Spring ecotone and gradient study of interstitial fauna along two floodplain tributaries of the river rhǒne,France

The hyporheic zone of two small tributaries of the upper Rhǒne River where they cross the floodplain (approximately 2 km wide) was studied. The streams originate in karstic areas which directly border the floodplain. The surveys were conducted at 11 sites along the course of the two tributaries at a depth of 50 cm in bed sediments. Ten litre samples were collected six times a year with a Bou-Rouch sampler. The paper examines the distribution of interstitial communities along two transverse (floodplain) profiles, defines the spring ecotone, analyses the heterogeneity, and underlines the importance of the tributaries in the functioning of the floodplain. A comparison between the spatial distributions of fauna and organic matter content along the two profiles underlines the important relationships between the groundwater and surface environment, and makes it possible to differentiate parts of the floodplain where the exchanges are most intense (interstitial spring, karst/floodplain interface). Along the longitudinal course of these streams, we observe the influence of groundwater circulation on community structure/i.e. the interactions between stream channel, alluvial aquifer and adjacent karstic aquifer.     

Aquatic macroinvertebrate assemblages of two contrasting floodplains: The rhǒne and ain rivers,France

The study examines the relationship between floodplain aquatic macroinvertebrates and sector-scale parameters such as geomorphology and history of regulation. The assemblages of six groups of invertebrates (Molluscs, Crustaceans, Ephemeroptera, Odonata, Trichoptera, and Coleoptera) were compared in various types of former channels from two contrasting but adjacent floodplain sectors: (1) the Jons sector of the Rhǒne River where successive meandering and braiding phases has left diversified fluvial forms in the landscape but where the main river is now embanked, and (2) the unregulated Ain River sector where the river is still actively meandering, although this process is being slowed by incision. The results demonstrate little difference in faunal composition between the two sectors but a significant difference in faunal structure. In the Rhǒne floodplain, there was a clear distinction between the faunal assemblages together with a high taxa richness at the scale of the sector (dominance of the beta diversity). In the Ain floodplain, the faunal assemblages were overlapping and the taxa richness was high at the sample scale (alpha diversity). Sector-scale spatial patterns of the faunal assemblages along former channels were also distinct: between-channel heterogeneity dominated in the Rhǒne, whereas within-channel heterogeneity dominated on the Ain. These results stress the influence of geomorphological and historical determinants on the floodplain communities and, conversely, the relevance of macroinvertebrate assemblages for the assessment, at the landscape scale, of aquatic systems within the floodplains.     

The impact of river regulation on the lotic macroinvertebrate communities of the lower rhǒne,France

Channelization and the construction of 12 dams on the Lower Rhǒne during the last 30 years increased the morphological and biological effects of 19th century embanking along the river. These trends were demonstrated on the main channel, i.e. the central axis of the alluvial floodplain, by the synchronic study of the benthic macrofauna of six lowhead hydroelectric impoundments. The variability of the most significant taxa was investigated by an ANOVA, and the data-samples matrix was processed with a Principal Components Analysis in order to analyse the communities organization and their significance. The benthic macroinvertebrate communities of the channel include some lentic potamic species topographically related with this kind of river (metapotamon), as well as eurytopic and pollution-tolerant species. Thus, the Lower Rhǒne has become a slow potamic river, in the same way as other large mid-European rivers. Flow velocity appears to be the most important structural factor in a large regulated river. The homogeneity of the macroinvertebrate communities and the absence of longitudinal typology show that, in a very intensely regulated river, the River Continuum Concept is too theoretical, and the disturbing effects of dams on longitudinal changes and species response to regulation must be taken into account.     

