Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China’s Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42 to 7.23 m; medium, 7.23 to 8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth, and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Interspecific competition decreased with the decreasing range (variation) of TN values and differed opposite with the variation of COD values in response to increasing water level, and reached its maximum in the medium regime. Ecosystem stability was promoted by maintaining high species richness and evenness and high differences among communities, and by reducing competition. Based on our results, the water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability.

The survival of waterbirds depends heavily on habitat, particularly aquatic plants. Previous studies usually focused on the use of hydrological management to achieve protection and restoration of aquatic plants. However, the hydrological processes in many lakes have been greatly changed and their ecological objectives usually cannot be achieved by hydrological management alone. This study proposes a new method to satisfy waterbird habitat requirements, by combining the management of hydrological processes and plant structure. In this study, the Hongze Lake National Wetland Nature Reserve was taken as the research area. Based on the water levels that different hydrophytes require for survival, and on waterbirds' needs for foraging and nesting area, we determined plantable area and plant structures under the current hydrological process. We then set three representative hydrological process scenarios and determined appropriate plantable area and plant structures under these hydrological processes. The results show that the current hydrological process of Hongze Lake is not conducive to the planting of the hydrophytes needed by waterbirds. A combination of hydrophyte planting and hydrological process management, however, can effectively expand the area of these aquatic plants. Within the constraints of flood control, the water level in March should be reduced, and the water level in July should be increased as much as possible. Therefore, a management method is provided for aquatic plant restoration and waterbird habitat protection in wetlands.

In water-deficient rivers, environmental flows (e-flows) are usually sustained via inter-basin water transfer projects from water-sufficient rivers, but these projects incur tremendous costs and may lead to many negative ecological effects, such as ecological invasion. This research proposed to transfer hydropower instead of water from water-sufficient rivers, because hydropower could substitute for water to promote economic development and reduce water withdrawal from water-deficient rivers. In this research, we established a computable general equilibrium model to analyze the substitution of hydropower for water in a water-deficient river basin, and determined the water withdrawal volume that could be reduced (conserved water). In addition, we adopted a range-of-variability approach to measure the effectiveness of e-flow provisions, and optimized the use of the conserved water to better maintain e-flows. The Luanhe River was adopted as a study case. The results showed that: the water-hydropower equivalent decreased as the transferred hydropower into the Luanhe River basin increased; a transferred hydropower amount of 22.46 kWh/s, equivalent to 18.30 m3/s conserved water, was optimal for the river basin; the conserved water should be distributed to the Luanhe River in the proportions of 0.55:0.1:0.35 during the wet, normal and dry seasons, respectively; the policy could transform the macro-economy toward a lower air-pollution pattern.