Do invertebrate communities in floodplains change predictably along a river's length?

1. Invertebrate assemblages were described for nine floodplain sites located on a longitudinal gradient of river discharge in the Altamaha River catchment. The Altamaha River and its tributaries constitute one of the few remaining ‘unregulated’ catchments in the southeastern U.S. We predicted that, as the character of lateral flood pulses into backwater swamps changed along the discharge gradient, so would the structure of invertebrate communities. We also examined the relationship between invertebrate assemblages and physicochemical factors (degree of floodplain inundation, pH, conductivity and nutrient concentrations). 2. Cluster analyses of both invertebrate abundance and biomass separated the nine sites into three groups corresponding to their positions in the catchment (upper, mid‐ and lower reach clusters). Non‐metric multidimensional scaling ordinations further corroborated the groupings (with combined axis scores of 92% and 73% for abundance and biomass, respectively) and showed significant correlations with degree of inundation and conductivity (abundance), and conductivity, nitrate and phosphate concentrations (biomass). 3. Floodplains in the upper reaches were dominated by terrestrial taxa, such as earthworms, oribatid mites, collembolans and assorted terrestrial fly larvae, and some rapidly developing aquatics (harpacticoid crustaceans and mosquitoes). In the mid‐reach, the dominant taxa were longer lived aquatic organisms such as mayflies and aquatic oligochaetes, although some terrestrial organisms (elaterid beetles and mites) were still common. Invertebrate families dependent on water flow, such as riffle beetles and some mayflies, were common only in mid‐reach floodplain sites. Lower reaches were dominated by lentic aquatic taxa such as dytiscid beetles and asellid isopods, which commonly persist in wetlands after they dry. 4. Our study indicates that invertebrate community structure varies predictably among floodplains in the Altamaha catchment, with headwater habitats being dominated by terrestrial and rapidly‐developing aquatic invertebrates, mid‐reaches characterised by an influx of invertebrates from the river and lower reaches being dominated by wetland taxa with desiccation‐resistant stages. This spatial variability should be considered when applying the Flood Pulse Concept.     

Fish recruitment in a large,temperate floodplain: the importance of annual flooding,temperature and habitat complexity

1. Large river floodplains are considered key nursery habitats for many species of riverine fish. The lower Volga River floodplains (Russian Federation) are still relatively undisturbed, serving as a suitable model for studying the influence of flooding and temperature on fish recruitment in floodplain rivers. 2. We examined the interannual variability in recruitment success of young‐of‐the‐year (YOY) fish in the lower Volga floodplain in relation to flood pulse characteristics and rising water temperatures in the spring. We sampled four areas with different flooding regimes, in three consecutive years (2006–2008). 3. Extensive areas with a long duration of flooding accommodated high densities of young fish. This suggests that extended inundation improves the recruitment success of river fish. In areas with extensive flooding, the biomass of YOY of most fish species was about three times higher in 2006 and 2007 than in 2008. We hypothesise that low spring temperatures in 2008 may have caused this reduced recruitment and that a flood synchronised with rising temperature enhances recruitment success. 4. Extensive flooding was particularly favourable for species characterised by large body size, delayed maturation, high fecundity and low parental investment, such as pike Esox lucius, roach Rutilus rutilus and ide Leuciscus idus. Gibel carp Carassius gibelio, a species tolerant of high temperature and hypoxia, did particularly well in small waterbodies in the driest parts of the floodplain. 5. Structural characteristics of floodplain waterbodies explained much of YOY fish density. These species–environment associations varied from year to year, but some species such as common bream Abramis brama, roach and gibel carp showed consistent relationships with structural habitat characteristics in all years, despite large interannual fluctuations in flood pulse and spring temperature.     

