Spatial Pattern of Phytoplankton Based on the Morphology‐Based Functional Approach along a River–Floodplain Gradient

Abstract

AbstractCurrent efforts to yield an appropriate method that would simplify the use of phytoplankton in the ecological evaluation of freshwaters resulted in different approaches based on clustering phytoplankton organisms. In this study, we applied the morphology‐based functional group (MBFG) concept to determine the spatial changes of phytoplankton in the natural riverine floodplain of the alluvial reaches of the Danube River along the horizontal gradient from the river towards the floodplain habitats.The obtained results showed that the magnitude of environmental changes depended on alternations in hydrological variables (hydropattern and water level) that influenced changes in the physical and chemical conditions. High‐intensity flood pulses caused environmental homogenizations and nitrate enrichment of the floodplain habitats. Phytoplankton dynamics were strongly associated with the environmental changes, and using the MBFG approach, two basic hydrological conditions were identified: inundation phase dominated by diatoms (GVI) and isolation phase dominated by filamentous cyanobacteria (GIII). Total diatom biomass decreased along the floodplain gradient with a diminishing of physical constraints, and site‐specific variables became more important in favouring diatom assemblages. The different response of cyanobacterial species to mixing regime was of particular significance for species successions during bloom period. Altogether, classifying very diverse diatoms (centrics and pennates and planktonic and benthic) and cyanobacterial taxa into single groups represents a weakness of the MBFG approach, which might make it impossible to reflect all the ecological differences governed by environmental constraints along river–floodplain gradients. Copyright © 2014 John Wiley & Sons, Ltd.