The influence of soil desiccation on plant production,nutrient uptake and plant nutrient availability in two French floodplain grasslands

The effects of summer soil desiccation on plant production and plant nutrient availability (determined by wet chemical extraction) in floodplain grasslands along the rivers Allier and Loire in France were investigated. Soil desiccation in these river floodplains is the result of human interference with the natural flooding regime of rivers, such as dam construction and gravel mining. Flooding periods along the Allier have a longer duration (maximum of 202 days as opposed to 38 days for the Loire). The main comparison was between floodplain grasslands along the two rivers. Additional comparisons were made between relatively high lying, wetter areas (‘ridges’) and low lying, drier areas (‘swales’) within both floodplains. Thus, areas with different soil moisture content were examined, independent of river influences. The availability of P was higher in the Allier floodplain than in the Loire floodplain, but it was similar between ridges and swales. It was concluded that P-availability was not related to soil wetness, but to river sedimentation. Plant production, plant nutrient uptake, and biologically mediated soil processes, such as N-mineralization and nitrification, were all higher on the wetter Allier floodplain and in the wetter swales. These higher process rates were noted where higher amounts of soil bound carbon and nutrients were found as well. Plant production, N-mineralization and nitrification were moisture limited at the dry ridge on the Loire floodplain, as moisture levels were below the wilting point here (pF>4.2). On the wetter parts of the floodplain, plant production was N-limited. This was concluded from low tissue N/P ratios (about 10) and a positive relation between plant production and N-mineralization. On the wetter parts, the rate of N-mineralization depended on the size of soil organic-N pools. The size of these pools was positively related to soil wetness, which can be interpreted as a positive effect of river flooding. Reduced flooding lowers the nutrient input to floodplains and contributes to the occurrence of soil desiccation in summer, which results in lower nutrient cycling and reduced accumulation of soil organic matter. These effects have negative consequences for important floodplain functions, such as nutrient retention and biomass production. © 1998 John Wiley & Sons, Ltd.     

Dynamics of river fish populations in response to hydrological conditions: a simulation study

Increasing multi‐sectoral demands on water resources have led to water abstraction and transfer activities, and the construction of dams and embankments that have significantly altered the flood regimes of rivers throughout the world resulting in the loss of fish production and biodiversity. The current emphasis on sustainable development and biodiversity conservation is leading efforts to mitigate these impacts by means of interventions such as the release of artificial floods downstream of dams and the manipulation of water levels within impounded floodplains. Whilst much work has been done to determine the hydrological requirements for the maintenance of salmonid populations, few equivalent studies are available from which to develop criteria for the management of hydrological regimes for fishes and fisheries in large floodplain–river systems such as the Mekong. The population dynamics of fish in such rivers are believed to respond to hydrological conditions in a density‐dependent manner. An age‐structured population dynamics model incorporating sub‐models describing density‐dependent growth, mortality and recruitment was used to explore how hydrological conditions within a theoretical floodplain–river system affect the dynamics of a common floodplain–river fish species. Graphical summaries of the response of exploitable biomass to a range of different drawdown rates, dry and flood season areas and volumes, and flood season durations are presented under five different model assumptions concerning density‐dependent processes. Optimal flooding patterns are also described for the model species and theoretical river system. The patterns of predictions that emerge from the simulations provide guidelines for managing or manipulating hydrological conditions in river systems for both fixed and variable volume hydrological scenarios. As a general rule of thumb, exploitable biomass is maximized by minimizing the rate of drawdown and maximizing the flood duration and flood and dry season areas or volumes. However, experiences from dam and other hydraulic engineering projects suggest that these predictions should be treated with caution until we better understand the influence of hydrology on spawning behaviour, system primary production, and critical habitat availability. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of flooding regime upon the decomposition of Eichhornia azurea (Sw.) Kunth measured on a tropical,flow‐regulated floodplain (Paraná River,Brazil)

