Changes Of Lake Organic Carbon Storage In China Since The Last Glacial Maximum

In order to understand the process and forcing mechanisms of carbon cycle under global warming,it is necessary to reconstruct the change pattern of carbon sources and sinks.Lakes are the constituent units in land system,which exchange broadly with other terrestrial ecosystems.The lake ecosystems are sensitive to climate change,which play key role in exploring the terrestrial carbon cycle.However,due to the relatively small surface area,lakes are rarely regarded as independent research units in earlier studies.Since the Last Glacial Maximum(LGM),the Earth has experienced drastic climate changes.The study of changes in lake carbon storage since the LGM can provide a reference for lake carbon sequestration potential under future global warming scenarios.The spatial scope is generally limited or the time span is short in the existing studies,and there is still no research on the estimation of lake carbon storage in China since the LGM.In addition,when reconstructing past lake carbon storage,most studies directly used the modern lake area in calculation,which ignored the lake evolution during the past time.Meanwhile,the number of lakes is not enough for comprehensive research in earlier studies,and the detailed location of the cores in each lakes has not been well considered.These flaws lead to large uncertainties on estimating the organic carbon storage in Chinese lakes and unclear understanding of forcing mechanisms in lake organic carbon accumulation.Therefore,it is essential to reconstruct changes in lake carbon storage in China since the LGM and explore its driving mechanisms.In this study,we synthesized the total organic carbon content(TOC)and sediment accumulation rate(SAR)of 142 sediment cores from 92 lakes in five lake regions of China(Northeast Mountain and Plateau,East Plain,Mongolia-Xinjiang Plateau,Qinghai-Tibetan Plateau,Yunnan-Guizhou Plateau)since the LGM.Then we calculated the lake organic carbon accumulation rate(CAR)at 1000-yr interval.On the basis of reconstructing the changes in lake area over the past 20000 years,the changes in organic carbon storage in Chinese lakes since the LGM were estimated.Combined with C/N,δ13Corg,Paq and PANN indices in lake sediments,we analyzed the sources of lake organic carbon and their potential links with climate,and explored the driving mechanisms of lake CAR and the role of lake organic carbon storage in regional carbon cycle.This study aims to generate fundamental data for predicting the future trend of lake carbon cycle and the potential of carbon sequestration,and to provide reference for adjusting lake protection strategies so as to increase the value of carbon storage and carbon trade in lake ecosystem.The research findings of this study are presented as follows.(1)The mean TOC,SAR and CAR values of lake sediments in China since the LGM are 5.31%,0.52 mm·yr-1 and 7.14 g·m-2·yr-1,respectively.There are spatial differences of both TOC and SAR values among the five lake regions,and CAR values are similar in the other four regions except for Mongolia-Xinjiang Plateau region,where CAR value is significantly lower(P<0.05).All the three parameters exhibit an upward trend since the LGM,with SAR and CAR showing a sharp increase over the last 3000 years.These findings suggest that the carbon sink function of Chinese lakes has rapidly increased.(2)Calculated from CAR values and paleo-lake areas,Chinese lakes have stored approximately 28.24 Pg of organic carbon since the LGM.This accounts for roughly 18%of the total carbon storage in terrestrial ecosystems in China today.The organic carbon density in Chinese lakes is 142.8 kg·m-2 since the LGM.The total accumulation rate of organic carbon in Chinese lakes is 1.44 Tg·yr-1.The annual contribution of Chinese lakes counts for～3.4%to global lake carbon accumulation.The results show the significance of Chinese lake sediments as a carbon sink within the regional terrestrial ecosystem.(3)Comprehensive analysis on TOC,C/N,δ13Corg,Paq and PANN data from lake sediments shows that endogenous organic matter sources have played a crucial role in organic carbon of Chinese lakes since the LGM,and terrigenous organic matter increased during the optimum climate periods.Generally,the TOC and C/N values changed consistently with regional precipitation.(4)The trends of CAR and SAR values in Chinese lakes are consistent.Factors such as higher temperatures,TOC and CO2 concentration,abundant precipitation,increased sources of terrestrial organic matter,smaller lake areas,lower vegetation coverage rates,and human activities have contributed to the CAR increases in lakes.Since the LGM,the two peaks of CAR values corresponded to warm-humid climate and rapid population growth,respectively.It is suspected that CAR values in lakes may continue to rise in the future due to increased human activities and global warming.As a result,lakes could become even more important in the regional carbon cycle.However,if the lake system becomes overloaded,it could lead to significant carbon emissions.Therefore,it is recommended to implement lake carbon sequestration strategies that combines biodiversity restoration,methane resource utilization,individuation and integrated management.