The Interplay between Environmental Conditions and Filamentous Algae Mat Formation in Two Agricultural Influenced South African Rivers

The regulation of nutrient inputs into rivers dominated by agriculture land use activities is an important aspect of ecological resilience of aquatic systems and the management of river eutrophication. The overabundance of benthic filamentous algae mats in river systems due to nutrient enrichment can modify the habitats of macroinvertebrate and fish communities as well as clogging irrigation crop sprayers of downstream water users. The current study examined over a period of 2 years (2013–2014) the interplay between physical and chemical river characteristics and epilithic filamentous algae biomass in two South African agricultural influenced rivers. The study area consisted of the Touw and Duiwe Rivers, which run into a proclaimed Ramsar site, namely, the Wilderness Lake System. A strong positive correlation was observed between the maximum filamentous algae biomass (97 chl‐a mg m^?2) observed during the dry season and the average water column alkalinity >30 mg l^?1. The benthic trophic status of the nine sampling sites during the dry seasons indicated the highest benthic algae biomass with mesotrophic (1.7–21 chl‐a mg m^?2) to hypertrophic (>84 chl‐a mg m^?2) conditions. During the dry season, only three sampling sites were below the suggested guideline value (35 µg l^?1) for total phosphorus (TP), while four sampling sites were below the total nitrogen guideline of 252 µg l^?1. In the wet season, two sites were below TP values with five sites below total nitrogen guideline values. From the data gathered, it was evident that water column alkalinity and hardness were the main drivers for the formation or absence of benthic filamentous algae mats in the two river systems and that nitrogen and/or phosphorus concentrations was overshadowed by the physical and chemical characteristics of the river systems at certain sites. Nutrient results for the river bottom sediments revealed that the sediment qualities were variable at the different sampling sites, but more specifically along the longitudinal paths of flow. It was apparent that the high TP concentrations in the water column and bottom sediment, which were lowest during the dry season, were associated with the highest epilithic filamentous algae mat formation. The outcome of the current study shows that a more holistic approach must be followed for the development of future eutrophication guidelines and nutrient thresholds in South African rivers influenced by agriculture land use activities. Copyright © 2016 John Wiley & Sons, Ltd.     

Spatial Pattern of Phytoplankton Based on the Morphology‐Based Functional Approach along a River–Floodplain Gradient

Current efforts to yield an appropriate method that would simplify the use of phytoplankton in the ecological evaluation of freshwaters resulted in different approaches based on clustering phytoplankton organisms. In this study, we applied the morphology‐based functional group (MBFG) concept to determine the spatial changes of phytoplankton in the natural riverine floodplain of the alluvial reaches of the Danube River along the horizontal gradient from the river towards the floodplain habitats. The obtained results showed that the magnitude of environmental changes depended on alternations in hydrological variables (hydropattern and water level) that influenced changes in the physical and chemical conditions. High‐intensity flood pulses caused environmental homogenizations and nitrate enrichment of the floodplain habitats. Phytoplankton dynamics were strongly associated with the environmental changes, and using the MBFG approach, two basic hydrological conditions were identified: inundation phase dominated by diatoms (GVI) and isolation phase dominated by filamentous cyanobacteria (GIII). Total diatom biomass decreased along the floodplain gradient with a diminishing of physical constraints, and site‐specific variables became more important in favouring diatom assemblages. The different response of cyanobacterial species to mixing regime was of particular significance for species successions during bloom period. Altogether, classifying very diverse diatoms (centrics and pennates and planktonic and benthic) and cyanobacterial taxa into single groups represents a weakness of the MBFG approach, which might make it impossible to reflect all the ecological differences governed by environmental constraints along river–floodplain gradients. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of Carbon Sequestration Ability and Effect of Elevation in Fenced Wetland Plant Communities of the Xilin River Floodplains: A Model Case Study

Floodplain habitats of the Xilin River in Inner Mongolia, China, were overgrazed by sheep and cattle until fencing of the floodplains was implemented in 2000. Carbon cycling of three plant communities of differing floodplain elevation after fencing showed that biomass in low‐elevation wetlands increased fastest until reaching its maximum at 20 years in the future, while a slower increase in biomass existed in high‐elevation and ‘hummock’ wetlands. Modelling and field experiments revealed differences between the three plant communities that were primarily attributed to different elevation levels and inundation periods. This study also determined the carbon sequestration capacity of the three floodplain wetland types (0.18 kg C m^?2 year^?1 in low‐elevation wetlands, 0.09 kg C m^?2 year^?1 in high‐elevation wetlands, and 0.05 kg C m^?2 year^?1 in hummock wetlands). Copyright © 2014 John Wiley & Sons, Ltd.     