Decomposition of macrophytes is an important process in river‐floodplain systems, especially in the Upper Paraná River floodplain, given that this ecosystem receives high inputs of detritus from this vegetation. Release of nutrients by decomposition is essential in this floodplain because it is located downstream from a reservoir chain where nutrients are being trapped. Water level fluctuations are considered one of the most important aspects that affect macrophyte decomposition. Anthropogenic alterations, such as the control of flooding regimes, observed in this floodplain, could change the dynamic of this process. To evaluate the influence of the hydrological cycle upon the decomposition of Eichhornia azurea (an aquatic macrophyte that has high biomass values in this ecosystem), litter bags with senescent leaves and petioles of this plant were submitted to four different flooding treatments, which differed in time of flooding and exposure to dry conditions. The decomposition rates and the detritus chemical composition (nitrogen and phosphorus concentrations) were measured over 113 days. There were significant effects of the flooding treatments and time upon all parameters. The materials that decomposed with flood conditions showed the greatest decomposition rates. The quality of the detritus seems to be highly linked with the flooding regime, showing highest releases of phosphorus in the submerged treatments. It was shown that floods, even the short duration ones, increase the decomposition velocity and the nutrient cycling relative to dry conditions. Thus, investigations that assess the nutrient budgets on the Upper Paraná River floodplain and the role of nutrients in its productivity should consider the detritus compartment and the effects of flood regimes upon its dynamics. Copyright © 2006 John Wiley & Sons, Ltd.     

POST‐DAMMING FLOW REGIME DEVELOPMENT IN A LARGE LOWLAND RIVER (VOLGA,RUSSIAN FEDERATION): IMPLICATIONS FOR FLOODPLAIN INUNDATION AND FISHERIES

Periodic flooding plays a key role in the ecology of floodplain rivers. Damming of such rivers can disturb flooding patterns and have a negative impact on commercial fish yield. The Volga River, the largest river in Europe, has a regulated flow regime after completion of a cascade of dams. Here, we study effects of damming on long‐term discharge variability and flood pulse characteristics. In addition, we evaluate the effects of the altered flood pulse on floodplain ecosystem functioning and commercial fish yields. Our results indicate that both flood pulse and fish populations of the Volga–Akhtuba floodplain have varied considerably over the past decades. After damming, annual maximum peak discharges have decreased, minimum discharges increased, but average discharges remained similar to pre‐damming conditions. Moreover, because of bed level incision of over 1.5 m, a higher discharge is needed to reach bankfull level and inundate the floodplains. Despite this significantly altered hydrological regime and subsequent morphological changes, current discharge management still provides significant spring flooding. However, commercial fish catches did decrease after damming, both in the main channel and in the floodplain lakes. All catches were dominated by species with a eurytopic flow preference, although catches from the main channel contained more rheophilic species, and floodplain catches contained more limnophilic and phytophilic species. The strong increase of opportunistic gibel carp (Carassius gibelio) around 1985 was apparent in the main channel and the floodplain lakes. Despite the hydrological changes, the decrease in overall catches, and the upsurge of gibel, we found a strong positive effect of flood magnitude in the previous year on commercial fish yield in the floodplain lakes. This suggests that under the current discharge management there still is an increased fish growth and/or survival during high floods and that functioning of the floodplain is at least partly intact. Copyright © 2011 John Wiley & Sons, Ltd.     

