Ecological Consequences of Altered Water-Level Regulation on Wetland Plant Succession

Wetlands represent highly variable ecosystems, where water level size, persistence, frequency, rate of changes and seasonality control plant colonization and community development. River regulation, reservoirs operation, water extraction, drainage and aquifer depletion may influence all these hydrological factors affecting plant viability, competition, species composition and succession processes. This review provides an analysis of scientific literature published from 2014 to 2022 that deals with the impact of modified water regimes on wetland and riparian vegetation. Three interrelated effects are examined: long-term flooding, long-term drawdown, and suppression of natural seasonal dynamics. Prolonged floods may cause oxygen and light limitation of flood-intolerant plants, whereas long-term drawdown may increase substrate exposure, reduce availability of aquatic habitats, and promote drought-resistant or terrestrial species. Regulation may also exclude major floods and substitute them with more small-scale frequent fluctuations, thus filtering plant communities by their tolerance abilities and life histories. This process is variable, as the response will depend on the type of wetland, geomorphology, the characteristics of the sediments, climate, the availability of propagules, and the amount of change in the hydrology. This literature review shows the consequences of hydrological change for biodiversity, habitat structure, nutrient cycling, productivity, and restoration. This paper emphasizes that the maintenance of a static water level is insufficient to achieve ecological goals. On the contrary, conservation should maintain an appropriate variability in the seasonality of the river-floodplain system, maintain connectivity, and study vegetation changes over many years.