Fish community characteristics of the lower Gambia River floodplains: a study in the last major undisturbed West African river

1. The Gambia River is the last major West African river that has not been impounded. However, a hydroelectric dam is being constructed and substantial changes to the hydrology and ecology of the system are expected. 2. Little information is available on the impact of water impoundments in semi‐arid regions on downstream floodplain fish communities, due to the scarcity of pre‐intervention data. Because profound impacts on physical habitat, salinity and nutrient transport can occur downstream of such impoundments, a knowledge of the species‐habitat associations of biota such as fishes is necessary for understanding likely changes and how to limit them. 3. Fish were sampled using cast and hand nets along two transects on the floodplain, and with fyke nets in two ‘bolongs’ (creeks) from May to November 2005 and 2006 in the lower reaches of the Gambia River, close to the salt water front where ecological changes due to the construction of the dam are likely to be pronounced. 4. Greatest fish species richness was associated with low conductivity, low pH and deep water. Bolongs held greater species richness compared with other floodplain habitats, probably because they acted as conduits for fish moving on and off the floodplain. Species richness and catch biomass increased rapidly following the first rains and then declined. 5. Using a multivariate analysis, three main species groups were identified on the floodplain; one associated with deeper water, one with less brackish water and one with shallow, open water. Tilapia guineensis was the commonest species on the floodplains. 6. The floodplains provide nursery habitats as many fish captured were immature, particularly for species where adults are mainly encountered in the main channel. Several small‐sized floodplain specialists were also represented by a high proportion of mature individuals. 7. Impoundment is expected to reduce seasonal flooding of the floodplain in the lower Gambia River, downstream of the impoundment, resulting in reduced occurrence of aquatic habitats, especially bolongs, together with lower dissolved oxygen and increased salinity, leading to alteration of the floodplain fish communities, benefiting salt‐tolerant species, reducing overall species richness and probably reducing floodplain fish production.     

Migration of bream between the main channel and floodplain lakes along the lower River Rhine during the connection phase

Mature bream (>30 cm L_F) dominated the fish communities in floodplain lakes along the lower River Rhine in The Netherlands, in terms of biomass, in all lakes at all times. In some lakes bream made up 99% of the total fish biomass. While immature, medium–sized bream (10-30 cm) and white bream and roach were abundant in the main channel of the river, these species were almost absent from the floodplain lakes. Inundation of the floodplains did not lead to spatial homogenization of species and length distributions. Small bream (<10 cm) left the floodplains to become resident in the main channel until maturity. Once mature (c. 30 cm), they returned to the lakes during the next inundation and stayed there. Mature bream that moved into the lakes were significantly smaller and had a lower condition than the resident bream. Turbid clay-pits were probably important sources of bream for the lower Rhine and the recruitment of the 0+ year group of bream to the riverine population was influenced by their discharge pattern.     

Winter fish community structures across floodplain backwaters in a drought year

We examined fish community structures in floodplain backwaters in the Kiso River, Central Japan, in an uncommon drought year. Nine floodplain backwaters with varying levels of flood inundation frequency were surveyed for winter fish communities, and measured for local environmental variables in summer and winter periods. The winter fish community was better represented, with less diverse and physiologically tolerant species in backwaters with a decreasing flood pulse frequency. The temporal frequency of hypoxic conditions (dissolved oxygen of <2 mg l^?1) and chlorophyll a in summer explained the heterogeneity of the fish community along the gradient of inundation frequency, while no variables measured in winter had an explanatory power. These results suggest that drought-induced, infrequent flood pulses in the autumn–winter period limited the dispersal opportunity of fishes, and thus maintained community structures selected by summer limiting factors until the survey took place in winter. Future comparisons of our data with those in non-drought years would provide important implications to the sustainable management of floodplains for wintering fishes against the increasing probability of future flow regime changes.     

Pleuston communities are buffered from regional flood pulses: the example of ostracods in the Paraná River floodplain, Brazil

1. It is widely acknowledged that sudden, large‐scale flood pulses are drivers of benthic and planktonic biodiversity change in floodplains. The impact of such pulses on pleuston (biotic communities associated with root systems of floating plants) remains to be demonstrated. Here, we investigate the effects of local and regional drivers on seasonal changes in abundance and diversity of ostracod communities in pleuston. 2. Temporal and spatial distribution patterns of species richness, abundance, diversity and evenness of ostracods associated with the floating water hyacinth, Eichhornia crassipes, in a lentic environment from the upper Paraná River floodplain, were investigated in relation to local, as well as regional, environmental factors. Ostracods were sampled monthly over an annual cycle (March 2004–February 2005). Twenty‐seven species were found, representing the families Cyprididae, Candonidae, Limnocytheridae and Darwinulidae. Both diversity and abundance of ostracod communities showed seasonal changes, although species turn‐over during the year was limited. 3. We tested two hypotheses concerning the causality of these fluctuations: seasonal recruitment and influx of allochthonous ostracods during the flood pulse. Our results indicate that seasonal recruitment is more likely to be the driver of fluctuations in relation to the flood pulse. We postulate that pleuston communities are buffered against possible detrimental effects of flood pulses.     

