Characterisation of the potamal Danube River and the Delta: connectivity determines indicative macrophyte assemblages

The complexity of water bodies in the eu-potamal river corridor and the main delta channels of the Romanian Danube is exemplified by the macrophyte vegetation. Two hypotheses provided the background for our study: (a) is the macrophyte vegetation of large, permanently connected branches significantly separated from that of the main river channel; (b) is the macrophyte composition of the Danube main stem significantly altered when the river divides into the three large navigable Delta channels. Water bodies considered were two contiguous sections of the main river channel, two large branches remaining from the historical floodplain, and the three main Delta channels. We quantified macrophyte diversity and floristic variation. Our data set was prepared from the MIDCC-project data base, in which macrophyte occurrence, abundance and habitat parameters are stored for contiguous survey units of the whole Danube river corridor. Field survey method followed that of Kohler and the European Standard EN14184. Results confirmed our first hypothesis: permanently connected side branches still support significantly different macrophyte assemblages, making them important indicators of floodplain connectivity. The diversion of the Danube into its three large navigable delta channels significantly alters the macrophyte vegetation from the c. 300 km of main stem up-river, substantially supporting our second hypothesis. Our results largely enhance the knowledge on aquatic plant biodiversity in the eu-potamal Danube, forming a solid base for long-term studies. We also discuss the relevance of our results regarding the ecological, as well as the conservational, quality of rivers and their floodplains.     

Ecological rehabilitation of the lowland basin of the river Rhine (NW Europe)

In this paper, the status of ecological rehabilitation of the Dutch lowland basin of the river Rhine has been reviewed. The historical perspective, mainly with regard to river regulation measures in the past, is given. The lower river Rhine comprises a man-dominated, strongly regulated catchment, polluted water and sediments, and annihilated and deteriorated ecosystems. During the past 25 years, the water quality and, to a lesser extent, the sediment quality, has improved considerably, hence leading to improvement of biotic diversity. The rehabilitation of lost and disturbed ecosystems started some 15 years ago. The non-refutable boundary conditions for restoration projects are protection against flooding and transport by cargo ships. Holistic ecological theories to promote river catchment management are available, but the rehabilitation projects dominantly rely on local and regional planning policies. The use and application of ecological criteria are increasingly playing a role in rehabilitation schemes. Ecological rehabilitation mainly focuses on nature conservation and restoration strategies, i.e. exploiting the hydrodynamic and morphodynamic potentials of the flowing river, and introducing a semi-natural grazing regime by large herbivores. Particularly the creation of new secondary channels contributes to the restoration of riverine habitat diversity and heterogeneity, and hence to the species diversity. The assessment of a number of rehabilitation projects has led to the conclusion that no general statement can be given concerning `success' or `failure' of specific restoration measures. The overall balance of 14 assessed projects out of approximately 30 running projects is positive. The highly dynamic river Waal offers the best possibilities for the restoration of natural sandy levees and back swamps. It will be very difficult to rehabilitate the hardwood floodplain forests under the present management conditions. Further recovery of the river biota depends on continued decrease of pollution, an increase of morphological dynamics, and the development of the original natural habitats.     

The rivers Rhine and Meuse in The Netherlands: present state and signs of ecological recovery

The ecosystems of the rivers Rhine and Meuse have suffered drastic environmental changes, for example because of the regulation of the stream bed and the construction of weirs and dams. Furthermore, discharges of industrial and municipal waste water have caused the water quality of these rivers to deteriorate; this problem became acute in the sixties and seventies. Recently some chemical parameters of water quality have improved in the Rhine, and as a consequence some aquatic communities are showing signs of recovery after decades of severe degradation. This paper describes the present state of the aquatic communities in the Dutch part of the rivers Rhine and Meuse, using published observations on plankton, macrophytes, invertebrates, and fish. The sparse information on the food chain in these rivers is summarized. The main channels of the Rhine and Meuse are characterized by a dense plankton that develops rapidly in the nutrient-rich river waters. The stream beds, now dominated by wave-exposed sand and gravel, have a sparse fauna and flora. The river banks, mostly consolidated by blocks of stone, offer a substratum for numerous benthic organisms, particularly now that the water quality has improved. The floodplain waters and old river channels harbour a flora and fauna rich in species. The degree of water exchange with the river is crucial for the ecological development of the river and its backwaters. Today the freshwater tidal reaches of the rivers occupy a very restricted area, and only remnants of the previously abundant vegetation of rushes are found. Losses in the numbers of animal and plant species, notably those specific to rivers, are evident, but over the last 15 years several species have returned. Allochthonous species (exotics), including crustaceans and molluscs, have also settled in the Rhine and Meuse. Fish species characteristic of these rivers, such as river lamprey, sea trout, barbel, and flounder, have recently been observed in appreciable numbers. The Rhine Action Programme provides a framework for the large-scale rehabilitation of the Rhine. Experiments on re-stocking the Rhine with Atlantic salmon and on the ecological rehabilitation of floodplains are being carried out on the assumption that there will be a further reduction of the pollution load. A similar programme is required for the Meuse.     