Inter‐habitat variation in the benthos of the Upper Missouri River (North Dakota,USA): implications for Great River bioassessment

We examined inter‐habitat variation in benthic macroinvertebrate assemblages in the 180‐km Garrison Reach of the Upper Missouri River, North Dakota (USA) in 2001–2003. The Garrison Reach is unchannelized with a mostly rural setting. Flows are regulated by Garrison Dam. We sampled benthos from three habitats defined a priori: channel, shoreline, and backwater. Benthic assemblages were different in each habitat. Average Bray‐Curtis dissimilarity in assemblage composition ranged from 89% for backwater versus channel habitat to 70% for backwater versus shoreline habitat. There were distinct intra‐habitat groups within a priori habitats: channel assemblages included moving‐sand assemblages and other‐substrate channel assemblages; backwater assemblages included connected (to the river channel) and unconnected backwater assemblages; shorelines assemblages varied between natural (unprotected) and riprap (rock revetment) shorelines. Abundance and taxa richness were lowest and spatial variability highest for moving‐sand channel assemblages. Abundance was highest in backwaters. Taxa richness in backwaters and along channel shorelines were similar. Assemblages in all three habitats were dominated by Nematoda, Oligochaeta and Chironomidae. Taxa in these groups comprised at least 80% of mean abundance in all three habitats. Taxa that discriminated among habitats included the psammophilic chironomid Chernovskiia for moving‐sand channel substrates versus all other habitats; Hydroptila (Trichoptera) for riprap vs natural shorelines, Aulodrilus (Oligochaeta) for connected versus unconnected backwaters; and Nematoda for backwater versus channel and shoreline versus channel. Based on overlap patterns in benthic assemblages among habitats, we concluded that sampling main channel shorelines should also capture much of the natural and stressor‐induced variation in connected backwater and channel habitat exclusive of moving‐sand channel habitat. Published in 2006 by John Wiley & Sons, Ltd.     

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.     

Scaling Down Habitat Selection by Large River Fishes to Understand Patterns Relevant to Individuals

Modification and homogenization of habitat in large‐river ecosystems have led to the reduction of >50% of native fish species. Rehabilitating these complex ecosystems to recover fish populations requires an understanding of habitat availability and selection at multiple scales. Habitat selection by river fishes is typically assessed at the functional unit scale (100–10 000 m²). For example, in large, sand‐dominated rivers of the Central USA, alluvial islands are critical functional units for endangered sturgeon. Functional units, however, can be subdivided into mesohabitats (<100 m²), but very little is known about mesohabitat selection by large river fishes. We evaluated the mesohabitat selection of the federally endangered pallid sturgeon (Scaphirhynchus albus) and more abundant shovelnose sturgeon (Scaphirhynchus platorynchus) experimentally. We tested for selection among four common mesohabitat types that are nested within alluvial island complexes: (1) sand‐only substratum with no structure; (2) sand substratum with a sand dune structure; (3) sand substratum with simulated vegetation; and (4) a gravel‐only substratum. Sturgeon selected for the sand substratum, structureless mesohabitat, followed by the mesohabitat with a sand dune. Vegetated habitat retained less sturgeon than these two habitats but more than the gravel mesohabitat. Age‐0 pallid sturgeon and shovelnose sturgeon almost completely avoided gravel substrate, perhaps because of increased energetic costs associated with turbulent benthic flow. We posit that age‐0 sturgeon may prefer the sand and sand dune habitats over the vegetation and gravel habitats because flow may be more linear (or unidirectional) and predictable in these habitat types, whereas vegetation and gravel can create substantial benthic turbulence. Lastly, shovelnose sturgeon were on average denser in vegetated habitat than pallid sturgeon. Scaled to the population level, patterns revealed here could have implications for the macro‐distribution of both species. Restoration efforts may want to consider selection differences in the management of these two species and rehabilitation of riverine habitats. Copyright © 2015 John Wiley & Sons, Ltd.     