The Significance of Meander Restoration for the Hydrogeomorphology and Recovery of Wetland Organisms in the Kushiro River,a Lowland River in Japan

The meanders and floodplains of the Kushiro River were restored in March 2011. A 1.6‐km stretch of the straightened main channel was remeandered by reconnecting the cutoff former channel and backfilling the straightened reach, and a 2.4‐km meander channel was restored. Additionally, flood levees were removed to promote river–floodplain interactions. There were four objectives of this restoration project: to restore the in‐stream habitat for native fish and invertebrates; to restore floodplain vegetation by increasing flooding frequency and raising the groundwater table; to reduce sediment and nutrient loads in the core wetland areas; to restore a river–floodplain landscape typical to naturally meandering rivers. In this project, not only the natural landscape of a meandering river but also its function was successfully restored. The monitoring results indicated that these goals were likely achieved in the short term after the restoration. The abundance and species richness of fish and invertebrate species increased, most likely because the lentic species that formerly inhabited the cutoff channel remained in the backwater and deep pools created in the restored reach. In addition, lotic species immigrated from neighboring reaches. The removal of flood levees and backfilling of the formerly straightened reach were very effective in increasing the frequency of flooding over the floodplains and raising the water table. The wetland vegetation recovered rapidly 1 year after the completion of the meander restoration. Sediment‐laden floodwater spread over the floodplain, and approximately 80–90% of the fine sediment carried by the water was filtered out by the wetland vegetation.     

Stream–floodplain connectivity and fish assemblage diversity in the Champlain Valley, Vermont, U.S.A.

To evaluate the influence of main channel–floodplain connectivity on fish assemblage diversity in floodplains associated with streams and small rivers, fish assemblages and habitat characteristics were surveyed at 24 stream reaches in the Champlain Valley of Vermont, U.S.A. Fish assemblages differed markedly between the main channel and the floodplain. Fish assemblage diversity was greatest at reaches that exhibited high floodplain connectivity. Whereas certain species inhabited only main channels or floodplains, others utilized both main channel and floodplain habitats. Both floodplain fish α-diversity and γ-diversity of the entire stream corridor were positively correlated with connectivity between the main channel and its floodplain. Consistent with these results, species turnover (as measured by β-diversity) was negatively correlated with floodplain connectivity. Floodplains with waterbodies characterized by a wide range of water depths and turbidity levels exhibited high fish diversity. The results suggest that by separating rivers from their floodplains, incision and subsequent channel widening will have detrimental effects on multiple aspects of fish assemblage diversity across the stream–floodplain ecosystem.     

Ichthyoplankton transport in relation to floodplain width and inundation and tributary creek discharge in the lower Savannah River of Georgia and South Carolina

We report the results of a 3-year study of ichthyoplankton in the lower Savannah River and its coastal plain tributaries. Sampling was weekly from February through July in 1983, 1984 and 1985. Ichthyoplankton transport was used as an estimate of ichthyoplankton production. Ichthyoplankton transport in the river, for both total and most common taxa, was highest in 1983 and lowest in 1985. Ichthyoplankton transport into the river from tributary streams was also highest in 1983 and lowest in 1985. Ichthyoplankton transported from these tributaries sometimes comprised a significant percent of the larval transport at the next river station downstream from the tributary mouth. The highest larval transport occurred when the spring flood pulse was most elevated for the longest time, and larval transport at particular river stations or creeks was correlated with floodplain width in 1983 and 1984, years when flood pulses were high enough so that the adjacent floodplain was inundated during or following spawning. In 1985 the flood pulse was brief, inundation levels were low, and inundation occurred in February before most fish had spawned. Except for American shad and sunfishes, larval transport for all common taxa was greatly reduced in 1985 compared to 1983.     