Sources of organic carbon supporting the food web of an arid zone floodplain river

SUMMARY 1. Many Australian inland rivers are characterised by vast floodplains with a network of anastomosing channels that interconnect only during unpredictable flooding. For much of the time, however, rivers are reduced to a string of disconnected and highly turbid waterholes. Given these features, we predicted that aquatic primary production would be light-limited and the riverine food web would be dependent on terrestrial carbon from floodplain exchanges and direct riparian inputs.
2. To test these predictions, we measured rates of benthic primary production and respiration and sampled primary sources of organic carbon and consumers for stable isotope analysis in several river waterholes at four locations in the Cooper Creek system in central Australia.
3. A conspicuous band of filamentous algae was observed along the shallow littoral zone of the larger waterholes. Despite the high turbidity, benthic gross primary production in this narrow zone was very high (1.7–3.6 g C m⁻² day⁻¹); about two orders of magnitude greater than that measured in the main channel.
4. Stable carbon isotope analysis confirmed that the band of algae was the major source of energy for aquatic consumers, ultimately supporting large populations of crustaceans and fish. Variation in the stable carbon and nitrogen isotope signatures of consumers suggested that zooplankton was the other likely major source.
5. Existing ecosystem models of large rivers often emphasise the importance of longitudinal or lateral inputs of terrestrial organic matter as a source of organic carbon for aquatic consumers. Our data suggest that, despite the presence of large amounts of terrestrial carbon, there was no evidence of it being a significant contributor to the aquatic food web in this floodplain river system.     

The distribution and environmental state of vegetated islands within human‐impacted European rivers

1. Vegetated islands within river corridors are pivotal landscape features and are among the first to disappear as a consequence of flow regulation and channelisation. However, how vegetated islands vary along human‐impacted rivers is poorly understood. 2. We carried out a detailed analysis of the contemporary distribution, diversity and environmental state of vegetated islands within 12 human‐impacted European rivers, using 75 Landsat 7 ETM+ satellite images (1999–2002), historical maps, DEM data and landscape metrics. We tested whether channel fragmentation, catchment land use and the environmental state of fringing floodplains determine the spatial patterns of the islands. We also analysed the historical change of islands within selected sections of the Upper Danube, Upper Rhine and Olt rivers. 3. We identified 2771 islands in the contemporary landscape, varying from 0.06 to 9828 ha. Islands covered up to 21% of the active channel area and contributed up to 32% of the total riparian ecotone length. Island density ranged from 0.06 islands per river‐km (River Sava) to 1.6 islands per river‐km (River Tagliamento). River regulation has led to a marked loss of island density: 94% in the Upper Danube, 93% in the Upper Rhine, and 69% in the Olt. The environmental state of the islands was significantly less altered by human activity than of their fringing floodplains; 93.4% of the vegetated islands exhibited a near‐natural state, while 86% of the fringing floodplains were expansively converted to agricultural and urban land uses. 4. Our results highlight the ubiquitous presence of vegetated islands, their sensitivity to river regulation and their pivotal role for the future restoration and management of river corridors.     

