Optimization and Assessment of Carbon Sink in the Water Level Fluctuation Zone in the Three Gorges Reservoir Area Adapted to Water Level Changes

Objective The water level fluctuation zone (WLFZ) in the Three Gorges Reservoir Area confronts substantial ecological challenges, primarily due to the periodic water level fluctuation and prolonged deep-water submersion in winter, which significantly compromise the carbon sink capacity of the WLFZ and result in multi-source carbon emissions. Transforming these challenges into opportunities for restoring and augmenting the carbon sink potential of the WLFZ’ s ecosystem constitutes a critical aspect of ecological management within the Three Gorges Reservoir Area.

Methods This research advocates for the implementation of a forest − pond system as a strategic framework for ecosystem restoration in the WLFZ, aimed at bolstering the WLFZ’ s carbon sink function. Taking the Dalangba WLFZ located at the epicenter of the Three Gorges Reservoir Area as the research object, the research evaluates the restoration effectiveness and functional efficiency of the forest − pond system. The research employs the Carnegie-Ames-Stanford approach (CASA) model to estimate the net primary productivity (NPP) of the Dalangba WLFZ, and evaluates the changes in carbon sink function before and after ecological restoration, unveiling the spatio-temporal dynamics of carbon sink in this intricate ecosystem that are influenced by significant fluctuations in water levels. This methodology entails a comprehensive analysis of vegetation type map, meteorological data, normalized vegetation index (NDVI), and land use information, which are synchronized under a unified projection system to ensure spatial congruence. Vegetation maps spanning the period from 2012 to 2020 are meticulously georeferenced to match environmental variables, offering an in-depth temporal perspective on vegetative transitions. To further explore the carbon sink capacity of the forest − pond system, detailed field surveys are undertaken across various elevation zones in the Dalangba WLFZ in the Three Gorges Reservoir Area, with the Dalangba WLFZ being compared with the Xiaolangba WLFZ not subject to ecological restoration for comparative research. Additionally, vegetation biomass — a key indicator of carbon sink potential that captures both the herbaceous and woody strata of the ecosystem through structured sampling in designated areas, is quantified by relevant methods.

Results A thorough temporal analysis illustrates an increase in vegetative productivity, transitioning towards a richer and more varied plant community. This change is quantitatively substantiated by the growth in NPP from 154.4 g C·m²·a⁻¹ before restoration to 182.5 g C·m²·a⁻¹ after restoration in 2020, signifying a significant enhancement in the ecosystem’s carbon sink capacity. Field surveys complement these results, showing a significant improvement in carbon storage throughout the restored area, with the highest storage levels found in the uppermost elevation zones, corroborating the spatial patterns identified by the CASA model. Utilizing the CASA model, the research highlights a significant rise in the net primary productivity (NPP) of the restored Dalangba WLFZ, underlining the efficacy of the forest-pond system in boosting local carbon sink capacity. The carbon sink capacity in the restored zone peaks at 1.235 kg C/m², markedly outperforming the 0.587,5 kg C/m² recorded in the non-restored control site. The carbon sink capacity of each elevation zone is significantly higher than that of the control group and exhibits a decreasing trend with lower altitudes. Specifically, the carbon sink reaches 1.827 kg C/m² in the 170 − 175 m elevation zone, whereas it is only 0.830 kg C/m² in the 160 − 165 m elevation zone. Moreover, the diverse carbon sink strategies designed along the elevation gradient in the Dalangba WLFZ have created rich spatial ecological niches, providing suitable conditions for the coexistence and growth of various life forms of plants. This has resulted in the formation of multi-layered plant communities, including terrestrial, hygrophytic, aquatic, and autochthonous herbaceous plants. An integrated “abovewater − underwater” three-dimensional carbon fixation model adapted to water level fluctuations has been constructed, effectively enhancing resource utilization efficiency and significantly increasing the carbon sink capacity per unit area of the Dalangba WLFZ.

Conclusion The forest − pond carbon system represents an adaptive exploration to address the complex water level fluctuations and prolonged deep-water submergence challenges in the Three Gorges Reservoir Area. It exhibits key characteristics of landscape optimization, biodiversity, economic benefits, and synergistic coupling with carbon sink. The research results may provide a scientific basis and a replicable and innovative technological model for the management and carbon enhancement of WLFZs in large reservoirs in China. The notable improvements in vegetative productivity and carbon storage after restoration corroborate the ecological importance of WLFZs and highlight their critical function as a significant carbon repository, contributing to the global carbon balance and climate change mitigation efforts. Additionally, the Dalangba forest − pond carbon sink model stands as an exemplar of ecological engineering, integrating the principles of sustainability, biodiversity enrichment, and economic feasibility. It reveals the synergistic relationship between ecological restoration and economic sustainability, positing that economic endeavors like ecotourism and the sustainable harvesting of non-timber forest products can be integrated into restoration initiatives, thus enhancing community involvement and ensuring the enduring efficacy of WLFZ projects. The insights derived from the Dalangba WLFZ project illuminate the capacity of restoration efforts to act as cornerstones in achieving ecological sustainability and carbon neutrality, charting a course toward a more sustainable and resilient future.