Study on the distribution characteristics of carbon storage in soil and rock in Liulin River Basin

Defining the distribution characteristics of carbon stocks in regolith layer (from the ground surface to above the bedrock layer) within mountainous areas is crucial for regional carbon sink management and ecological restoration. This study focuses on the Liulin River Basin in the Taihang Mountains, a typical mountainous area in northern China. Using a combination of stratified field sampling and laboratory experiments, the study clarified the vertical distribution characteristics of carbon content in regolith layer of different vegetation types, the distribution characteristics of carbon density in soil layer (regolith particles particles >2 mm by mass <50%) and weathered rock-soil layer (regolith particles particles >2 mm by mass >50%), and the distribution characteristics of carbon storage in regolith layer within the basin. The results showed that: 1) Except for the relatively small fluctuations in total carbon content at different depths in Pinus tabuliformis, which is dominated by inorganic carbon, and the decrease in total carbon content with increasing depth in Zea mays fields, which are dominated by organic carbon, the total carbon content of most vegetation types was concentrated in the 0~1.5m depth range, with organic carbon dominating. After 1.5m, the total carbon content was affected by the increase in inorganic carbon content, showing a trend of first decreasing and then fluctuating upward; 2) For all vegetation types, total carbon and organic carbon contents were higher in the soil layer than in the weathered rock-soil layer. Except for Quercus mongolica and Shrub communities, inorganic carbon content was higher in the soil layer than in the weathered rock-soil layer for other vegetation types. However, due to thickness effects, carbon density was consistently higher in the weathered rock-soil layer than in the soil layer; 3) The total carbon stock in the Liulin River basin is 19.32×10⁶ t C, with a carbon stock per unit area of 10.42×10² t∙hm⁻². weathered rock-soil layer account for 74.7% of the carbon storage, inorganic carbon accounts for 58.4%, and forest land accounts for 79.6%. These results indicate that as the soil layer transitions to weathered rock-soil layer, inorganic carbon gradually becomes the main component of the carbon storage in deeper regolith layer. Especially in watersheds dominated by forests, neglecting the inorganic carbon reserves in weathered rock-soil layer would lead to an underestimation of the carbon reserves of the entire watershed by more than 70%. This understanding provides an important basis for further accurate assessment of carbon reserves in the rocky mountainous areas of northern China.