Geomorphic dynamics of floodplains: ecological implications and a potential modelling strategy

1.  The dynamics of channel migration and floodplain renewal constitute an important control of the ecological diversity of river corridors. Restoration initiatives should therefore assess whether these dynamics must be reinstated in order to address the cause rather than the symptoms of floodplain biodiversity decline.
2.  Restoration of reach-scale dynamism in rivers where this is a natural behavioural process will restore smaller-scale geomorphological and sedimentological processes that encourage vegetation regeneration, but may require catchment-scale management of material flows.
3.  Channel dynamics depend on the style of river–floodplain interaction, and this may be summarised in qualitative, classificatory, sedimentological models of floodplain architecture that have been somewhat neglected in the ecological literature.
4.  One approach to the assessment of floodplain biodiversity and its restoration would be through the development of simulation models based on specified channel styles, and involving simplified hydrodynamics and successional changes. Such models, currently the subject of research as a spin-off from modelling studies of landscape evolution, would permit evaluation of the consequences for ecological diversity of implementing various management options that may affect the dynamics of channel migration.     

Input, movement and exchange of organic matter within a subtropical coastal black water river-flood plain system

SUMMARY. 1. Inputs, movements and exchanges of particulate organic matter were measured on two contrasting floodplains of the Ogeechee River, Georgia, U.S.A. A model, which incorporated measurements of standing crop, respiration, litterfall, inundation, and litter processing rates, was used to estimate annual exchanges of organic matter between the river and floodplains.
2. Annual litterfall was higher on the East floodplain than on the lower elevation West floodplain (902 v. 784 g ash-free-dry-mass [AFDM] m⁻²).
3. Experiments with tagged leaves and sticks demonstrated that litter was readily displaced during floods. The distance and direction of displacement varied within and between floodplains but tended to be higher closer to the river and was generally parallel to the river.
4. The model indicated that both floodplains lost organic matter to the river. The lower elevation floodplain (East) lost more organic matter to the river (208 g AFDM m⁻² year⁻¹) than did the higher elevation (West) floodplain (79g AFDM m⁻² year⁻¹).
5. Inputs of organic matter from the floodplain to the river exceeded the amount of litterfall typically entering heavily forested high gradient headwater streams (5.5 v. 0.4-0.6 kg AFDM m⁻² year⁻¹).
6. Floodplain organic matter inputs may exert a greater influence upon structure and function within these streams than do upstream inputs or primary production. Consequently, current conceptualizations of stream structure and function need to be modified to account for the effects of floodplain inputs on stream channel processes within large, low-gradient rivers.     

Invasion phylogeography of the Ponto-Caspian crustacean Limnomysis benedeni dispersing across Europe

Aim  Limnomysis benedeni Czerniavsky, 1882 is a mysid crustacean native to the Ponto-Caspian (Black and Caspian Sea) rivers and estuaries, and has recently spread across Europe through intentional and unintentional introductions. We explored the structuring of genetic variation in native and non-native populations with an aim to trace the sources of the invasions, and to infer whether the spread has occurred through a single or multiple invasion waves.
Location  Native estuaries in the Ponto-Caspian basin (Volga, Don, Dnieper, Dniester, Danube) and the recently colonized range along the Danube–Rhine river systems and Lithuania.
Methods  A fragment of the mitochondrial COI gene was sequenced to assess genetic affinities and diversity in native and recently established populations.
Results  The genetic diversity in the native regions is organized into several strongly diverged haplotype groups or lineages, partly allopatric, partly sympatric. All these lineages have also spread beyond the native range. Even the recent rapid dispersal across Europe along the Danube–Rhine system towards the North Sea basin involved several lineages from the Danube delta sector. The structuring of genetic diversity among invaded sites suggests multiple invasion events to the Danube–Rhine drainage. This contrasts with data from some other Ponto-Caspian species, where a single haplotype seems to have occupied most invaded areas. There is no evidence that intentionally stocked reservoirs in the Baltic Sea basin would have contributed to further unintentional spread of L. benedeni.
Main conclusions  Limnomysis benedeni is spreading across Europe using the southern invasion corridor. The invasion most likely involved several waves from differentiated sources in the native Danube delta area.     

