Effects of Spartina alterniflora invasion on mercury speciation in vegetated sediments of the wetland in Changjiang River Estuary, China
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摘要: 通过分析长江河口湿地典型植物根际沉积物柱样(0～40 cm)中总汞(THg)、甲基汞(MeHg)及其与粒度、总有机碳(TOC)、还原态硫等环境因子之间的关系，探讨了互花米草(Spartina alterniflora)入侵对沉积物中汞形态特征的影响及主控因子。结果表明：(1)不同植物(互花米草、芦苇(Phragmites communis)、海三棱藨草(Scirpus mariqueter)和水葱(Scirpus tabernaemontani))根际沉积物中THg均值为49.9～100.9 μg/kg，其与粒径小于16 µm颗粒物组分体积百分比及TOC含量之间存在显著正相关关系(r2=0.85，p<0.01；r2=0.58，p<0.01)，这意味着沉积物中矿物−有机物复合体细颗粒物的空间分异决定着总汞的空间分异。互花米草入侵促进了细颗粒的沉积，进而间接促进了沉积物中总汞含量的增加。(2)不同植物根际沉积物中MeHg均值为0.3～1.4 μg/kg，MeHg/THg均值为0.4%～1.4%，互花米草、芦苇及海三棱藨草根际沉积物中MeHg含量及MeHg/THg值随深度增加不断减小，但无显著差异，表明了互花米草入侵对沉积物中汞甲基化过程的影响可能有限。Pearson相关分析表明，MeHg/THg与THg、TOC、酸挥发性硫之间不存在显著的正相关关系。硫的K边同步辐射结果进一步表明了硫形态(如有机硫和S2−)变化与MeHg变化关系不大。MeHg/THg值呈表层(0～8 cm)高，底层低的分布规律，表明了表层沉积物中汞的甲基化潜势较大，这可能与表层新鲜有机质(如藻类和植物凋落物)的不断供给及其降解过程密切相关，还需深入研究。Abstract: To investigate the changes in mercury (Hg) speciation in vegetated sediments of the wetlands in Changjiang River Estuary, China, following the invasion of Spartina alterniflora, we determined total mercury (THg), methylmercury (MeHg), toatal organic carbon (TOC), reduced sulfur (S) and grain size in core sediments (0−40 cm) vegetated with different plants in wetlands. The results showed that: (1) the mean concentrations of THg were 49.9−100.9 μg/kg in sediments vegetated by S. alterniflora,
Phragmites communis, Scirpus mariqueter and Scirpus tabernaemontani had a significant positive correlation with the fraction of fine particles (<16 µm) and TOC content (r2=0.85, p<0.01; r2 =0.58, p<0.01), indicating that the distribution of Hg levels in sediments could be dominated by the spatial differentiation of the mineral-organic complexes in fine particles. The invasion of S. alterniflora promoted the deposition of fine particles, and thus could facilitate Hg storage indirectly in wetland sediments. (2) The mean concentrations MeHg and average values of MeHg/THg (%) in vegetated sediments were 0.3−1.4 μg/kg and 0.4%−1.4%, respectively. The profiles of MeHg and MeHg/THg exhibited decrease with increasing depth across all sites. There was no significant difference in the content of MeHg and the values of MeHg/THg in vegetated sediments dominated by S. alterniflora, P. australis and S. mariqueter, indicating that the impact of S. alterniflora invasion on Hg methylation may be limited. In addition, there was no significant positive correlation between MeHg/THg and THg, TOC and acid volatile sulfur (AVS). S-K edge XANES further revealed that the reduced sulfur (S) (e. g., thoil and sulfide) changed greatly in depth profiles. These results suggested that the changes in reduced sulfur could have limited impacts on MeHg production. The values of MeHg/THg was higher in surface horizon (0～8 cm) than in deeper horizon, indicating that the higher rates of Hg methylation in surface sediments and the degradation of fresh organic matter (e. g., algae and plant litter) could be the key biogeochemical process on controlling MeHg production in surface sediments of wetland in Changjiang River Estuary. -
