Reproductive migration is an essential phase in the life of many fish. During this process, swimming behaviour and gonad development are key factors related to the migration quality, and both factors are strongly influenced by water temperature and flow velocity. Many studies have explored the separate effects of these variables on fish swimming ability or gonad development, but researchers have seldom investigated the simultaneous effects of low flow velocity and water temperature on the fish swimming behaviour and gonad development. To provide that knowledge, we conducted laboratory experiments that explored the coupled effects of low water temperature and flow on warm water fish swimming behaviour and gonad development. At five temperatures (16, 18, 20, 22, and 24 C), we observed the movement of migratory warmwater grass carp (Ctenopharyngodon idellus) at seven flow velocities (0.15, 0.2, 0.25, 0.3, 0.35, 0.40, and 0.45 m/s), then explored their gonad development by comparing the level of plasma 17β-estradiol and testosterone in fish travelling through a simulated fish way (flow stimulation) and in a fish tank (no flow stimulation). We used Bayesian networks to explore the acceptable hydrological condition for fish migration.We found that the minimum flow velocity for acceptable migration quality is a function of the water temperature, and that increasing water temperature improves fish movement success and increases the movement distance, especially at a low flow velocity. In addition, increasing water temperature (between 16 and 24 C in this experiment design) can enhance the effect of flow stimulation on gonad development. Overall, our results can broaden the understanding of reducing water temperature and flow velocity in fish swimming behaviour and gonad development, provide basic data to support hydrological process controls and the development of measures to protect fish migration.

The survival of waterbirds depends heavily on habitat, particularly aquatic plants. For each kind of aquatic plant, there are specific water level regime requirements to meet its germination and growth. Previous studies usually focused on the use of water level management to achieve protection and restoration of aquatic plants. However, the water level regimes in many wetlands have been greatly changed and their ecological objectives usually cannot be achieved by water level management alone. Accordingly, this study combined water level management and artificial planting for waterbird habitat provision in wetlands. The Hongze Lake National Wetland Nature Reserve was taken as the research area. In this study, we considered the needs of waterbirds for nesting and foraging, and determined the aquatic plant species to be planted. According to the seasonal water level requirements of these plants, we simulated the plantable areas of different aquatic plants under different water level regimes. We then further optimized the water level regimes according to the needs of waterbirds, and determined the optimal water level management scheme. In addition, we formulated planting principles, explored the planting structure under each water level regime, so that the plant structure can better serve the waterbirds. The results showed that the current water level regime of Hongze Lake is not consistent with the growth rhythm of aquatic plants. Because of the human regulation, the water level of the wetland is high in winter and low in summer, which is contrary to the requirements of aquatic plant growth. A combination of water level regimes and plant structure management, however, could effectively expand the area for waterbird habitat. The results of this study will help wetland managers to make informed decisions about how to restore the waterbird habitat in other similar regulated wetlands.

Environmental flow (e-flow) assessment is essential for the ecological protection and restoration of lake-marsh systems. Previous studies on e-flow assessment for lakemarsh systems focused on lake-marsh systems with natural seasonal hydrological patterns (i.e., low water level in winter and high water level in summer). However, they have not considered lake-marsh systems with reverse seasonal hydrological patterns (i.e., high water level in winter and low water level in summer). The reverse seasonal hydrological patterns impose seriously negative impacts on waterbirds, because the hydrological patterns could lead to limited plant germination in spring and massive plant death in summer, leaving few plants available as food for waterbirds in winter, and could consequently reduce the sheltering and forageable areas for waterbirds. This study took Hongze Lake Wetland National Nature Reserve in China as the study area. Based on the habitat requirements of waterbirds, the sheltering and forageable areas for waterbirds under different water-depth and aquatic plant distribution scenarios were calculated. By exploring the impacts of reverse seasonal hydrological processes on waterbird habitats, we determined the necessary e-flows for lake-marsh systems with reverse seasonal hydrological patterns to meet the needs of waterbird habitat. The results showed that the water level of Hongze Lake should be controlled to 13.0-13.1 m in March, 12.5-12.6 m in July, and 12.9-13.0 m in October, which can meet the needs of waterbirds for both shelter and foraging.

Emergent plants in river riparian zones (RRZs) are an important part of the river ecosystem, and the evolution of their spatial distribution patterns is a direct indicator of the health of river ecosystems. In previous studies, the simulation of the spatiotemporal pattern evolution process for emergent plants mainly focused on the overall pattern change of emergent plant communities. However, they did not distinguish the types of emergent plants and ignored the differences in response of different emergent plants to environmental changes. The difference in the competitiveness of different emergent plants will affect the distribution of emergent plants. In this research, the transformation rules of five emergent plants under different water levels were determined, and the Cellular Automata model was constructed to dynamically simulate the proliferation of emergent plants in RRZs. The results showed that when the water level was 11.5 m, the total area of emergent plants reached the maximum, and among the five emergent plants, Phragmites australis was the dominant species. When the water level dropped to 12.5 m, the shallow water area in the east of the riverside zone increased, and P. australis expanded rapidly in the east. By dynamically simulating the distribution of emergent plants in RRZs, the distribution status of the emergent plants in RRZs in the future can be obtained. It is of great significance for biodiversity conservation and resource management in riparian zones.

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