Natural Floodplain Research Articles

Sedimentation in the floodplains of the Mekong Delta, Vietnam Part II: deposition and erosion

AbstractDeposition and erosion play a key role in the determination of the sediment budget of a river basin, as well as for floodplain sedimentation. Floodplain sedimentation, in turn, is a relevant factor for the design of flood protection measures, productivity of agro‐ecosystems, and for ecological rehabilitation plans. In the Mekong Delta, erosion and deposition are important factors for geomorphological processes like the compensation of deltaic subsidence as well as for agricultural productivity. Floodplain deposition is also counteracting the increasing climate change induced hazard by sea level rise in the delta. Despite this importance, a sediment database of the Mekong Delta is lacking, and the knowledge about erosion and deposition processes is limited. In the Vietnamese part of the Delta, the annually flooded natural floodplains have been replaced by a dense system of channels, dikes, paddy fields, and aquaculture ponds, resulting in floodplain compartments protected by ring dikes. The agricultural productivity depends on the sediment and associated nutrient input to the floodplains by the annual floods. However, no quantitative information regarding their sediment trapping efficiency has been reported yet. The present study investigates deposition and erosion based on intensive field measurements in three consecutive years (2008, 2009, and 2010). Optical backscatter sensors are used in combination with sediment traps for interpreting deposition and erosion processes in different locations. In our study area, the mean calculated deposition rate is 6.86 kg/m2 (≈ 6 mm/year). The key parameters for calculating erosion and deposition are estimated, i.e. the critical bed shear stress for deposition and erosion and the surface constant erosion rate. The bulk of the floodplain sediment deposition is found to occur during the initial stage of floodplain inundation. This finding has direct implications on the operation of sluice gates in order to optimize sediment input and distribution in the floodplains. Copyright © 2013 John Wiley & Sons, Ltd.

Primary production, food web structure, and fish yields in constructed and natural wetlands in the floodplain of an African river

In the Ouémé River, Africa, whedo (artificial pond) aquaculture on the floodplain is an important method of fishery production. We surveyed fishes in whedos and adjacent main-channel and floodplain habitats during the receding-water period (December 2010 – January 2011) and analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of fish and primary producer tissue samples to investigate food web structure. We also measured instream respiration, net primary production, algal biomass (chlorophyll a), and nutrient concentrations in the habitats. Floodplain habitats were more nutrient-rich than the river channel, and whedos were net heterotrophic (net primary production < 0). Phytomicrobenthos and C3 macrophytes accounted for a large fraction of fish biomass in whedos and the natural floodplain depression, while the river channel was mainly supported by seston and C3 macrophytes. Whedo food webs were dominated by piscivorous fishes and had fewer trophic transfers compared with the food web of the river channel. Our results suggest that control of aquatic macrophyte growth in whedos may yield greater algal production and consumer biomass, including harvestable fish stocks.

Fish Assemblages in Borrow‐Pit Lakes of the Lower Mississippi River

AbstractBorrow‐pit lakes encompass about a third of the lentic water habitats (by area) in the active floodplain of the Lower Mississippi River, yet little is known about their fish assemblages. We investigated whether fish assemblages supported by borrow‐pit lakes resembled those in oxbow lakes to help place the ecological relevance of borrow‐pit lakes in context with that of natural floodplain lakes. In all, we collected 75 fish species, including 65 species in eight borrow‐pit lakes, 52 species in four riverside oxbow lakes, and 44 species in eight landside oxbow lakes. Significant differences in several species richness metrics were evident between borrow‐pit lakes and landside oxbow lakes but not between borrow‐pit lakes and riverside oxbow lakes. All three lake types differed in fish assemblage composition. Borrow‐pit lakes and riverside oxbow lakes tended to include a greater representation of fish species that require access to diverse environments, including lentic, lotic, and palustrine habitats; fish assemblages in landside oxbow lakes included a higher representation of lacustrine species. None of the fish species collected in borrow‐pit lakes was federally listed as threatened or endangered, but several were listed as species of special concern by state governments in the region, suggesting that borrow‐pit lakes provide habitat for sensitive riverine and wetland fish species. Differences in fish assemblages among borrow‐pit lakes were linked to engineered morphologic features, suggesting that diversity in engineering can contribute to diversity in fish assemblages; however, more research is needed to match engineering designs with fish assemblage structures that best meet conservation needs.