Key words:
- sediment /
- mercury /
- acid volatile sulfur /
- spartina alterniflora /
- Changjiang River Estuary /
- wetland
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图 1 研究区域与采样点（A、B、C1、C2和D）分布示意图
Fig. 1 Map of the study area showing sampling locations (A, B, C1, C2 and D) for cores
图 2 长江河口湿地不同植物根际沉积物中THg含量与THg/TOC值特征
a1, b1. 互花米草；a2, b2. 芦苇；a3, b3. 海三棱藨草；a4, b4. 水葱
Fig. 2 Concentrations of total Hg and THg/TOC in vegetated sediments in different wetlands, Changjiang River Estuary
a1, b1. Spartina alterniflora; a2, b2. Phragmites australis; a3, b3. Scirpus mariqueter; a4, b4. Scirpus tabernaemontani
图 3 长江河口湿地不同植物根际柱状沉积物中MeHg含量与MeHg/THg特征
a1, b1. 互花米草；a2, b2. 芦苇；a3, b3. 海三棱藨草；a4, b4. 水葱
Fig. 3 MeHg concentrations and MeHg/THg in vegetated sediments in different wetlands, Changjiang River Estuary
a1, b1. Spartina alterniflora; a2, b2. Phragmites australis; a3, b3. Scirpus mariqueter; a4, b4. Scirpus tabernaemontani
图 4 长江河口湿地不同植物根际柱状沉积物中酸挥发性硫（AVS）含量
a1. 互花米草；a2. 芦苇；a3. 海三棱藨草；a4. 水葱
Fig. 4 Concentrations of acid volatile sulphides in vegetated sediments in different wetlands, Changjiang River Estuary
a1. Spartina alterniflora; a2. Phragmites australis; a3. Scirpus mariqueter; a4. Scirpus tabernaemontani
图 5 不同植物根际沉积物中硫的X射线吸收近边结构谱线及拟合结果
a1. 互花米草；a2. 芦苇；a3. 海三棱藨草；a4. 水葱
Fig. 5 S-K edge XANES spectra of samples taken from different vegetated sediments
a1. Spartina alterniflora; a2. Phragmites australis; a3. Scirpus mariqueter; a4. Scirpus tabernaemontani
图 6 不同植物根际沉积物TOC与THg（a）及THg/TOC（b）关系
拟合不包含三角和圆圈数据；三角是D点4～8 cm深度样品；圆圈是文献[26]的研究结果
Fig. 6 Relationships between TOC and THg (a) and THg/TOC (b) in vegetated sediments
The fitting does not contain the date of triangular and circle; the triangular indicates the sample from the depths of 4～8 cm in site D; the open circle indicates the data from reference[26]
表 1 长江河口湿地不同植物根际柱状沉积物理化特征
Tab. 1 Physical and chemical parameters of vegetated sediments in wetlands, Changjiang River Estuary
植被类型 E EN EN EN E E E 粒径小于
16 µm体积
百分比/%TOC/% THg含量
/(μg·kg−1)THg(mg)/
TOC(kg)MeHg含量
/(μg·kg−1)AVS含量
/(mg·kg−1)(MeHg/Hg)
/%互花米草
（Spartina alterniflora）A点，高潮滩（n=6） 81.0±2.9a 1.7±0.3a 90.0±6.0a 5.3±1.0b 0.5±0.3 811.4±392.4a 0.6±0.4 B点，中潮滩（n=6） 66.4±3.9b 1.2±0.4ab 79.8±9.1ab 7.5±2.2ab 0.5±0.2 10.1±13.0c 0.6±0.3 芦苇
（Phragmites australis）B点，中潮滩（n=6） 66.1±11.7b 1.3±0.4ab 80.4±16.3ab 6.5±1.8b 0.4±0.3 10.1±14.3c 0.5±0.3 C2点，中潮滩（n=6） 54.7±6.5bc 0.9±0.3bc 67.0±6.0b 7.6±2.1ab 0.3±0.1 97.8±42.3b 0.4±0.1 海三棱藨草
（Scirpus mariqueter）C1点，中潮滩（n=6） 58.5±5.7bc 1.0±0.4bc 72.8±5.6b 8.3±3.1ab 0.4±0.4 92.5±94.3bc 0.6±0.5 C2点，中潮滩前缘（n=6） 34.6±5.3c 0.5±0.2c 49.9±5.7c 11.6±3.1a 0.4±0.3 29.2±37.3c 0.9±0.6 水葱（Scirpus
tabernaemontani）D点，中潮滩前缘（n=4） 80.5±1.7 2.0±1.3 100.9±6.1 6.5±2.7 1.4±1.4 411.6±236.4 1.4±1.5 注：表中E，EN分别表示数据方差齐（equal variances assumed）和方差不齐（equal variances not assumed），不同字母a，b，c表示差异显著（p<0.05），无字母标注和含有相同字母表示无显著差异（p>0.05）。由于水葱主要生长在盐度较低的横沙岛湿地，故主要对崇明东滩湿地不同植物根际沉积物中各理化指标进行对比分析。 
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