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

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

Multi‐annual contemporary flood event overbank sedimentation within the vegetated lower Orinoco floodplain,Venezuela

Multi‐annual contemporary flood event overbank sedimentation rates were quantified on the World's third largest river in terms of discharge, the tropical lower Orinoco. We discuss the role of variables at the basin and reach scales that contributed to the complexity of spatio‐temporal overbank sediment deposition patterns. Monitored in situ plots were characterized by distance to the main channel, hydroperiod, different geomorphological units, and vegetation cover. Flood event sedimentation rates showed a high spatial variability ranging from the absence of sediment deposition up to 225.46 kg m^‐2 yr^‐1. Banks and levees received relatively high amounts of sediment (39.6 kg m^‐2 yr^‐1), whereas observed mean sedimentation rates on the more distant floodplain and backswamps tended to be lower (17.7 kg m^‐2 yr^‐1). Significant differences in sedimentation rates were observed in two major vegetation types: dense herbaceous and shrubby vegetation (42.2 kg m^‐2 yr^‐1) and floodplain forest (12.7 kg m^‐2 yr^‐1). However, overbank sedimentation patterns also reflected imbricated hydrosedimentary and biogeomorphological vegetation feedbacks that co‐construct fluvial landforms. The incidence of an El Niño–Southern Oscillation–La Niña episode during the study period on sediment availability and floodplain sedimentation suggests that within whitewater rivers, where suspended sediment concentrations are naturally high, hydrological connectivity seems to be more important for floodplain sedimentation than variations in suspended sediment concentrations. These results may provide a good basis for future biogeomorphological investigation projects using complementary methodologies, in order to better anticipate global change and fluctuations in the occurrence, strength or duration of El Niño–La Niña episodes in the tropical zone and their consequences for flood discharge and sediment dynamics during channel–floodplain exchanges.     

Recent habitat association and the historical decline of Notropis simus pecosensis

Small‐bodied, riverine minnows that historically characterized fish assemblages of Great Plains rivers in North America have declined because of river fragmentation, dewatering, river channel degradation, river salinization and nonnative species introductions. The Pecos bluntnose shiner Notropis simus pecosensis, a member of this guild, persists in one segment of the Pecos River, New Mexico, USA. We characterized habitat associations for the species at two spatial scales. In general, N. s. pecosensis associated with fluvial habitats, but velocity association depended on body size, with larger individuals using swifter habitats. All N. s. pecosensis associated with relatively low depths (3–51 cm), which were most abundant in sites with relatively wide river channels (>25 m), especially when discharge was between 0.5 and 4.0 m³ s^?1. The Pecos River sub‐segment that is occupied by the core population of N. s. pecosensis (V‐ii) had a unique combination of being buffered from direct dam effects by intervening segments and sub‐segments, high sub‐segment length, substantial sediment inputs from numerous uncontrolled tributaries, substantial base flow provided by irrigation return flows and groundwater inflows, high channel width in relation to discharge and low salinity. Although no unoccupied Pecos River segment appears to be suitable for N. s. pecosensis, habitat restoration opportunities exist within all occupied sub‐segments (V‐i, V‐ii and V‐iii) via base flow enhancement and river channel restoration. Restoration that offsets chronic effects of dams may be necessary to conserve the species. Restoration would also benefit other rare riverine minnows that coexist with N. s. pecosensis. Copyright © 2008 John Wiley & Sons, Ltd.     

Reconstruction of pristine morphology,flow, nutrient conditions and submerged vegetation of lowland river spree (Germany) from palaeomeanders

The European Water Framework Directive requires the definition of reference conditions for each type of surface waters as a base to establish a classification system in which deviations from this high quality status must be determined. In order to reconstruct pristine conditions in the lower river Spree we investigated palaeomeanders using palaeohydrological and palaeolimnological methods. The settlement history of this region suggests low anthropogenic impact for all periods before ～700 cal AD. Three palaeomeanders representing the conditions of the late Sub‐boreal/early Sub‐atlantic were investigated. River width and depth at bankfull stage were reconstructed using cross‐sections of the meanders. Based on these data and experiments on the recent river, a parametric model was developed to calculate the bankfull palaeodischarge. Reconstructions show narrower and shallower channels for the undisturbed lower Spree (～20 m mean width and 0.8 m mean depth at bankfull stage) as compared to recent conditions (35 m and 1.6 m, respectively). Flow velocities and discharge at bankfull stage have been smaller in reconstructed sub‐fossil channels (0.5 m s^?1 and 8 m³ s^?1 in the pristine lower Spree as compared to 0.9 m s^?1 and 52 m³ s^?1 in the recent lower Spree) and flow variability was higher. The increase in bankfull discharge was mainly attributed to deforestation and drainage of the catchment as well as channelization, bank protection and river regulation measures. The organic silt at the base of the sediment cores contained well‐preserved fossil diatom assemblages. Diatom‐inferred total phosphorus (DI‐TP) concentrations of 59–73 µg L^?1 (median 62 µg L^?1) indicate eutrophic to hypertrophic conditions and suggest naturally slightly lower nutrient levels than today. These past nutrient conditions, morphology and large numbers of macrofossil remains indicate optimum growth conditions for submerged macrophytes growth. The combination of palaeohydrological and palaeolimnological parameters proved to be a useful approach for the determination of pristine conditions in a lowland river. Copyright © 2008 John Wiley & Sons, Ltd.     