Simulating the influence of the height of HPP dams on the environmental conditions in small river Virvyte

AbstractIn natural floodplains, the grassed areas usually entrap fine suspended sediments (wash products rich in nutrients) of the floodwater, thus contributing to the process of self-purification. However, hydroelectric power plants (HPPs), built with the purpose of employing the renewable energy, can worsen this process, it occurs if they pond the floodplains and decrease these grassed areas. In the present paper, the sediment deposition in the floodplains with existing weir heights is investigated. The mathematical-hydraulic model is used for it. The 12 km length interval of the river Virvyte, having three ponds was investigated. The average volume of sedimentation in this region is 500–2000 t/year, i.e. quite large. In the investigated region of the river Virvyte, the sediment deposition decreased by about 50%, due to the impact of a too high dam (H=5.5 m) of the Kapėnai HPP.

Fish assemblages of an African river floodplain: a test of alternative models of community structure

AbstractIn the Oueme River, a lowland river in Benin, Africa, artificial ponds constructed in the floodplain (whedos) are colonised during the high‐water period by a presumably random sample of fishes from the river channel. As water slowly recedes from the floodplain, fishes are isolated in whedos until they are harvested near the end of the dry season. We surveyed fishes in whedos and adjacent main‐channel and floodplain habitats during two low‐water periods (2008 and 2009) and one falling‐water period (2010–2011) to evaluate the relevance of four alternative metacommunity models to these systems. In 2010–2011, we also measured a suite of physicochemical variables including dissolved oxygen, temperature, specific conductivity and per cent cover of aquatic vegetation. Whedos were covered with dense growth of aquatic vegetation, and dissolved oxygen concentrations were lower in whedos and a natural floodplain depression compared with the main channel. Multivariate analyses revealed that habitat types were distinct with regard to assemblage structure and abiotic conditions. Assemblages in whedos and natural floodplain depressions were differentiated from those of the river channel, with the floodplain habitats being dominated by piscivorous fishes that tolerate aquatic hypoxia. Dispersal, aquatic hypoxia and predation act in concert to shape local community structure. Patch dynamics, species sorting and mass effect models all were consistent with patterns in fish assemblage structure in this system. We conclude that the underlying mechanisms of drift, speciation, selection and dispersal ultimately may be more useful for explaining patterns in ecological communities than alternative metacommunity models.

Floodplain management in temperate regions: is multifunctionality enhancing biodiversity?

Floodplains are among the most diverse, dynamic, productive and populated but also the most threatened ecosystems on Earth. Threats are mainly related to human activities that alter the landscape and disrupt fluvial processes to obtain benefits related to multiple ecosystem services (ESS). Floodplain management therefore requires close coordination among interest groups with competing claims and poses multi-dimensional challenges to policy-makers and project managers. The European Commission proposed in its recent Biodiversity Strategy to maintain and enhance European ecosystems and their services by establishing green infrastructure (GI). GI is assumed to provide multiple ecosystem functions and services including the conservation of biodiversity in the same spatial area. However, evidence for biodiversity benefits of multifunctional floodplain management is scattered and has not been synthesised. This protocol specifies the methods for conducting a systematic review to answer the following policy-relevant questions: a) what is the impact of floodplain management measures on biodiversity; b) how does the impact vary according to the level of multifunctionality of the measures; c) is there a difference in the biodiversity impact of floodplain management across taxa; d) what is the effect of the time since implementation on the impact of the most important measures; and e) are there any other factors that significantly modify the biodiversity impact of floodplain management measures? Within this systematic review we will assess multifunctionality in terms of ESS that are affected by an implemented intervention. Biodiversity indicators included in this systematic review will be related to the diversity, richness and abundance of species, other taxa or functional groups. We will consider if organisms are typical for and native to natural floodplain ecosystems. Specific inclusion criteria have been developed and the wide range of quality of primary literature will be evaluated with a tailor-made system for assessing susceptibility to bias and the reliability of the studies. The review is intended to bridge the science-policy interface and will provide a useful synthesis of knowledge for decision-makers at all governance levels.

