Spatiotemporal variation characteristics and driving forces of vegetation net primary productivity in the Yellow River Delta from 1995 to 2020

Understanding the spatiotemporal patterns and driving mechanisms of high-resolution net primary productivity (NPP) in coastal areas is a crucial foundation for the scientific management of wetlands. The distribution of land cover in the Yellow River Delta was interpreted according to the refined wetland classification criteria. Using the Carnegie-Ames-Stanford Approach (CASA) model in conjunction with measured biomass data, the biomass of common Phragmites australis, Suaeda salsa and their mixed stands with Tamarix chinensis, as well as Spartina alterniflora—a total of five different wetland vegetation communities—to analyse the spatio-temporal evolution of NPP in the study area. Multivariate regression residual analysis was employed to identify the natural factors and human activities driving the evolution of NPP. The results indicate that between 1995 and 2020, the cumulative loss of natural wetland area in the Yellow River Delta amounted to 3 849 km², with P. australis suffering the greatest loss, decreasing from 1 368 km² to 310 km². The ε_max values for P. australis, S. salsa, and S. alterniflora were 1.04 g/MJ, 0.32 g/MJ and 0.88 g/MJ, respectively. The long-term average annual NPP in the study area was 8 724.73 t/a, peaking in 2000 at 10 809.64 t/a; due to their extensive area and high NPP, farmland accounts for approximately 90.0% of the total each year; The total NPP of natural wetlands fluctuated and declined in line with the contraction of their area, with P. australis exhibiting the highest NPP 564.76 g/(m²·a), exceeding that of other land cover types. The driving mechanisms in the study area are complex and related to land-use changes and vegetation succession. In farmland, the primary driving factor is human activity, whereas in marsh and tidal flat wetland areas, human activity exerts a marked inhibitory effect; furthermore, stable sedimentation promotes NPP, but dynamic changes in erosion and sedimentation lead to instability in NPP fluctuations. This study reveals the spatio-temporal distribution characteristics and multi-factor driving mechanisms of vegetation NPP in the Yellow River Delta wetlands, clarifying the combined effects of natural processes and human activities on the NPP function of coastal wetlands. It provides scientific support for regional wetland blue carbon sequestration, ecological conservation and restoration, and the sustainable development of high-efficiency ecological and economic zones.