Seasonal variation in diet and trophic relationships within the fish communities of the lower Slave River, Northwest Territories, Canada

Increased industrial activities on the Peace and Athabasca River systems have raised concerns about cumulative impacts on fish and water resources downstream, in the Slave River of Alberta and the Northwest Territories, Canada. Because very little information was available on the fish communities in this system, we examined spatial and temporal patterns of diet for nine species (four piscivores and five invertebrate feeders) from three different types of habitat along the lower Slave River system and assessed trophic relationships within the communities. All actively feeding species exhibited seasonal variations in diet within and among the study areas. Dietary overlap was generally low throughout all seasons and locations. In the lower Slave River and its major tributary, the Salt River, substantial dietary overlap between piscivores (particularly walleye, Stizostedion vitreum), and invertebrate feeders occurred in the spring. In the summer no overlap occurred as walleye shifted to a more piscivorous diet, attaining a moderate degree of overlap with northern pike, Esox lucius. Compared with the Slave River, which is a large but homogeneous system upstream of its delta at Great Slave Lake, there was a greater diversity of actively feeding invertebrate feeders in the Salt River. Three of the latter were benthic feeders exhibiting moderate degrees of diet overlap during spring and summer. During the fall, few fish were feeding. Most fishes in the lower Slave River system are generalist, opportunistic feeders, consuming a number of different prey, the importance of which varies spatially and seasonally, as the abundance of these prey varies in the environment.     

Significance of a floodplain in the formation of fish communities in small rivers of Ryazan oblast

In total, 37 fish species from 30 genera and 10 families are registered in small rivers of the Ryazan oblast. In addition to other significant factors, the floodplain width is important for the formation of species structure of fish communities. In the rivers with small floodplains (less than 0.2 km in width), mainly small and short-lived fishes are represented in the catches. In the rivers or in their parts with wide floodplains (0.2–0.5 km), the dominant complex (in addition to short-lived fish species) includes roach Rutilus rutilus and/or perch Perca fluviatilis. In the rivers with wider floodplains (more than 0.5 km), long-lived phytophils represented by mainly the limnophilous group prevail.     

Estimation of minimum area requirement of river‐connected lakes for fish diversity conservation in the Yangtze River floodplain

Aim Hydrological disconnection of floodplains from rivers is among the top factors threatening river‐floodplain ecosystems. To keep enough floodplain area is of great importance to biodiversity conservation. In the Yangtze River floodplain, most lakes were disconnected from the mainstream by dams in 1950–1970s. By analysing fish diversity data, we aim at determining the effects of river‐lake disconnection on fish diversity, at estimating the minimum protected area of river‐connected lakes and at proposing a holistic strategy for fish conservation in the mid‐lower reaches of the river. Location The Yangtze River floodplain, China. Methods We collected recorded data of fish diversity of 30 Yangtze floodplain lakes. Species–area relationships were analysed and compared between river‐connected and river‐disconnected lakes. Cumulative species–area models were constructed to estimate the minimum protected area of river‐connected lakes. Results River‐lake disconnection reduced fish diversity of Yangtze lakes by 38.1%, so that the river‐connected lakes play an important role in maintaining the floodplain biodiversity. The minimum protected area of river‐connected lakes was estimated to be 14,400 km². Therefore, we should not only protect the existent connected lakes of 5500 km², but also reconnect disconnected lakes of at least 8900 km² in the Yangtze basin. Main conclusions Species–area relationships are of importance in reserve design. We suggest that cumulative species–area model might be more suitable for ecosystems with high connectivity among regions such as floodplains. As the Yangtze River floodplain is an integrative ecosystem, we suggest establishing a holistic nature reserve in the mid‐lower basin for effective conservation of biodiversity.     

Macroinvertebrate community composition and diversity in ephemeral and perennial ponds on unregulated floodplain meadows in the UK

Ponds are common and abundant landscape features in temperate environments, particularly on floodplains where lateral connectivity with riverine systems persists. Despite their widespread occurrence and importance to regional diversity, research on the ecology and hydrology of temperate ephemeral and perennial floodplain ponds lags behind that of other shallow waterbodies. This study examines the aquatic macroinvertebrate diversity of 34 ponds (20 perennial and 14 ephemeral) on two unregulated riverine floodplain meadows in Leicestershire, UK. Perennial ponds supported nearly twice the diversity of ephemeral ponds. Despite frequent inundation of floodwater and connectivity with other floodplain waterbodies, ephemeral ponds supported distinct invertebrate communities when compared to perennial ponds. When the relative importance of physical, chemical, biological and spatial characteristics was examined, physical and chemical characteristics were found to account for more variation in community composition than biological or spatial variables. The results suggest that niche characteristics rather than neutral colonisation processes dominate the structure of invertebrate communities of floodplain ponds. The maintenance of pond networks with varying hydroperiod lengths and environmental characteristics should be encouraged as part of conservation management strategies to provide heterogeneous environmental conditions to support and enhance aquatic biodiversity at a landscape scale.     

Otolith trace element and stable isotopic compositions differentiate fishes from the Middle Mississippi River, its tributaries, and floodplain lakes

Naturally occurring stable isotope and trace elemental markers in otoliths have emerged as powerful tools for determining natal origins and environmental history of fishes in a variety of marine and freshwater environments. However, few studies have examined the applicability of this technique in large river-floodplain ecosystems. This study evaluated otolith microchemistry and stable isotopic composition as tools for determining environmental history of fishes in the Middle Mississippi River, its tributaries, and floodplain lakes in Illinois and Missouri, USA. Fishes were collected from 14 sites and water samples obtained from 16 sites during summer and fall 2006 and spring 2007. Otolith and water samples were analyzed for stable oxygen isotopic composition (δ¹⁸O) and concentrations of a suite of trace elements; otoliths were also analyzed for carbon isotopic composition (δ¹³C). Tributaries, floodplain lakes, and the Mississippi and Lower Missouri Rivers possessed distinct isotopic and elemental signatures that were reflected in fish otoliths. Fish from tributaries on the Missouri and Illinois sides of the middle Mississippi River could also be distinguished from one another by their elemental and isotopic fingerprints. Linear discriminant function analysis of otolith chemical signatures indicated that fish could be classified back to their environment of capture (Mississippi River, floodplain lake, tributary on the Illinois or Missouri side of the Mississippi River, or lower Missouri River) with 71–100% accuracy. This study demonstrates the potential applicability of otolith microchemistry and stable isotope analyses to determine natal origins and describe environmental history of fishes in the Middle Mississippi River, its tributaries, and floodplain lakes. The ability to reconstruct environmental history of individual fish using naturally occurring isotopic markers in otoliths may also facilitate efforts to quantify nutrient and energy subsidies to the Mississippi River provided by fishes that emigrate from floodplain lakes or tributaries.     

Just add water: sources of chironomid drift in a large river floodplain

Although seasonal floodplains represent one of the most dynamic and productive of aquatic ecosystems, the sources of this productivity are poorly understood. We examined composition and sources of chironomid drift in the Yolo Bypass, the primary floodplain of the Sacramento River. We found that invertebrate drift during winter floodplain inundation is dominated by a single species, the newly identified chironomid Hydrobaenus saetheri (Diptera: Chironomidae). In order to determine sources of chironomids in the Yolo Bypass, invertebrates were sampled from several potential sources prior to and during initial floodplain inundation. Rehydration of dried floodplain sediments from several locations showed that H. saetheri dominated insect emergence from this colonization pathway. By contrast, H. saetheri was not a substantial component of inundated floodplain ponds or of tributary inputs to the floodplain. We conclude that the initial pulse of invertebrate abundance in Yolo Bypass floodwaters is dominated by chironomid emergence from sediments in multiple regions of the floodplain. Handling editor: S. Declerck     

Effects of hydroperiod and predation on a Mississippi River floodplain invertebrate community

