Zhang Hongmei, Wang Fuqiang, Shan Sen, Ren Peng, Luo Chunle, Fu Wenjing, Sun Shuwen, Wang Xuchen
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, Qingdao, China.
Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
Sci Total Environ. 2022 Dec 10;851(Pt 1):158123. doi: 10.1016/j.scitotenv.2022.158123. Epub 2022 Aug 18.
Tibetan Plateau lakes are sensitive to climate variabilities and affect regional temperature, precipitation and ecosystems. In this study, we investigated the concentrations and carbon isotope (C and C) compositions of dissolved organic and inorganic carbon (DOC and DIC) along with the concentrations of major lithologic ions (Na, Mg, K, Ca) and dissolved silicate (DSi) in a large lake, namely, Qinghai Lake, and its seven inflowing rivers on the northeastern Qinghai-Tibetan Plateau of China. Our results revealed large differences in concentrations and isotopic compositions between DOC and DIC, as well as differences in the concentrations of major ions between the rivers and lake. The chemical weathering of carbonate and silicates in the catchments played important roles in controlling the fates of major ions in the rivers. In Qinghai Lake, evaporation resulted in 40-290 times the accumulation of Na, Mg, and K observed in the rivers, while biological uptake and precipitation reduced the concentrations of Ca and DSi in the lake by 4-17 times compared with those in the rivers. In addition, the concentrations of DOC and DIC in the lake were 6-7 times those in the rivers. The carbon isotope (δC and ΔC) signatures of DOC and DIC revealed that the rivers transport millennium-aged DOC (1254 ± 316 years) and DIC (1513 ± 857 years), as influenced largely by the chemical weathering of rocks and preaged soil carbon on the plateau. In contrast, in Qinghai Lake, the ages of DOC are significantly younger (684 ± 378 years) than the ages of riverine DOC, as regulated by newly biologically produced modern DOC. Moreover, the DIC ages in Qinghai Lake are all modern, indicating that exchange with atmospheric CO is the dominant process controlling the lake DIC. The accumulation and removal of riverine-aged DIC in Qinghai Lake, however, are not well understood, and the unbalanced radiocarbon in lake DIC remains a mystery that needs further study.
青藏高原湖泊对气候变化敏感，并影响区域温度、降水和生态系统。在本研究中，我们调查了中国青藏高原东北部一个大型湖泊——青海湖及其七条流入河流中溶解有机碳和无机碳（DOC和DIC）的浓度和碳同位素（δ¹³C和Δ¹⁴C）组成，以及主要岩性离子（Na、Mg、K、Ca）和溶解硅酸盐（DSi）的浓度。我们的结果揭示了DOC和DIC在浓度和同位素组成上的巨大差异，以及河流和湖泊中主要离子浓度的差异。流域内碳酸盐和硅酸盐的化学风化在控制河流中主要离子的归宿方面发挥了重要作用。在青海湖，蒸发导致Na、Mg和K的积累量是河流中观测值的40 - 290倍，而生物吸收和沉淀使湖泊中Ca和DSi的浓度比河流中降低了4 - 17倍。此外，湖泊中DOC和DIC的浓度是河流中的6 - 7倍。DOC和DIC的碳同位素（δ¹³C和Δ¹⁴C）特征表明，河流输送的是具有千年历史的DOC（1254 ± 316年）和DIC（1513 ± 857年），这在很大程度上受高原岩石化学风化和老化土壤碳的影响。相比之下，在青海湖，DOC的年龄明显比河流DOC的年龄年轻（684 ± 378年），这是由新生物产生的现代DOC所调节的。此外，青海湖中的DIC年龄均为现代年龄，这表明与大气CO₂的交换是控制湖泊DIC的主要过程。然而，青海湖中河流老化DIC的积累和去除情况尚不清楚，湖泊DIC中不平衡的放射性碳仍然是一个需要进一步研究的谜团。
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