Patchiness of River–Groundwater Interactions within Two Floodplain Landscapes and Diversity of Aquatic Invertebrate Communities

In fluvial systems, the interactions between rivers and groundwater significantly affect various ecological structures (for example, riparian vegetation) and functions. To examine the effects of hydrological exchange between groundwater and surface water on the distribution of aquatic invertebrates within a riverine landscape, we investigated the main stem, tributaries, and various surface and subsurface waters of two floodplains of a southern Alpine river (Brenno, Switzerland) in terms of their physicochemical, hydraulic, substratum, and faunal characteristics. The origins of the water were investigated by analyzing geomorphic settings and physicochemical variables. The two floodplains had different hydrological regimes. The middle floodplain was dominated by lateral inputs and exfiltration of hillslope groundwater from two different subcatchments. Bank filtration of river water sustained subsurface water only close to the channel. The aquatic habitats of the middle floodplain formed a rather homogeneous group with high taxon richness and intrahabitat diversities. These aquatic habitats resembled mountain springbrooks in their physicochemical characteristics and faunal compositions. In the lower floodplain, the exchange between river water and groundwater was more extensive. The aquatic floodplain habitats of the lower floodplain were fed mainly by deep and shallow alluvial groundwater, hyporheic exfiltration, and partly by surface water. In contrast to aquatic habitats of the middle floodplain, habitats of the lower floodplain showed a low intrahabitat and a high interhabitat diversity in terms of both substrate characteristics and faunal compositions. For both floodplains, ordination analyses showed a high concordance between the structure of the invertebrate community and the characteristics of the environmental habitat, including chemical, geomorphic, and hydraulic variables. Ordinations grouped aquatic habitats according to the origins of the waters. Taxon richness was related to local structural diversity, but species turnover was related to differential vertical and lateral connectivity. Exfiltration of groundwaters provided aquatic floodplain habitats for several specialized species. The results of this study show the significance of the river–groundwater connectivity for the creation of the habitat mosaic that sustains biodiversity in floodplains and thus have important implications for managing the ecological integrity of floodplains.     

Comparative use of side and main channels by small‐bodied fish in a large,unimpounded river

相似文献   

Impact of hydrology on the chemistry and phytoplankton development in floodplain lakes along the Lower Rhine and Meuse

The impact of hydrology (floods, seepage) on the chemistry of water and sediment in floodplain lakes was studied by a multivariate analysis (PCA) of physico-chemical parameters in 100 lakes within the floodplains in the lower reaches of the rivers Rhine and Meuse. In addition, seasonal fluctuations in water chemistry and chlorophyll-a development in the main channel of the Lower Rhine and five floodplain lakes along a flooding gradient were monitored. The species composition of the summer phytoplankton in these lakes was studied as well.At present very high levels of chloride, sodium, sulphate, phosphate and nitrate are found in the main channels of the rivers Rhine and Meuse, resulting from industrial, agricultural and domestic sewage. Together with the actual concentrations of major ions and nutrients in the main channel, the annual flood duration determines the physico-chemistry of the floodplain lakes. The river water influences the water chemistry of these lakes not only via inundations, but also via seepage. A comparison of recent and historical chemical data shows an increase over the years in the levels of chloride both in the main channel of the Lower Rhine and in seepage lakes along this river. Levels of alkalinity in floodplain lakes showed an inverse relationship with annual flood duration, because sulphur retention and alkalinization occurred in seepage waters and rarely-flooded lakes. The input of large quantities of nutrients (N, P) from the main channel has resulted, especially in frequently flooded lakes, in an increase in algal biomass and a shift in phytoplankton composition from a diatom dominated community towards a community dominated by chlorophytes and cyanobacteria.     

Biodiversity in the Lower Rhine and Meuse river-floodplains: Its significance for ecological river management

The diversity of aquatic biota in two large river systems of The Netherlands,viz. the Lower Rhine and Meuse, is discussed in order to: (1) reveal historical changes in biodiversity; (2) examine the role of river-floodplain connectivity; (3) set guide lines for ecological river management. The taxonomical diversity, or species richness, is used to describe the former and recent state of aquatic biota in these river systems. The ecological diversity, obtained by incorporating the concept of ecological groups into the concept of biodiversity, appears very useful in delineating guide-lines for ecological river management. The present species richness in the main channels still appears to be relatively low, despite major water quality improvements. Although present biodiversity is much improved compared with a few decades ago, it is evident that the present species are mainly eurytopic, including many exotics. The inhibition of a further biodiversity recovery results from river regulation and normalization, which have caused the deterioration and functional isolation of main channel and floodplain biotopes. The importance of connectivity for the diversity of aquatic biota is found to be different for various taxa. Moreover, a transversal zonation by the biota in the floodplain lakes is found, emphazising the importance of differences in the degree of connectivity for a diverse aquatic flora and fauna. It is concluded that floodplain lakes contribute significantly to the total biodiversity of the entire riverine ecosystem. The redevelopment of active secondary channels is required to restore the most typical riverine habitats and biota.     