Environmental and biological responses of former channels to river incision: A diachronic study on the upper rhǒne river

The impacts of river incision should be a lowering of the river level, which would increase the rate of water flow from the hillslope aquifer to the river and its former channels. If this aquifer is nutrient-poor, it should favour the oligotrophication of the former channels. However, if the lowering of the water-table exceeds the depth of the former channels, then it should lead to the drainage of these channels. These hypotheses were tested on two former channels located in a degrading reach of the Rhǒne River (France); the former channels were influenced by floods, seepage water from the river and hillslope groundwater in 1989. The rate of river incision in this reach has increased since 1980 because of gravel extraction from the river bed (0.5 m between 1989 and 1993). Between 1989 and 1993, the reduction of river infiltration and the increase in the amount of water from the hillslope aquifer in the former channels were demonstrated by the decrease in the phosphate and ammonia content of the water, and its increased alkalinity and conductivity. The responses of aquatic vegetation to river incision depended on the vegetation zone investigated. Two floristic zones that were frequently flooded and species-poor in 1989 remained species-poor in 1993. Two floristic zones, which were species-rich and patchily organized, became dry or very shallow in 1993; as a consequence, aquatic vegetation disappeared, and was replaced by helophytes and terrestrial species. In the last vegetation zone, the increase in the amount of water coming from the hillslope aquifer caused the appearance and development of Chara hispida, an oligotraphent species. Unforeseen impacts of river incision were a decrease in the spatial and temporal heterogeneity of the former channels and lower aquatic macrophyte richness.     

Juvenile fishes as functional describers of fluvial ecosystem dynamics: Applications on the river rhǒne,France

Biological indicators may signal changes in freshwater quality but offer little information on long-term trends in ecosystem succession. As an improvement over biological indicators in river management we propose the use of ‘functional describers’, abiotic and biotic elements that reflect alterations in ecosystem function and succession through changes in their concentration or abundance, including the appearance and/or extinction of organisms or groups of organisms. Juvenile (0 +) fishes have been found to be useful functional describers in many fluvial situations encountered in Europe, not least because the ontogeny of European fishes is strongly reflected in the type of habitat chosen for reproduction. Using the regulated River Rhǒne, France, as an example, the absence or presence of 0 + juveniles is shown to provide a direct reflection of a biotope's potential as a spawning area, particularly if recent hydrological conditions have not facilitated 0 + fish displacement and the lone presence of a predator species has not suggested the elimination of other fish species. Identification of the ecological function and successional state of a fluvial ecosystem is aided by consideration of species reproductive styles and tolerances. When time, labour, and/or funding is limited, the function and succession of numerous biotopes within a catchment or large fluvial system can be monitored cost effectively by analysing the 0 + fishes assemblages via the functional describer approach.     

Structure of interstitial assemblages in a regulated channel of the river rhine (France)

The interstitial assemblages of the River Rhine were studied in the Rhinau sector (France). The studied area is located in aVegulated channel of the river, controlled by a hydroelectric dam. Twenty stations were sampled in September 1988. Ten litres of interstitial water were pumped at 50 cm depth in each station using the Bou-Rouch technique. Interstitial waters were poorly oxygenated and the hyporheic fauna had three major characteristics: (1) microcrustaceans were dominant, (2) the insects were rare and (3) the stygofauna was absent. The richest stations were well oxygenated and did not correspond to any particular geomorphological features. These findings contrast with the situation observed on other large European rivers (Rhǒne, Danube) where the interstitial assemblages appear to be locally more diversified and rich in stygofauna.     

Spatial and temporal variations of niphargus populations in interstitial aquatic habitat at the karst/floodplain interface

Artificial substrates buried in stream sediments at the karst/floodplain interface were used to examine the spatial and temporal variations of Niphargus populations. The study was carried out at two stations in two different areas of the French Jura. One was mainly supplied by karst water (Verna station), the other by both karst and surface waters (Pissoir station). The occupation of interstitial habitat was found to depend on several interacting factors:

• 1 The waterflow and its changes at the outlet. The correlation between abundance of individuals and discharge was strongest with the discharges two to four days before sampling. The structure and restoration of populations after a spate related to geological characteristics. In particular, restoration was slower and more difficult in the sediments located at the base-level of a massif (Verna) than at an overflow level (Pissoir).
• 2 The location of the sediments. At the Pissoir station, the number of individuals was higher at the main outflow, but also for both stations, on the banks opposite the outlet. Animals drifting from the karst system found refuge in the sediment of the opposite bank. Almost no Niphargus were found upstream from the outlets. At the Verna station, Niphargus were only found inside the cave.
• 3 The variability of the number of animals at different depths in the sediment was more difficult to explain. At the station mainly supplied by karst water, which presented a relatively constant flow during the study, the distribution seemed to be random. At the other station, where discharge varied considerably, the vertical distribution globally presented a gradient in abundance with more individuals in the upper sediment level. This gradient varied according to the samples. Discharge changes partly explained these results.

     

Macroinvertebrate assemblages in floodplain habitats of the lower river murray,South Australia

Macroinvertebrates were sampled in seven microhabitats (submerged woody debris, reeds, sedges, inundated grass, floating aquatic vegetation, lignum, and the unvegetated littoral) at thirteen sites representing six macrohabitats (single temporary and permanent ox-bow lakes (billabongs), fast and slow-flowing anabranches, backwaters, and the main channel) of the River Murray, and Australian lowland river. Sites were sampled in spring 1988, shortly after floodwaters had receded. Most of the 95 taxa collected were aquatic insects. Detritivores were most abundant in all macrohabitats except the temporary billabong where predators predominated. Scrapers were only abundant in the permanent billabong. The temporary billabong harboured the most species and individuals whereas slowly-flowing anabranches contained the fewest species and individuals. At the microhabitat level, most taxa and individuals occurred in stands of aquatic vegetation. The unvegetated littoral zone was the most depauperate microhabitat. Multivariate analyses illustrated the distinctiveness of the faunal assemblage found in the temporary billabong. Subsequent analyses of the permanently inundated macrohabitats indicated gradients related to current velocity and the extent to which the sites were continuous with the main river. Current velocity apparently determined assemblage composition at the macrohabitat scale whereas the structural complexity of submerged vegetation operated at the microhabitat scale. The relatively large number of taxa collected from this area emphasizes the importance of a range of macrohabitats and microhabitats to faunal diversity in a floodplain ecosystem. Although there was little faunal overlap between billabongs and the main river, billabongs probably serve as refuges for many lentic taxa that rely upon regular inundation to survive. Surveys of floodplain rivers for management purposes must include samples from aquatic habitats adjacent to the main channel because the fauna of the floodplain is potentially most threatened by regulation and alteration of the flooding regime.     

Flooding frequency and invertebrate emergence from dry floodplain sediments of the river murray,Australia

Regulation of lowland rivers often alienates large areas of the floodplain, altering the natural regime of flooding frequency, duration, and magnitude. The extent to which such changes alter the productivity of river-floodplain ecosystems and the contribution of aquatic invertebrates emerging from dry floodplain sediments is unknown. To examine this in a section of the River Murray in South Australia, fourteen replicate sods of dry sediment collected from four areas of the floodplain that had experienced different average flood recurrence frequencies (annually, 1 in 7, 1 in 11, and 1 in 22 years) were inundated in the laboratory, simulating flooding. Invertebrates emerging from the dry sediments were sampled with replacement 1, 2, 3, 7, 10, 14, 21, and 28 days after inundation, enabling comparisons of temporal changes in faunal composition and biomass. The greatest biomass and numbers of invertebrates emerged from annually-flooded sods whereas sediments usually flooded once in 22 years yielded only protozoans. Large numbers of cladocerans and rotifers were recorded within two days of inundation whereas ostracods were not numerous until two weeks later. Heterogeneity in faunal composition and biomass among replicates probably reflected patchiness in microtopography and resting stage settlement, and variable hatching ‘strategies’. Although experimental conditions rapidly diverged from the natural situation over time because of the unrealistic constraints of enclosure, results suggest a potentially significant contribution by emergent invertebrates to the newly-inundated floodplain foodweb. Reducing floodplain inundation frequency through regulation and flood mitigation probably severely reduces this reserve, removing a food resource for young fish and other predators.     

