Assessment of Ecosystem Carbon Sink Capacity and Strategies for Biodiversity Enhancement in the Yongding River Basin

This study pioneers the construction of a carbon sink monitoring and assessment system specifically designed for intermittent rivers in northern China. It innovatively integrates carbon-nitrogen isotope analysis with eDNA technology to elucidate food web structures, and validates the synergistic enhancement mechanism between carbon sink capacity and biodiversity through key species habitat construction demonstrations, thereby filling a critical research gap in this field. Along the 170-kilometer Beijing section of the Yongding River, 34 fixed monitoring sites were established employing stratified random sampling to cover the Guanting section (23. 5%) , mountain gorge section (29. 4%) , urban section (20. 6%) , and suburban section ( 26. 5%) . These monitoring sites encompass various habitat types including streams (12 sites) , lakes (8 sites) , wetlands (10 sites) , and floodplains (4 sites) . Using water TOC analyzers, soil carbon flux monitoring equipment, and OTC-Auto in-situ community photosynthesis-respiration monitoring systems, the study conducted monthly-scale monitoring of carbon flux variations in both beach areas and water bodies. Key findings reveal that the Beijing section of the Yongding River has an annual average carbon sink capacity of 153, 400 tons of CO2 equivalent, with a unit area annual average carbon sink capacity of 5. 28tCO2·hm-2·a-1, which is 40. 8% higher than the national average for rivers; after ecological water replenishment, the carbon sink capacity increased by 28. 7%, and food web connectivity improved from 1. 8 to 2. 5; the construction of key species habitat resulted in black stork sightings reaching 9. 3 times per month, with benthic animal species increasing from 2 to 22, and Margalef richness index and Shannon-Wiener diversity index improving by 116. 7% and 66. 7%, respectively; a significant positive correlation exists between carbon sink capacity and biodiversity (r=0. 83, p<0. 01) , with each unit increase in Shannon-Wiener diversity index corresponding to a 0. 78tCO2 ·hm-2 ·a-1 increase in carbon sink capacity. This research confirms the synergistic enhancement mechanism between carbon sink capacity and biodiversity, proposes integrated pathways including restoration of ecological connectivity, construction of key species habitats, and optimization of food web structure. It provides scientific basis for ecological restoration of the Yongding River Basin and offers a replicable and scalable technical model for carbon sink measurement and biodiversity conservation in seasonal intermittent river ecosystems in China, holding significant practical value for achieving basin carbon neutrality goals and advancing ecological civilization construction.