FISH RECRUITMENT IS INFLUENCED BY RIVER FLOWS AND FLOODPLAIN INUNDATION AT APALACHICOLA RIVER,FLORIDA

High human demand for limited water resources often results in water allocation trade‐offs between human needs and natural flow regimes. Therefore, knowledge of ecosystem function in response to varying streamflow conditions is necessary for informing water allocation decisions. Our objective was to evaluate relationships between river flow and fish recruitment and growth patterns at the Apalachicola River, Florida, a regulated river, during 2003–2010. To test relationships of fish recruitment and growth as responses to river discharge, we used linear regression of (i) empirical catch in fall, (ii) back‐calculated catch, via cohort‐specific catch curves, and (iii) mean total length in fall of age 0 largemouth bass Micropterus salmoides, redear sunfish Lepomis microlophus and spotted sucker Minytrema melanops against spring–summer discharge measures in Apalachicola River. Empirical catch rates in fall for all three species showed positive and significant relationships to river discharge that sustained floodplain inundation during spring–summer. Back‐calculated catch at age 0 for the same species showed positive relationships to discharge measures, but possibly because of low sample sizes (n = 4–6), these linear regressions were not statistically significant. Mean total length for age 0 largemouth bass in fall showed a positive and significant relationship to spring–summer discharge; however, size in fall for age 0 redear sunfish and spotted sucker showed no relation to spring–summer discharge. Our results showed clear linkages among river discharge, floodplain inundation and fish recruitment, and they have implications for water management and allocation in the Apalachicola River basin. Managed flow regimes that reduce the frequency and duration of floodplain inundation during spring–summer will likely reduce stream fish recruitment. Copyright © 2012 John Wiley & Sons, Ltd.     

THE IMPORTANCE OF VARIABLE LATERAL CONNECTIVITY BETWEEN ARTIFICIAL FLOODPLAIN WATERBODIES AND RIVER CHANNELS

The rehabilitation of lowland rivers subjected to channelization and artificial levee construction should attempt to improve habitat heterogeneity and diversity of floodplain hydrological connectivity. However, rehabilitation efforts rarely consider the importance of variable lateral hydrological connectivity between floodplain waterbodies and main river channels (ranging from those permanently connected to those temporarily connected during river level rises), instead focusing on increasing individual floodplain waterbody connectivity. This study investigated the young‐of‐the‐year (YoY) fish communities in 10 artificial floodplain waterbodies of variable hydrological connectivity with the river Trent, England, between May and November 2006, inclusive. Floodplain waterbody connectivity to the main river was positively correlated with the number of species captured (alpha diversity), Shannon–Wiener diversity, Margalef's species richness index and the relative abundance of rheophilic species and negatively correlated with species turnover (beta diversity). YoY fish communities in poorly connected water bodies were most dissimilar to riverine communities. The results demonstrate the importance of variable lateral connectivity between artificial floodplain waterbodies and main river channels when rehabilitating lowland river fish communities. Copyright © 2011 John Wiley & Sons, Ltd.     

PAST AND PREDICTED FUTURE CHANGES IN THE LAND COVER OF THE UPPER MISSISSIPPI RIVER FLOODPLAIN,USA

This study provides one historical and two alternative future contexts for evaluating land cover modifications within the Upper Mississippi River (UMR) floodplain. Given previously documented changes in land use, river engineering, restoration efforts and hydro‐climatic changes within the UMR basin and floodplain, we wanted to know which of these changes are the most important determinants of current and projected future floodplain land cover. We used Geographic Information System data covering approximately 37% of the UMR floodplain (3232 km²) for ca 1890 (pre‐lock and dam) and three contemporary periods (1975, 1989 and 2000) across which river restoration actions have increased and hydro‐climatic changes have occurred. We further developed two 50‐year future scenarios from the spatially dependent land cover transitions that occurred from 1975 to 1989 (scenario A) and from 1989 to 2000 (scenario B) using Markov models. Land cover composition of the UMR did not change significantly from 1975 to 2000, indicating that current land cover continues to reflect historical modifications that support agricultural production and commercial navigation despite some floodplain restoration efforts and variation in river discharge. Projected future land cover composition based on scenario A was not significantly different from the land cover for 1975, 1989 or 2000 but was different from the land cover of scenario B, which was also different from all other periods. Scenario B forecasts transition of some forest and marsh habitat to open water by the year 2050 for some portions of the northern river and projects that some agricultural lands will transition to open water in the southern portion of the river. Future floodplain management and restoration planning efforts in the UMR should consider the potential consequences of continued shifts in hydro‐climatic conditions that may occur as a result of climate change and the potential effects on floodplain land cover. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.     

