[Estimation of Vegetation Carbon Source/sink and Its Response to Land Use Change in the Loess Plateau,A Case Study of Yanhe River Basin].

Abstract

The transformation of ecosystem types caused by land use change plays an extremely important role in the regional carbon cycle. Studying the response of vegetation carbon source/sink systems to land use change is helpful to improve the understanding of the vegetation carbon sink effect in the process of land use change. However, few studies have focused on the response of vegetation carbon sources/sinks to land use change. The CASA model and soil microbial respiration model were combined to estimate the net ecosystem productivity （NEP） of vegetation in the Yanhe River Basin in the Chinese Loess Plateau from 2000 to 2020 based on remote sensing, meteorological, and land use data. The spatiotemporal pattern evolution characteristics of the carbon source/sink and land use were identified using a significance test, univariate linear regression analysis, and land use status transition matrix methods, and the response of the carbon source/sink to land use change was further analyzed. The results showed that from 2000 to 2020, the multi-year average NEP in the Yanhe River Basin showed a spatial distribution pattern of lower in the upstream and higher in the midstream and downstream. The Yanhe River Basin belonged to a weak carbon sink area as a whole, with this type of area accounting for 88.81% of the basin area. The annual NEP of the basin showed a significant increase trend in fluctuations, and the carbon sequestration capacity was gradually improving. The areas with significant and extremely significant increases in annual NEP accounted for 65.78% of the basin area, and the types of annual NEP restoration, basic stability, and degradation accounted for 79.70%, 10.15%, and 10.15% of the basin area, respectively. Over the past 20 years, the land use transformation of Yanhe River Basin mainly included five types, that is, cropland was converted into grassland, woodland, and construction land, and grassland was converted into cropland and woodland. The land use in the Yanhe River Basin was mainly shifting towards promoting the improvement of the carbon sink capacity, and the transformation of land type to woodland had a more significant effect on improving carbon sink capacity. During the five main land use transformation processes in the Yanhe River Basin, the area ratio of NEP recovery-recovery type for cropland shifting to woodland was the highest at 80.78%. The area ratios of NEP recovery-recovery type for grassland shifting to cropland and cropland shifting to grassland were relatively low, at 48.05% and 51.97%, respectively. The stability of NEP restoration when shifting cropland to woodland was the strongest, and the fluctuation of NEP restoration when shifting between cropland and grassland mutually was strong. When adjusting cropland and grassland mutually, attention should be paid to select suitable vegetation types and increase vegetation coverage reasonably to improve carbon sequestration and sink enhancement capabilities, so as to avoid carbon losses during land transformations. The research methods and results in this study can provide reference for land management departments to formulate scientific and reasonable land use decisions to promote vegetation carbon sequestration and sink enhancement.