 The objective of this study was to determine if pond permanence and vertebrate predation (by fish and waterfowl) affect invertebrate community structure in the mudflat habitat of floodplain ponds. Invertebrate communities were studied for 1 year in four Mississippi River floodplain ponds with different hydroperiods. Pond 1 experienced five dry periods, pond 2 experienced four, pond 3 dried once, and standing water remained in pond 4 for the entire year. Vertebrate predator exclusion treatments (all access, no access, small-fish access and cage controls) were placed in all ponds. As pond duration increased, predatory invertebrate richness and abundance increased while overall invertebrate richness and abundance decreased. With the exception of the cladoceran Diaphanosoma, all commonly encountered taxa were strongly affected by pond permanence in terms of abundance, biomass and, generally, individual biomass. Taxa were nearly early divided between those that were more abundant in less permanent ponds and those that were more abundant in longer-duration ponds. Invertebrate taxa richness, abundance, and total biomass were lower in the all-access treatment than in the treatments that restricted predator access, and these effects were stronger in the more permanent ponds. In general, there were no significant differences in responses to the treatments with small-fish access and no access. These results support models that predict relatively weak effects of predation in frequently disturbed habitats. Received: 30 May 1995 / Accepted: 21 June 1996     

Ordination of breeding birds in relation to environmental gradients in three southeastern United States floodplain forests

We used an ordination approach to identify factors important to the organization of breeding bird communities in three floodplains: Cache River, Arkansas (AR), Iatt Creek, Louisiana (LA), and the Coosawhatchie River, South Carolina (SC), USA. We used 5-min point counts to sample birds in each study area each spring from 1995 to 1998, and measured ground-surface elevations and a suite of other habitat variables to investigate bird distributions and community characteristics in relation to important environmental gradients. In both AR and SC, the average number of Neotropical migrant species detected was lowest in semipermanently flooded Nyssa aquatica Linnaeus habitats and greatest in the highest elevation floodplain zone. Melanerpes carolinus Linnaeus, Protonotaria citrea Boddaert, Quiscalus quiscula Linnaeus, and other species were more abundant in N. aquatica habitats, whereas Wilsonia citrina Boddaert, Oporornis formosus Wilson, Vireo griseus Boddaert, and others were more abundant in drier floodplain zones. In LA, there were no significant differences in community metrics or bird species abundances among forest types. Canonical correspondence analyses revealed that structural development of understory vegetation was the most important factor affecting bird distributions in all three study areas; however, potential causes of these structural gradients differed. In AR and SC, differences in habitat structure were related to the hydrologic gradient, as indexed by ground-surface elevation. In LA, structural variations were related mainly to the frequency of canopy gaps. Thus, bird communities in all three areas appeared to be organized primarily in response to repeated localized disturbance. Our results suggest that regular disturbance due to flooding plays an important role in structuring breeding bird communities in floodplains subject to prolonged inundation, whereas other agents of disturbance (e.g., canopy gaps) may be more important in headwater systems subject to only short-duration flooding. Management for avian community integrity in these systems should strive to maintain forest zonation and natural disturbance regimes.     

Input, movement and exchange of organic matter within a subtropical coastal black water river-flood plain system

SUMMARY. 1. Inputs, movements and exchanges of particulate organic matter were measured on two contrasting floodplains of the Ogeechee River, Georgia, U.S.A. A model, which incorporated measurements of standing crop, respiration, litterfall, inundation, and litter processing rates, was used to estimate annual exchanges of organic matter between the river and floodplains.
2. Annual litterfall was higher on the East floodplain than on the lower elevation West floodplain (902 v. 784 g ash-free-dry-mass [AFDM] m⁻²).
3. Experiments with tagged leaves and sticks demonstrated that litter was readily displaced during floods. The distance and direction of displacement varied within and between floodplains but tended to be higher closer to the river and was generally parallel to the river.
4. The model indicated that both floodplains lost organic matter to the river. The lower elevation floodplain (East) lost more organic matter to the river (208 g AFDM m⁻² year⁻¹) than did the higher elevation (West) floodplain (79g AFDM m⁻² year⁻¹).
5. Inputs of organic matter from the floodplain to the river exceeded the amount of litterfall typically entering heavily forested high gradient headwater streams (5.5 v. 0.4-0.6 kg AFDM m⁻² year⁻¹).
6. Floodplain organic matter inputs may exert a greater influence upon structure and function within these streams than do upstream inputs or primary production. Consequently, current conceptualizations of stream structure and function need to be modified to account for the effects of floodplain inputs on stream channel processes within large, low-gradient rivers.     

Comparing the fish assemblages and food‐web structures of large floodplain rivers

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