Dynamic characteristics and degradation transformation mechanism of dissolved organic matter in estuarine wetlands: A case study of Chongming Dongtan salt marsh wetland in Shanghai

doi:10.3969/j.issn.1000-5641.2025.02.006

Abstract

Abstract:

Estuarine wetlands are important components of coastal ecosystems that contribute tremendously to global blue carbon sinks. The amount and quality of dissolved organic matter (DOM) vary significantly with tidal exchange and seasonal cycles. Focusing on the Chongming Dongtan salt marshes in Shanghai under the influence of the Yangtze River, we conducted high-frequency sampling across a complete tidal cycle in each season and characterized the dynamics of the quantity (expressed by the C content in DOM, i.e., the concentration of dissolved organic carbon (DOC)) and spectral characteristics (expressed by the light absorption characteristics of chromophoric DOM (CDOM)) of DOM across tidal and seasonal scales. The results indicated that on the tidal scale, waters leaving the marshes during the ebbing tide were rich in DOC, strong in optical absorbance (${a_{{\rm{CDOM}}}} $(350) and ${a_{{\rm{CDOM}}}^*} $(350)), with high aromaticity (specific ultraviolet absorbance, SUVA₂₅₄) and low spectral slope (S_275-295), compared to water entering the marshes during the flooding tide. On a seasonal scale, waters in the ebbing tide during summer and fall had elevated DOC concentrations, high absorption and aromaticity, and correspondingly lower spectral slopes relative to waters collected in winter and spring. The results of on-site incubation experiments demonstrated that photochemical degradation was the major process that removed the colored fraction from the DOM pool, whereas microbial processing played an important role in affecting the bulk DOM. This study helps improve our understanding of the dynamics of marsh DOM and the mechanisms of its degradation processes associated with lateral transport from estuarine marshes to adjacent estuaries.

Key words: estuary salt marshes, dissolved organic carbon, chromophoric dissolved organic matter, tidal exchange, biogeochemical cycle

CLC Number:

P748

Run LI, Jienan CHEN, Hao CHEN, Fang CAO. Dynamic characteristics and degradation transformation mechanism of dissolved organic matter in estuarine wetlands: A case study of Chongming Dongtan salt marsh wetland in Shanghai[J]. J* E* C* N* U* N* S*, 2025, 2025(2): 55-67.

Figures/Tables 7

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季节	采样时间	潮汐状况	潮差/m	样品数量/个
季节	采样时间	潮汐状况	潮差/m	CDOM	DOC
早春	2023年2月10—11日	小潮	1.49	25	25
夏季	2022年6月13—14日	大潮	2.32	17	17
秋季	2022年9月16—17日	小潮	1.57	25	25
冬季	2021年12月18—19日	大潮	1.21	25	25
合计				92	92

培养实验	${a_{{\rm{CDOM}}}} $(350)/m^–1	c_DOC/(mg·L^–1)	S_275-295/nm^–1	${a_{{\rm{CDOM}}}^*} $(350)/(m²·g^–1)
培养前 (t = 0)	8.37	6.78	0.016	1.23
光化学降解 (A组)	6.23 ± 0.02	6.04 ± 0.16	0.017 ± 0.0001	1.03 ± 0.03
微生物降解 (B组)	7.77 ± 0.14	6.02 ± 0.11	0.016 ± 0.00004	1.29 ± 0.02
光化学 + 微生物降解 (C组)	6.10 ± 0.13	6.07 ± 0.07	0.018 ± 0.0003	1.01 ± 0.02
对照组 (避光 + 去除微生物影响, D组)	7.81 ± 0.07	6.25 ± 0.10	0.016 ± 0.0001	1.25 ± 0.01

研究区域	c_DOC/(mg·L^–1)	S_275-295/nm^–1	SUVA₂₅₄/(L·mg^–1·m^–1)	参考文献
美国Kirkpatrick盐沼湿地	春季: 2.9 ~ 7.1; 夏季: 4.4 ~ 713.5; 秋季: 3.4 ~ 711.2	N/A	N/A	[21]
美国北卡罗来纳州东部盐沼湿地	5月: 9.6 ± 2.6; 7月: 11.7 ± 2.8; 8月: 10.0 ± 2.4; 10月: 10.4 ± 2.1	N/A	N/A	[19]
新英格兰尼庞西特盐沼湿地	春季: 3.6 ± 1.44; 夏季: 4.56 ± 0.84; 秋季: 4.68 ± 0.96; 冬季: 3.12 ± 2.88	N/A	N/A	[56]
崇明西沙盐沼湿地	春季: 2.23; 夏季: 4.10; 秋季: 2.70; 冬季: 1.78 夏季强降雨后 LT: 6.87 夏季洪水事件后: 2.97	夏季 LT: 0.0169 ± 0.0002	夏季 LT: 5.31 ± 0.06	[55]
上海九段沙盐沼湿地	春季: 2.06 ± 0.77; 夏季: 2.81 ± 0.98; 秋季: 2.70 ± 0.85; 冬季: 1.67 ± 0.94	夏季 LT: 0.0167 ± 0.0002	夏季 LT: 6.85 ± 0.11	[55]
崇明东滩盐沼湿地	春季: 2.64 ± 0.83; 夏季: 3.04 ± 1.26; 秋季: 2.50 ± 0.84; 冬季: 2.39 ± 0.33	夏季 LT: 0.0169 ± 0.0007	夏季 LT: 5.37 ± 0.12	本研究

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[2]	ZHU Kun, WU Ying, Qi Lijun. Spatiotemporal variations and influencing factors of organic carbon content in the urban rivers of Shanghai [J]. Journal of East China Normal University(Natural Science), 2020, 2020(1): 150-158.