Lowland Floodplain Research Articles

Distinguishing past from present gene flow along and across a river: the case of the carnivorous marsupial (Antechinus flavipes) on southern Australian floodplains

Humans have altered many floodplain ecosystems around the world by clearing vegetation, building towns and regulating river flows. Studies discerning gene flow and population structure of floodplain-dwelling animals are rare yet are necessary for understanding the effects of human actions on native populations. In south-eastern Australia, the yellow-footed antechinus (Antechinus flavipes) is the only carnivorous marsupial on many lowland floodplains, yet our knowledge of impacts of human activities is limited. The control region of mitochondrial DNA and 11 microsatellite DNA markers were used to explore historic and current gene flow in A. flavipes across and along the Murray River. Simulations were carried out to test different migration models. We found evidence for historic gene flow along and across the river but inferred that small towns and farmland or cleared floodplain sections restricted current gene flow along the river. Populations along the river appear to be isolated, and should be maintained at large enough sizes to avoid genetic problems such as inbreeding depression and loss of evolutionary potential. We also investigated whether 50-year-long maintenance of high water levels for irrigation in summer, at the time of juvenile dispersal, has led to restrictions in gene flow across the river. We found no evidence for restrictions to gene flow across the river and suggest that large floods and dropping tree branches may aid dispersal across the river.

Spatial distribution and internal metal concentrations of terrestrial arthropods in a moderately contaminated lowland floodplain along the Rhine River

Soil metal concentrations, inundation characteristics and abundances of 14 arthropod taxa were investigated in a moderately contaminated lowland floodplain along the Rhine River and compared to the hinterland. Internal metal concentrations were determined for the orders of Coleoptera (beetles) and Araneida (spiders) and were related to soil concentrations. The floodplain was characterized by larger arthropod abundance than the hinterland, in spite of recurrent inundations and higher soil metal concentrations. Most arthropod taxa showed increasing abundance with decreasing distance to the river channel and increasing average inundation duration. For Cd, Cu, Pb and Zn, significant relations were found between arthropod concentrations and concentrations in soil. Significant relations were few but positive, indicating that increasing soil concentrations result in increasing body burdens in arthropods. For arthropod-eating vertebrates, these results might imply that larger prey availability in the floodplain coincides with higher metal concentrations in prey, possibly leading to increased exposure to metal contamination.

Mind the gap: an absence of valley-fill deposits identifying the Holocene hypsithermal period of enhanced flow regime in southeastern Australia

The Holocene sedimentary record in southeastern Australia is present in a range of landscape settings, such as upland swamps (dells), internally drained lake basins, alluvial fans, and mid-catchment and lowland floodplains. An assessment of the best-constrained basal radiocarbon dates in valley-fill locations between 30 and 42°S and upstream of last-glacial eustatic influences yields an intriguing pattern. The record for fluvial sites with catchment areas > 30 km2 exhibits a distinct gap in the alluvial record between 8 and 4 ka BP (10—4.5 ka). In contrast, data for eleven upland-swamp sites with catchment areas < 50 km2 exhibit a broader spectrum of basal ages, albeit with some reduction of activity during the alluvial gap. We suggest that the period 8—4 ka BP in the sedimentary record at the fluvial sites reflects the early to mid-Holocene climatic optimum independently recognized in proxy climate data in the region. It was a period of enhanced water discharges, stable well-vegetated catchments and low sediment yields, and therefore greatly limited sediment sequestration, and it has been termed the Nambucca Phase. In upland swamps, however, threshold-driven processes produce an episodic landscape responses during much of the Holocene. Contrasting results in upland compared with middle and lower basin locations demonstrate the nonuniform landscape response to climatic changes during the Holocene in southeastern Australia.

Water Exchange and Deposition of Sediment and Phosphorus during Inundation of Natural and Restored Lowland Floodplains

Water exchange, flow patterns and deposition of sediment and phosphorus were measured in cross-sections of a naturally functioning floodplain during one winter and in three restored floodplains following remeandering of formerly straightened and channelized rivers. Sediment and phosphorus depositional processes were studied, deploying artificial grass mats at different distances from the river channel. In addition, a mass-balance approach was applied on the experimental site. Our results show that the deposition of sediment and particulate phosphorus constituted 3,000–4,700 g DW m−2 and 1.2–7.3 g P m−2, respectively, on the four floodplains studied during a winter where flood duration lasted between 20 and 76 days. The storage efficiency for sediment ranged between 28–47 and 4.0–7.0% for phosphorus.