Problems in management of the Yellow river

This paper deals with the management of the Yellow River, and particularly the main problems of flood and sedimentation control in the river's lower reaches. The available and adoptable measures for managing the river are itemized. These various measures can be coordinated to obtain an integrated effect on flood prevention.     

Macrozoobenthos of floodplain waters of the rivers rhine and meuse in the Netherlands: A structural and functional analysis in relation to hydrology

The river systems of the Rhine and Meuse include a large number of floodplain waters showing differences in hydrology and geomorphology. A classification of 100 water bodies based on their macroinvertebrate communities has been worked out as a tool for ecological management. Analyses were performed on structural (species composition) and functional (trophic relations) aspects of macrozoobenthos in relation to hydrological, vegetational, and physicochemical parameters. Based on the classification of macroinvertebrate communities, three major groups of water bodies can be distinguished, which are related to the frequency of inundation. The flood frequency constitutes the major environmental gradient which structures the zoobenthos communities in the Dutch floodplain waters. Faunal composition is mediated by substrate availability, water chemistry, and the availability of nutritional resources. This typology serves as a basis for the prediction of the impact of hydrology changes on the macrozoobenthic communities of floodplain waters of highly eutrophic and polluted rivers.     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial distribution of diatom assemblages in the surface sediments of Selin Co,central Tibetan Plateau,China, and the controlling factors

Currently there are few studies on modern diatom ecology in large lakes on the Tibetan Plateau. To illustrate spatial patterns of diatom communities and study the correlation with environmental variables, 143 surface sediments were sampled from the largest lake (Selin Co) on the central Tibetan Plateau. A total of 143 diatom species belonging to 30 genera were identified, most of which were halophilic and basophilic species. Our results show that diatom communities exhibit a distinct spatial pattern in different environments including fluvial rivers, the inlet of Selin Co, the small lake region and the large lake region of Selin Co. Based on a depth-constrained cluster analysis, the diatom taxa were divided into three different communities: the shallow sedimentary zone (0–12 m), middle sedimentary zone (12–22 m) and deep sedimentary zone (22–48 m). The dominant species were Cocconeis placentula, Nitzschia hungarica and Anomoeoneis costata respectively. Through Canonical correspondence analysis, it was indicated that the spatial distribution of the diatom assemblages was mainly influenced by water depth, grain size and temperature, with water depth being the dominant factor. WA-PLS and WA regression models were used to establish a diatom-depth transfer function (r²_boot = 0.73, RMSEP = 0.19; r²_boot = 0.76, RMSEP = 0.19), further demonstrating the correlation between the diatom community and water depth. Our results defined the spatial distributions and controlling factors of diatom assemblages from the different environments.     

Role of the floodplain and riparian zone in suspended matter and nitrogen retention in the adour river,south-west France

The retention capacity of the floodplain and riparian zone for suspended matter and nitrogen has been investigated in the Adour River, a seventh order stream in south-west France. Suspended matter and nitrogen fluxes through a 25 km meandering stretch of the river were measured during two flood events and compared with the amount of sediment trapped in the riparian zone (1.1 km²) and the major floodplain (16.8 km²) of the studied area. It was estimated that the floodplain and the riparian zone together retained between 10 and 20% of the suspended matter entering the stretch under study during the two main floods (138 700 Mg). Moreover, they retained about 11% of the total particulate nitrogen fluxes (640 Mg). Although the riparian zones are 15 times smaller than the major floodplain, the total suspended matter and particulate nitrogen deposition were, 50 and 17 times, respectively, larger in the riparian zone. The results obtained on the Adour River floodplain show that large river systems should not be considered only as export systems as riparian zones can retain a significant amount of suspended organic and mineral matter during floods.     