RESERVOIR FLOODPLAINS SUPPORT DISTINCT FISH ASSEMBLAGES

Reservoirs constructed on floodplain rivers are unique because the upper reaches of the impoundment may include extensive floodplain environments. Moreover, reservoirs that experience large periodic water level fluctuations as part of their operational objectives seasonally inundate and dewater floodplains in their upper reaches, partly mimicking natural inundations of river floodplains. In four flood control reservoirs in Mississippi, USA, we explored the dynamics of connectivity between reservoirs and adjacent floodplains and the characteristics of fish assemblages that develop in reservoir floodplains relative to those that develop in reservoir bays. Although fish species richness in floodplains and bays were similar, species composition differed. Floodplains emphasized fish species largely associated with backwater shallow environments, often resistant to harsh environmental conditions. Conversely, dominant species in bays represented mainly generalists that benefit from the continuous connectivity between the bay and the main reservoir. Floodplains in the study reservoirs provided desirable vegetated habitats at lower water level elevations, earlier in the year, and more frequently than in bays. Inundating dense vegetation in bays requires raising reservoir water levels above the levels required to reach floodplains. Therefore, aside from promoting distinct fish assemblages within reservoirs and helping promote diversity in regulated rivers, reservoir floodplains are valued because they can provide suitable vegetated habitats for fish species at elevations below the normal pool, precluding the need to annually flood upland vegetation that would inevitably be impaired by regular flooding. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Revealing 35 years of landcover dynamics in floodplains of trained lowland rivers using satellite data

Lacking substantial erosive and sedimentation forces, regulated rivers allow their floodplains to become overgrown with forest, increasing the flood risk of the hinterland. In the Netherlands, floodplains have therefore been subjected to interventions, like clear cutting, lowering and creation of side channels, and management, consisting of grazing and mowing. However, the comprehension of how those activities influence landcover dynamics is lacking. The aim of this study is therefore to investigate long‐term landcover dynamics of a regulated river system through the lens of remote sensing. What transitions between landcover classes can be observed? And how (if) do management and interventions impact succession and retrogression of landcover classes? The study area comprised the upstream part of the Dutch Rhine River, its three branches and five adjacent floodplains. Satellite data (LandSat 5 and 8), encompassing a 35‐year period (1984–2018), were used for studying landcover dynamics. Landcover classification was based on seven classes: water, built‐up area, bare substrate, grass, herbaceous vegetation, shrubs and forest. Retrogression was highest for the landcover classes obstructing water flow (shrubs, forest and herbaceous vegetation), succession was most frequent on bare substrate, and water and grass were the most stable landcover classes. The regulated nature of the system became apparent from the spatial and temporal cacophony of landcover dynamics which differ from those of natural meandering rivers. This study showed that satellite data are useful for analyzing the impact of human activities within floodplains of regulated rivers and may assist in floodplain management aimed at combining water safety and nature policies.     

Potential effects of a major navigation project (Paraguay–Paraná Hidrovía) on inundation in the Pantanal floodplains

The Pantanal wetland of Brazil, a vast complex of seasonally inundated floodplains along the Paraguay River, is renowned for its outstanding biological resources. A proposed navigation project known as the Paraguay–Paraná Waterway (or Hidrovía) would deepen the Paraguay River channel to facilitate year‐round navigation through the Pantanal. The possibility of decreases in river levels (stage) has aroused concerns in relation to the potential environmental impacts, however the poor understanding of the hydrological relationships between rivers and floodplains has hampered evaluation of these impacts. The present study evaluates the potential impact of river modifications on adjacent floodplains by examining the relationship between the Paraguay River stage and the extent of floodplain inundation. Satellite observations of flooded area (from passive microwave emission; monthly data for 1979–1987) are plotted against river stage from several stations throughout the region to show the stage–inundation relationships for eight subregions along the Paraguay River. Scenarios in which the Paraguay River stage is decreased from the 20th and 80th percentile values reveal large potential impacts on inundation. For stage decreases of 0.10 and 0.25 m, the total flooded area is reduced by 1430 and 3830 km² at low‐water, and by 2410 and 5790 km² at high‐water, respectively. The floodplains of the two northernmost subregions appear to be most susceptible to reductions in flooding, losing more than half of their flooded area with a 0.25‐m decrease in the low‐water stage. The ecological impacts of these reductions in flooded area may be particularly severe at low water, when the few areas that typically remain flooded throughout the dry season serve as important refuges for aquatic animals. These results underscore the need for better understanding of the hydrology of the integrated river floodplain systems in the Pantanal before river channel modifications are carried out. Copyright © 1999 John Wiley & Sons, Ltd.     

