| The carbon stored in carbonate rocks is the largest carbon pool in the earth.Its weathering and dissolution processes under natural conditions continuously respond to global changes,and this causes 1/3 of "missing carbon sinks".With the acceleration of urbanization,allogenic acids?sulfuric acid,nitric acid?brought by other activities,such as the increasing transformation intensity of human activities on nature,also take an active part in the karst process,but this process does not constitute a carbon sink.In the case of high concentration of allogenic acid,carbon source is formed instead,so it can be seen that the participation of allogenic acid disturbs the process of karst carbon cycle.Therefore,it is of great practical and scientific significance to understand the interference effect of allogenic acids on the karst process in order to accurately evaluate the strength of karst carbon sink and construct the global carbon cycle framework.In this thesis,we select Lijiang River catchment with the rapid acceleration of urbanization as our study area.A total of 52 water sampling points were set up,and water samples were collected in November 2018,March 2019,July2019,and October 2019.Using the method of combining water chemistry indicators and ?13CDIC isotopes qualitatively analyzes the process of allogenic acids participating in the karst carbon cycle;use the isotope mass mixed model to quantitatively analyze the contribution of nitrate from different sources in the Lijiang River basin;The influence of karst carbon sink/source of allogenic acid?sulfuric acid,nitric acid?on watershed scale was quantitatively evaluated by establishing a corresponding conceptual model and applying the hydrochemical-run off method.The main conclusions are shown as following:?1?Organic fertilizer and sewage are the most contribution to nitrate in the study area.The contribution ratio of organic fertilizer and sewage in the dry season?October 2018,57.%?was higher than that in the rainy season?July 2019,44.67%?.The contribution of soil N in the rainy season?25.30%?was significantly higher than than in the dry season?6.55%?.?2?The molar ratio of(Ca2++Mg2+)and HCO3-is from 0.5 to 1?0.5,weathering of carbonate rocks in the natural state?.(Ca2+ Mg2+)was significantly correlated with(HCO3-+ SO42-+ NO3-),and the molar ratio was also adjusted to be around 4/7?0.571?.However,in the areas with great influence of human activities,such as KA,G,and C,(Ca2+ Mg2+)/(HCO3-+ SO42-+ NO3-)is from 0.56 to 5.59,distributed in both sides of the theoretical value of the molar ratios 4: 7?0.571?.According to the relationships between(Ca2+Mg2+)/HCO3-and ?13CDIC,The sampling points of the groundwater area?G?is located near the end of hydrocarbon dissolving carbonate rocks.The sampling points of the karst agricultural area and urban area?KA and C?are located between the ends of hydrocarbon dissolving carbonate rocks and sulfuric/nitric acids dissolving carbonate rocks.?3?On a basis of method of water chemistry and runoff,the net CO2 sink is0.537×103 t?rainy season,July?and 0.105×103 t?dry season,October?,respectively.Among them,the DIC produced by allogenic acids?nitric acid and sulfuric acid?was0.225 × 103 t in the rainy season and 0.032 × 103 t in the dry season,respectively.DIC produced by allogenic acids?nitric acid,sulfuric acid?accounts for 12.89%?July?and10.29%?October?of the total DIC,respectively. |
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