SEDIMENT DYNAMICS IN THE RESTORED REACH OF THE KISSIMMEE RIVER BASIN,FLORIDA: A VAST SUBTROPICAL RIPARIAN WETLAND

Historically, the Kissimmee River Basin consisted of a broad nearly annually inundated riparian wetland similar in character to tropical Southern Hemisphere large rivers. The river was channelized in the 1960s and 1970s, draining the wetland. The river is currently being restored with over 10 000 hectares of wetlands being reconnected to 70 river km of naturalized channel. We monitored riparian wetland sediment dynamics between 2007 and 2010 at 87 sites in the restored reach and 14 sites in an unrestored reference reach. Discharge and sediment transport were measured at the downstream end of the restored reach. There were three flooding events during the study, two as annual flood events and a third as a greater than a 5‐year flood event. Restoration has returned periodic flood flow to the riparian wetland and provides a mean sedimentation rate of 11.3 mm per year over the study period in the restored reach compared with 1.7 mm per year in an unrestored channelized reach. Sedimentation from the two annual floods was within the normal range for alluvial Coastal Plain rivers. Sediment deposits consisted of over 20% organics, similar to eastern blackwater rivers. The Kissimmee River is unique in North America for its hybrid alluvial/blackwater nature. Fluvial suspended‐sediment measurements for the three flood events indicate that a majority of the sediment (70%) was sand, which is important for natural levee construction. Of the total suspended sediment load for the three flood events, 3%–16% was organic and important in floodplain deposition. Sediment yield is similar to low‐gradient rivers draining to the Chesapeake Bay and alluvial rivers of the southeastern USA. Continued monitoring should determine whether observed sediment transport and floodplain deposition rates are normal for this river and determine the relationship between historic vegetation community restoration, hydroperiod restoration, and sedimentation. Published in 2011 by John Wiley & Sons, Ltd.     

TRACING GROUNDWATER DISCHARGE IN THE FLOODPLAIN OF THE PARANA RIVER,ARGENTINA: IMPLICATIONS FOR ITS BIOLOGICAL COMMUNITIES

Groundwater discharge can be an important determinant of the functioning of aquatic environments and their associated biological communities. However, the presence and the importance of groundwater have not been considered in the Parana River floodplain owing to the large quantity of surface water. The present study aimed to identify groundwater discharge conditions in a sector of the middle of the floodplain of the Parana River by studying groundwater flow systems. Eight piezometers were installed to record groundwater movement in the vertical plane weekly for 2 years. Water samples were collected in piezometers, domestic wells, the river and other water bodies to study the groundwater flow systems. Rising of the water level during piezometer installation and recording suggested that the study zone represents groundwater discharge conditions. Residence time proxy allowed identification of local flows and intermediate flows. Local rainfall (in Santa Fe) showed an isotopic signature (δD and δ¹⁸O) similar to some local flows detected in the study zone, and this suggested local recharge. The chemical characteristics of an intermediate flow suggest that water would have travelled from a recharge area ~30 km from the study zone. Local rainfall and the intermediate flow have different isotopic signature. Results suggest that the willow forest is associated with the recharge area of a local flow, which plurispecific‐canopy forest is related to a transit area of a semi‐intermediate flow, and that tall grassland and marshy community colonize discharge areas of local and intermediate flows, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

