Estimation of karst carbon sink and its contribution to CO2 emissions over a decade using remote sensing imagery

Research on the carbon source and sink imbalance in global carbon cycle has demonstrated that the mass of CO2 consumed by rock weathering is a portion of the "missing carbon sink." To further understand the karst carbon sink contributions to atmospheric CO2 emissions, the present study establishes the relationship between the karst carbon sinks and the atmospheric CO2 emissions. We first estimated the mass of CO2 consumed by rock weathering using the Global Erosion Model for CO2 fluxes (GEM-CO2), based on the distribution of different types of rock in Guangxi, China. The rocks were classified using remote sensing imagery, and we estimated the relationship between the mass of CO2 consumed by rock weathering and the CO2 emitted into atmosphere from 2003 to 2012. The analyses reveal that (1) the mass of CO2 consumed by rock weathering could be rapidly estimated using remote sensing imagery, as it not only considers different types of rocks but also simultaneously considers the geological structure and meteorological data, such as rainfall, temperature, and vegetation coverage; (2) the mass of CO2 consumed by rock weathering from 2003 to 2012 displays a "wavy pattern", which might have been primarily caused by the annual variations in rainfall, whose tendency could be fitted by a straight line at an average annual increasing rate of approximately 8.7%; (3) the mass of emitted CO2 from 2003 to 2012 in Guangxi display a "straight line" at an average annual increasing rate of approximately 12.7%; (4) the mass of CO2 consumed by rock weathering is positively correlated with the mass of emitted CO2 with a correlation coefficient of R-2 = 0.62; this implies that an increasing concentration of CO2 in the atmosphere reversely fosters the CO2 consumption by rock weathering; (5) due to different increasing rates, annually 7 x 10(6) t of CO2 is accumulated in the atmosphere in Guangxi, and a total of 506.42 x 10(6) t of CO2 is accumulated over a decade; (6) the mass of the karst carbon sinks in Guangxi, China, and globally are estimated to be 1.01 x 10(6) tC.a(-1), 1.49 x 10(7) tC.a(-1), and 0.95 x 10(8) tC.a(-1), respectively. Therefore, the results of this study not only help to understand the relationship between karst carbon sink and the global carbon cycle, but also provide an important basis for predicting the variations in CO2 in the atmosphere and climate change, which could further provide a scientific basis for the rational use of resources and the formulation of environmental protection policies.