Fatty Acid Profiles Distinguish Channel Catfish from Three Reaches of the Lower Kaskaskia River and its Floodplain Lakes

Despite the increasing use of fatty acids (FAs) as biomarkers in aquatic food web analysis, little information is available regarding differences in FA profiles of fish among habitat types in river–floodplain ecosystems. The objectives of this study were to (i) test whether the FA profiles of channel catfish (Ictalurus punctatus) differed among three reaches of the lower Kaskaskia River and its floodplain lakes, and (ii) to compare FA profiles among muscle, liver, and adipose fin tissues collected from these fish. Profiles differed significantly among sites, especially between upper and lower river sites, and between river channel and oxbow lake sites, suggesting differences in FA availability for channel catfish occupying different habitats and river reaches in the Kaskaskia River system. Specifically, the essential FAs 18:2n‐6 and 18:3n‐3 increased in catfish tissues from upstream to downstream reaches, which could reflect increased floodplain connectivity and decreasing impoundment effects downstream. Ratios of n‐3 to n‐6 FAs were higher in fish from oxbow lakes, perhaps suggesting increased use of autochthonous production in the floodplain relative to the main river channel. Muscle and adipose fin FA profiles exhibited similar location‐related trends, whereas liver FA profiles were markedly different from the other tissue types. These results suggest that adipose fin tissue samples may be a viable, less‐invasive alternative to muscle tissue for analysis of FA profiles in channel catfish. Our study supports the use of tissue FA profiles in identifying habitat utilization by channel catfish, and perhaps habitat‐specific energy contributions to riverine consumers. Furthermore, our work highlights floodplain habitat as a potential source of essential n‐3 FA and the associated importance of maintaining river–floodplain connectivity to support aquatic food webs. Copyright © 2014 John Wiley & Sons, Ltd.     

Impacts of water resource development on hydrological connectivity of different floodplain habitats in a highly variable system

Floodplains and their associated wetlands are important features of semiarid and arid landscapes, providing habitat and refugia for native species as well as contributing to human needs for freshwater. Globally, floodplain habitats are some of the most modified ecological communities because of water resource development and land‐use changes. However, the hydrological changes that have occurred in highly variable semiarid and arid systems are rarely quantified in a way that helps us understand the consequences for different floodplain habitat types. This study investigated changes in floodplain‐river connectivity that have occurred because of water resource development on four floodplain habitat types in the Lachlan River Catchment, Australia: (a) temporary floodplain lakes, (b) intermittent river red gum (Eucalyptus camaldulensis) swamps, (c) intermittent black box (Eucalyptus largiflorens) swamps, and (d) terminal wetlands (wetlands along distributary creeks). Changes to floodplain‐river connectivity characteristics were calculated using their commence to fill thresholds and flow scenarios derived from a river hydrology model, enabling comparison of long‐term data sets (120 years) encompassing a range of climate conditions. Connection regime metrics have changed significantly in all floodplain habitats except intermittent black box swamps. Temporary floodplain lakes have experienced the greatest reduction in number of connection events (60% reduction), followed by intermittent river red gum swamps (55% reduction). Intermittent black box swamps and terminal wetlands have experienced the least change in number of connection events (35% reduction). The nature of the change in connection suggests a change in vegetation communities will occur in response to long‐term hydrological change.     