Factors affecting the distribution and abundance of aquatic plants in a navigable Lowland river; the River Nene,England

Investigations were conducted into the causes of a decline in the abundance of rooted aquatic plants in the River Nene. These were formerly troublesome to navigation and obstructed summer storm flows and were regularly cut by Anglian Water until 1976. After 1977 plant growth caused only localized problems so cutting ceased. An investigation into the causes of the plant decline was initiated in order to provide predictions for management decisions about the future use of machinery and personnel. It was concluded that there was a natural loss of plants by scouring in the abnormally high flows of 1976/7 winter. The regular pattern of maintenance dredging, which had been implemented following water industry reorganization in 1974, was shown to suppress abundance for at least five years after dredging. These two sequential events had lowered abundance over the navigable Nene to levels which no longer warrant weedcutting.     

分形理论在河型研究中的应用探讨

简述了当前河型研究现状、分形理论的特点方法及其目前在天然河道的应用现状,并结合分形理论对基于最小能耗率的河流演变理论进行探讨,研究了一定水沙条件下,河流能耗的分形理论表示公式,扩展了河道几何边界条件对于能量损耗的表述方法,推导了河型判别的分维数公式,并提出了目前的不足与进一步研究的方向。     

Cross-channel distribution patterns of zoobenthos in a regulated reach of the tennessee river

The importance of substrate type and water depth was investigated in a regulated reach of a large, navigable river in the U.S.A. Benthic grab samples were collected in June and August, 1989, along two shore-to-shore transects in the lower Tennessee River, approximately 1.5 km downstream from Kentucky Lock and Dam. Diversity, averaged over all samples, was not significantly different from June to August. River depth of our samples, which ranged from 3.1 m to 6.5 m, significantly influenced macroinvertebrate density but had no detectable effect on the total number of taxa collected. Densities of flatworms, Asiatic clams, snails, isopods, and mayflies increased significantly with increasing depth, whereas the abundance of native mussels (Unionidae) and caddisflies decreased with depth. Substrate type (sand through cobble) influenced both the total number of taxa and the total number of organisms collected. Sample areas dominated by cobble contained significantly fewer individuals than areas composed predominantly of gravel substrate. Asiatic clams, the single most abundant species collected, were consistently more numerous on intermediate substrate sizes. In contrast, densities of native mussels, snails, and mayflies were not correlated with bottom type. Sample areas included relatively little mud and sand, resulting in relatively low numbers of oligochaetes and midges in our collections.     

珠江流域洪水时空分布特征

根据珠江流域的地形地貌条件和气候变化特点，对流域内各主要河段大于１０年一遇的历史洪水和实测超定量洪水进行统计，分析珠江流域洪水发生的地区分布和时空变化规律     

Hydrosedimentary classification of natural and engineered backwaters of a large river,the lower Rhône: possible applications for the maintenance of high fish biodiversity

At the end of the last century, the shorelines of the Lower River Rhône were embanked and submersible dikes were built in the main channel, delimiting dike fields. We compared the morphological, hydrological and sedimentary variables of nine dike fields, four sites in dead arms and one in the main channel, in order to describe the fluviosedimentary functioning and to produce a classification of these different natural and engineered backwaters. Within these ‘artificial floodplains’, the different types of backwaters and their long-term changes bear a strong similarity to those observed within a natural floodplain. The long-term frequency of submersion by the water of the main river channel is the first factor that controls the erosion and sedimentation within the different backwaters. Three types of site can be distinguished: the lotic sites are the main channel and one dike field, five dike fields comprise the semi-lotic sites and the cluster lentic sites include the three remaining dike fields and the four dead arms sites. These three groups also differ in their riparian habitats and in their juvenile fish assemblages. As juvenile fish were most abundant in the semi-lotic dike fields, the use of such structures can be envisaged in order to restore high fish diversity in rivers where the former floodplain has disappeared or is no longer accessible to fish because of human modifications. © 1997 John Wiley & Sons, Ltd.