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River channels are regulated in various ways and the fertile soils of valleys are occupied for agricultural purposes, accompanied by human settlements. In many places on the floodplains, gravel or sand is mined and former pits fill with water. The consequences are changes in water relations, changes in land use and land cover. Natural riparian ecosystems gradually disappear. In addition, river valleys are susceptible places for the spread of invasive plant species. In the section of the Upper Odra Valley discussed in this article, all of the aforementioned factors have played roles in shaping modern habitats. The present study shows the impact of human-induced changes on the transformation of the plant cover of the Upper Odra Floodplain. In designated transects, we studied land use changes from 1910 to the present day and examined plant species diversity. The results show that the more heavily transformed floodplain adjacent to the channelized channel has a higher level of species diversity than agricultural areas located along a section of the river with a natural channel course. Most of the river valleys are colonized by geographically invasive alien species, such as Reynoutria japonica, Reynoutria sachalenesis and Impatiens glandulifera, which have contributed to the fact that all of the species typical of the ash, poplar and willow riparian forests characteristic of this habitat type have retreated, which is the main reason for the very low biodiversity. [ABSTRACT FROM AUTHOR]

River channels are regulated in various ways and the fertile soils of valleys are occupied for agricultural purposes, accompanied by human settlements. In many places on the floodplains, gravel or sand is mined and former pits fill with water. The consequences are changes in water relations, changes in land use and land cover. Natural riparian ecosystems gradually disappear. In addition, river valleys are susceptible places for the spread of invasive plant species. In the section of the Upper Odra Valley discussed in this article, all of the aforementioned factors have played roles in shaping modern habitats. The present study shows the impact of human-induced changes on the transformation of the plant cover of the Upper Odra Floodplain. In designated transects, we studied land use changes from 1910 to the present day and examined plant species diversity. The results show that the more heavily transformed floodplain adjacent to the channelized channel has a higher level of species diversity than agricultural areas located along a section of the river with a natural channel course. Most of the river valleys are colonized by geographically invasive alien species, such as Reynoutria japonica, Reynoutria sachalenesis and Impatiens glandulifera, which have contributed to the fact that all of the species typical of the ash, poplar and willow riparian forests characteristic of this habitat type have retreated, which is the main reason for the very low biodiversity.

Data are presented on the results of geobotanical studies along a 27.7-km permanent transect across the northern Volga–Akhtuba floodplain on which 88 geobotanical sampling plots are located. The transect was established in 1955, before the largest hydroelectric complexes were built on the Volga. As a result of their operation, the annual average floodwater discharge to the Volga–Akhtuba floodplain has decreased by 10–15% since 1959, amounting to 40–45% of the total annual water discharge. The water released from the Volgograd Reservoir falls from high height, has much kinetic energy, and its impact leads to deepening of the Volga riverbed in the northern part of the floodplain. Therefore, the same volumes of releases from the reservoir during floods result in increasingly lower rise in water level and, as a consequence, reduction in the inundated floodplain area. The results of surveys in 1982, 2008, and 2019 showed that xerophytization of vegetation in the floodplain region crossed by the transect has progressed during the 64-year period. Changes in the vegetation caused by the impairment of moisture conditions in the floodplain are accompanied by successions of phytocenoses resulting from invasion by new species. Among them, the North American species Fraxinus pennsylvanica has the most significant effect on the natural vegetation. [ABSTRACT FROM AUTHOR]

The results of studies of floodplain landscapes of the Don tributaries in its middle reaches are presented. The rivers under consideration are the Khoper, Medveditsa, Ilovlya, and Chir, as well as the tributaries of the Khoper―the Kosarka and Buzuluk. At the preliminary office stage, hydrological data on water levels and spring flood discharges over 1988–2018 were analyzed, and the inundation areas were determined by satellite images. In July–October 2019, field landscape-ecological studies were carried out, including instrumental profiling, soil and geobotanic studies, and evaluation of the depth to groundwater table. The floodplains of the Middle Don tributaries were found to have formed under the conditions of much higher water abundance in the rivers. The probability of the spring inundation of the floodplain does not exceed 10%. Under such conditions, cereal grass communities form on the high and, partly, middle floodplain, their composition being close to the zonal steppe vegetation of nearby areas. Some species in the vegetation indicate to a minor salinity of soils. [ABSTRACT FROM AUTHOR]