Alien aquatic macroinvertebrates along the lateral dimension of a large floodplain

Floodplains are simultaneously among the most species-rich and the most threatened ecosystems. Alien aquatic macroinvertebrates contribute to this threat but remain scarcely studied in the lateral dimension of floodplains. We modelled the realized ecological niches of the alien species occurring in 24 floodplain channels of the Rhône River. Environmental variables depicting the ecological niches were associated to the lateral hydrological connectivity and light availability, both being modified during floodplain restoration works. Eight alien species were observed and they demonstrated either ubiquity or a restricted niche, with no link to the date of introduction. For most of them, the main river channel appeared as an important dispersal route in the lateral dimension of the floodplain. An increase of both lateral connectivity and light availability favoured most of the modelled species. Consequently, we recommend that sector-scale restoration programmes preserve varying levels of lateral connectivity for floodplain channels to prevent the expansion of alien aquatic macroinvertebrates.     

Stream–floodplain connectivity and fish assemblage diversity in the Champlain Valley, Vermont, U.S.A.

To evaluate the influence of main channel–floodplain connectivity on fish assemblage diversity in floodplains associated with streams and small rivers, fish assemblages and habitat characteristics were surveyed at 24 stream reaches in the Champlain Valley of Vermont, U.S.A. Fish assemblages differed markedly between the main channel and the floodplain. Fish assemblage diversity was greatest at reaches that exhibited high floodplain connectivity. Whereas certain species inhabited only main channels or floodplains, others utilized both main channel and floodplain habitats. Both floodplain fish α-diversity and γ-diversity of the entire stream corridor were positively correlated with connectivity between the main channel and its floodplain. Consistent with these results, species turnover (as measured by β-diversity) was negatively correlated with floodplain connectivity. Floodplains with waterbodies characterized by a wide range of water depths and turbidity levels exhibited high fish diversity. The results suggest that by separating rivers from their floodplains, incision and subsequent channel widening will have detrimental effects on multiple aspects of fish assemblage diversity across the stream–floodplain ecosystem.     

Riparian vegetation diversity along regulated rivers: contribution of novel and relict habitats

1. The creation and maintenance of spatial and temporal heterogeneity by rivers flowing through floodplain landscapes has been disrupted worldwide by dams and water diversions. Large reservoirs ( novel ecosystems ) now separate and isolate remnant floodplains ( relict ecosystems ). From above, these appear as a string of beads, with beads of different sizes and string connections of varying lengths.
2. Numerous studies have documented or forecast sharp declines in riparian biodiversity in relict ecosystems downstream from dams. Concurrently, novel ecosystems containing species and communities of the former predam ecosystems have arisen along all regulated rivers. These result from the creation of new environments caused by upper reservoir sedimentation, tributary sedimentation and the formation of reservoir shorelines.
3. The contribution of novel habitats to the overall biodiversity of regulated rivers has been poorly studied. Novel ecosystems may become relatively more important in supporting riverine biodiversity if relict ecosystems are not restored to predam levels. The Missouri River of the north-central U.S.A. is used to illustrate existing conditions on a large, regulated river system with a mixture of relict and novel ecosystems.     

Archaic and contemporary topographic diversification of Upper Mississippi River forests

Topographic diversity is an important component of environmental heterogeneity. Topographic diversity within the Upper Mississippi River floodplain has been degraded because of modifications for navigation improvement. Efforts aimed at restoring topographic diversity in the Upper Mississippi River floodplain have been extensive but have not focused on reversing the effects of forest loss and degradation. We investigated habitat features associated with Cerulean Warbler (Setophaga cerulea) locations both within and outside of river floodplains and hypothesized this species would select topographically diverse habitats. Both topographic diversity and the distance to the upland forest/floodplain forest interface were useful predictors of Cerulean Warbler presence. We conclude that incorporation of topographic diversity into floodplain forest restoration planning would likely benefit Cerulean Warblers and the other species with similar habitat requirements. Incorporating topographic diversity into floodplain forest conservation planning will be challenging on major rivers that serve multiple purposes.     

