Dam reservoirs in headwater catchments,as critical zones for their proximity to terrestrial sources,play important roles in dissolved organic carbon(DOC)cycling.However,the effects of ecosystem metabolism(EM)on DOC cycling are not well known.Here,in-situ diurnal and monthly observations were conducted to measure EM(including gross primary production(GPP),ecosystem respiration(ER)and heterotrophic respiration(HR)),DOC turnover and CO2 emissions in a headwater catchment reservoir in Southeastern China in 2020.Our study showed the nocturnal CO2 emission rate was about twice as high as in daytime,and was strongly driven by EM.The values for DOC turnover velocity ranged from 0.10 to 1.59 m/day,and the average DOC turnover rate was 0.13 day-1,with the average removal efficiency of 12％.The contribution of respired DOC to daily CO2 emissions ranged from 17％to 61％.The accumulated efficiencies were estimated to be 13％for the selected 15 reservoirs throughout the Changjiang River network,corresponding to about 0.34 Tg C/year of the respired DOC.The modified CO2 flux was 0.75 Tg C/year,and respired DOC accounted for about 45％of total emitted CO2 from the 15 larger reservoirs.Our research emphasizes the necessity of incorporating the effects of EM into studies of reservoir DOC removal and CO2 emissions.

Peipei Zhang;Ruyuan Jiao;Chen Gong;Fang Wang;Weijin Yan;Qingqian Li;Dongsheng Wang

Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences,Beijjing100101,China;University of Chinese Academy of Sciences,Beijing 100049,China;State Key Laboratory of Environmental Aquatic Chemistry,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,Beijing 100085,China;Yangtze River Delta Branch,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,Zhejiang 322000,China

环境科学学报（英文版）

[1]Peipei Zhang;Ruyuan Jiao;Chen Gong;Fang Wang;Weijin Yan;Qingqian Li;Dongsheng Wang-.Turnover of dissolved organic carbon fuels nocturnal CO2 emissions from a headwater catchment reservoir,Southeastern China:Effects of ecosystem metabolism on source partitioning of CO2 emissions)[J].环境科学学报（英文版）,2022(11):98-111

headwater,respired

Turnover,dissolved,organic,carbon,fuels,nocturnal,emissions,from,Southeastern,China,Effects,ecosystem,metabolism,partitioning,Dam,reservoirs,catchments,critical,zones,their,proximity,terrestrial,sources,play,important,roles,DOC,cycling,However,effects,EM,are,not,well,known,Here,situ,diurnal,monthly,observations,were,conducted,measure,including,gross,primary,production,GPP,respiration,ER,heterotrophic,turnover,Our,study,showed,rate,was,about,twice,high,daytime,strongly,driven,by,values,velocity,ranged,average,removal,efficiency,contribution,daily,accumulated,efficiencies,estimated,be,selected,throughout,Changjiang,River,network,corresponding,Tg,year,modified,flux,accounted,total,emitted,larger,research,emphasizes,necessity,incorporating,into,studies

0.499115