Aim. Islands and peninsulas in the Volga are of great environmental and recreational importance for the Volgograd agglomeration. Identifying the current state of geocomplexes in the Sareptsky peninsula allow us to assess the developmental trends of the floodplain ecosystems in the Lower Volga, which are under intense economic pressures.Material and Methods. The mapping was done by decoding Sentinel-2 satellite imagery and drawing landscape contours using the QGIS program. Field work was carried out in June 2019. Seven test plots were laid out. Inventory of forest plantations was undertaken with distribution of trees according to condition and a geobotanical description of the grass stand was done.Results. The Sareptsky peninsula was revealed to be an island by origin that was artificially attached to the native coast. The landscape structure of the peninsula includes 6 natural-anthropogenic complexes, of which the largest area (62.9%) is occupied by natural floodplain forest and cultivated forest. 13.9% is occupied by water meadows of the central floodplain, 8.0% by aquatic complexes of inland water bodies, 7.3% by anthropogenically transformed areas (settlements and industrial lands, roads and hydraulic structures), 5.1% by open areas of fresh-water floodplain and 2.8% by beach shoals of the river channel floodplain. The signs were revealed of a negative effect on the Volga through the regulation of its flow from desiccation of poplars and meagre species composition of meadow vegetation. It was established that the territory of the peninsula is exposed to a small extent by recreational activities.Conclusion. Landscape-ecological studies made in the Sareptsky peninsula allowed the assessment of the current state of forest and meadow ecosystems, the identification of the principal factors involved in the deterioration of their ecological status and the articulation of a better way to optimize nature management.

Graphical abstract Highlights • Tritium and carbon-14 used to assess pattern of Murray River floodplain recharge. • Pike floodplain recharged via inundation through surficial clay unit. • Katarapko floodplain recharged via riverbank recharge. • Results critical to maintaining health of floodplain ecosystems. Abstract Floodplains may alternate between discharge zones for regional groundwater and areas of recharge from river water during high-flow events. Understanding the mechanisms and timescales of recharge on floodplains is important for their management and for the protection of fragile ecosystems. The floodplains of the River Murray host important ecosystems, particularly remnant eucalypt forests that are vulnerable to changes in inundation, rising regional water tables, and salt accumulation. This study addresses floodplain recharge and groundwater mixing on the Pike and Katarapko floodplains of South Australia. At Pike, 3H activities of groundwater in the low hydraulic conductivity Coonambidgal Formation that crops out on the floodplain are ∼0.25 TU. 3H activities of groundwater in the underlying higher hydraulic conductivity Monoman Formation decrease from ∼1 TU near the contact with the Coonambidgal Formation to <0.02 TU at >15 m depth. Groundwater 14C activities are between 40 and 95 pMC but are less well correlated with depth. The 3H or 14C activities do not vary systematically with distance from the surface water channels on the floodplains. These observations imply that groundwater recharge at Pike is dominantly through the floodplain rather than through the channel banks. In contrast to the regional groundwater where total dissolved solids (TDS) concentrations are commonly >35,000 mg/L, the TDS of groundwater on the floodplain is locally <500 mg/L. A correlation between 3H activities and TDS and the presence of groundwater with relatively low 14C activities but above detection 3H activities implies that recently recharged waters have mixed with regional groundwater in the floodplain sediments. The 3H activities in these mixed waters implies that mixing occurs over a few years. By contrast, at Katarapko, the highest 3H activities in the Monoman Formation groundwater (up to 2.35 TU) are closer to the Murray River, implying that recharge through the bank may occur. These contrasting patterns of recharge probably reflect local topographic controls. Understanding the recharge-discharge relationships are vital for managing proposed floodplain inundation programs aimed at improving ecosystem health. [ABSTRACT FROM AUTHOR]

Abstract: We continued the complex ecological studies in the Lower Volga Region that we started in 2014 in order to investigate the current state of floodplain terrestrial ecosystems and to describe the tendencies in the transformation of the natural environment and the responses of terrestrial ecosystems to changing climate conditions and the influence of anthropogenic factors. The study was conducted with the original two-step method for the estimation of disorders in terrestrial ecosystems after changes in the water content of studied areas. The first step included the determination of possible changes in the water content based on an analysis of long-term annual changes in climatic and hydrological data. The second step included the estimation of disorders in the ecosystems and landscapes based on various biological parameters. We determined the main factors of changes in the abiotic (hydrological and climatic) components of ecosystems in the Lower Volga Region influencing the transformation of landscapes. We described the main causes of changes in a separate component of terrestrial ecosystems related to the increased water flow rate of the winter low-water period and winter runoff, which contribute to a higher level of gleying throughout the entire soil profile and to the degradation of floodplain ecosystems (along with climatic changes). [ABSTRACT FROM AUTHOR]

We continued our complex ecological studies in the Lower Volga region started in 2014-2015 (Kuz'mina et al., 2015a) in order to investigate the current state of floodplain terrestrial ecosystems in changing climate conditions (Kouzmina and Treshkin, 2014a) and during regulation of the river flow. We studied typical ecosystem changes in two of four geological and geomorphological regions: western substeppe ilmens and the central part of the Volga-Akhtuba floodplain, which had not been investigated earlier (Kuz'mina et al., 2015a). We estimated changes in ecosystems and the tendencies of landscape dynamics in current conditions. [ABSTRACT FROM AUTHOR]

