Influence of agricultural activity on hydro-chemical characteristics and dissolved inorganic carbon leakage in epi-karst springs

In this study, three epi-karst springs under different intensity agricultural activity in Nanchuan area, Chongqing have been investigated to discuss the impact of agricultural activity on karst carbon sink by analyzing hydro-chemical characteristics and estimating the △DIC of water samples in different springs. The results show that compared to the Lanhuagou spring and the Hougou spring, the amplitude of variation in temperature in the Baishuwan spring is relatively small; EC and pH are relatively low. Because of the impact of agriculture activity, the Lanhuagou spring and the Hougou spring have a higher Ca2+ concentration and lower HCO3- concentration that are not consistent with Ca2+. The concentrations of NO3- and SO42-in the Lanhuagou spring and the Hougou spring are far higher than that in the Baishuwan spring for the same reason. With the enhancement of agricultural activity, the △DIC increases as follows,1.64 mmol/L in the Baishuwan spring ＜ 4.28 mmol/L in the Lanhuagou spring ＜ 4.36 mmol/L in the Hougou spring. The △DIC represents positive correlation with the concentration of (SO42-+NO3-) among the three different springs. It can be inferred that the more intensity of agricultural activity, the larger amount of △DIC, which means the less amount of CO2 sink.