杞麓湖孟氏螺蛳(Anularya mansuyi)壳体碳同位素记录的水体溶解无机碳变化

Changes in dissolved inorganic carbon recorded by carbon isotopes of the living Anularya mansuyi shells in Lake Qilu

湖泊中腹足类壳体碳酸盐的碳同位素与水体溶解无机碳密切相关,是研究区域湖泊水体碳循环的重要材料之一。滇中地区湖泊众多,然而该区域湖泊中水体溶解无机碳的变化特征仍不清楚。孟氏螺蛳壳体为滇中湖泊特有属,本文通过对杞麓湖现生孟氏螺蛳壳体采集,并对其壳体沿生长方向开展碳酸盐δ~(13)C测试,尝试利用孟氏螺蛳壳体δ~(13)C分析杞麓湖水体溶解无机碳变化的变化特征。研究结果表明:(1)孟氏螺蛳壳体δ~(13)C与壳体生长环境密切相关,QLH-A与QLH-B在母体环境中的δ~(13)C平均值分别为-3.78‰与-5.55‰,变化幅度分别为2.07‰与3.03‰;在湖泊水体环境中的δ~(13)C平均值分别为-2.90‰与-3.28‰,变化幅度分别为1.81‰与1.74‰。(2)孟氏螺蛳在湖泊水体环境中生长时,壳体δ~(13)C记录了湖泊水体DIC的δ~(13)C_(DIC)变化特征,揭示出杞麓湖水体DIC主要受大气交换和湖泊中生物系统共同影响,其δ~(13)C_(DIC)在季节尺度变化不显著。(3)杞麓湖湖泊中大量水生藻类的死亡引起的有机质分解将导致湖泊水体δ~(13)C_(DIC)发生显著偏负变化,据此推断壳体δ~(13)C记录的偏负变化与云南2013年大旱期事件吻合,揭示出孟氏螺蛳壳体δ~(13)C具有记录湖泊生态系统自身重大变化的潜力。孟氏螺蛳古螺壳在滇中湖泊广泛分布,本文研究结果将有利于基于地层中的壳体识别地质历史时段滇中湖泊水体DIC特征及其湖泊生态系统的变化。

Carbon isotope of gastropod shell carbonates in lakes is directly correlated with dissolved inorganic carbon(DIC)in lake water,providing vital signals for the regional carbon cycle in lakes.Lakes are widely distributed in the central Yunnan region,and little is known about the DIC characteristics of these lakes.Anularya mansuyi shells are a unique genus of the lakes in central Yunnan Province.Here,two living Anularya mansuyi shells(QLH-A and QLH-B)were collected from Lake Qilu and their carbon isotope composition of shell carbonate(δ13 C shell),longitudinally along their growth span were studied to reveal possible dissolved inorganic carbon shifts in Lake Qilu s waters.Results showed that:(1)Theδ13 C shell values could be used to identify the two Anularya mansuyi shells growth in the mother s internal environment,the average values ofδ13 C shell were-3.78‰and-5.55‰,with ranges of variation of 2.07‰and 3.03‰,respectively.In lake water environment,the averageδ13 C shell values of the two shells were-2.90‰and-3.28‰,with ranges of variation of 1.81‰and 1.74‰,respectively.(2)During the period when Anularya mansuyi grows in the lake water,theδ13 C shell recorded theδ13 C DIC characteristics of lake water DIC,indicating that the DIC of the Lake Qilu water body was mainly affected by atmospheric exchange and the biological system.Theδ13 C DIC values of DIC showed no significant seasonal variation in Lake Qilu.(3)Followed algal bloom,the organic matter decomposition caused by the death of aquatic algae in lake system would lead to negativeδ13 C DIC.Basingδ13 C DIC records of 2012-2013,the negativeδ13 C shell during the second half of 2013 was consistent with the Yunnan Drought Event in 2013 and revealed theδ13 C shell of the Anularya mansuyi had the potential to record significant changes in the lake ecosystem.The fossil shells of Anularya mansuyi are widely distributed around lakes in central Yunnan,and these fossil shells can be used as potential documents to identify the DIC characteristics of water bodies and changes in lake ecosystems during geological historical periods.