FISH ASSEMBLAGES RESPOND TO HABITAT AND HYDROLOGY IN THE WABASH RIVER,INDIANA

Detailed relationships between fish assemblages and habitat and hydrology variation are largely unknown for large rivers. We evaluated hydrology, habitat variation and fish assemblages at 28 sites on the Wabash River, Indiana, USA, during 2005–2008. We calculated hydrologic variation with the Indicators of Hydrologic Alteration software and tested for temporal hydrologic effects on habitat variation of substrate particle size, water depth and water velocity by reducing data into principal component axes that were tested for differences among years with ANOVAs. We then tested for effects of habitat and hydrology variation on fish assemblages with canonical correspondence analysis. These analyses showed significant relationships between hydrologic variation and local habitats, and hydrology and habitat variables had significant relationships with fish assemblage structure. Our Mantel tests resulted in significant concordance among hydrology, local habitat variation and fish assemblage structure, suggesting associations of these variables. These results supported strong connections for hydraulic control over habitat variation and subsequent effects on fish assemblages. Copyright © 2011 John Wiley & Sons, Ltd.     

HYDROLOGIC CONNECTIVITY OF FLOODPLAINS,NORTHERN MISSOURI—IMPLICATIONS FOR MANAGEMENT AND RESTORATION OF FLOODPLAIN FOREST COMMUNITIES IN DISTURBED LANDSCAPES

Hydrologic connectivity between the channel and floodplain is thought to be a dominant factor determining floodplain processes and characteristics of floodplain forests. We explored the role of hydrologic connectivity in explaining floodplain forest community composition along streams in northern Missouri, USA. Hydrologic analyses at 20 streamgages (207–5827 km² area) document that magnitudes of 2‐year return floods increase systematically with increasing drainage area whereas the average annual number and durations of floodplain‐connecting events decrease. Flow durations above the active‐channel shelf vary little with increasing drainage area, indicating that the active‐channel shelf is in quasi‐equilibrium with prevailing conditions. The downstream decrease in connectivity is associated with downstream increase in channel incision. These relations at streamflow gaging stations are consistent with regional channel disturbance patterns: channel incision increases downstream, whereas upstream reaches have either not incised or adjusted to incision by forming new equilibrium floodplains. These results provide a framework to explain landscape‐scale variations in composition of floodplain forest communities in northern Missouri. Faust ( 2006 ) had tentatively explained increases of flood‐dependent tree species, and decreases of species diversity, with a downstream increase in flood magnitude and duration. Because frequency and duration of floodplain‐connecting events do not increase downstream, we hypothesize instead that increases in relative abundance of flood‐dependent trees at larger drainage area result from increasing size of disturbance patches. Bank‐overtopping floods at larger drainage area create large, open, depositional landforms that promoted the regeneration of shade‐intolerant species. Higher tree species diversity in floodplains with small drainage areas is associated with non‐incised floodplains that are frequently connected to their channels and therefore subject to greater effective hydrologic variability compared with downstream floodplains. Understanding the landscape‐scale geomorphic and hydrologic controls on floodplain connectivity provides a basis for more effective management and restoration of floodplain forest communities. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

DYNAMICS OF IN‐STREAM WOOD AND ITS IMPORTANCE AS FISH HABITAT IN A LARGE TROPICAL FLOODPLAIN RIVER

The recruitment of wood from the riparian zone to rivers and streams provides a complex habitat for aquatic organisms and can influence both aquatic biodiversity and ecosystem function. The Daly River in the wet–dry tropics of northern Australia is a highly seasonal, perennially flowing sand‐bed river where surveys of river wood aggregations at the reach scale (~2 km) in 2008 and 2009 recorded densities of 37–78 km^?1 and identified distinct types of river wood aggregations: key pieces, standing trees, fallen trees, wrack and single pieces. After larger than average flows in the 2008/2009 wet season, between 46% and 51% of the surveyed river wood had moved. The distribution of wood age classes indicated continual recruitment and slow turnover of wood within the river. Surveys of fish and habitat characteristics at the mesohabitat scale (~100 m) showed fish species richness; diversity and fish abundance were not correlated to the proportion of wood present. Fish assemblage structure was associated with wood cover as well as other environmental variables such as stream width and depth. The importance of in‐stream wood also varied for different species and age classes of fish. This study documents the dynamic nature of river wood aggregations and their complex and variable distribution and suggests their importance as fish habitat in this tropical river. Copyright © 2012 John Wiley & Sons, Ltd.     