Modelling the impacts of land-use and drainage density on the water balance of a lowland–floodplain landscape in northeast Germany

This study presents the modelling approach and impact assessment of different strategies for managing wetland water resources and groundwater dynamics of landscapes which are characterised by the hydrological interactions of floodplains and the adjacent lowlands. The assessment of such impacts is based on the analysis of simulation results of complex scenarios of land-use changes and changes of the density of the drainage-network. The method has been applied to the 198 km 2 Lower Havel River catchment as a typical example of a lowland–floodplain landscape. The model used consists of a coupled soil water and groundwater model, where the latter one is additionally coupled to the surface channel network. Thus, the hydrological processes of the variable saturated soil zone as well as lateral groundwater flow and the interactions between surface water and groundwater are simulated in an integrated manner. The model was validated for several years of significantly different meteorological conditions. The comparison of lateral and vertical water balance components showed the dominance of lateral flow processes and the importance of the interactions between surface water and groundwater for the overall water balance and the hydrological state of that type of landscape. The simulation of land-use change scenarios showed only minor effects of land-use change on the water balance and groundwater recharge. Changes of groundwater recharge were particularly small within the wetland areas being part of the floodplain where interactions between surface water and groundwater are most pronounced. Alterations in vertical groundwater recharge were counter-balanced by the lateral interaction between groundwater and surface water. More significant deviations in groundwater recharge and storage were observed in the more peripheral areas towards the catchment boundaries which are characterised by greater groundwater distance from the surface and less intense of ground water–surface water interactions. However, the simulation results assuming a coarsening of the drainage network density showed the importance of drainage structure and geometry for the water balance: The removal of the artificial draining ditches in the floodplain would result in significant alterations of total groundwater recharge, i.e., less recharge from winter to early summer and an increase of groundwater recharge during summer and autumn. Furthermore the different effects of groundwater recharge alterations on the dynamics of groundwater stages within the wetland areas close to the floodplains compared to the more peripheral areas could be quantified. Finally, it will be discussed that a well-adjusted co-ordination of different management measures is required to reach a sustainable water resources management of such lowland–floodplain landscapes.

Immediate Impact of an Extensive Summer Flood on the Adult Fish Assemblage of a Channelized Lowland River

ABSTRACT The fish community of a channelized stretch of a lowland floodplain River Morava (Danube basin) was surveyed before and after an exceptionally extensive flood in July 1997. Water discharge peaked at 2,000% of long-term average and discharge > 1,000 % lasted for 20 days. Electrofishing survey along the bank in three inter-weir reaches revealed 26 species, with the same species (chub Leuciscus cephalus, gudgeon Gobio gobio) dominating before and after the flood. The flood had a minor effect on the assemblage structure. The total density of fish was not significantly different before and immediately after the flood. The largest decline was observed for pelagic species (e.g. bleak Alburnus alburnus, roach Rutilus rutilus) and benthic species (e.g. barbel Barbus barbus). The overall gudgeon abundance did not decrease significantly after the flood, though length-frequency distribution revealed a decrease in abundance of one-year-old individuals. The flood had no effect on abundance of chub and burbot (Lota lota) but increased the abundance of perch (Perca fluviatilis).