Contribution of microspatial factors to benthic diatom communities

Large rivers are worldwide under severe pressure and there is a lack of information on large river restoration. The present paper represents a meta-analysis of available data on river rehabilitation projects performed at the Austrian Danube River consisting of six rehabilitation projects addressing 19 sites. The overall goal was to analyse the response of fish assemblages to different rehabilitation types based on (1) morphological type (“Instream Habitat Enhancement”, “backwater Enhancement”, “extended Enhancement”), (2) length of rehabilitation measure (3) time after construction (4) applied monitoring design. Biological metrics evaluated included number of fish species and relative density, habitat guilds and Leitbild species. In total, number of species increases by 55% comparing rehabilitated with unrestored sites. The number of species of all habitat guilds is higher after rehabilitation. The proportion of rheophilic species increased and the community evolved toward a more type-specific community, according to the Leitbild. Significant differences between measure types were not detected. The rehabilitation success depends mainly on its spatial extent. Highest positive response of number of rheophilic species is achieved by a length >3.9 km. The results show that habitat rehabilitation of large rivers is effective if the spatial extent of the measure is in accordance with river size.     

Island-dominated landscapes of large floodplain rivers, a European perspective

1. The landscapes of large floodplain rivers are characterised by heterogeneous environments related to the interplay of flood flows, sediment transport and vegetation dynamics.
2. The large rivers of Europe, and probably most rivers throughout the forest biomes, were characterised by islands but over the period of major human interference, many have become dominated by incision and narrowing so that they are now characterised by single-thread and relatively simple channel forms.
3. Vegetation plays an active role in developing heterogeneous channel forms through (a) biotic processes such as seed dispersal, vegetative regeneration and succession and (b) abiotic effects such as increasing flow resistance inducing sedimentation, and decreasing bank erodibility.
4. In particular, accumulations of living driftwood (cf. dead driftwood accumulations and dispersed seedlings) accelerate sedimentation and island development.
5. River reaches with vegetated islands have a high habitat diversity.
6. The natural influences of flood disturbance, wood accumulation, vegetation growth, island development and tree die-off, cause island-dominated reaches to undergo cycles of island growth and decay that are related to cycles of aquatic habitat diversification and simplification.     

Biodiversity in the floodplain of Saône: a global approach

Biodiversity of European floodplains is seriously threatened mainly due to (1) modifications of river courses such as channelisation or embankments, and (2) changes in traditional agricultural practices (i.e. usually pastures), into intensive production using drainage and fertilisation. A upstream-downstream survey of the Saône floodplain (France) has been done to identify the contribution of habitats to the floodplain biodiversity. Selected taxa were aquatic and terrestrial vegetation, Odonata, Coleoptera, Amphibians, and birds. The taxa were sampled in different habitat types that were: forests, grasslands and aquatic habitats. Tributary confluences with the river and cut-off channels contributed greatly to the floodplain diversity according to their invertebrates and aquatic vegetation communities. The abundance of rare species (benefitting of a national or regional protection status) was the highest in hygrophilous grasslands. Moreover, we demonstrated that diversity of breeding bird communities was correlated with the size of these habitats. We demonstrated also that alluvial forests contributed to maintain some particular species as Middle-spotted Woodpecker (Dendrocopus medius), while new plantations were colonized by openland bird communities sensible to the edge effect. Grassland fragmentation for agriculture appeared to be a major cause in biodiversity loss. Any alteration of the floodplain dynamics must be avoided to preserve the present diversity of riverine wetlands.     

Zooplankton biomass and community structure in a Danube River floodplain system: effects of hydrology

1. Zooplankton density and biomass was examined in a Danube River floodplain section with highly variable hydrological dynamics. Temporal patterns were analysed to assess the effects of hydrological conditions on zooplankton community structure and the differential response of the two major zooplankton taxa, rotifers and crustaceans.
2. Calculated floodplain water age was used as an integrated parameter describing hydrological conditions and connectivity.
3. Total zooplankton biomass, crustacean biomass and crustacean species number were significantly positively related to water age. Rotifer biomass followed a hump-shaped relationship with water age, and rotifer species number decreased with increasing water age.
4. Rotifers dominated the community in periods of low to medium water ages. In periods of higher water ages the community was dominated by crustaceans.
5. We propose that the hydrological regime of floodplains is crucial for zooplankton biomass patterns and succession, through the alternation of washing-out effects, taxon-specific potential of reproduction and biological interactions. Flood events and high water levels reset the community to an early successional phase.