Carbon Balance Of Groundwater In Tumochuan Plain

The series of ecological and environmental issues caused by global warming have had a serious impact on human survival and security,and research on carbon sources and sinks has become a hot topic of current focus.Due to the huge amount of groundwater and high DIC content,the carbon related water rock interaction in the recharge,runoff and discharge process of groundwater may have an important impact on the global carbon cycle.The research on the change of carbon in groundwater can provide some reference for clarifying its role in the global carbon cycle.Based on the theory of groundwater flow system and the principle of mass conservation,a regional groundwater carbon balance model is established by using groundwater balance equation and hydrogeochemical simulation method to quantitatively calculate the annual carbon sequestration or emission of groundwater in the Tumochuan Plain.The main research conclusions are as follows:（1）The total amount of groundwater in the entire Tumochuan Plain that receives lateral recharge from the mountain front is 34416.96×10⁴m³/a;Precipitation infiltration is the main source of groundwater supply in the Tumochuan Plain,reaching 44705.3-48373.0×10⁴m³/a;The total amount of agricultural irrigation recharge groundwater is 5987.3×10⁴m³/a.he mining output of groundwater in the whole Tumochuan Plain is about 11000×10⁴m³/a;The evaporation of groundwater in Tumochuan Plain is 49492.9×10⁴m³/a.The situation of groundwater receiving recharge:The total amount of groundwater in the entire Tumochuan Plain receiving lateral recharge from the front of the mountain is 34416.96×10⁴m³/a;Precipitation infiltration is the main source of groundwater supply in the Tumochuan Plain,reaching 44705.3-48373.0×10⁴m³/a;The total amount of agricultural irrigation recharge groundwater is 5987.3×10⁴m³/a.Groundwater discharge:the mining output of groundwater in the whole Tumochuan Plain is about 85600×10⁴m³/a;The evaporation of groundwater in Tumochuan Plain is 49492×10⁴m³/a.（2）The partial pressure of groundwater carbon dioxide（p CO₂）is at a high level in the western alluvial plain and the northeastern sloping piedmont plain;In the central alluvial plain,it is between 4000 and 10000μatm,gradually decreasing from west to east;The values in the eastern piedmont sloping plain and the southeastern lacustrine plateau region are relatively low,but much higher than the atmospheric CO₂partial pressure value.The total reverse simulation results of each division show that albite is in the state of weathering and dissolution,while anorthite and potassium feldspar are generated in the aquifer;The carbonate rocks such as dolomite and calcite are in the state of weathering and dissolution;CO₂（g）dissolves into groundwater.（3）The amount of carbon replenished by various replenishment items in the research area is as follows:the amount of carbon replenished laterally from the mountain front to the Tumochuan Plain is 13087.4 t C/a;The amount of carbon replenished by atmospheric precipitation reaches 34562.3-37397.8 t C/a,which is the largest contributor to the amount of carbon replenished;The carbon supply for agricultural irrigation infiltration water is 4240.1 t C/a.The total amount of carbon supplied to the Tumochuan Plain is approximately 52713.1-54825.7 t C/a.The main discharge item in the research area is groundwater extraction,and the amount of carbon emitted is approximately 10153.0 t of inorganic carbon per year,including a large amount of CO₂generated during the extraction process.Approximately13232.6t of CO₂are emitted into the atmosphere each year,equivalent to a net carbon amount of approximately 3608.9 t;The annual amount of Ca CO₃precipitation generated is24651.0 t,equivalent to a net carbon content of approximately 2958.1 t.（4）Establish a carbon balance equation for groundwater in the Tumochuan Plain:ΔM=R-D+/-S.According to the calculation results of the groundwater carbon balance model in the Tumochuan Plain,the groundwater system in this area is in a carbon sink state,with the carbon sequestration of 45150.9-47986.4 t C/a,which is approximately 6.45-6.86 g C/m².Due to the extensive exploitation of groundwater by human activities,a large amount of inorganic carbon is discharged into the outside environment in the form of HCO₃^-and CO₂,thereby weakening the carbon sequestration effect in this region.