Study On The Effect Of Iron Oxides On Organic Carbon Sequestration In Typical Lake Sediments In Yunnan

As an important carbon reservoir in terrestrial ecosystem,lake sediments play an important role in regulating atmospheric CO₂ content and mitigating regional climate variability.Understanding the long-term preservation mechanism of organic carbon in lake sediments has been the focus of lake carbon cycle research.The widely existing iron oxides(Fe R)in nature are important components of organic matter adsorbed in clay minerals.The combination of organic carbon and iron oxides can promote the preservation of organic carbon in sediments.Iron-bound organic carbon complexes are also called"rusty sink"in sediments.Therefore,taking Dianchi Lake and Erhai Lake in Yunnan plateau lake as an example,in August 2019,the surface sediments and columnar sediments of the lake were collected,the relationship between organic carbon and iron oxides in lake sediments of Yunnan plateau was analyzed,the content and distribution characteristics of iron bound organic carbon were analyzed,and the effects of nutrients,physical and chemical properties and sedimentary environment on the formation of iron bound organic carbon complex were investigated.The following conclusions were obtained:(1)In Erhai,the Fe-bound organic carbon in surface sediments accounted for0.69?5.34%of the total organic carbon,and the content was mainly higher in the southwest lake area,but the difference was small in the lake area,which was mainly affected by the change of organic carbon content and the form of iron oxide.Fe-bound organic carbon accounted for 0.35?14.8%of total organic carbon in columnar sediments,and the vertical variation was great.The content and source of organic carbon were the important influencing factors.(2)For Dianchi,Fe-bound organic carbon in surface sediments accounted for0.9?16%of total organic carbon.In the spatial scope,the northern lake area was higher than the southern lake area,and the difference was greater in the lake area,which was mainly affected by the contents of total organic carbon,total nitrogen and iron oxides.The content of Fe-bound organic carbon in the columnar sediments accounted for 0.35-15.65%of the total organic carbon content,which fluctuated and decreased with the increase of depth in the vertical direction and was relatively stable.The content and source of organic carbon in the columnar sediments of Dianchi were mainly affected.(3)Through the comparison of the research results,the average content of iron-bound organic carbon in Erhai is lower than that in Dianchi,but the difference is small.Meanwhile,the binding mode of iron-bound organic carbon in Erhai and Dianchi is mainly adsorption,which reflects the regional consistency.(4)According to the comparison of laboratory measurement results,the C/N in lake sediments and the C/N in iron-bound organic matter showed opposite results in Dianchi and Erhai.At the same time,according to the comparison of?¹³C,TOC and C/N in the columnar sediments of Erhai,the organic matter in the columnar sediments of Erhai was not affected by early diagenesis,while the organic matter in the columnar sediments of Dianchi was affected by early diagenesis.Therefore,the iron oxides in the sediments of the two lakes were selective in preserving organic carbon.The iron oxides in sediments from Erhai had a priority to combine with endogenous organic carbon,while the iron oxides in sediments from Dianchi had a priority to combine with external organic carbon.(5)According to the soil type method,the carbon storage of lake sediments was estimated.The total organic carbon storage in Erhai sediments was 24.1×10¹¹g,and the iron-bound organic carbon storage was about 15×10¹⁰g.The total organic carbon storage in Dianchi sediments is about 34.47×10¹¹g,and the iron-bound organic carbon storage is about 19×10¹⁰ g.Compared with the contents of Fe-bound organic carbon in Marine sediments and soil,the content of Fe-bound organic carbon in lake sediments is relatively low,which contributes to the function of"carbon sink"in the lake basin.