸盐扩散通量大于甲烷的重要因素，且SMTZ下边缘沉积层出现明显的¹³CH₄亏损亦与CR反应有关。本研究认为，定量评估海底沉积物中AOM作用的相对强弱时，SMTZ内可能存在的“隐藏的”产甲烷作用（如CR、ME等）不能忽视。
- 甲烷厌氧氧化 /
- 硫酸盐—甲烷转换带内碳循环 /
- “隐藏的”产甲烷作用 /
- 箱式模型 /
- 杭州湾
Abstract: Large amount of shallow biogenic gas occurs in the marine sediments of Hangzhou Bay. As an important greenhouse gas and carbon carrier, methane and its anaerobic oxidation (AOM) and carbon cycle within the sulfate-methane transition zone (SMTZ) in marine sediments are of great significance for accurately assessment of the eco-environmental effects. Based on the test results and geochemical parameters, such as those from pore water and headspace gas in the YS6 sediment cores, following the principles of mass conservation and carbon isotope mass conservation, the internal carbon cycle in SMTZ for the YS6 was quantitatively studied with the “box model”. It is found that the SMTZ occurs in the 6～8 mbsf sediment layer.In addition to organoclastic sulfate reduction (OSR), AOM and carbonate precipitation (CP), there are concealed methanogenesis by carbon dioxide reduction of DIC produced from AOM (CR). However, methanogenesis from organic matter degradation (ME) almost not observed in the SMTZ-internal carbon cycling. The reaction rates of OSR, AOM, CP, CR and ME were 9.14 mmol·m⁻²·yr⁻¹, 7.42 mmol·m⁻²·yr⁻¹, 4.36 mmol·m⁻²·yr⁻¹, 2.72 mmol·m⁻²·yr⁻¹ and 0.00 mmol·m⁻²·yr⁻¹, respectively. The contribution rate of each reaction to pore water DIC in SMTZ was in an order of OSR＞AOM＞ME (ME= 0), while the consumption rate was CP＞CR. Methane diffused upward from deeper methane zone was not the only electron donor to drive the internal sulfate reduction (SR) in SMTZ. CR and OSR were also the important factors for sulfate flux into SMTZ to be greater than methan , and the obvious ¹³C-depletion of methane in the lower border of SMTZ was also related to the CR. When quantitatively evaluating the relative strength of AOM in marine sediments, the “cryptic” methanogenesis (such as CR, ME, etc.) in SMTZ cannot be ignored.
- AOM /
- SMTZ-internal carbon cycling /
- cryptic methanogenesis /
- box model /
- Hangzhou Bay

HTML全文

图 1 YS 6站位位置

Figure 1. Map showing the locations of Core YS 6 in Hangzhou Bay

下载: 全尺寸图片幻灯片

图 2 SMTZ内碳循环“箱式模型”图^[14]

溶解组分用黄色框表示，固体组分用灰色框表示；灰线箭头表示模型域之外的DIC、SO₄²⁻和CH₄的输入/输出；5个主要反应路径AOM、OSR、CR、ME和CP分别用不同颜色的箭头标识。

Figure 2. Illustration of box model for SMTZ-internal carbon cycling^[14]

The dissolved components are shown in yellow and the solid components in gray; The gray arrow represents the input/output of DIC, SO₄²⁻ and CH₄ outside the box model; The reaction paths of AOM, OSR, CR, ME and CP are marked by different colored arrows.

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图 3 YS6孔孔隙水部分溶解组分的垂直分布剖面

阴影为SMTZ示意层；0 mbsf处为底层海水数据。

Figure 3. Pore water profiles of Core YS6

Yellow shaded layer for SMTZ; Green shaded layer for MEZ; the data of 0 mbsf from bottom water.

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图 4 5种反应对SMTZ内DIC碳库的相对贡献率

Figure 4. The relative contribution of each reaction to pore water DIC in SMTZ

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表 1 孔隙水部分溶解组分的扩散通量

Table 1 Diffusion fluxes of dissolved components in pore water

组分	扩散系数D₀/（m²·s⁻¹）	扩散通量F/（mmol·m⁻²·a⁻¹）	符号
SO₄²⁻	8.91E-10	11.87	F_SO4.in
CH₄	1.39E-09	4.65	F_CH4.in
Ca²⁺	6.72E-10	2.29	F_Ca.in
Ca²⁺	6.72E-10	0.76	F_Ca.out
Mg²⁺	5.91E-10	4.15	F_Mg.in
Mg²⁺	5.91E-10	1.33	F_Mg.out
DIC	9.89E-10	16.72	F_DIC.out
DIC	9.89E-10	7.23	F_DIC.in

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表 2 SMTZ内轻、重碳同位素反应速率和总反应速率

Table 2 The reaction rates of light and heavy carbon isotopes in SMTZ and the total reaction rates

项目	参数	计算结果
轻、重DIC通量（mmol·m⁻²·a⁻¹）	¹²F_DIC.out	−16.53
	¹²F_DIC.in	−7.15
	¹³F_DIC.out	−0.18
	¹³F_DIC.in	−0.08
碳同位素值（‰）	δ¹³C_OM	−23.32
	δ¹³C_CH4-SMTZ	−90.34
	δ¹³C_DIC-SMTZ	−17.04
	δ¹³C_CH4-bottom	−71.31
	δ¹³C_DIC-bottom	−0.42
¹³C/¹²C比值	r_std	0.011 237
	r_OM	0.010 975
	r_CH4-SMTZ	0.010 222
	r_DIC-SMTZ	0.011 046
	r_CH4-bottom	0.010 436
	r_DIC-bottom	0.011 232
分馏系数	α_CR	1.070 9
	α_AOM	1.017 0
反应分数	f	0.00	0.50	1.00
	b	0.37	0.37	0.37
轻同位素反应速率（mmol·m⁻²·a⁻¹）	¹²R_AOM	11.87	9.26	7.35
	¹²R_CR	4.35	3.39	2.69
	¹²R_CP	4.31	4.31	4.31
	¹²R_OM	12.34	10.44	9.04
	¹²R_ME	12.34	5.22	0.00
	¹²R_ME-CH4	6.17	2.61	0.00
	¹²R_ME-DIC	6.17	2.61	0.00
	¹²R_OSR-C	0.00	5.22	9.04
重同位素反应速率（mmol·m⁻²·a⁻¹）	¹³R_AOM	0.12	0.09	0.07
	¹³R_CR	0.04	0.03	0.03
	¹³R_CP	0.05	0.05	0.05
	¹³R_OM	0.14	0.11	0.10
	¹³R_ME	0.14	0.06	0.00
	¹³R_ME-CH4	0.06	0.03	0.00
	¹³R_ME-DIC	0.07	0.03	0.00
	¹³R_OSR-C	0.00	0.06	0.10
总反应速率（mmol·m⁻²·a⁻¹）	R_AOM	11.99	9.35	7.42
	R_CR	4.39	3.42	2.72
	R_CP	4.36	4.36	4.36
	R_OM	12.48	10.55	9.14
	R_ME	12.48	5.28	0.00
	R_ME-CH4	6.24	2.64	0.00
	R_ME-DIC	6.24	2.64	0.00
	R_OSR-C	0.00	5.28	9.14
甲烷通量绝对差值（mmol·m⁻²·a⁻¹)	△F_CH4	3.29	1.36	0.06
注：△F_CH4= F_CH4.in−（R_AOM−R_CR−R_ME-CH4）。

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