How flooding regimes shape temperate-zone butterfly communities has received little attention. At the river Danube in eastern Austria, a levee has largely interrupted natural river dynamics since the late nineteenth century. Only a fraction of the floodplain area still experiences annual summer inundations after snow-melt in the Alps. We surveyed meadow butterfly communities on either side of the levee in a year with an unusually strong flood (2013), and in a season with a weak flood typical for the region (2012). Altogether we observed 67 butterfly species. Butterfly abundance and species richness were lower on meadows with stronger flood impact, but differences were modest. In contrast, species composition differed prominently relative to flooding regime and nectar availability. Grass-feeding species tended to be rarer on flooded meadows, while Brassicaceae-feeding species were more prevalent on nutrient-rich flood-prone meadows. Highly dispersive butterflies made up a larger share on flooded meadows, whereas highly philopatric species were relatively more common at sites with little or no inundation. These results indicate that summer inundations at the river Danube act as filters for the local species composition of butterflies on floodplain meadows. Local resource availability and the differential potential of species to re-colonize meadows after catastrophic floods are likely drivers of these differences. Effects of inundations were not consistently stronger in a year of a catastrophic flood than in a normal season. Butterfly communities on non-flooded meadows had a higher regional conservation value. [ABSTRACT FROM AUTHOR]

Spatial and temporal variability in flooding plays a significant role in the productivity of semi-arid floodplain ecosystems. Floodplains may be perceived as boom-bust systems, but this model does not account for transitions that may occur between wet and dry floodplain states. This study used the concept of adaptive cycles to examine how floodplain vegetation productivity changes in response to wetting and drying. Floodplain vegetation productivity was tracked through a wet and dry state using the normalized difference vegetation index (NDVI). Floodplain inundation revealed complex vegetation productivity responses to resource availability. There was low NDVI in the dry phase, whereas vegetation vigour increased and decreased through the wetting, wet and drying phases. There was a marked difference in NDVI class area, number of transitions, direction of transitions, probability of transitions and NDVI class diversity between the dry phase and the combined wetting, wet and drying phases of floodplain inundation. The distribution of transition probabilities was platykurtic in the dry phase and bimodal during the wetting, wet and drying phases. Overall, anti-clockwise hysteresis was the dominant direction of hysteresis. All vegetation productivity measures demonstrated a switch in direction during the wet phase. The hysteresis observed in this study indicates the cyclic nature of vegetation response to floodplain inundation through dry, wetting, wet and drying phases. We propose that vegetation productivity response follows an adaptive cycle and that this is an appropriate model for understanding the complexity of semi-arid floodplain vegetation response to wetting and drying. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Comprehensive ecological studies performed in the lower reaches of Volga during the low-flow period of 2014 revealed the unsatisfactory ecological condition of the floodplain, river meadows, and floodplain and delta forests in the Lower Volga area. Climate change in the region and regional hydrotechnical impact on the floodplain and delta of the Volga River were identified as the main causes of the deterioration of floodplain and delta ecosystems. Considerable dynamic changes caused by human activity and climate change occurred in the terrestrial ecosystems of the floodplain and delta. The regulation conditions downstream of the Volgograd reservoir should be changed in order to prevent complete destruction of floodplain and delta terrestrial ecosystems under the current conditions of climate instability. [ABSTRACT FROM AUTHOR]

In the basin of the Lower Volga, the main trends of climate change and their impact on the dynamics of ecosystems are identified. The results were obtained by analysis of longitudinal meteorological characteristics (average, maximum, and minimum air temperature and total seasonal and year precipitation) and the establishment of expected changes in the land ecosystems and landscapes. The basic directions of the aggregate impact of changes of the humid-temperature regime in the basin of the Lower Volga are identified, and the general directions of the dynamics of terrestrial ecosystems in this regard are stated. [ABSTRACT FROM AUTHOR]

Floodplains are ecotones that form a transition between aquatic and terrestrial environments. These important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface. Hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system. This paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large Australian floodplain to a river channel, and the effects of land and water developments on these exchanges. The paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach—a recognition of the importance of the three disciplines hydrology, geomorphology and ecology. Large-scale water-resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the Lower Balonne floodplain, Australia. The magnitude, frequency and duration of flooding events have all been reduced. The construction of levees and water storages has also reduced the reactive floodplain surface area. The presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation. Annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less. Some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water-resources and floodplain developments. [Copyright &y& Elsevier]