International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 217-228 http://ecoevopublisher.com/index.php/ijmec 21 8 Meanwhile, the still water wetland environment promotes sediment deposition and nutrient retention, often improving downstream water quality, such as reducing nitrate and suspended sediment concentrations (Dewey et al., 2022; Grudzinski et al., 2022); On the other hand, it may also lead to the accumulation of organic carbon in wetlands and promote the emission of greenhouse gases such as methane (Fairfax and Westbrook, 2024). Furthermore, the new habitats created by beavers have greatly enhanced the diversity of regional habitats: microhabitats such as still ponds, floodplains, and dead water depressions provide special Spaces for the reproduction and habitat of numerous animal and plant species (Bashinskiy, 2020; Orazi et al., 2022). Therefore, beaver dam construction not only changes the physical environment, but also has a cascading effect on the ecosystem through food web and habitat changes, and is regarded as one of the key factors shaping the watershed landscape (Brazier et al., 2021). This study will systematically review the impact and ecological value of beaver ecological engineering behavior from two dimensions: biodiversity and hydrological processes. It will summarize the characteristics of beavers as ecological engineers and how their dam-building behavior alters hydrological conditions and habitat structure. It will also analyze the mechanism and empirical research on the impact of beaver dam-building on water flow processes and biodiversity. Discuss the ecosystem services provided by beaver activities and the possible human conflicts they may trigger, and explore management strategies for the coexistence of humans and beavers. This study will also combine regional case studies to demonstrate the diversity of beaver impacts, look forward to future research directions and challenges, and expect to deepen the understanding of this typical ecological engineering species, the beaver, and provide scientific references for wetland ecological restoration and natural resource management. 2 The Ecological Engineering Characteristics of Beavers 2.1 Dam construction and water body renovation The dam-building behavior of beavers is at the core of their ecological engineering role. Beavers use branches and soil to build DAMS in narrow sections of streams, forming multiple stepped dam and pond systems. These wooden DAMS significantly reduce the longitudinal connectivity of the river, causing the upstream water to converge in front of the DAMS and form still water ponds. On average, each beaver dam can raise the water level in front of the dam, expand the water surface area, and slow down the flow velocity, thereby transforming the river from the previous linear rapids to the form of meandering slow flow and connected ponds (Figure 1) (Brazier et al., 2021; Puttock et al., 2021; Tape et al., 2022). Meanwhile, the dam body often has seepage and overflow. Some of the water flow seeps into the ground or flows around, thereby maintaining a certain water flow connectivity (Wohl and Inamdar, 2025). Unlike artificial DAMS, beaver DAMS are usually small in scale, porous in structure and dynamic in succession - beavers constantly repair old DAMS or build new ones, and some old DAMS may burst and collapse after being abandoned (Wohl and Inamdar, 2025). This "build - abandon - rebuild" cycle introduces intermittent disturbances and diverse habitat structures to rivers. Overall, beaver dam-building has greatly transformed local water conditions: not only has it raised the surface water level and shaped still water areas, but it has also increased soil moisture content and groundwater recharge through water diversion and seepage (Grudzinski et al., 2022; Oleszczuk et al., 2024). For example, in the multi-site experimental study in the UK, after beavers built DAMS, the peak flow during heavy rain decreased by an average of more than 30%, and the lag time of water flow was prolonged, effectively "shaving the peak and filling the valley" (Puttock et al., 2021). 2.2 Habitat heterogeneity creation and ecosystem reshaping The pond-wetland complex formed by beavers building DAMS has significantly enhanced the heterogeneity of habitats within the basin. Still water ponds provide new habitats for many aquatic organisms that prefer slow-flowing or still water, such as some aquatic plants, plankton, amphibians and aquatic invertebrates, which can thrive in the ponds (Dalbeck et al., 2020). Meanwhile, the dam body retains water flow and submerges the riverbank, creating wetland and marsh landforms on both sides and giving rise to marsh plant communities. These wetland buffer zones have created feeding and resting places for waterfowl, amphibians and semi-aquatic mammals, significantly enriching the regional habitat types (Orazi et al., 2022).
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