River regulation influences the composition and distribution of inland frog communities

Frogs are widespread through inland rivers and floodplains and are an important component of floodplain food chains. Despite this, studies of frog communities in inland river systems are limited and the impacts of river regulation on frog communities have received very little attention. Surveys for frogs, tadpoles and egg masses along with assessment of vegetation, hydrology and water chemistry were conducted along 10 km reaches of three creek systems in the Lachlan River catchment, a major regulated river in Australia's Murray–Darling Basin. A total of 23 sample sites were surveyed at locations above and below in‐stream weirs as well as adjacent floodplain depressions. The hydrological regimes of sample sites were classified according to the length of time that they were known to hold water (water permanence). The sample sites fell into two distinct categories, 14 were classified as permanent and occurred upstream of weirs while nine were classified as temporary and were located downstream of weirs and in depressions adjacent to the weir pool. Permanent sample sites had a significantly higher percentage of dead standing timber and were deeper with less aquatic vegetation cover than temporary sample sites. Seven frog species were identified; there were no significant differences in species richness between permanent and the temporary waterbodies but the composition of frog assemblages differed significantly between them. This suggests that alteration to the hydrology of inland creek systems can lead to changes in the distribution frog species, with some becoming more common due to increases in the availably of permanent waterbodies while others decline due to reductions in the availability of seasonally flooded waterbodies. Copyright © 2010 John Wiley & Sons, Ltd.     

Habitat loss as the main cause of the slow recovery of fish faunas of regulated large rivers in Europe: the transversal floodplain gradient

In large European rivers the chemical water quality has improved markedly in recent decades, yet the recovery of the fish fauna is not proceeding accordingly. Important causes are the loss of habitats in the main river channels and their floodplains, and the diminished hydrological connectivity between them. In this study we investigate how river regulation has affected fish community structure in floodplain waterbodies of the rivers Rhône (France), Danube (Austria), Rhine and Meuse (The Netherlands). A typology of natural and man‐made aquatic habitats was constructed based on geomorphology, inundation frequency and ecological connectivity, along the transversal river–floodplain gradient, i.e. perpendicular to the main stream of the river. Fish species were classified in ecological guilds based on their flow preference, reproduction ecology and diet, and their status on national red lists was used to analyse the present state of the guilds and habitats. Ecological fish guilds appear to be good indicators of ecological integrity and functioning of river–floodplain systems. A transversal successional gradient in fish community structure that bears some resemblance to the gradient found in natural rivers can still be discerned in heavily regulated rivers. It resembles the longitudinal river gradient; even some predictions of the River Continuum Concept are applicable. Overall, richness and diversity of species and ecological guilds decrease with decreasing hydrological connectivity of floodplain waterbodies. Anthropogenic disturbances have affected fish species unevenly: guilds of specialized species that are highly adapted to specifically riverine conditions have declined far more than generalist species. Fish habitats in the main and secondary channels have suffered most from regulation and contain the highest percentage of threatened species. Rheophilic fishes have become rare because their lotic reproductive habitats are severely degraded, fragmented, absent or unreachable. Limnophilic fishes have become rare too, mainly as a result of eutrophication. Eurytopic fishes have become dominant everywhere. Copyright © 2003 John Wiley & Sons, Ltd.     

