Analysis of long-term changes in inundation characteristics of near-natural temperate riparian habitats in the Lower Basin of the theBiebrza Valley, Poland

Studying reference ecosystems and their specific features provides information to be used as background principles for ecosystem management. In the case of riparian wetlands, these are hydrological indicators (such as average water levels, flooding extents and flood duration) that are either used as criteria for ecosystem conservation or remain easy-to-measure targets for habitat restoration. We focused on revealing whether any trends in flood extents and durations of inundation exist within near-natural temperate floodplains persisting under the natural lowland river flow regime. We analysed whether the fraction of inundation time in a year (FIT) changed over time. River discharge data from 1951 to 2011 applied as boundary conditions in a 1D hydrodynamic model were used to generate flood extents and durations in the Lower Basin of the Biebrza Valley. We found no substantial trends in flood extents and flood durations in both time-dependent mean and standard deviation. We revealed that the average, long-term values of the FIT, influence the persistence of Caricetum approprinquatae, Caricetum gracilis, Glycerietum maximae and Phragmitetum communis, reached, respectively, 0.33, 0.43, 0.49 and 0.53 and did not present trends. Variability of the FIT within particular plant communities was high. The main challenges in conservation of temperate riparian wetlands are likely related to appropriate management addressing nonlinear climatic pressures.