| 摘要: |
| 洱海作为一个受人类活动影响强烈的典型湖泊，经历了富营养化和人为生态修复的过程，其碳库特征和碳循环模式可能随之改变。溶解性有机质(DOM)是湖泊有机碳循环过程的直接参与者，不同来源DOM具有不同的生物地球化学过程和归宿。因此，研究洱海水体DOM的组成和来源特征，有利于更好地理解湖泊富营养化和环境修复过程的有机碳循环模式。本研究以洱海中北部四个区域的水柱为研究对象，利用稳定碳同位素、紫外-可见吸收光谱和三维荧光光谱技术，解析洱海中北部水体DOM浓度、组成和来源的空间分布特征，并探究其地球化学指示意义。研究结果表明，洱海中北部水体DOM浓度整体稳定，变化范围为4.21~4.66 mg-C L-1(均值为4.37±0.12 mg-C L-1)。对比洱海早期DOM浓度结果发现周期性的富营养化对DOM表现出季节性波动但长期不断积蓄的特征；与其他云南高原湖泊相比，洱海DOM浓度处于中等水平，DOM浓度记录了湖泊生产力的强度并与营养类型有一定的响应关系。洱海中北部水体稳定碳同位素变化范围为-26.2~-26.8‰(均值为-26.4±0.2‰)，吸光系数a355值、紫外吸光度SUVA254、荧光指数FI值和自生源指数BIX值变化范围分别为1.36~2.58 m-1(均值为1.78±0.33 m-1)、3.10~3.38 L mg-C-1m-1(均值为3.20±0.08 L mg-C-1m-1)、1.57~1.69(均值为1.64±0.03)和1.13~1.34(均值为1.19±0.06)。稳定碳同位素和光谱参数结果表明有色溶解性有机质、荧光溶解性有机质和总DOM在来源上存在一定的相似性，受到浮游藻类等内源物质和陆源腐殖类有机物输入的共同影响；对比其他湖泊发现光谱参数的绝对值主要用于判断水体DOM的整体背景特征，参数波动则可能表征了水体DOM的变化。空间分布上，近岸区域具有较高的新鲜内源DOM输入，与北部农业活动导致的近岸初级生产力提升有关；湖心区域内源DOM对水体的贡献逐渐减弱，水体更多体现为腐殖化更强的残留DOM特征。水柱变化上，近岸区域的水柱有机碳降解较快，表层富营养化产生的内源DOM在水柱过程会被一定程度的消弭，最终导致近岸区域深层水的DOC浓度和其他点位的差异相对于表层水变小；湖心区域受控于多因素的共同影响，但DOM特征总体变化不大。因此，洱海富营养化导致的初级生产力对水体DOM碳库有直接贡献，但这种效应主要体现在表层水体，对湖泊水体长期碳汇的影响可能并不显著，而DOM的性质除了受到初级生产力和有机质来源的影响之外，地理、水文、生态环境等属性对DOM的影响也不容小觑。 |
| 关键词: 洱海 溶解性有机质 碳同位素 紫外-可见吸收光谱 三维荧光光谱 富营养化 |
| DOI： |
| 分类号: |
| 基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目） |
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| Isotopic and fluorescence characteristics of DOM in the water column of the north-central Lake Erhai and their geochemical significance |
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Chen Yue1, Zhao Qingfeng1, Zhang Can2, Li Xiangzhong3, He Yuxin4
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1.Zhejiang University;2.Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences;3.Yunnan Key Laboratory of Earth System Science, Yunnan University;4.School of Earth Sciences, Zhejiang University
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| Abstract: |
| As a typical lake strongly influenced by human activities, Lake Erhai has experienced eutrophication and anthropogenic ecological restoration, and its carbon pool characteristics and carbon cycling patterns may change accordingly. As a direct participant in the organic carbon cycling process in lakes, dissolved organic matter (DOM) of different sources have different biogeochemical processes and fates. Therefore, studying the composition and source characteristics of DOM in Lake Erhai is beneficial for better understanding the organic carbon cycling patterns of lake eutrophication and environmental remediation processes. In this study, spatial distribution in concentrations, compositions and sources of DOM from water columns in the north-central areas of Lake Erhai were investigated by methods of stable carbon isotopes, ultraviolet fluorescence spectroscopy and three-dimensional fluorescence spectroscopy. The geochemical significances of isotopic and fluorescence characteristics of DOM in Lake Erhai also were discussed. The results showed that the total dissolved organic carbon concentration in the water body of the north-central Lake Erhai was stable, with a range of 4.21~4.66 mg-C L-1(mean 4.37±0.12 mg-C L-1). By comparing the results of early DOM concentration in Lake Erhai, it was found that periodic eutrophication exhibited seasonal fluctuations but long-term accumulation. Compared with other lakes on the Yunnan Plateau, the DOM concentration in Lake Erhai was at a moderate level, which recorded the intensity of lake productivity and had a certain response relationship with the degree of eutrophication. The stable carbon isotopes variation range of the water body in the north-central Lake Erhai was -26.2~-26.8‰(mean -26.4±0.2‰), and the variation ranges of absorption coefficient a355, specific ultra violet absorbance at 254 nm, fluorescence index and biological index were 1.36~2.58 m-1(mean 1.78±0.33 m-1), 3.10~3.38 L mg-C-1m-1(mean 3.20±0.08 L mg-C-1m-1), 1.57~1.69(mean 1.64±0.03)and 1.13~1.34(mean 1.19±0.06), respectively. The stable carbon isotopes and spectral parameters suggested that chromophoric dissolved organic matter, fluorescent dissolved organic matter, and the overall DOM share similar organic source, and was influenced by both endogenous substances such as planktonic algae and humic organic matter from land-based sources. Comparison with other lakes revealed that absolute values of spectral parameters were mainly used to determine the overall background characteristics of DOM, while fluctuations in the parameters may characterize changes in lake water DOM. In terms of spatial distribution, the relative contributions of fresh endogenous DOM in surface waters from the lakeshore were associated with high primary productivity due to nutrient inputs from agricultural activities in the north. Meanwhile, the water bodies in the lake central area were characterized by residual DOM reflecting a stronger humification, largely due to lower contribution of fresh endogenous DOM. In terms of vertical variabilities in the water column, higher DOM degradation was observed in the water column at the lakeshore site, and the additional inputs of endogenous DOM from surface eutrophication being eliminated to a certain extent during the water column process. Although the DOM in the lake central area was influenced by multiple factors, the overall changes of DOM in the water column in the lake central area were relatively small. Therefore, primary productivity under lacustrine eutrophication condition contributes directly to lake DOM carbon pools, but mainly at the surface layer and in a relatively short-term manner. In the long-term perspectives, the lacustrine eutrophication does not have significant impact on the long-term organic carbon pool in the water bodies. In addition to being influenced by primary productivity and organic matter sources, the properties of DOM, such as geography, hydrology, and ecological environment, also have significant impacts on DOM. |
| Key words: Lake Erhai dissolved organic matter carbon isotopes ultraviolet fluorescence spectroscopy three-dimensional fluorescence spectroscopy eutrophication |