Mesoscale river restoration enhances the diversity of floodplain vegetation

Effective river restoration aims for the recovery of ecosystem functions by restoring processes and connectivity to the floodplain. At the straightened lowland river Stör in northern Germany, a sequence of 15 new meanders was created in 2008, with wavelengths up to 70 m. The newly created areas within the meander bends range in size from 215 to 1,115 m² and function as a series of 15 restored floodplain sites, which are subject to succession. After 7 years of restoration measures, we investigated the vegetation dynamics on the (a) restored floodplains and compared them with adjacent floodplain sites that were used as (b) low‐intensity grazed grassland or as (c) abandoned grassland. We analysed the species diversity, functional vegetation parameters, and plant communities of 200 plots within the floodplain area of the three floodplain types and of 246 plots at their river banks. Plant species diversity and composition differed with respect to restoration measure and site management. Restored floodplains revealed a higher coverage in species of wet grasslands and softwood forests and higher species diversity than abandoned grasslands. Grazed grasslands showed the highest species number and coverages of pioneer vegetation. The banks indicated fewer differences in species composition between floodplain types. The construction of restored floodplains revealed greater overall plant diversity due to promoting the development of typical floodplain vegetation. Shallow meanders with increased flooding intensity and the creation of a varying microreliefs are recommended as combined river/floodplain measures in order to foster processes and connectivity between valley components.     

The effect of altered flow regime on the frequency and duration of bankfull discharge: Murrumbidgee River,Australia

On meandering rivers with well‐developed floodplains, bankfull stage has geomorphological and ecological significance because it approximates the level of connection between the channel and the floodplain. As a river rises to bankfull stage, sediment begins to be deposited on the floodplain, wetlands are progressively inundated and organisms migrate between the channel and floodplain habitats. On many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream. However, the lack of reliable pre‐regulation flow data has made it difficult to quantify the effects of river regulation. This study used historical regulated and modelled natural flow data to determine the effects of regulation on the frequency and duration of bankfull flows on the Murrumbidgee River, one of Australia's largest and most heavily regulated rivers. In combination with floodplain surveys the flow data show that regulation has halved the frequency and duration of bankfull flows. This reduction in channel–floodplain connection has implications for the ecological health of the Murrumbidgee River. Copyright © 2005 John Wiley & Sons, Ltd.     

Coupled Hydrological/Hydraulic Modelling of River Restoration Impacts and Floodplain Hydrodynamics

Channelization and embankment of rivers has led to major ecological degradation of aquatic habitats worldwide. River restoration can be used to restore favourable hydrological conditions for target species or processes. However, the effects of river restoration on hydraulic and hydrological processes are complex and are often difficult to determine because of the long‐term monitoring required before and after restoration works. Our study is based on rarely available, detailed pre‐restoration and post‐restoration hydrological data collected from a wet grassland meadow in Norfolk, UK, and provides important insights into the hydrological effects of river restoration. Groundwater hydrology and climate were monitored from 2007 to 2010. Based on our data, we developed coupled hydrological/hydraulic models of pre‐embankment and post‐embankment conditions using the MIKE‐SHE/MIKE 11 system. Simulated groundwater levels compared well with observed groundwater. Removal of the river embankments resulted in widespread floodplain inundation at high river flows (>1.7 m³ s^?1) and frequent localized flooding at the river edge during smaller events (>0.6 m³ s^?1). Subsequently, groundwater levels were higher and subsurface storage was greater. The restoration had a moderate effect on flood peak attenuation and improved free drainage to the river. Our results suggest that embankment removal can increase river–floodplain hydrological connectivity to form a more natural wetland ecotone, driven by frequent localized flood disturbance. This has important implications for the planning and management of river restoration projects that aim to enhance floodwater storage, floodplain species composition and biogeochemical cycling of nutrients. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd.     

THE IMPORTANCE OF VARIABLE LATERAL CONNECTIVITY BETWEEN ARTIFICIAL FLOODPLAIN WATERBODIES AND RIVER CHANNELS

The rehabilitation of lowland rivers subjected to channelization and artificial levee construction should attempt to improve habitat heterogeneity and diversity of floodplain hydrological connectivity. However, rehabilitation efforts rarely consider the importance of variable lateral hydrological connectivity between floodplain waterbodies and main river channels (ranging from those permanently connected to those temporarily connected during river level rises), instead focusing on increasing individual floodplain waterbody connectivity. This study investigated the young‐of‐the‐year (YoY) fish communities in 10 artificial floodplain waterbodies of variable hydrological connectivity with the river Trent, England, between May and November 2006, inclusive. Floodplain waterbody connectivity to the main river was positively correlated with the number of species captured (alpha diversity), Shannon–Wiener diversity, Margalef's species richness index and the relative abundance of rheophilic species and negatively correlated with species turnover (beta diversity). YoY fish communities in poorly connected water bodies were most dissimilar to riverine communities. The results demonstrate the importance of variable lateral connectivity between artificial floodplain waterbodies and main river channels when rehabilitating lowland river fish communities. Copyright © 2011 John Wiley & Sons, Ltd.     

VEGETATION–LANDFORM ASSEMBLAGES ALONG SELECTED RIVERS IN THE CZECH REPUBLIC,A DECADE AFTER A 500‐YEAR FLOOD EVENT

Rivers with a natural flow regime strongly influence the dynamics of riparian plant communities through hydrological and geomorphological processes. In this study, associations between fluvial landforms and vegetation are investigated on three near‐natural rivers in the Czech Republic a decade after a 500‐year return period flood in July 1997. This extreme disturbance destroyed the anthropogenically modified river channels and created suitable conditions for a range of ecosystems with high diversity and ecological stability. Field surveys were conducted on fluvial landforms (bars, islands, banks, floodplains and terraces) along three ‘renaturalized’ rivers, where no technical modifications had subsequently been made to their channels outside urban areas and the floodplains had been left in a post‐flood state. Vegetation species abundance and 13 environmental variables (topographical, hydrological and soil) were investigated in summer 2007, 10 years after the extreme flood disturbance. The results suggest that the recently created fluvial geomorphic forms are key environmental determinants of riparian vegetation distribution patterns. A range of statistical analyses illustrate that some plant species show predictable patterns of occurrence that correspond with the fluvial forms, supporting a fourfold grouping of herbaceous and woody species and the identification of typical plant communities associated with gravel bars, islands, banks, floodplains and terraces. An investigation of the species richness found on different fluvial landforms showed that the highest number of species occurred on the floodplain and decreased gradually towards the channel bed and towards terraces. Investigation of existing conditions in reaches of rivers with natural dynamics of fluvial processes provides valuable information that can be used as an effective tool for planning restoration strategies and precise management. However, the most important finding of this study is the remarkable establishment of complex river corridor vegetation–landform associations within 10 years of a 500‐year flood that removed the heavily cultivated landscape that had existed before the event. Copyright © 2011 John Wiley & Sons, Ltd.     

Ecological strategies successfully predict the effects of river floodplain rehabilitation on breeding birds

To improve the ecological functioning of riverine ecosystems, large‐scale floodplain rehabilitation has been carried out in the Rhine–Meuse Delta since the 1990s. This paper evaluates changes in abundance of 93 breeding bird species over a period of 10 years in response to rehabilitation, by comparing population changes in 75 rehabilitated sites with 124 non‐rehabilitated reference sites. Such quantitative, multi‐species, large‐scale and long‐term evaluations of floodplain rehabilitation on biodiversity are still scarce, particularly studies that focus on the terrestrial component. We try to understand the effects by relating population trends to ecological and life‐history traits and strategies of breeding birds. More specifically, we try to answer the question whether rehabilitation of vegetation succession or hydro‐geomorphological river processes is the key driver behind recent population changes in rehabilitated sites. Populations of 35 species have significantly performed better in rehabilitated sites compared to non‐rehabilitated floodplains, whereas only 8 have responded negatively to rehabilitation. Differences in effects between species are best explained by the trait selection of nest location. Reproductive investment and migratory behaviour were less strong predictors. Based on these three traits we defined eight life‐history strategies that successfully captured a substantial amount of variation in rehabilitation effects. We conclude that spontaneous vegetation succession and initial excavations are currently more important drivers of population changes than rehabilitation of hydrodynamics. The latter are strongly constrained by river regulation. If rehabilitation of hydro‐geomorphological processes remains incomplete in future, artificial cyclic floodplain rejuvenation will be necessary for sustainable conservation of characteristic river birds. Copyright © 2010 John Wiley & Sons, Ltd.     

CHANNEL ADJUSTMENTS AND ISLAND DYNAMICS IN THE BRENTA RIVER (ITALY) OVER THE LAST 30 YEARS

Many gravel bed rivers in the European Alpine area suffered different ranges and types of human pressure that modified their morphology and altered their processes. This work presents the case of the middle portion of the Brenta River, historically impacted by human activities such as floodplain occupations, bank protection, gravel mining, hydropower schemes and water diversion. Dam operation and gravel mining have produced considerable modifications in the natural sediment regime generating important morphological channel responses (narrowing and incision). Large areas of the former active channel have been colonized by riparian vegetation, both as islands and as marginal woodlands. Overall, the river changed its morphological pattern from braided to wandering. The present study analyses the timing and extent of the planform morphological changes that occurred over the last 30 years along the middle portion of the river (20 km long) through the examination of aerial photos, repeated topographic measurements and hydrological data. A series of recent aerial photos (1981, 1990, 1994, 1999, 2003, 2006, 2008, 2010 and 2011) have been used to assess the medium and short‐term morphological changes of the floodplains and the active channel area. As to the medium‐term modification, the recent changes in in‐channel gravel mining have determined a new trend of active channel widening through erosion of vegetated areas. The analysis has also allowed to assess the morphological effect of single flood events. Only floods with recurrence interval higher than 8–10 years appear to be able to determine substantial erosion of floodplain and island margins. Copyright © 2013 John Wiley & Sons, Ltd.     

Differential macrohabitat use by birds on the unregulated Ovens River floodplain of southeastern Australia

In many lowland floodplains around the world, upriver interferences to flows (weirs, dams, off‐takes) have led to much reduced frequency and duration of flooding. As a result, many floodplain wetlands are now inundated relatively rarely if at all. Given regulation of most lowland rivers in southeastern Australia, we assessed use of wetlands by birds in the essentially unregulated Ovens River in northeastern Victoria. Twelve sites (0.4–1.2 ha) were studied after flooding. Four sites were ‘permanent billabongs’, four were temporary wetlands and the other four were randomly selected woodland sites >60 m from the nearest water body (including the river) acting as ‘control’ or ‘reference’ sites. Aquatic birds were not recorded using woodland sites, but many species were differentially associated with either billabongs or temporary wetlands. A surprising number of non‐aquatic birds either exclusively or differentially were associated with wetland sites compared with woodland sites. We concluded that heterogeneous macrohabitat will increase local avian biodiversity on lowland floodplains. Moreover, densities and diversity of non‐aquatic, woodland species also increased with the presence of wetlands. Temporary wetlands were used differently from permanent billabongs by birds, especially in foraging methods. This suggests that the reinstatement of major flooding on heavily regulated floodplains would be ecologically advantageous for birds by providing foraging and breeding opportunities. Copyright © 2002 John Wiley & Sons, Ltd.     

DISCONNECTING THE FLOODPLAIN: EARTHWORKS AND THEIR ECOLOGICAL EFFECT ON A DRYLAND FLOODPLAIN IN THE MURRAY–DARLING BASIN,AUSTRALIA

