夏季汾河干流溶解无机碳同位素组成及其来源

根据2019年8月对汾河干流水文参数和碳酸盐参数的调查，初步探讨了溶解无机碳（DIC）及同位素值（δ¹³C_DIC）的沿程变化及其影响因素.结果显示，源头水DIC为2756μmol/kg，δ¹³C_DIC为-9.6‰，土壤CO₂输入和碳酸岩化学风化可能是其主要来源；在太原市区上游的水库影响区，较强的初级生产使得水体DIC（平均值为2377μmol/kg）和CO₂分压（pCO₂）（平均值为552μatm）偏低，δ¹³C_DIC（平均值为-5.2‰）偏正，而在市区下游的水坝滞流影响区，城市污水的大量输入和有机物的降解使得DIC（>4900μmol/kg）和pCO₂（>5000μatm）显著升高，δ¹³C_DIC（<-10.3‰）偏负；在流经主要粮食产区的汾河下游，δ¹³C_DIC偏正（~-8.0‰）于源头，可能与C4植被（如玉米）的存在有关.可见，人为干扰已成为影响汾河DIC沿程变化的重要因素，表现为大气CO₂强源的城市下游水坝滞留区在今后需受到更多关注.

Isotopic composition of dissolved inorganic carbon and its source in the main stream of the Fenhe River during summer

Based on hydrographic and carbonate data collected from an investigation in the main stream of the Fenhe River in August 2019, the variations of dissolved inorganic carbon (DIC) and isotope value (δ¹³C_DIC) along the river as well as their possible factors were preliminarily discussed. The results showed that the DIC concentration was 2756μmol/kg and the δ¹³C_DIC value was -9.6‰ at the headstream, and CO₂ input from soil and carbonate chemical weathering may be the main sources. In the upstream reservoir-affected area of Taiyuan downtown, due to strong primary production both DIC (the average value was 2377μmol/kg) and partial pressure of CO₂ (pCO₂) (the average value was 552μatm) were lower, and δ¹³C_DIC (the average value was -5.2‰) was more positive compared to those at the headstream, whereas in the downstream dam stagnation affected area because of large amounts of municipal sewage inputs and degradation of organic matter both DIC (&ggt;4900μmol/kg) and pCO₂ (>5000μatm) increased substantially, and δ¹³C_DIC became more negative (<-10.3‰). In the lower reaches of the Fenhe River flowing through the main grain production areas, the δ¹³C_DIC value (~-8.0‰) was more positive than that at the headstream of the river, possibly related to the existence of C4 plants such as corn. Overall, human disturbance had become a very important factor affecting the DIC variations along the Fenhe River. Moreover, the dam stagnation affected area at the downstream of the city, which acts as a strong CO₂ source of the atmosphere, should be paid more attention in the future.