Short‐term effects in a reduced flow stretch: The case of the Antas River in South Brazil

The building of adduction channels (penstocks) that conduct water from reservoirs to turbines, which are located kilometres from the dam, is becoming common, optimizing the electricity generation in small dams. This design creates a river stretch with reduced discharge between the dam and the powerhouse. This study evaluates the short‐term impacts of the below‐dam decrease in river flow on fish assemblages. Samples were collected in the reduced flow stretch of the Castro Alves Hydropower Plant (Antas River, Rio Grande do Sul, Brazil) before the reservoir started operating (January 2008; mean discharge of 103.7 m³/s) and immediately after operation began (March 2008; mean discharge of 12.4 m³/s). Sampling was conducted in distinct habitats of the reduced flow stretch (slow waters—gillnets, sand beaches—seining nets, structured littoral—electrofishing, and fast waters—cast nets) with a strongly standardized effort. The attributes of the fish assemblages were not negatively affected by the flow reduction in any habitat sampled. However, distinct changes in the spatial structure were observed considering the different types of habitat predominantly used by the species, which represents an entire reorganization of the fish assemblages in the short term. It is fundamental that these short‐term aspects be considered in the licensing of hydropower plants in addition to the long‐term changes.     

Variability in benthic respiration in three southeastern Australian lowland rivers

Benthic respiration is an important measure of decomposition processes occurring in streams, but our understanding of benthic respiration in lowland rivers is not well developed, particularly the factors that affect benthic respiration. In our study we measured benthic respiration at three sites in three contrasting lowland rivers in southeastern Australia. On most sampling occasions, rates of oxygen consumption in benthic chambers were linear. However, oxygen consumption rates fitted exponential decay curves during periods of highest microbial activity. Benthic community respiration ranged from 289 to 619 mg O₂ m² d^?1 in the Broken River, from 178 to 1438 mg O₂ m² d^?1 in the River Murray and from 127 to 2178 mg O₂ m² d^?1 in the Ovens River. Benthic respiration was closely correlated with water temperature, but not with sediment carbon content, sediment particle size, water column nutrients or water column dissolved organic carbon concentrations. Average carbon turnover periods were between 1.7 and 6 years for the three rivers, but were as low as 0.1 year immediately following an event that gave rise to mobilization of in‐stream dissolved organic carbon, sufficient to produce coloured water. The latter occurred in the Ovens River as a consequence of a rain event during a period of base‐flow. Flow regime as such did not have a major impact on benthic community respiration. Induced changes in respiration, by altering flows, would only occur by altering the quality and timing of carbon inputs, since temperature and carbon quality, rather than quantity, appear more important in determining lowland river benthic respiration. Copyright © 2005 John Wiley & Sons, Ltd.     

Sediment chemistry and nutrient influx in a hydrologically restored bottomland hardwood forest in Midwestern USA

Exchanges of total N and C between a river and its floodplain forest have been enhanced by sedimentation processes during flood pulses at a 5‐ha bottomland hardwood forest located at the Olentangy River Wetland Research Park in central Ohio. In the spring of 2000, the forest was hydrologically restored by notching an artificial levee that had separated the Olentangy River and its floodplain forest for 100 years. One‐hundred flat sediment traps (30 cm × 30 cm) were used to collect sediment samples during spring/summer flooding events from 2003 to 2005. Results showed that sediment deposition is determined by the landscape variability during flooding events, Net sediment deposit in the wettest area averaged 134 ± 12 g‐dry wt m^?2 in 2003, 127 ± 17 g‐dry wt m^?2 in 2004 and 149 ± 23 g‐dry wt m^?2 in 2005. Total N and C sedimentation ranged from 0.49 to 0.92 g‐N m^?2 and 5.2 to 19.9 g‐C m^?2. Fe dominates the sediment chemistry and results show the elemental abundance in the order of Al > Fe > Ca > K > Mg > S > P > Na > Mn > Zn > B > Cu > Mo. A hydrologic pulsing index (HPI) could be used as an indicator for mass changes of energies with hydrologic pulsing events. Restoration of seasonally flooded bottomland forests could stimulate potentially large nutrient and Fe releases, which would eventually lead to an enhanced forest productivity and biodiversity. Copyright © 2007 John Wiley & Sons, Ltd.     