SPATIAL RELATIONS OF TOPOGRAPHY,LITHOLOGY AND WATER QUALITY IN A LARGE RIVER FLOODPLAIN

Floodplains exert important controls on water and nutrient processing, yet spatial heterogeneities in floodplain characteristics result in variable effectiveness. In this study, we evaluated the spatial relations among topographic, lithologic and water quality features within the Cedar River floodplain located in southeastern Iowa. Floodplain topography and lithology were dominated by a series of sandy ridges and fine‐textured swales typical of a natural meandering river floodplain complex. Groundwater sampling results from 10 monitoring wells placed in representative ridge and swale environments indicated that water quality varied systematically. Beneath sand‐dominated ridges, water was aerobic and had low specific conductance, and higher concentration of NO₃–N and lower concentrations of PO₄–P and dissolved organic carbon (DOC). Groundwater beneath swales was anaerobic and typified by high specific conductance, and higher concentrations of NH₄–N, PO₄–P and DOC. We extrapolated the results from point measurements to the entire floodplain area using surface geophysics and light detection and ranging using co‐kriging to map the distribution of groundwater geochemical environments at the study site. Results are seen to provide an approach to better predict shallow groundwater quality in large river floodplains and improve our ability to manage ecosystem services in these strategic locations. Copyright © 2011 John Wiley & Sons, Ltd.     

THE INFLUENCE OF HYDROLOGICAL CONNECTIVITY ON FOOD WEB STRUCTURE IN FLOODPLAIN LAKES

Hydrological connectivity is an important driver of ecosystem structure in floodplain rivers; however, little is known of how hydrological connectivity affects the structure and functioning of food webs in these systems. This study examines aquatic food web structure in 10 floodplain lakes on a dryland river floodplain in eastern Australia across a connectivity gradient. Results for fishes suggest that benthic carbon sources are more important in high connectivity billabongs than in low connectivity billabongs and that pelagic sources are more important in low connectivity billabongs than in high connectivity billabongs. Fishes in less connected billabongs were also found to feed at higher trophic levels than in more connected billabongs. We hypothesize that in high connectivity billabongs, where suitable benthic primary sources are abundant, common fish species such as carp and bony bream feed as detritivores or herbivores; while in low connectivity billabongs, where benthic sources are less abundant, the same species feed as planktivores, insectivores or piscivores. This dietary difference may also be promoted by greater predation efficiency in less structurally complex low connectivity billabongs. The feeding behaviour of these fish species subsequently influences the trophic positions of fishes higher in the food chain and ultimately the total food chain lengths that high and low connectivity billabongs support. The results of this study highlight the importance of hydrological connectivity to the structure of food webs in these systems and the potential for them to be affected by water resource development. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

SPATIAL AND TEMPORAL PATTERNS OF NITRIFICATION RATES IN FORESTED FLOODPLAIN WETLAND SOILS OF UPPER MISSISSIPPI RIVER POOL 8

Overbank flooding is thought to be a critical process controlling nitrogen retention and cycling. Yet, studies aimed at quantifying these effects, specifically nitrification, are relatively few. In this study, we investigated the effects of season and flood frequency on soil nitrification rates in forested floodplains of Upper Mississippi River, Pool 8. Samples were collected from three plots within each site in April, August and November 2006. Plots were equally divided among three flood frequency categories as follows: rare, moderate and frequent based on elevation and flood probability model. We found a significant difference in nitrification rates among flood frequency categories as follows: rare > moderate > frequent (F = 4.49, p < 0.01) and over season: spring > summer > autumn (F = 8.88, p < 0.01). Regression for all samples showed that elevation, NH₄‐N, bulk density and soil temperature explained a moderate amount of variation in nitrification rates (R² = 0.29, p < 0.01). Models for moderately flooded, spring, summer and autumn samples improved when analysed individually. The absence of a correlation between nitrification rates and hydrology limits our ability to predict rates based on hydrology alone. The model based on elevation and season allows us to estimate nitrification rates with moderate confidence (R² = 0.27, p < 0.01). A rough calculation of forest floodplain nitrification rates suggests that 473 mt of NO₃‐N are produced annually, about 0.5% of Pool 8 total annual NO₃‐N budget. Copyright © 2013 John Wiley & Sons, Ltd.     