Incorporating Floodplain Inundation as a Strategy in Flood Mitigation Plan

This paper is promoting the awareness that nature and engineering structure can co-exist together. Natural floodplain inundation is usually restrained to separate floodplain lands for human uses. In contrary to conventional flood control systems, a vision of restoring floodplain inundation in Kuching Bypass Floodway is presented as a flood mitigation plan. Modelling of the approach indicates a reduction of flooded areas up to 61%. By means of modelling, portions of floodplains are virtually preserved in their natural states and functions, a role that often has been undervalued. Floodplain permits storage and conveyance of floodwaters. At the same time, it provides replenishment of the adjoining wetlands. The strategy proves beneficial to both human and natural systems. It also calls for a systemic change in flood management that we can live with the natural forces instead of forbidding them.

The pygmy mole cricket Xya variegata as an indicator for dynamic river systems

There is an urgent need to conserve and restore dynamic floodplains as one of the last wildernesses in Europe and to maintain their unique plant and animal communities. Disturbance-dependent ecosystems such as natural floodplains harbour many highly specialised and endangered insect species. One of these species is the pygmy mole cricket Xya variegata Latreille, 1809 (Orthoptera: Tridactylidae), a floodplain specialist of the Ponto-Mediterranean region. However, as with many endangered insect species detailed knowledge on the requirements of X. variegata is largely unknown, even though such knowledge is of particular importance for successful nature conservation. The aim of this study was to analyze the ecological requirements of X. variegata and to verify the species’ suitability as an indicator for dynamic river systems of the Ponto-Mediterranean region. Therefore, microhabitat analyses were conducted in August 2010 on 42 plots in a nearly natural floodplain of the western Spanish Pyrenees. The results show that patch occupancy in X. variegata was determined by a high amount of fine sediment particles and low vegetation coverage. Moreover, population sizes were positively correlated with low vegetation and gravel/stone coverage. The plots with the highest population sizes (29 and 36 individuals/0.5 m²) had no vegetation at all. Habitats of X. variegata were usually located distant to the main channel; that is areas where fine sediment particles are deposited after a flood event. Disturbance is thus mandatory for the persistence of the species and makes X. variegata a suitable indicator for dynamic river systems.

Impact of land use activities on Subin and Aboabo Rivers in Kumasi Metropolis

Water resources have come under a lot of threat in recent years from human activities especially in the urban environment as their protection seem to be neglected not only by the populace but also the responsible institutions as well. Within this context, study seeks to address the issues of compatibility of land uses with water bodies. Sample size of 90 activity units selected at 90% confidence level and a margin of error 0.1 was used for data collection. It was found that common threats emanate from land use activities carried out along the buffer zones of these vital resources. The study identifies the various factors such as land, land users and their desires that influence land use activities along water bodies and makes recommendations such as the adoption of buffer zone policy towards land use management along water bodies in an urban area in the case of Subin and Aboabo Rivers in the Kumasi Metropolitan Area. The study reveals that there has been a massive encroachment of the buffer zones of the Subin and the Aboabo Rivers leaving patches of vegetative cover thereby exposing the river bodies to direct sunshine. In addition, activities located along these rivers are as a result of proximity to market, cheaper lands, availability of water, and closer to work place. According to the 1963 Town Planning Scheme, all land close to the main streams should be green belt zone. These natural flood plains of streams, no buildings were supposed to be erected on them. With increase in population and urbanisation however, these green belts have been encroached upon. Therefore, creating community awareness of the need to protect water bodies, enforcement of water protection related laws and institutional strengthening are imperative. Key words: Rivers bodies, land use change, water resource management.

