Characteristics Of Dissolved Carbon Export Under Impact Of Human Activity In A Karst Small Catchment

River was the channel of the terrestrial carbon cycle and an important carbon exchange place,particularly,with the small watershed as a hotspot.In order to explore the characteristics of dissolved inorganic carbon(DIC)and dissolved organic carbon(DOC)export in karst watersheds under the effect of human activities,the water samples were collected in Youyu River,Baiyan River and Jinzhong River of Aha Lake.The main DIC and DOC concentration were analyzed from June 2017 to May2018,based on which the DIC and DOC export flux in the basin were calculated.Explored the spational and temporal distribution of DIC and DOC concentration,as well on which the influence under the impact of rianfall and human activties.The mian conclusions as follows:(1)The DIC concentration of Youyu River,Baiyan River and Jinzhong River were 38.03,32.28,48.39 mg/L,respectively,while the DIC export fluxs were 22.77,23.69,27.42 t/(km~2.a).The DIC concentration in spring was significantly higher than other seasons,the DIC concentration and export flux tendency showed as Jinzhong River>Youyu River>Baiyan River.Compared with domestic mian rivers,the small watershed in this study usually possessed higher DIC concentration and export flux than that of large rivers.(2)The DOC concentration of Youyu River,Baiyan River and Jinzhong River were 4.78,5.61,7.40 mg/L,respectively,while the DOC export flux were 22.77,23.69,27.42 t/(km~2.a).The seasonal distribution of DOC concentration was showed as spring>winter>summer and autumn,the DOC concentration and export flux tendency showed as Jinzhong River>Baiyan River>Youyu River.Compared with different types of rivers,the small watershed usually possessed higher DOC concentration and export flux than that of large rivers.(3)The dissolved carbon concentration of study was significantly affected by rainfall and human activities.The effects of rainfall on dissolved carbon concentration were mainly expressed as leaching effect,dilution effect,and microbial activity effect.The effect of rainfall on dissolved carbon concentration of river water was different in different seasons due to different rainfall characteristics.Combined with the basic physical and chemical parameters and quality indexs of water and land-use types,our results demonstrated that the dissolved carbon concentration varies significantly with land-use types.The urban rivers possessed significantly higher DIC and DOC concentration,and the concentration of DIC and DOC was significantly positively correlated with the concentration of nitrogen and phosphorus that demonstrated the nutrients and DIC as same as DOC came from the same source.