Heavy Rainfall Increasing Carbon Sink in Shallow Groundwater in Vegetable Growing Areas

Gao Zhenpeng; Xiao Chunyan; Chen Hao; Xue Tian; Cao Ying; Fan Hekai; Zhang Dong

doi:10.3799/dqkx.2023.201

Abstract：In the backdrop of global climate change,the quest for effective methods to sequester atmospheric carbon dioxide(CO2)is both urgent and indispensable.The acidifying substances generated by artificial inputs such as manure and chemical fertilizers in agricultural areas release more dissolved inorganic carbon(DIC)into shallow groundwater,altering the process of inorganic carbon cycling.However,the influence of heavy rain events on this process remains unclear.Shallow groundwater in a vegetable cultivation area in North Henan Province was selected as the primary research focus,while shallow groundwater samples from grain growing region and local deep groundwater samples were also collected in April and October 2021.The water chemistry composition,hydrogen and oxygen isotope compositions(δDH2O and δ18OH2O),and δ13CDIC compositions were analyzed to investigate the influence of rainfall processes on inorganic carbon cycling in shallow groundwater of agricultural areas.The results show that heavy rainfall led to more anthropogenic pollutants entering groundwater under the vegetable cultivation areas during the rainy season,resulting in an increase in mean TDS values from 649 mg/L in April to 1 195 mg/L in October,and a decrease in average δ13CDIC values from-12.25‰ to-14.14‰.The changes of mean TDS values and δ13CDIC values in groundwater under the vegetable cultivation areas were larger than those in groundwater under other sites,displaying more organic matter had entered and decomposed in the shallow ground water under the vegetable cultivation areas.The average DIC concentrations varied little from 7.78 mmol/L in April to 7.74 mmol/L in October,however,as groundwater table elevated about 11 to 15 m after heavy rainfall,it implied more DIC input and thereby obviously increased carbon sink capacity in shallow groundwater.This study confirms the impact of anthropogenic inputs in vegetable cultivation areas on DIC in shallow groundwater and verifies that heavy rainfall will transport more DIC into shallow groundwater and increasing more dissolved components,elevating carbon sink capability of groundwater.