Revisiting the Flood Pulse Concept: hydrological processes steering spatial floodplain zonation

Abstract

River floodplain wetlands are highly diverse and productive ecosystems. Water dynamics are the major factor for their ecosystem services and nutrient flows, vegetation productivity and biodiversity. The Flood Pulse Concept describes the coupling of river dynamics and adjacent floodplain processes, defining the moving edge of inundation as the indicator of the zone of high productivity. Where multiple water flows play a role in flooding, such as in the Biebrza Lower Basin in Poland, this coupling is probably less evident than proposed by the concept. Linking floodplain floodwater quality to water sources showed that the extent of floodwater from the river is limited to a relatively narrow zone along the river. Also, the deposition of sediment-bound nutrients N and P sharply decreased with distance from the river, indicating the limited sideways influence of the river for sediment input to the floodplain. Furthermore, sediment-bound nutrient deposition of upstream farmland was only high near the river and sharply decreased with distance. Flooding with dissolved nutrients seemed to result in high algae growth and deposition. The main conclusion related to the relevance of the Flood Pulse Concept is that the moving edge of inundation is not a good indicator of the zone of high productivity. Therefore, for temperate floodplains with multiple water flow processes, we proposed three additions: 1) delineation of the edge of river floodwater; 2) delineation of the zone of particulate sediment-bound nutrient deposition; and 3) identifying the zone where upstream nutrients are imported as either sediment-bound. The ecosystem service nutrient retention is mostly limited to a narrow zone along the river. For the service of biodiversity, this PhD thesis showed the importance of upwelling groundwater in the central part of the Biebrza Lower Basin.