Karst-related carbon sink and the carbon neutral potential by carbonate liming in non-karst areas in China

The carbon dioxide captured by carbonate weathering is an important part of the land carbon sink. The karst landform is widely distributed in China, and the karst-related carbon sink is of great significance to realizing the goal of “double carbon” in China, so it has attracted wide attention. The development of artificial controllable atmospheric CO capture process is a significant measure to control the global climate and to tackle the greenhouse effect, and carbon sequestration technology based on enhanced weathering is an important new direction. The carbon capture process of carbonate weathering is sensitive to both climate and land use changes, and has great prospects for human utilization, but the control of carbonate weathering carbon sink still be limited to karst areas where carbonate rocks are distributed. Due to the rapid dissolution dynamics of carbonate, carbonate-rich soil in non-karst areas can produce carbon sink flux similar to that in karst areas, so the spreading of carbonate powder in non-karst areas could be developed as an enhanced weathering technology which may has a great potential for increasing carbon sequestration. This paper uses high-resolution remote sensing and meteorological data and carbonate dissolution equilibrium model to quantify the karst carbon sink flux in national carbonate exposed areas. To estimate the intensity of carbonate weathering carbon sink flux, the maximum potential dissolution formula of carbonate weathering (MPD, assuming that the chemical dissolution approaches to equilibrium), a NPP-based soil pCO model and the common carbonate weathering-driven DIC carbon sink flux equation are applied. The results show that the carbon sink flux is about 6.93 t of carbon per square kilometer per year, and the total carbon sink generated in karst areas is 17.6 million tons of carbon per year. The provinces that generate the higher karst-related carbon sink flux are occurred in the southeast of China, such as Jiangxi, Fujian and Guangdong, while the largest total carbon sink is captured in southwest China. Spreading carbonate powder in non-karst areas may increase 38.59 million tons per year in China, with the highest carbon sink increase potential occurring in the southeast. Based on the CMIP6 model, from 2015 to the 2060 carbon neutral year, the national flux of karst-related carbon sink increases by about 1 tonne of carbon per square kilometer per year, the total carbon sink increases by about 2.54 million tons of carbon (+14.4%) per year, and the potential sink of carbon in non-karst areas increases by about 6.97 million tonnes of carbon (+18.1%) per year. The model results further imply that the increasing runoff in China would be the major driving force for the total carbon sink enhancement. Meanwhile, due to the behaviour of carbonate weathering intensity and relevant carbon sink flux response to climate and land-use dynamics, the strategies to regulate the the future CO sequestration (carbonate area or limed non-karst soils) should aim at different directions. For cold area (T<15°C), the best approach to keep the high carbon sink is to protect the natural vegetation cover or to reforest. By contrast, irrigation and catchment water management would be the rational CO sequestration enhancement approaches in warm area (T>15°C). This study shows that the negative feedback of karst-related carbon sinks on future global climate change and the huge potential of carbon sequestration by carbonate liming in non-karst areas will contribute to the realization of the future carbon neutral goals in China.