Airborne Laser Scanning as a Tool for Lowland Floodplain Vegetation Monitoring

Monitoring of three-dimensional floodplain vegetation structure is essential for ecological studies, as well as for hydrodynamic modelling of rivers. Height and density of submerged vegetation and density of emergent vegetation are the key characteristics from which roughness parameters in hydraulic models are derived. Airborne laser scanning is a technique with broad applications in vegetation structure mapping, which therefore may be a promising tool in monitoring floodplain vegetation for river management applications. This paper first provides an introduction to the laser scanning technique, and reviews previous studies on the extraction of vegetation height and density of forests, low vegetation and meadows or unvegetated areas. Reliable predictions using laser scan data have been reported for forest height (R2=0.64–0.98), parameters related to forest density, such as stem number, stem diameter, biomass, timber volume or basal area (R2=0.42–0.93), and herbaceous vegetation height (summer condition; R2=0.75–0.89). No empirical relations have been reported on density of herbaceous vegetation. Laser data of meadows and unvegetated areas show too much noise to predict vegetation structure correctly. In a case study for the lower Rhine river, the potential of laser scan mapping of vegetation structure was further explored for winter conditions. Three laser-derived metrics that are often reported in the literature have been applied to characterize local vertical distributions of laser reflections. The laser data clearly show the large structural differences both between and within vegetation units that currently are the basis of floodplain vegetation and roughness mapping. The results indicate that airborne laser scanning is a promising technique for extraction of 3Dstructure of floodplain vegetation in winter, except for meadows and unvegetated areas.

Seasonally varying impact of detritivorous fishes on the benthic ecology of a tropical floodplain river

AbstractThe Cinaruco River, a lowland floodplain river in the Venezuelan llanos, has a strongly seasonal hydrology, low nutrient concentrations, and high fish diversity and abundance. Fish exclosure/enclosure experiments were conducted in the littoral zone of the river channel and connected lagoons to examine seasonal variation in the magnitude of fish effects on benthic organic matter and algal biomass. During the dry season, large-fish exclosures in the channel accrued significantly more sediment, organic material, and chlorophyll than control cages after 20 d. Grazing scars suggested the bocachico, Semaprochiloduskneri, was a major consumer of organic-rich sediments. Further experiments were conducted to test the hypothesis that the relative strength of top−down (grazer) control of organic matter in sediments varies according to species, hydrologic period, and habitat. At flooding onset (May), S. kneri migrate to the Orinoco River to reproduce and feed. Thus, their densities are extremely low in the Ci...

A geomorphic monitoring and adaptive assessment framework to assess the effect of lowland floodplain river restoration on channel–floodplain sediment continuity

AbstractThe state of the science of lowland river floodplain restoration reflects the relatively new and experimental nature of large river floodplain rehabilitation efforts. Based on results of a case study of floodplain restoration at the lowland Cosumnes River, California, we present a geomorphic monitoring and adaptive assessment framework that addresses the need to inform and utilize scientific knowledge in lowland floodplain river restoration activities. Highlighting hydrogeomorphic processes that lead to habitat creation, we identify a discharge threshold for connectivity and sediment transfer from the channel to the floodplain and integrate discharge magnitude and duration to quantify a threshold to aid determination of when geomorphic monitoring is warranted. Using floodplain sand deposition volume in splay complexes as one indicator of dynamic floodplain habitat, we develop a model to aid prediction of the sand deposition volume as an assessment tool to use to analyze future monitoring data. Because geomorphic processes that form the physical structure of a habitat are dynamic, and because the most successful restoration projects accommodate this fundamental characteristic of ecosystems, monitoring designs must both identify trends and be adapted iteratively so that relevant features continue to be measured. Thus, in this paper, adaptive assessment is defined as the modification of monitoring and analysis methods as a dynamic system evolves following restoration activities. The adaptive monitoring and assessment methods proposed facilitate long‐term measurements of channel–floodplain sediment transfer, and changes in sediment storage and morphology unique to lowland river–floodplain interactions and the habitat that these physical processes support. The adaptive assessment framework should be integrated with biological and chemical elements of an interdisciplinary ecosystem monitoring program to answer research hypotheses and to advance restoration science in lowland floodplain river systems. Copyright © 2005 John Wiley & Sons, Ltd.

