The importance of relief for explaining the diversity of the floodplain and terrace soil cover in the Dnipro River valley: The case of the protected area within the Dnipro-Orylskiy Nature Reserve

Abstract

Floodplains are centers of species diversity, so floodplain habitats often contain protected areas. However, conservation strategies pay little attention to soils, on which the functional stability of both individual ecosystems and landscape chains as a whole depends. Soil morphology provides structural and functional information about floodplain ecosystems. The spatial and temporal heterogeneity of soil morphology is a cost-effective ecological indicator that can be easily integrated into rapid assessment protocols for floodplain and riverine ecosystem restoration projects. Therefore, the aim of our work was to consider the morphological features of soils of the Dnipro-Orylskiy Nature Reserve and assess the role of soil diversity as a factor of structural and functional sustainability of ecosystems of the protected area, as well as to identify the significance of geomorphological predictors for differentiation of soil types to create a soil map of the territory. The World Reference Base for Soil Resources reference soil groups were classified using geomorphological predictors. Soil types were able to explain 90% of the variation in elevation occupied by soils. Arenosols occupied a statistically significantly higher position in topography than other soil types. In turn, Eutric Arenosols occupied a higher position (68.91 ± 0.48 m) than Eutric Lamellic Arenosols (63.32 ± 0.54 m). Other soils occupied positions in the topography that were not statistically significantly different in height. Soil types were able to explain 38% of the variation in elevation that the soils occupied. The highest Topography Wetness Index values were found for Fluvisols (12.73 ± 0.23) and Solonetz (13.06 ± 0.28 m). Differences between these soils were not statistically significant. Topography Wetness Index was slightly lower for Cambisols (11.80 ± 0.21) and Eutric Lamellic Arenosols (12.21 ± 0.28), which also did not differ on this measure. The lowest Topography Wetness Index value was found for Gleysols (11.15 ± 0.17) and Eutric Arenosols (10.95 ± 0.24), which did not differ from each other on this index. Eutric Arenosols and Eutric Lamellic Arenosols are formed at great depths of the water table (7.89 ± 0.50 and 2.62 ± 0.46 m, respectively). Gleysol and Solonetz form at close groundwater level to the surface (0.28 ± 0.27 and 0.21 ± 0.46 m, respectively) compared to Fluvisol and Cambisol (0.46 ± 0.38 and 0.41 ± 0.35 m, respectively). Elevation was the most informatively valuable predictor, but Topography Wetness Index and Vertical Distance to Channel Network significantly improved discrimination. Arenosols were very different from other soils which occupy an automorphic position. Cambisols occupied a transitional position. Other soils occupied hydromorphic positions. Fluvisols and Solonetz occupied wetter positions, while Gleysol occupied less wet positions. Fluvisols and Solonetz differed in the groundwater table. Solonetz predominantly occurred at close groundwater levels. The classification matrix confirmed the possibility of using geomorphological predictors to build a model of spatial variation of soils in the study area. The spatial model demonstrates the organization of the soil cover of the reserve. Calculations showed that Cambiosols occupy 20.7% of the area, Eutric Arenosols occupy 16.0%, Eutric Lamellic Arenosols occupy 17.9%, Fluvisols occupy 15.2%, Gleysols occupy 28.7%, and Solonetz occupy 1.5%.