EVALUATION OF RIPARIAN HABITAT RESTORATION IN A LOWLAND RIVER

For many years, navigable lowland rivers have been embanked artificially or suffered from substantial shipping wave action, leading to habitat degradation. Recently, riparian habitats were restored by creating foreshores and spawning grounds in the river Yser, a lowland river in Flanders, Belgium. The aim of this paper was to evaluate the role of these restored habitats for spawning and nursery of juvenile fish. To cover a wide range of anthropogenic disruption, four riparian mesohabitat types were selected and compared, ranging from semi‐natural over artificial spawning grounds and foreshores to artificial embankments. Juvenile fish were subjected to sampling by using electrofishing between June and September 2009 at different microhabitats located in five sites of each riparian mesohabitat type. Juvenile fish strongly preferred natural riparian habitats, whereas artificial embankments showed the lowest species richness, abundance and functional organization of juvenile fish species. Restored riparian habitats appeared to be an appropriate alternative for artificial embankments in navigable lowland rivers but still score significantly less than natural habitats. Juvenile fish avoided bare microhabitats but did not prefer any other microhabitat type (reed, woody or grassy vegetation), emphasizing the importance of microhabitat diversity. This paper provides valuable insights into riparian habitat restoration to river managers and stakeholders. Copyright © 2011 John Wiley & Sons, Ltd.     

MACROINVERTEBRATE COMMUNITIES OF THE DOUBS RIVER PRIOR TO COMPLETION OF THE RHINE–RHONE CONNECTION

The Rhine–Rhône connection project concerns the part of the Doubs River between Montbéliard and Dôle (France), i.e. downstream from the confluence of the Allan River. In order to update our knowledge of the benthic macroinvertebrate communities of the Doubs River, three types of aquatic environments of this hydrosystem were sampled (main channel, backwaters and the Freycinet canal). Hydraulic characteristics are the most explanatory environment variables of lotic macroinvertebrate distribution of the Doubs hydrosystem. The aquatic fauna of the Doubs River is varied due to the diversity of biotopes, microhabitats and current velocities. The lotic aspect is well defined. Rheophilic taxa are present in the main stream in riffle areas or located downstream from weirs where the current velocity is rapid (>75 cm s⁻¹). The physics of flow (‘stream hydraulics’) create the richness of habitats and thereby the biological diversity. Backwaters have a relatively high richness, similar to that of stations in the main stream located in the same sector. Conservation management must be oriented towards the present ecological situation of the Doubs River, i.e. that of a lotic ecosystem with active connections with its backwaters. The primary goal from a conservation perspective must be the maintenance and the improvement of areas highly sensitive to disturbances.     

ASSESSMENT OF CONSEQUENCES OF SEDIMENT DEFICIT ON A GRAVEL RIVER BED DOWNSTREAM OF DAMS IN RESTORATION PERSPECTIVES: APPLICATION OF A MULTICRITERIA,HIERARCHICAL AND SPATIALLY EXPLICIT DIAGNOSIS

As regards river restoration, it is fundamental to better link human pressures and environmental responses and to take into consideration not only target species or habitat but diverse ecological elements. This permits to assess sustainable restoration plan, especially concerning sediment augmentation below dams. The use of a hierarchical multicriteria approach on the Ain River permits us to assess a diagnosis of sediment deficit impact integrating several morphological (channel shifting, river bed degradation and river bed coarsening) and ecological components (Riparian and floodplain lake and fish communities). Our diagnosis also integrates a temporal and spatial approach better to link human pressures and environmental responses and to identify the dam effects amongst other drivers (e.g. grazing decline and channel regulation). The results confirm causality links between sediment deficit and slight channel bed degradation (0.01 m.year^?1) or channel bed paving and thus highlight the impact of the dam on the drying of the riparian forest and on former channel community. However, the relationship between incision and reduction in active channel lateral mobility is more difficult to establish. The role of sediment deficit in the current variability of the riparian regeneration capacity and, thereby, landscape diversity along the lower valley remains unclear. This study also confirms the relevance of using different ecological indicators, notably because all components present different adjustment time scales, whereas some of them are more sensitive to other impacts. Copyright © 2013 John Wiley & Sons, Ltd.     