An advanced approach for catchment delineation and water balance modelling within wetlands and floodplains

Abstract. Water balance of wetlands within lowland floodplains is strongly influenced by the temporally variable spatial extent of the interactions between groundwater and surface water. A robust algorithm will be introduced which makes it possible to delineate the interaction zone between the lowland river and the floodplain. This interaction zone is specified as the "Direct Catchment" which is defined by the part of the connected floodplain in which wetland water balance is mainly affected by the surface water dynamics of the adjacent river. The delineation algorithm is based on transfer functions which were assessed by local simulation results of the integrated water balance and nutrient dynamics model IWAN. The transfer functions are further determined by mean annual groundwater depths and by simulated groundwater dynamics. They are controlled by simulation results of the maximal transversal extent of surface water influence on groundwater stages. The regionalisation of the developed delineation algorithm leads to the specification of the maximal extent of groundwater - surface water - interaction processes along the river. By application of this approach to the Havel River basin, located within lowlands of Northeaster Germany, it was possible to specify a 998.1 km2 part of the floodplain which is directly connected with the surface waters and thus called the "Direct Catchment" of the Havel river. The IWAN model was applied to simulate the water balance of the floodplain. The simulation results prove the tight interaction between river and floodplain. It is shown that the spatially and temporally variable influences of the connected floodplain on the river discharge were only important during low discharge in summer.

Lateral organization of aquatic invertebrates along the corridor of a braided floodplain river

Although spatial scale, upstream–downstream gradients, environmental variability, and floodplain connectivity and complexity have been recognized as integral components of our understanding of riverine pattern and process, aquatic invertebrate community structure across lateral gradients from headwaters to the lowland of a river has received little empirical documentation. Aquatic invertebrate density, distribution, and richness were investigated at 29 study sites distributed laterally (main channel–floodplain) among 6 geomorphologically distinct river reaches from the headwaters to near the mouth of one of the last seminatural river corridors draining the European Alps, the Tagliamento River in northeastern Italy. Community relationships were examined using multivariate and diversity analyses to investigate patterns of taxonomic richness. Diversity parameters were scaled at the site, reach, and catchment levels to better understand local and regional patterns. Mean invertebrate density increased from 7484 ± 2480 (±1 SE) individuals/m2 in the headwaters to 98,811 ± 18,037 individuals/m2 on the lowland floodplain. Crustacea, Coleoptera, and Ephemeroptera richness increased and nonchironomid Diptera and Plecoptera richness declined along the corridor. Richness (α diversity) and turnover (β diversity) showed no consistent increase or decrease along connectivity gradients within geomorphic reaches along the river corridor, possibly because each reach had unique characteristics. α diversity was similar among geomorphic reaches along the corridor, whereas β diversity between reaches increased as a function of distance between them. Direct gradient analysis indicated high taxa-to-environment concordance along lateral (i.e., floodplain water bodies) and longitudinal (upstream–downstream) dimensions and indicated distinct floodplain communities. These results demonstrate how lateral gradients (floodplain dimension) structure zoobenthic communities and how this structure can change along the longitudinal dimension (upstream–downstream). Our results highlight the importance of off-channel environments to macroinvertebrate community structure and diversity. Conservation, restoration, and preservation measures must consider the lateral dimension along river corridors as integral to maintaining diversity and community structure.

Abundance and Production of Riparian Trees in the Lowland Floodplain of the Queets River, Washington

Riparian zones associated with alluvial rivers are spatially dynamic, forming distinct vegetative mosaics that exhibit sharp contrasts in structure and processes related to the underlying biophysical template. The productivity of riparian plants, especially trees, influences streamside community characteristics as well as the forms and fluxes of organic matter to adjacent streams – thereby strongly impacting patterns of channel morphology, water flow, sedimentation, and habitat in rivers. As part of a comprehensive investigation of riparian dynamics in coastal rain forest rivers of the Pacific Northwest (USA), we examined riparian tree abundance (density, basal area, and biomass) and rates of production (basal area growth [BAI] and bole wood biomass increase [P]) of seven common species – red alder (Alnus rubra), Sitka spruce (Picea sitchensis), bigleaf maple (Acer macrophyllum), western hemlock (Tsuga heterophylla), black cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and willow (Salix spp.) – in the lowland floodplain of the Queets River (Olympic National Park), Washington. Measurements were made annually for three years (1999 – 2001) in 16 permanent plots on three biophysical templates that formed a toposequence – active floodplain, young terrace and mature terrace. Stem density was highest in the active floodplain (∼27,000 stems/ ha), decreasing in the young terrace (∼2,700 stems /ha) and the mature terrace (∼500 stems/ha). Basal area and total stem biomass were lowest in the active floodplain (∼16 m²/ha and ∼18 Mg dry weight/ha, respectively) and higher on the young terrace (∼32 m²/ha and ∼134 Mg dry weight/ha) and on the mature terrace (∼69 m²/ha and ∼540 Mg dry weight /ha). Total plot-scale BAI was not significantly different among the physical templates with mean values ranging from approximately 1.4 (low terrace) to approximately 2.8 m²/ha/y (active floodplain). In contrast, P was significantly higher on the mature terrace (10.3 Mg/ha) than the active floodplain (3.2 Mg/ha) but there was no significant difference between young terrace (6.5 Mg/ha) and mature terrace. For the entire Queets River floodplain (57 km2 over 77 km of river length), the mature terrace contributed 81% of the total annual production (28,764 Mg) whereas the active floodplain and young terrace accounted only for 5 and 14%, respectively. Overall, we show that riparian trees grow quickly in this coastal Pacific Northwest system and that the older riparian forests on mature terraces are the main contributors to stem production at the plot and floodplain scales for at least 350 years after stand initiation. This suggests that, in combination with the rapid lateral migrations of many alluvial rivers, the older riparian forests on those terraces are important and sustained sources of organic matter (especially large woody debris, LWD) that, over decades to centuries, shape the character of coastal rivers in the Pacific Northwest.

VASCULAR FLORA OF GOLDEN AND SILVER FALLS STATE NATURAL AREA IN THE OREGON COAST RANGE, COOS COUNTY, OREGON

ABSTRACT A descriptive plant survey was conducted of Golden and Silver Falls State Natural Area in the Coast Range northeast of Coos Bay in Coos County, Oregon, during 1988, 1990, and 1997. The 63.6 ha natural area was established in 1936 to preserve an old-growth stand of Pseudotsuga menziesii surrounding the area of two scenic waterfalls. Vascular flora consisted of 241 specific and infraspecific taxa in 162 genera from 61 families, of which 70 taxa (29 %) were exotics. The five plant habitats were steep coniferous mountain slopes (Pseudotsuga menziesii-Tsuga heterophylla/Acer circinatum/Polystichum munitum association) and (Pseudotsuga menziesii-Tsuga heterophylla/Gaultheria shallon/Polystichum munitum association), sandstone cliff escarpments, lowland valley hardwoods (Acer macrophyllum-Umbellularia californica/Polystichum munitum association), ruderal, and riparian floodplain (Alnus rubra/Rubus spectabilis/Oxalis oregana association).

Safeguarding the Pantanal Wetlands: Threats and Conservation Initiatives

Abstract: The Pantanal, one of the largest wetlands on the planet, comprises 140,000 km2 of lowland floodplain of the upper Rio Paraguai basin that drains the Cerrado of central Brazil. The diverse mosaics of habitats resulting from the varied soil types and inundation regimes are responsible for an extraordinarily rich terrestrial and aquatic biota, exemplified by the bird richest wetland in the world—463 birds have been recorded there—and the largest known populations of several threatened mammals, such as Pampas deer (Ozotoceros bezoarticus), marsh deer (Blastocerus dichotomus), giant otter (Pteronura brasiliensis), and jaguar (Panthera onca). Until recently, deforestation of the adjoining Brazilian central plateau was considered the major threat to this area, but now deforestation is a critical problem within the floodplain itself. More than 40% of the forest and savanna habitats have been altered for cattle ranching through the introduction of exotic grasses. And there are other threats that lead to large‐scale disruption of ecological processes, severely affecting biodiversity. Although the Pantanal wetland is a Biosphere Reserve and is considered a Wetland of International Importance, only 2.5% of the upper Paraguai River basin is formally protected. To date, protected areas have been created opportunistically and as such, although of undoubted value, protect only a fraction of the Pantanal's wildlife and habitats. Among the conservation initiatives in the area, the private sector is increasingly participating in the establishment of private reserves. The prospects are far from optimistic, however, and the major challenge is to find alternative socioeconomic models that allow for conservation and economic uses of the land in association with the development of specific environmental legislation that reflects the unique characteristics of the region.

Quantitative evaluation of the petal shape variation in Primula sieboldii caused by breeding process in the last 300 years

Primula sieboldii: (E. Morren) has been a popular garden plant at least since the Edo period, about 300 years ago. We compared petal form between cultivars and wild populations in order to characterise the changes that have occurred during domestication. The comparison was made using EF-PCA analysis, which describes overall petal shape mathematically by transforming petal contour coordinates into elliptic Fourier descriptors; it subsequently summarises these descriptors by principal component analysis (PCA). Rearing cultivars in a common-garden experiment identified the PCs with a substantial genetic element. A clear heritable component was detected for the PCs characterising symmetrical variation in flower shape, but not the asymmetrical variation. Wild populations of this species have become endangered owing to habitat destruction by human activity, and many lowland floodplain habitats have been lost. Variation within the remaining wild populations was significantly lower than in the cultivars for PC1 (aspect ratio), PC3 (curvature of proximal and distal parts) and petal area; but not for PC2 (depth of head notch) and PC4 (position of the centre of gravity). The shifts in petal form from the wild populations to the cultivars parallel those seen in other crop-types following domestication, including an increase in size and diversity of forms: cultivars have shallower head notches, more fan-shaped petals and larger petals than do wild P. sieboldii.

An early Carboniferous (Mississippian), Tournaisian, megaspore assemblage from Three Mile Plains, Nova Scotia, Canada

Mississippian, Tournaisian, lycopsid megaspores isolated from lacustrine deposits of the Horton Bluff Formation at Three Mile Plains in Nova Scotia, Canada, are identified and illustrated by scanning electron microscopy. Three morphospecies of Sublagenicula: S. brasilliensis (Dijkstra) Glasspool, S. dulcis (Dijkstra) Dybová-Jachowicz et al., and S. variabilis (Winslow) Dybová-Jachowicz et al., one morphospecies of Auritolagenicula: A. angulata (Zerndt) Dybová-Jachowicz et al., three morphospecies of Lagenicula: L. subpilosa (Ibrahim) Potonié and Kremp, L. cervicornis (Winslow) comb. nov., and cf. L. rarispinosa (Dijkstra) Dybová-Jachowicz et al., one morphospecies of Setosisporites: S. aries (Winslow) Dybová-Jachowicz et al. and four megaspores assigned to Laevigatisporites cf. cheveriensis (Bell) comb. nov., are described. This assemblage is compared with other assemblages from contemporaneous strata in North America, Western Europe and North Africa. Gulate morphotaxa, which are considered to have been produced by an arborescent lepidodendropsid parent vegetation, dominate this assemblage, which is diverse in comparison with coeval assemblages and probably represents a lowland floodplain rather than a lycopsid-dominated mire vegetation.

Barrier to gene flow between two ecologically divergent Populus species, P. alba (white poplar) and P. tremula (European aspen): the role of ecology and life history in gene introgression

The renewed interest in the use of hybrid zones for studying speciation calls for the identification and study of hybrid zones across a wide range of organisms, especially in long-lived taxa for which it is often difficult to generate interpopulation variation through controlled crosses. Here, we report on the extent and direction of introgression between two members of the "model tree" genus Populus: Populus alba (white poplar) and Populus tremula (European aspen), across a large zone of sympatry located in the Danube valley. We genotyped 93 hybrid morphotypes and samples from four parental reference populations from within and outside the zone of sympatry for a genome-wide set of 20 nuclear microsatellites and eight plastid DNA restriction site polymorphisms. Our results indicate that introgression occurs preferentially from P. tremula to P. alba via P. tremula pollen. This unidirectional pattern is facilitated by high levels of pollen vs. seed dispersal in P. tremula (pollen/seed flow = 23.9) and by great ecological opportunity in the lowland floodplain forest in proximity to P. alba seed parents, which maintains gene flow in the direction of P. alba despite smaller effective population sizes (N(e)) in this species (P. alba N(e)c. 500-550; P. tremula N(e)c. 550-700). Our results indicate that hybrid zones will be valuable tools for studying the genetic architecture of the barrier to gene flow between these two ecologically divergent Populus species.

Toward a conceptual model of floodplain water table response

Hydrological processes operating within floodplains in temperate midlatitudes have significant implications for water management by controlling pollutant transfer between the catchment and the fluvial system. However, there is a lack of relevant high‐resolution data from which the dynamics of floodplain hydrology during flood events can be inferred. A detailed analysis of water table fluctuations during flood events within a typical European lowland floodplain system (River Severn, United Kingdom) is presented. Data collected hourly along two 120‐meter‐long transects, each comprising four piezometers, plus one river stage sensor, are analyzed for the winter season 1998–1999 using correlation analysis, hysteresis curves, and water table maps. The objective is to develop a conceptual model that provides mechanistic understanding of floodplain water table response during flood events. River stage is shown to be the principal driver of water table fluctuations. Piezometers with similar water table response are identified; their consistent pattern of response in different flood events is attributed to sedimentary and morphological controls on the floodplain and adjoining hillslopes. Deviations from the general pattern are a function of low antecedent soil moisture, which is only a significant factor at the beginning of the winter season, when the floodplain is initially dry. Our conceptual model adopts a kinematic wave process whereby river stage change induces rapid responses of the water table over many tens of meters across the floodplain, associated with flux velocities several orders of magnitude higher than would be expected for Darcian flow. The occurrence of a groundwater ridge within the floodplain dams hillslope drainage and causes the water table to rise at the back of the floodplain. The disappearance of the groundwater ridge during the recession reestablishes hillslope flow into the floodplain, resulting in significant three‐dimensional hydraulic gradients directed both perpendicular and parallel to the channel axis.

The role of floods in particulate organic matter dynamics of a southern Appalachian river–floodplain ecosystem

We investigated the effect of a flood on particulate organic matter (POM) dynamics in the floodplain and active channel of the Little Tennessee River in western North Carolina. We measured litterfall, leaf breakdown, and floodplain litter (before and after the flood) at 12 sites. Annual litterfall (256–562 g m−2 y−1) was typical of a temperate deciduous forest but lower than lowland floodplain forests in the eastern US. Leaf breakdown rates of 4 tree species (Acer rubrum, Carpinus caroliniana, Juglans nigra, and Platanus occidentalis) ranged from 0.001 to 0.010/d. We separated the 12 sites into 2 groups (inundated and non-inundated) based on the degree of flooding after a flood on 8 January 1998 and determined POM exchange between the active channel and floodplain. Significant transport of leaves from the floodplain to the river occurred at inundated sites, but transport of herbaceous or woody material did not occur. The flood increased leaf breakdown rates of all 4 tree species. Our measurements of litterfall, leaf breakdown, and floodplain litter standing crop suggest that leaves entrained from the floodplain of Little Tennessee River during floods are a source of POM to the active channel. However, flood input of leaves to the river were a small source of POM compared to direct leaffall.

Suitability of different groups of terrestrial invertebrates for assessment of heterogeneity of terrestrial parts of lowland floodplains.

In 2001 and 2002 a survey has been carried out on several taxonomic invertebrate groups in five floodplain areas along the river Waal in the Netherlands. Studied groups are: aculeate wasps (Hymenoptera: Chrysididae, Crabronidae, Tiphiidae, Pompilidae, Sphecidae, Vespidae), Apidae s.l. (Hymenoptera), Carabidae (Coleoptera), Mollusca (only terrestrial species), Odonata, Orthoptera, Syrphidae (Diptera). The study focused on sand dunes, high river banks, grasslands and marshes. The aim of the study was to compare the investigated invertebrate groups in terms of betadiversity to determine their sensitivity for heterogeneity of floodplain ecosystems. The results have been analysed in combination with the faunistic database of EIS (European Invertebrate Survey) - the Netherlands. Based on this database, species were selected of which at least 5 % of their distribution is situated in the Dutch Rhine branches ('preferential species'). Considering their high diversity in floodplain areas, both in absolute numbers and in betadiversity, and high number of preferential species in the Dutch Rhine branches, aculeate wasps, Apidae and Carabidae seem to be the most suitable of the studied groups for assessment of the heterogeneity of floodplain ecosystems. In aculeate wasps and Apidae, the highest diversity occurs in high parts of the floodplains. In Carabidae and Syrphidae with aquatic larvae, the highest diversity occurs in low parts of the floodplains.