The Indus basin in the framework of current and future water resources management

Abstract. The Indus basin is one of the regions in the world that is faced with major challenges for its water sector, due to population growth, rapid urbanisation and industrialisation, environmental degradation, unregulated utilization of the resources, inefficient water use and poverty, all aggravated by climate change. The Indus Basin is shared by 4 countries – Pakistan, India, Afghanistan and China. With a current population of 237 million people which is projected to increase to 319 million in 2025 and 383 million in 2050, already today water resources are abstracted almost entirely (more than 95% for irrigation). Climate change will result in increased water availability in the short term. However in the long term water availability will decrease. Some current aspects in the basin need to be re-evaluated. During the past decades water abstractions – and especially groundwater extractions – have augmented continuously to support a rice-wheat system where rice is grown during the kharif (wet, summer) season (as well as sugar cane, cotton, maize and other crops) and wheat during the rabi (dry, winter) season. However, the sustainability of this system in its current form is questionable. Additional water for domestic and industrial purposes is required for the future and should be made available by a reduction in irrigation requirements. This paper gives a comprehensive listing and description of available options for current and future sustainable water resources management (WRM) within the basin. Sustainable WRM practices include both water supply management and water demand management options. Water supply management options include: (1) reservoir management as the basin is characterised by a strong seasonal behaviour in water availability (monsoon and meltwater) and water demands; (2) water quality conservation and investment in wastewater infrastructure; (3) the use of alternative water resources like the recycling of wastewater and desalination; (4) land use planning and soil conservation as well as flood management, with a focus on the reduction of erosion and resulting sedimentation as well as the restoration of ecosystem services like wetlands and natural floodplains. Water demand management options include: (1) the management of conjunctive use of surface and groundwater; as well as (2) the rehabilitation and modernization of existing infrastructure. Other demand management options are: (3) the increase of water productivity for agriculture; (4) crop planning and diversification including the critical assessment of agricultural export, especially (basmati) rice; (5) economic instruments and (6) changing food demand patterns and limiting post-harvest losses.

Landscape transformation of an Alpine floodplain influenced by humans: historical analyses from aerial images

AbstractNatural floodplains are spatially heterogeneous and dynamic ecosystems but at the same time, a highly endangered landscape feature due to climate change and human impacts such as water storage, flood control and hydropower production. Flow is considered a master variable that shapes channel morphology and the heterogeneity, distribution, and turnover of floodplain habitats. Despite their highly dynamic nature, the relative abundance of different habitat elements (islands, gravel bars) in natural floodplains seems to remain relatively constant over ecological periods and is referred to as the shifting mosaic steady state concept. In this conceptual context, we analysed spatiotemporal changes in relative habitat abundance and channel complexity of an alpine floodplain from its near natural state in 1940 before water abstraction and levee construction until 2007 using historical aerial images. Within the first decades of impairment, the relative abundance of floodplain habitats that depend on flood and flow pulses such as parafluvial channels and islands shifted toward a greater abundance of terrestrial forest and grassland habitats. After 1986, the duration and frequencies of high‐precipitation events (>60 mm 24 h–1) triggering major, channel‐reworking floods increased substantially and caused a restructuring of the floodplain and decrease in the abundance of more terrestrial habitat types. These results are contrary to expectations of the shifting mosaic steady state concept yet suggest its potential application as an indicator of landscape transformation and human impacts on floodplain ecosystems. Last, the results raise the applied question as to whether an increased frequency of high flow events induced by climate change can contribute to floodplain restoration. Copyright © 2011 John Wiley & Sons, Ltd.

A Theory on Urban Resilience to Floods--A Basis for Alternative Planning Practices

River cities require a management approach based on resilience to rather than on resistance. Resisting by means of levees, dams, and channelization neglects inherent uncertainties arising from human-nature couplings and fails to address the extreme events that are expected to increase with climate change, and is thereby not a reliable approach to long-term flood safety. By applying resilience theory to address system persistence through changes, I develop a theory on resilience to floods as an alternative framework for urban flood hazard management. Urban resilience to is defined as a city's capacity to tolerate flooding and to reorganize should physical damage and socioeconomic disruption occur, so as to prevent deaths and injuries and maintain current socioeconomic identity. It derives from living with periodic as learning opportunities to prepare the city for extreme ones. The theory of urban resilience to challenges the conventional wisdom that cities cannot live without flood control, which in effect erodes resilience. To operationalize the theory for planning practice, a surrogate measure—the percent floodable area—is developed for assessing urban resilience to floods. To enable natural floodplain functions to build urban resilience to floods, flood adaptation is advocated in order to replace flood control for mitigating flood hazards.

Měkkýši v nivě Milešovského potoka [Molluscs of the Milešovský Potok floodplain (Northwest Bohemia, Czech Republic)

This paper presents a research of mollusc assemblages in the Milešovský Potok floodplain (Northwest Bohemia, Czech Republic). Altogether, 72 mollusc species (70 species of Gastropoda, 2 species of Bivalvia) have been recorded at the selected sites during previous and recent researches in 1947–2010 representing 29% of the total Czech malacofauna. Widespread forest species dominate there (40% of all recorded species) with some less common woodland species such as Platyla polita, Oxychilus glaber, Macrogastra ventricosa, Sphyradium doliolum, and Perforatella bidentata. The rest of malacocoenoses is formed by mesophile species (22%), hydrophilous species (6%), species of wetlands (8%), freshwater habitats (8%) and species of open habitats (10%). Vertigo angustior, a rare wetland species protected by the NATURA system, and Helicella itala, endangered species of open habitats, were also found. The malacofauna of the Milešovský Potok stream can be used as a model of mollusc assemblages of natural floodplain environment in warm areas of Central Europe.

Cyanobacterial blooms in a temperate river-floodplain ecosystem: the importance of hydrological extremes

In the past decade, extreme hydrological events were expressed with extreme droughts and floods in temperate regions. The aim of this paper is to explain how such changes in hydrology can influence cyanobacterial populations in floodplain ecosystems. We therefore analyzed a 6-year (2003–2008) study of the phytoplankton in the Kopacki Rit floodplain, one of the largest natural floodplains in the middle section of the Danube River (Europe). During the studied period, the shallow floodplain lake shifted between a state of turbid water, characterized by high phytoplankton biomass and regular appearance of cyanobacteria blooms, to a state of clear water with very low phytoplankton biomass and absence of cyanobacteria, and back to the turbid state. Apparently, the major forces driving the cyclic shift were closely related to extremely high and long-lasting flood events. Significant increase in water level, low hydraulic residence time of water, decrease in transparency and low-light climate, together with mass developed aquatic macrophyte vegetation in the whole inundated floodplain were unfavorable conditions for growth and proliferation of cyanobacteria. With the establishment of the flood regime characterized by long-lasting periods without flooding, in-lake processes prevailed leading to cyanobacterial bloom. The most successful were filamentous non-N-fixing cyanobacteria tolerant to mixed and low-light conditions (Planktothrix and Limnothrix) and invasive species Cylindrospermopsis raciborskii. Their massive development led to the establishment of a phytoplankton steady state. All our results demonstrate that the altered intensity and frequency of flood events will have pronounced effects on the appearance of cyanobacterial blooms and generally on alternative stable states in the floodplain. Relating to this, management objectives should be focused on qualifications of changes in hydrology and projecting those effects for potential floodplain restoration.

Carbon Cycling in Floodplain Ecosystems: Out-Gassing and Photosynthesis Transmit Soil δ13C Gradient Through Stream Food Webs

Natural braided river floodplains typically possess high groundwater–surface water exchange, which is vital to the overall function and structure of these complex ecosystems. Spring-fed streams on the floodplain are also hotspots of benthic invertebrate diversity and productivity. The sources of carbon that drive these productive spring-fed systems are not well-known. We conducted field assessments and a manipulation, modeling, and a laboratory experiment to address this issue. Initially δ13C values of both dissolved inorganic carbon (DIC) and food-web components of five springs were used to assess the sources of carbon to spring food webs. Partial pressures of CO2 in upwelling water ranged from 2 to 7 times atmospheric pressure, but rapidly approached equilibrium with the atmosphere downstream commensurate with 13C enrichment of DIC. Speciation modeling and a laboratory out-gassing experiment suggested that downstream changes in pH could be explained solely by CO2 out-gassing. However, field results indicated that both out-gassing and photosynthetic drawdown by aquatic plants controlled the net flux of CO2. A whole stream manipulation indicated out-gassing was the primary effect at the spring source, which was confirmed by invariant diel pH. At 1296 m downstream from the spring source a large diel shift in pH indicated a plant effect on CO2 concentration which would contribute to the overall downstream gradient in δ13C DIC. Within the first 1296 m the gradient in δ13 DIC was transmitted through three trophic levels of the spring food web. These findings indicate dependency on groundwater inorganic carbon by spring stream food webs and strong hydrologically mediated linkages connecting terrestrial, subsurface, and aquatic components of the floodplain.

Spatial variation in abiotic and biotic factors in a floodplain determine anuran body size and growth rate at metamorphosis

Body size at metamorphosis is a critical trait in the life history of amphibians. Despite the wide-spread use of amphibians as experimental model organisms, there is a limited understanding of how multiple abiotic and biotic factors affect the variation in metamorphic traits under natural conditions. The aim of our study was to quantify the effects of abiotic and biotic factors on spatial variation in the body size of tadpoles and size at metamorphosis of the European common toad (Bufo b. spinosus). Our study population was distributed over the riverbed (active tract) and the fringing riparian forest of a natural floodplain. The riverbed had warm ponds with variable hydroperiod and few predators, whereas the forest had ponds with the opposite characteristics. Spatial variation in body size at metamorphosis was governed by the interactive effects of abiotic and biotic factors. The particular form of the interaction between water temperature and intraspecific tadpole density suggests that abiotic factors laid the foundation for biotic factors: intraspecific density decreased growth only at high temperature. Predation and intraspecific density jointly reduced metamorphic size. Interspecific density had a negligible affect on body size at metamorphosis, suggesting weak inter-anuran interactions in the larval stage. Population density at metamorphosis was about one to two orders of magnitudes higher in the riverbed ponds than in the forest ponds, mainly because of lower tadpole mortality. Based on our results, we conclude that ponds in the riverbed appear to play a pivotal role for the population because tadpole growth and survival is best in this habitat.

Institutional challenges to robustness of delta and floodplain agricultural systems

The farming of natural coastal deltas and floodplains was in many parts of the world the cradle of civilization. Through history the transformation of risky floodplain systems into socially controlled environments was the result of an intricate interplay between ecology, demography, religion, social organization and technology of the time. After the harnessing of most large tropical rivers, there are in our time few natural deltas and floodplains left to study in the warm regions of the world. One such floodplain is the Rufiji coastal delta and floodplain in Tanzania. Here an artificial irrigation culture has not been developed, but a robust risk-minimizing system based on rice, maize, cotton and peas has evolved for delta and floodplain agriculture. Through the Arab, German and British colonization, attempts were made to ‘modernize’ this agricultural system, resulting in new crops and varieties being incorporated into the system in a way that made it even more robust. This study explains the genesis of this as a socio-ecological system, that is, an interaction of resource systems, resource units, governance and users. It analyses some fundamental challenges to this agricultural system during the last 100 years: the removal of the floodplain population to ‘safe ujamaa villages’, the recurring large infrastructure development initiatives and the modern institutional challenges such as individualized tenure, urban food market expansion, coastal and marine conservation, and the recent development of ‘land-grabbing’ practices.

Differential resource selection within shared habitat types across spatial scales in sympatric toads

Differential habitat selection is a central component in the evolution of species, but it has been quantified rarely for sympatric species in relation to the multiple impacts of resources at the spatial scales at which animals operate. Our main goal was to quantify the selection of terrestrial summer habitats in a natural floodplain in Italy by two sympatric amphibians (Bufo bufo spinosus and B. viridis) as a function of habitat type, prey density, and temperature. We applied a Bayesian resource selection model at three spatial scales: (1) home range placement within the floodplain, (2) space use within 95% home ranges, and (3) space use within 50% core areas. Using these data we explored whether processes acting at large scales lead to space use patterns at small scales and whether the two species use the same habitat types in a way that would facilitate coexistence. Habitat selection was determined by habitat type, prey density, and temperature at all spatial scales, resulting in slightly higher prey density and significantly lower temperature within than outside home ranges. We conclude that amphibians perceive the distribution of habitat types as well as gradients in prey density and temperature at all spatial scales. The effects of habitat type dominated home range placement while prey density and temperature most strongly affected space use within home ranges. Our results suggest that home range placement relies on broad habitat features that indicate resource availability at small spatial scales. At the smallest spatial scale, the selection of prey and refugia is most probably facilitated due to the accumulation of environmental information as animals may sample the entire area. Both species largely preferred the same habitat types, but used them differently in relation to resources across the three spatial scales. For example, while one species used the same habitat type for foraging, the other used it for resting or both resting and foraging. Niche differentiation through differential resource selection within shared habitat types at all spatial scales may therefore facilitate the coexistence of the two species in terrestrial summer habitats.

A Process-Based View of Floodplain Forest Patterns in Coastal River Valleys of the Pacific Northwest

Floodplains in the Pacific Coastal Ecoregion (PCE) stem from steep eroding mountain landscapes in a rain forest environment, and sustain a rich array of natural resources. Like floodplains elsewhere, many of the approximately 200 coastal river valleys are profoundly altered by flow regulation and land conversion for agriculture and urban development, and these activities have contributed to widespread declines in anadromous fishes and environmental quality. Some of the coastal river valleys, however, still retain many of their natural features, thereby providing important reference sites. Understanding fundamental biophysical processes underpinning natural floodplain characteristics is essential for successfully protecting and restoring ecological integrity, including inherent goods and services. This article examines factors underpinning the ecological characteristics of PCE floodplains, particularly riparian soils and trees. Drawing on over two decades of research and literature, we describe the spatial and temporal characteristics of physical features for alluvial PCE floodplains, examine the importance of sediment deposition and associated biogeochemical processes in floodplain soil formation, quantify vegetative succession and production dynamics of riparian trees, discuss how epiphytes, marine-derived nutrients, and soil processes contribute to tree production, describe the roles and importance of large dead wood in the system, the role of termites in its rapid decomposition, and show how large wood contributes to vegetative succession. These highly interconnected features and associated processes are summarized in a model of system-scale drivers and changes occurring over several centuries. Collectively, this integrated perspective has strong implications for floodplain rehabilitation, and we identify appropriate metrics for evaluating floodplain condition and functions. We draw heavily from our own experience on several well-studied rivers, recognizing additional studies are needed to evaluate the generality of concepts presented herein. As in any complex adaptive system, fundamental uncertainties remain and constraints imposed by the legacies of past human actions persist. Nevertheless, the evolving knowledge base is improving conservation strategies of lightly modified floodplains and is supporting the incorporation of emerging process-based perspectives into the rehabilitation of heavily modified systems.

The importance of surrogate habitats in lowland river floodplains for fish community composition

Abstract Floodplain borrow pits created during dike construction for flood protection along regulated lowland rivers are suggested as convenient surrogate habitats for fish communities where natural floodplain features have been lost. Fish community structure and reproduction success in three borrow pits located in the channelised floodplain of the River Dyje, Czech Republic were studied over 3 years. Short-term floods supported the spawning of phytophilic and phyto-lithophilic species; batch spawners capitalised on late summer flood conditions. The highest species richness of 0+ juvenile fishes occurred at sites with extended periods of flooding, at least for 2 months. Flooded vegetation was inhabited mainly by juvenile cyprinids, while 0+ percids were distributed evenly along the littoral zone. Shoreline remained bare even during higher water levels before complete inundation because of the steep banks, and therefore fish were not able to benefit from higher water levels. Borrow pits appear to function as a substitute habitat for fish and their reproduction, but only if they are properly constructed with shallow areas providing appropriate nursing conditions for 0+ fish growth and survival.