Globally, dams and water extractions are well‐recognised disruptors of flow regimes in floodplain wetlands, but little is known of the hydrological and ecological impacts of floodplain earthworks constructed for irrigation, flood mitigation and erosion control. We mapped the distribution of earthworks with high‐resolution SPOT (Système Probatoire d'Observation de la Terre) imagery in an internationally recognised Ramsar wetland, the Macquarie Marshes of the Murray–Darling Basin, Australia. There were 339 km levees, 1648 km channels, 54 off‐river storages and 664 tanks (0.5–5 m high), detected within the 4793 km² floodplain study area. Earthworks reduced localised flooding compared with undeveloped sites. The most pronounced disconnection of the original floodplain (73.0%) occurred where earthworks were most concentrated compared with areas with few earthworks (53.2%). We investigated relationships between hydrological connectivity and mortality of the perennial flood‐dependent river red gum Eucalyptus camaldulensis at 55 floodplain sites (225 × 150 m). Over half of the river red gums were dead at 21.8% of the sites. Earthworks blocked surface flows to flood‐dependent vegetation and drowned vegetation in artificially inundated off‐river storages. Mortality was due to impacts of earthworks and potentially exacerbated by effects of river regulation, water extraction and climate. River red gums were healthiest in narrow river corridors where earthworks confined flows and flows could recede freely. Rehabilitation of flood‐dependent ecosystems should focus on reinstating lateral connectivity and protecting environmental flows. Copyright © 2011 John Wiley & Sons, Ltd.     

Relationships between fisheries and the integrity of river systems

Human use of river systems has intensified considerably in the last century due to increasing population and the associated higher demand for water through industrial and agricultural technologies. This intensification process has impacted rivers and resident organisms. Natural rivers have rich and varied fish faunas adapted to the variable climate and morphology of such systems. Much of the diversity and resilience can be traced to the connectivity between two very different components, the channel and the floodplain. Fisheries in rivers are as diverse as the fish communities and are adjusted for capturing most species and life stages throughout the year. Fisheries reasonably conducted have proved sustainable with a high rate of catch correlated with the intensity of flooding in the same or preceding years. Fish communities react in a predictable manner to externally imposed stresses, whether eutrophication, induced by humans or natural environmental modification, or fishing, through successive loss of large species and their replacement by smaller, faster growing species. Generally, the overall weight of catch remains little affected by this process until excessive levels of exploitation are reached and the stock collapses. Damage to fish communities through overfishing and environmental modification is widespread. Improvement of the situation demands stricter management of riverine systems through the protection of the few that remain in a relatively pristine state, and those modified should be restored if social, political and economic conditions allow. Should this not be possible, approaches to the mitigation of externally imposed stresses should be sought and applied.     

Hydrological changes and ecological impacts associated with water resource development in large floodplain rivers in the Australian tropics

The majority of rivers in the Australian tropics possess near‐natural flow regimes and are an ecological asset of global significance. We examined flow variability in large floodplain rivers in the Gulf of Carpentaria, northern Australia, and the potential ecological impacts of future water resource development (WRD). Flow metrics based on long‐term records were used to classify flow regimes and predict hydrological drivers of ecological function. Flow regimes of selected rivers were then compared with those simulated for pre‐ and post‐WRD flows in the Darling River, a highly modified river in Australia's south‐east. Generally, rivers were classified as typically ‘tropical’ (more permanent, regular flows) or ‘dryland’ (more ephemeral, with greater flow variability). In addition, all rivers displayed wet–dry seasonality associated with changes in flow magnitude or number of zero‐flow days. We propose that these features (flow permanence and regularity; flow variability and absence; wet–dry seasonality) are the key hydrological drivers of biodiversity and ecological function in the floodplain rivers of Australia's north. In terms of WRD, inter‐annual flow variability was predicted to increase or decrease depending on rivers' natural flow regimes, specifically their tendency toward lower or higher flow magnitudes. Either outcome is expected to have adverse effects on the biodiversity and ecological function of these relatively pristine rivers and floodplain habitats. In particular, reduced and homogenized habitat, loss of life‐history cues, inhibited dispersal and shifts in community composition, as a result of WRD, threaten the ecological integrity of rivers adapted to the three hydrological drivers above. These findings serve as a caution for careful consideration of WRD options for rivers in the Australian tropics and for those with similar flow regimes the world over. Copyright © 2008 John Wiley & Sons, Ltd.