| 摘要: |
| 水体碳库是全球碳库的重要组成部分，对区域乃至全球碳循环具有重要影响。溶解性有机碳（DOC）是水体主要的有机碳库，受自然和人类的双重影响，存在不同碳赋存方式之间的转化，代表了水体中的生物活动水平和受污染程度，并在水体碳循环乃至全球碳循环中发挥重要作用。碳来源是研究碳循环的基础，目前，碳同位素示踪方法是研究水体DOC来源最为有效的手段之一，并已进行了一系列颇有成果的研究，得出水体DOC大致有两种来源，即内源和外源，内源包括水生生物有机碳释放和颗粒有机碳（POC）降解等，外源包括陆源输入、大气降解、污水汇入等。本文验证了一种将δ13C与Δ14C值相结合示踪水体DOC来源的有效方法。碳来源示踪方法的不断改进和研究的不断深入，将有助于区分人为干扰对碳来源的影响，识别碳的储存与释放过程，从而进一步了解碳循环模式。 |
| 关键词: 溶解有机碳 来源 δ13C Δ14C |
| DOI：10.7515/JEE192050 |
| CSTR： |
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| 基金项目:中国科学院战略性先导科技专项（B类）（XDB40000000）；国家自然科学基金项目（41991252）；中国科学院战略性先导科技专项（A类）（XDA23010302） |
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| Sources analysis of dissolved organic carbon in water using carbon isotope method |
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WANG Ya, ZHOU Weijian, CHENG Peng
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. Xi’an AMS Center, Xi’an 710061, China
3. University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Background, aim, and scope Carbon in aquatic ecosystems is an important part of the global biogeochemical cycle and has profound effects on global carbon cycles. The carbon in the water includes dissolved inorganic carbon, particulate inorganic carbon, dissolved organic carbon and particulate organic carbon. Dissolved organic carbon (DOC) is the largest organic carbon pool in water and one of the largest activated carbon pools on the planet. Additionally, DOC is affected by both nature and humans. Any slight fluctuations may break the balance between carbon pools. The changes in the DOC content and isotope values also reflect the effects of the natural environment and human activities on the biogeochemical system. Therefore, DOC has important research significance. At present, the global warming situation is still severe. The carbon emission and sequestration process and the entire carbon cycle process have attracted the attention of many scholars. The DOC carries many signals of natural and human activities and constantly enters and exits the major carbon pools. Especially in the water carbon pool, the turnover time of DOC is fast, and the variation of DOC is diverse. Therefore, distinguishing the source of DOC will help to understand the role of the “carbon source” and “carbon sink” of water bodies and reveal the impact of environmental and human activities on carbon behavior. We hope to find a reliable way to trace the carbon sources of water and confirm the feasibility of this approach. Materials and methods Because of the different properties of light and heavy isotopes, different carbon behaviors and carbon cycle processes have different carbon isotope characteristics in biogeochemical processes, and carbon from different sources can be traced by carbon isotopes. However, a single δ13C value does not enable effective recognition of DOC in water. Many sources have overlapping signals and are difficult to distinguish. In recent years, with the rapid development of accelerator mass spectrometry (AMS) analysis and testing technology, the radioactive carbon isotope Δ14C has gradually begun to be applied in carbon analysis. The combination of Δ14C and δ13C values enables high-resolution analysis of organic matter sources. When measuring the carbon isotope value of the DOC of a sample, we first need to extract the DOC from the sample, which is basically divided into two steps: oxidation of DOC to CO2 and reduction of CO2 to graphite. We have improved the process on the basis of persulfate oxidation. After enriching the sample DOC, the oxidant made from potassium persulfate was mixed with the sample, subjected to vacuum at 5×10−2 torr (1 torr=133.322 Pa) , heated in a 98℃ water bath for 1 h, and cooled after completion of the reaction. The reaction mixture was cooled to room temperature, water was removed with isopropanol and liquid nitrogen, and the gas was removed to obtain relatively pure CO2. Some of the CO2 was detected by a MAT251 stable isotope mass spectrometer to detect the δ13C value; another part of CO2 was reduced to graphite, where Zn was used as a reducing agent and Fe was used as a catalyst. The Δ14C value of the graphite target was then detected by AMS. Results We compared the persulfate oxidation method with the high-temperature catalytic oxidation method and found that they have good consistency, and the obtained carbon isotope values have no isotopic fractionation effect, which indicates the reliability of the wet chemical oxidation method. Discussion We have found that carbon isotopes can reveal algae activity, land-source input, pore water surges and natural or humanmade events such as submarine volcanic eruptions, oil spills, and nuclear explosions through several studies using carbon isotope tracing of DOC sources in oceans and lakes. Conclusions At present, the carbon isotope method is one of the most effective methods for studying the source of water DOC. Comparing the carbon isotope data of the water body and the source end can be used to obtain the source information. IsoSource software can demonstrate the contribution ratio of each source end element. Recommendations and perspectives Constraining the source of carbon helps to further understand the carbon cycle process and provide a detailed scientific basis for regional carbon budgets. As a reliable source analysis method, the carbon isotope tracing method will provide scientific data and evidence in the research process to further enhance the understanding of the relationship between humans and the environment. |
| Key words: dissolved organic carbon sources δ13C Δ14C |
