First approach to understanding riparian wetlands in the Middle Ebro River floodplain (NE, Spain): structural characteristics and functional dynamics

摘要

In Spring of 2005, the relationships between the physical and chemical characteristics of the aquatic and benthic environments and macroinvertebrate assemblages in seven wetlands representative of the floodplain of the Middle Ebro River (NE Spain), were analyzed. The selected wetlands differed in their hydrological connectivity, local environmental conditions and anthropic influence. Through multivariate analyses, two environmental gradients and three main wetland groups were detected. The hydrological connectivity differences generate a heterogenous landscape of structurally and functionally different wetlands in the Ebro Middle floodplain. Confined wetlands, such as older ox bow lakes, showed higher salt and organic matter contents and lower macroinvertebrates’ density and biodiversity than did the other wetlands. This suggests that confinement and lack of disturbance events have led to water salinization and eutrophication, habitat homogenization and natural succession of the communities towards more adapted structures with lower biodiversity. Wetlands that still maintain some functional relationship with the river, such as newer ox bow lakes, constructed wetlands, and backwaters, show a higher inorganic nutrient concentration and suspended solids. They also show higher taxa richness and evenness, which suggests that higher disturbance frequencies enhance habitat’s heterogeneity and resource availability, and therefore primary and secondary production that allow adapted and opportunistic species to coexist. The progressive flow regulation tends to homogenise this complex system, endangering its conservation. Therefore, the key processes identified here should be taken under consideration for the planning and execution of ecological monitoring, management and restoration.