Contribution Of Upstream Tributaries And Returned Irrigation Groundwater To Chemical Consumption In The Yellow River Basin

The chemical weathering of continental rocks constitutes an important carbonsink for atmospheric CO2. However, Tibetan Plateau contributes to DIC of YellowRiver Basin, including not only the Yellow River source region (from the birthplaceto Dari) and the main water source area (from Dari to Lanzhou), but also the TaoRiver, Datong River and Huangshui. Based on the datas of summer, autumn in2013and winter, spring in2014of the mainstream and tributaries in the Yellow Riverupstream, we conclude that: about30%of the DIC flux from the tributariescontribution, while the Yellow River source region accounts for roughly14%of theDIC flux and the main water source area contribution of over50%. Meanwhile thereare a lot of irrigation areas in Loess Plateauv of Yellow River. Due to the impact ofirrigation methods, geology, topography and other factors, there will be a lot ofirrigation groundwater back to the river.However, the returned irrigation groundwaterback to rivers, with high cation concentrations, will definitely overestimate thosederiving from rock weathering in the river water and have an impact on CO2consumption in the river basins. Based on groundwater samples from the Henan,Ningxia and Inner Mongolia irrigation districts in June,2012and May,2013as wellas data from references, this paper discusses the chemical distribution characteristicsof groundwater in the Yellow River basin. The results show that: since theevaporation process and human activities impose little impact on the deepgroundwater, the total dissolved solids (TDS) and the concentration of HCO3-inwhich are much lower than those in the shallow groundwater. In contrast, thepercentage of HCO3-in anions (HCO3-%) of the deep groundwater is larger.Influenced by factors such as evaporation, rainfall and lithology, shallow groundwaterchemical compositions of these three irrigation districts show different characteristics.HCO3-%is the largest in the Henan irrigation district followed by the central region ofInner Mongolia and Ningxia irrigation district, with those in the east and west regionsof the Inner Mongolia irrigation district are the smallest. The cation concentrationsfrom rock weathering in the Henan and Inner Mongolia irrigation districts are almost the same and they are both larger than that in Ningxia. The flux of CO2consumptionwhich is overestimated by returned irrigation groundwater in the Yellow Riverdrainage basin is23.3×108mol/a.