Changes in global rainfall patterns and the construction of artificial dams have led to widespread alteration of hydrological processes in riparian ecosystems. Meanwhile, intensified agricultural activities have resulted in enhanced inputs of nitrogen (N) and phosphorus (P) into the riparian ecosystems associated with the Yangtze. However, it remains unclear how the greenhouse gases (GHGs, including CO₂, CH₄, and N₂O) respond to both the hydrological alterations and nutrient input in the riparian zone.  

To investigate the effects of hydrological changes and nutrients input on the GHGs in riparian zone, Ph.D. student SHI Wenjun, supervised by Prof. ZHANG Quanfa and YE Chen of Wuhan Botanical Garden, conducted an in situ experiment in the water level fluctuation zone of the Three Gorges Reservoir (TGR). 

This in situ experiment was carried out at Zhongxian Revegetation Station (Chongqing, China). The prescribed hydrological alterations (continuous flooding, CF; periodic flooding, PF; no flooding, NF) and nutrients addition experiments (N addition, P addition, N + P addition, and control plots) were established at nine 15×3 m blocks along the elevation gradient (145-155 m a.s.l., 155-165 m a.s.l., and 165-175 m a.s.l.).  

Results revealed that hydrological alterations significantly affected the emissions of three GHGs, which CF significantly reduced CO₂ and N₂O emissions across all the nutrient addition treatments, but greatly increased CH₄ emissions. The simultaneous addition of N and P promoted the emission of GHGs, while P addition alone significantly reduced the N₂O fluxes. The qPCR analysis revealed that CF significantly reduced the abundances of functional genes associated with CH₄ oxidation, nitrification, and denitrification process, while N+P addition increased the abundances of functional genes.  

Therefore, hydrological alterations and nutrients input mainly affect GHGs emissions by changing soil environmental factors (soil redox conditions, moisture content, soil organic carbon) and the abundance of related functional genes.  

Using the widely used global warming potential (GWP, on a 100-year time horizon), this study estimates that the water level fluctuation zone of the TGR has a positive net GWP with the value of 0.83 ± 0.08×10⁶ tCO_2-eq yr^-1. CF treatment could reduce GWP by 0.28×10⁶ t CO_2-eq yr^-1, while N+P will increase GWP by the value of 0.24×10⁶ t CO_2-eq yr^-1.  

This research is of great significance for clarifying the mechanism of GHGs emissions of the riparian ecosystems and calculating the carbon budget of the water level fluctuation zone of the TGR.  

The research was funded by the National Natural Science Foundation of China, and Youth Innovation Promotion Association of Chinese Academy of Sciences. 

Results were published online in Water Research entitled "Divergent effects of hydrological alteration and nutrient addition on greenhouse gas emissions in thewaterlevelfluctuationzone of the Three Gorges Reservoir, China".  

Experimental design and the divergent effects of hydrological alteration and nutrients input on GHGs emissions (Image by WBG)