Fish assemblages and biotic integrity of a highly modified floodplain river,the Upper Mississippi,and a large,relatively unimpacted tributary,the Lower Wisconsin

The Upper Mississippi River is a dynamic floodplain river that has been largely transformed by navigational levees and dams since the 1930s. The pools upstream of each dam are lake‐like and only about the upper third of each reach retains a riverine character. In contrast, the Wisconsin River is not managed for commercial navigation and today its lower 149 km represent one of the least‐degraded large river reaches in central North America. Riverine reaches in both the Mississippi and Wisconsin rivers have similar macro‐habitats including numerous islands, large side channels, and connected backwaters and floodplain lakes. In this study, shoreline electrofishing samples were collected during summer 2002 and 2003 to characterize resident fish assemblages. We compared fish species abundance, biomass, and biotic integrity along main and side channel borders between the Upper Mississippi River and the Lower Wisconsin River. We expected that, in the absence of environmental degradation, fish composition and structure would be similar between the Mississippi and Wisconsin rivers, and between channel types within each river. Nonmetric multidimensional scaling and redundancy analysis revealed that fish species in the Mississippi River, unlike in the Wisconsin River, were characteristic of non‐riverine habitats. We consider non‐riverine fish assemblages indicative of environmental impairment. The main and side channel sites in the Mississippi River had more variable fish assemblages than the Wisconsin River. Analyses of fish index of biotic integrity scores showed that environmental condition was excellent for both channel types in the Wisconsin River, whereas in the Mississippi River the side channel was rated good and the main channel only fair. We conclude that differences between the two rivers and between channel types of the Mississippi River are consistent with direct and indirect effects of navigation. This study demonstrates the utility of a fish index of biotic integrity, an inexpensive and rapid bioassessment tool, for detecting change in ecological health on one of the world's largest rivers. Copyright © 2006 John Wiley & Sons, Ltd.     

Environmental characteristics and phytoplankton productivity of a shallow Ramsar‐site floodplain in the western Himalaya

Hokersar wetland (altitude of 1584 masl), a shallow (0.5 m) floodplain waterfowl habitat in Kashmir, India, gained international importance in 2005 with its declaration as a Ramsar site. Although isolated in the western Himalayan mountains, it is being impacted by a silt‐laden river (Doodhganga). Human activities, not the least of which is affected by the closeness of the wetland to suburban areas, have gradually altered its trophic state. Its alkaline‐ and calcium‐rich waters contain many planktonic diatoms, green algae and cyanobacteria. Nitrate–nitrogen and total phosphorus concentrations are high (370–4750 and 101–968 μg L^?1, respectively). A pronounced seasonal cycle in phytoplankton production (g C m^?2 day^?1) was evident in a minimum value of 0.38 (Jan–Feb, 2002) and a maximum value of 4.02 (July, 2002), closely paralleling the seasonal cycles of temperature and light. The photosynthetic efficiency of the wetland was highest (1.97%) during the summer. The annual phytoplankton production of this wetland ecosystem was 210 × 10² KJ m^?2, suggestive of a meso‐eutrophic status.     

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

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

INTRA‐ANNUAL VARIATION IN RIVER–RESERVOIR INTERFACE FISH ASSEMBLAGES: IMPLICATIONS FOR FISH CONSERVATION AND MANAGEMENT IN REGULATED RIVERS

While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

SPATIAL VARIATION OF STRUCTURAL AND FUNCTIONAL INDICATORS IN A LARGE NEW ZEALAND RIVER

The ecological responses of large rivers to human pressure can be assessed at multiple scales using a variety of indicators, but little is known about how the responses of ecological indicators vary over small spatial scales. We sampled phytoplankton, zooplankton and macroinvertebrates and measured river metabolism and cotton strip breakdown rates (loss in tensile strength) in contrasting habitats along a 21‐km urban‐industrial reach on a constrained section of the Waikato River, New Zealand's longest river. Rates of gross primary production (2.8–7.8 g O₂/m²/d) and ecosystem respiration (3.5–12.7 g O₂/m²/d) did not differ consistently between near‐shore (2–3 m from river side) and far‐shore (ca. 10 m from side) locations, urban and industrial reaches or between autumn and spring sampling occasions. Rates of cotton decay (?k) ranged from 0.014 to 0.112 per day and were typically faster at far‐shore locations and in the section of river receiving industrial inputs, but slower in spring compared with autumn. Nonmetric multidimensional scaling analysis of phytoplankton and zooplankton data did not reveal spatial patterns relating to pressure or location (embayment, edge, mid‐river). However, the macroinvertebrate ordination suggested distinct communities for the mid‐river benthos compared with near‐shore communities and a distinction between sites in the urban reach and the industrial reach. Our results suggest that large‐river macroinvertebrate communities and cotton decay rates can be influenced to varying degrees by reach‐scale pressures and local habitat conditions. Monitoring designs in spatially complex rivers should account for habitat heterogeneity that can lead to differences in structural and functional indicator responses. Copyright © 2012 John Wiley & Sons, Ltd.