PATTERNS OF FISH PASSAGE IN THE UPPER MISSISSIPPI RIVER

Dams have been implicated in the alteration of natural river processes. Quantifying spatial and temporal movement and passage patterns of large river fishes are critical for determining the extent of restricted passage and the needs for fish passage improvements. However, limited information regarding this topic exists because of the inherent difficulties associated with large river systems and assumptions associated with movement studies. Because of this lack of information, we investigated broad scale passage patterns of several riverine fish species through seven locks and dams complexes of the Upper Mississippi River using telemetry. Over the course of our 5‐year evaluation, we observed species‐specific movement and passage patterns, and how these trends were affected by factors such as water level and lock and dam management. Stationary receivers placed in a monitoring array detected a total of 1036 passage events. Eighty‐four percent of the passage occurred through all but one of the lock and dam structures during both open and closed river conditions. While 70% of the passage occurred during open river conditions, further investigation of passages that occurred during closed river conditions (when gates are extended into the water column at some level) revealed that the majority of passage occurred when the average opening for all gates ranged from 0.6 to 1.2 m. Lock usage was also quantified, and most species were not routinely using the lock chambers for passage. Ultimately, these data have shown that individuals of each study species were able to negotiate most of the locks and dams during open and closed river conditions in both directions. Copyright © 2013 John Wiley & Sons, Ltd.     

POTENTIAL FOR VEGETATION‐BASED RIVER MANAGEMENT IN DRYLAND,SALINE CATCHMENTS

The approaches used to manage rivers have been developed and adapted to many different problems and settings. Because of their relatively low cost, vegetation‐based approaches implemented at the reach, landholder and catchment scales have become the foundation for river management in most landscapes. In many dryland agricultural catchments, secondary (anthropogenic) salinity caused by clearing native vegetation has resulted in rising saline groundwater, streamflow salinity values that exceed seawater and severe the degradation of riparian vegetation communities. The potential effectiveness of vegetation‐based strategies in these landscapes remains largely unknown, yet these strategies are still widely pursued. This study initially investigated the patterns of vegetation recovery and recolonization following a large flood in a saline river that disturbed the system. A conceptual model was developed to describe spatial patterns of where different vegetation types had regrown and recovered in relation to controls exerted by streamflow salinity, surface texture characteristics, topography and reach morphology. Using this model, vegetation‐based river management options for different reaches were developed, and their potential effectiveness in stabilizing reaches was investigated using a 1‐D hydraulic modelling approach. This study finds that in a dryland catchment with high stream salinity (20 000–93 000 mg L^?1), there is still a strong potential for successful vegetation‐based management, but only in selected reaches. Results showed that changes in stream power and channel velocity were not associated with the areas of most severe vegetation degradation. Rather, there is a complex interplay between channel morphology, channel slope and places of potential vegetation growth within a reach. This paper outlines an approach to evaluate the potential success of vegetation‐based river management in saline landscapes. It identifies the need to prioritize investment based on the following: an understanding of factors controlling revegetation potential, the likely impact of revegetation in mitigating adverse channel changes and the proximity of reaches to high‐value infrastructure and biodiversity assets. Copyright © 2011 John Wiley & Sons, Ltd.     

UPPER HUDSON RIVER ESTUARY (USA) FLOODPLAIN CHANGE OVER THE 20TH CENTURY

Detailed surveys of the upper Hudson River Estuary and its floodplain from the early 1900s and digital mapping of the same areas today provide an opportunity to evaluate changes over the 20th century. This study uses a geographic information system to quantitatively compare water areas and islands mapped by the United States Army Corps of Engineers in 1907 and 1911 along an approximately 60‐km reach from Athens to Troy, NY, with the same features mapped in the late 20th century. The comparison shows a substantial decrease in total water area approximately 30% less than the 1907–1911 quantity, with secondary channels disproportionally affected (~70% less). The number and total area of islands has also dramatically decreased by approximately 65% and 85%, respectively. These changes primarily reflect the success of navigation improvement projects undertaken since the 19th century that transformed a shallow, island‐braided river in the study reach to one characterized by a deeper, single‐thread channel. Dredge spoils from the main channel were used to fill secondary channels and other backwater areas, a practice with implications for reproduction, growth and/or survival of native plants and animals. Published in 2011 by John Wiley & