The impact of stress factors on riparian and drawdown zones degradation around dams and reservoirs

There is currently a lack of evidence about changes in the health of riparian and drawdown zones under different land-use patterns within mega-reservoirs, below and around dams. Scientific evidence for the quantitative effects of stress indicators is vague and varies significantly among reservoirs and dams worldwide. In this study, we used a field-based approach to evaluate riparian and drawdown zones health changes-influenced by pressure indicators-across 274 transects from three land-use areas (rural, rural-urban transitional, and urban) in the Three Gorges Dam Reservoir (TGDR) in China during 2019. Multivariate statistical techniques were applied to test for riparian and drawdown zones (termed riparian zones in this paper) changes under these variant land-use patterns. Our results showed that 13 pressure indicators significantly influenced 27 health indicators (including parameters for habitat, plant cover, regeneration, erosion, and exotics) of the riparian zones from the three land-use areas differently. Our results also showed that parameters for plant cover, erosion, and exotics were major contributors within the selected riparian health indicators, whereas land-use designs, farming systems, and pollutant activity variables were the pressure indicators with the strongest impact. Pearson correlation (with r ranging from -0.731 to 0.989) showed that urban transects exhibited the strongest comparative interaction, whereas rural-urban transitional transects formed the weakest association. Furthermore, the agglomerative hierarchical cluster analysis revealed similarities between rural and rural-urban transitional sites while confirming substantial dissimilarity in urban locations. These comprehensive and relevant results provide essential information for reservoir administrators to implement functional changes suited to TGDR land-use scenarios.