Summary 1.One of the main targets of river-floodplain restoration is the reconnection of former side channels. While there is information about the overall impact of such measures, far less is known about specific species' response patterns to hydrological connectivity. 2. The present study examined the composition of aquatic mollusc communities based on the performance of individual species with respect to hydrological connectivity in the Donau-Auen National Park, Austria. Species' traits were used to make generalizations about community responses to hydrological changes. 3. We introduced a connectivity parameter (Cd, expressed in days year −1 ) that could easily be derived from the river hydrograph and altitude of the inflow areas. This parameter integrated several key features of floodplain waterbodies and reflected the causeeffect chain of restoration schemes, thus allowing the outcome of restoration measures to be quantitatively predicted. Endangered rheophilic mollusc species reached higher frequencies as connectivity increased; for most eurytopic molluscs, however, increased connectivity reduced abundance. 4. With respect to species' traits, the proportion of large gastropods declined continuously with increasing Cd, whereas the percentage of gastropods with globolose shells and the relative number of strongly calcified (thick-shelled) individuals both increased. Species dominating in isolated sites were characterized by a higher resistance to desiccation, a food preference for higher plants and a preference for less shaded habitats. They matured later and typically had more offspring than rheophilic species. 5. Species number peaked at connectivity (Cd) values of about 1 month year −1 . Isolated and lotic habitats hosted significantly fewer mollusc species. Species turnover was highest when Cd was between 0 days and 2 months. 6. Synthesis and applications. Empirical models based on a connectivity parameter can be used to predict the consequences of restoration measures on the aquatic mollusc community in the Donau-Auen National Park. The analysis of species' traits also allows general prognoses for other river-floodplain systems. Furthermore, initial results based on other taxa indicate a broad applicability of the parameter. The methodology thus provides both an urgently needed and a practical tool for predicting the impact and success of restoration schemes.

Summary• Exotic plant invasions can alter ecosystem processes, particularly if the invasive species are functionally different from native species. We investigated whether such alterations can be explained by differences in functional traits between native and invasive plants of the same functional group or by differences in functional group affiliation.• We compared six invasive forbs in Europe with six native forbs and six native graminoids in leaf and whole-plant traits, plasticity in response to nutrient supply and interspecific competition, litter decomposition rate, effects on soil nutrient availability, and allelopathy. All traits were measured in a series of pot experiments, and leaf traits additionally in the field.• Invasive forbs differed from native forbs for only a few traits; they had less leaf chlorophyll and lower phosphorus (P) uptake from soil, but they tended to have a stronger allelopathic effect. The invasive forbs differed in many traits from the native graminoids, their leaves had lower tissue densities and a shorter life span, their litter decomposed faster and they had a lower nitrogen-use efficiency.• Our results suggest that invasive forbs have the potential to alter ecosystem properties when invading graminoid-dominated and displacing native graminoids but not when displacing native forbs.

Summary1. We used an isolated floodplain of the river Danube as a model system to gain an understanding on the functioning of retention areas to predict future developments and to sustain their ecological services. 2. We applied correlation analysis and spline regression models to assess the effects of geomorphology, hydraulics, and seasonality on sediment characteristics, suspended solids, hydrochemistry and primary producers. 3. The spatio-temporal connection to the river is the primary factor influencing the hydrochemical characteristics and sediments. Allochthonous processes such as nutrient and sediment input during high waters dominate in connected parts of the floodplain, whereas autochthonous processes, for example, the release of phosphorus from the sediments and internally driven eutrophication, dominate in isolated parts. These conditions also affect the dominating primary producers, biodiversity, the degree of floodplain aggradation and thus the potential life span of aquatic habitats. 4. Measures to improve the functional basis for ecological services may use both allochthonous and autochthonous processes as a starting point, that is, minimizing sediment storage and nutrient input and improving the water balance to prolong the life span of isolated waters, and thus maximizing water body diversity and associated biodiversity. 5. Based on the results of our analysis and literature, eight alternative management measures have been evaluated. As a result, we propose a stepwise adaptive approach beginning with a controlled water supply with low sediments and nutrient loads. If these measures prove insufficient to sustain ecological functions and conservation value, more radical steps must be considered. 6. Synthesis and applications The increasing problems with catastrophic flooding have forced decision makers to seek basin-wide solutions with focus on 'more room for the river' and the reintegration of former floodplains as retention basins. Such reintegrations also represent opportunities to improve the ecological conditions for nature development in addition to their principal function, that is, the storage of water during floods. The results of our study can serve as an effective tool to predict the effects of alternative management options and to establish and define the design criteria of water retention areas with regard to their ecological functions, life spans and biodiversity.

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Summary We investigated the effects of temporary surface water connections with the main river on the water chemistry of large and small waterbodies in a Danube floodplain by comparing hydrochemical data before, during and after water exchange with the Danube during two large floods in 2009 and 2013. In addition, we studied the effects of an increased frequency of flood pulses on the water chemistry of the floodplain via long‐term monitoring data. We used conservative (i.e. biologically non‐reactive) parameters (alkalinity, Ca, Cl, K, Mg, Na, SO4, conductivity) to identify hydrochemical changes due to the mixing with river water. Changes in non‐conservative parameters (PO4‐P, NO3‐N, NO2‐N, NH4‐N, total phosphorus, dissolved organic carbon, dissolved oxygen, chlorophyll‐a), which deviated from pure mixing effects, were ascribed to alterations of biogeochemical processes induced by the imported river water. In large floodplain waterbodies, both conservative and non‐conservative parameters changed towards Danube water concentrations during the connection with the main river and returned to pre‐connection levels after the water exchange ended. Only chlorophyll‐a concentrations were almost twice as high in the post‐connection phase than before the connection. In small floodplain waterbodies, conservative and non‐conservative parameters showed similar changes during the connection with the main river. However, the concentrations of PO4‐P, total phosphorus and chlorophyll‐a did not return to pre‐connection levels, but increased further in the post‐connection phase, exceeding even Danube water concentrations. We attribute these changes to phosphorus releases from the sediments and enhanced primary and bacterial production induced by the river water. In years with an increased flooding frequency, both conservative and non‐conservative parameters approached Danube water concentrations in large floodplain waterbodies due to the increased surface water exchange. In small floodplain waterbodies, conservative parameters remained unaffected by the increased connection with the river, while nitrate, ammonium, phosphate, total phosphorus and chlorophyll‐a concentrations were considerably higher in wet years than in dry years. We conclude that the temporary input of oxygen‐ and nutrient‐rich river water to small, mainly isolated backwaters can induce changes in benthic biogeochemical processes, which may provoke an internal eutrophication of these waterbodies.

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For centuries, rivers have experienced massive changes of their hydromorphic structures due to human activities. The Danube River, the second largest river in Europe, is a case in point for longterm societal imprint. Resulting human-induced pressures are a key issue for river management, aiming to improve the ecological conditions and guarantee the provision of ecosystem services.As the most international river basin in the world, the management of the Danube is particularly challenging and needs a well-organized cooperation of 19 nations. The recent river basin management plan has identified pollution and hydromorphological alterations as most pressing problems, but it has also acknowledged newly emerging issues. In this article, we present 3 specific exam- ----------------------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.