International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 217-228 http://ecoevopublisher.com/index.php/ijmec 22 0 to the hydrology and landscape of the large area of permafrost plateau (Tape et al., 2022). In terms of time, Beaver DAMS and wetlands exhibit dynamic succession characteristics. A dam body can often last for several years to over a decade, but it requires beavers to constantly maintain and reinforce it. Once the population migrates away, the dam body often collapses within a few years, the pond dries up and is restored as a river channel (Wohl and Inamdar, 2025). However, the long-term occupation of beavers leaves a lasting mark in the sedimentary landforms of the basin - silted peat wetlands and floodplain puddles can still exist for many years or even decades after beavers leave, continuously providing habitats for wetland species (Fairfax and Westbrook, 2024). Therefore, the impact of the beaver project is characterized by delay and inheritance. The spatio-temporal pattern of beaver activities is usually manifested as follows: frequent dam-building and dam-abandonment on a local scale cause habitat cycle replacement, and on a large scale, the spread of beaver populations brings more river sections into the influence range (Tape et al., 2022). Current monitoring in many places in North America and Europe indicates that it takes about 5 to 10 years after beavers return for the wetland network they create to stabilize and enter the expansion stage (Halley et al., 2021). In addition, factors such as climate and terrain also affect the breadth and persistence of beaver engineering: For example, in high mountains or arid areas, beaver dam construction tends to be seasonal or phased, and the dam body may fall into disrepair and be damaged during severe winters or dry seasons (Janiszewski and Hanzal, 2021). 3 The Influence of Beavers on Hydrological Processes 3.1 Water Flow velocity and water level regulation Beaver dams change the river’s hydrodynamic pattern by raising the upstream water level and slowing the flow. On the one hand, the dam body blocks the current and makes the velocity drop sharply (Puttock et al., 2017). The upstream water almost stops and slowly becomes a pond. As a result, flood waves move more slowly, and water stays longer in the channel. Field studies show that in reaches with beaver dams, the average retention time of water can be several times longer, especially in dry periods (Dewey et al., 2022). On the other hand, building a dam also raises both the surface water level and the groundwater table. The deeper and wider pond in front of the dam lifts the groundwater level of nearby areas, which helps wetland plants and adds to groundwater storage. Studies report that in basins with active beavers, the depth of groundwater near riverbanks is usually lower, while soil moisture is higher. In dry seasons, this plays the role of a “natural reservoir” (Oleszczuk et al., 2024). More importantly, beavers' dam construction significantly buffered the peak flood flow and played a regulatory role similar to that of a small reservoir (Larsen et al., 2021). In the long-term observation of four pilot river basins in the UK, the responses of the multi-level dam systems rebuilt by Beavers to over 1,000 rainstorm events showed that the total runoff volume of the basin decreased after the dam construction, the time lag from the rain peak to the flow peak increased, and the peak flow generally decreased. Even under extremely heavy rainfall conditions, the Beaver Dam still has a significant effect on reducing flood peaks. It can be seen from this that beavers effectively "shave peaks and fill depressions" by building DAMS and play an active role in natural flood management. Many nature-based solutions propose to utilize beavers or simulated beaver DAMS to achieve river ecological restoration and flood control and disaster reduction (Puttock et al., 2021). It should be noted that the influence of beaver DAMS on water level and flow velocity is contextual: During high-flow seasons or major floods, the dam body may overfill or break, causing some floodwaters to discharge, and thus the peak shaving effect will be reduced (Auster et al., 2021). 3.2 Surface water-groundwater exchange mechanism Beaver dam construction not only alters surface water flow, but also enhances the exchange between surface water and groundwater by influencing riverbed infiltration and lateral overflow (Smith et al., 2020). After the dam is built, a raised head difference is formed in front of the dam. The water body forms a pressure gradient before and after the dam, pushing the river water to seep into the underground aquifer through the riverbed and riparian soil (Grudzinski et al., 2022). Research has found that the retention of the beaver dam causes a change in the
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