Transportation of dissolved inorganic carbon and the controlling factors

<p indent="0mm"> Dissolved inorganic carbon (DIC) is an important carbon sink in rivers, however it is controlled by many factors and its influence on the carbon cycle is still unclear. In this paper, a typical watershed (Hanjiang River Basin) in North China was selected as the research object. River water and groundwater samples were collected from the mainstream and tributaries in the wet season (August) and dry season (March), respectively. The samples were analyzed for water chemistry, water hydrogen and oxygen isotopes (δD and δ¹⁸O_H₂O) and carbon DIC isotopes (δ¹³C-DIC). The results showed that the DIC concentration and δ¹³C-DIC value of surface water in the Hanjiang River Basin had no significant difference between the dry season and the wet season (<italic>p</italic>​&gt;0.05), but there was a significant difference between surface water and groundwater was (<italic>p</italic>​&lt;0.05). In tributary waters that are less affected by anthropogenic input (Cl^– concentration less than 1.0mg/L), CO₂ mainly participates in the chemical weathering of soil minerals in the Earth’s Critical Zone of the basin, and the DIC concentration in the lower reaches of Danjiangkou increases along the river flow direction, indicating that algae photosynthesis and CO₂ escape have an effect on DIC of water body. The impacts of anthropogenic input and natural processes on DIC transport in river water in the Hanjiang River Basin have obvious spatial distributioncharacteristics. The slowdown of river water flow velocity below the Danjiangkou Reservoir, coupled with the biological utilization of DIC in the river water, led to an increase of the δ¹³C-DIC value in the river water.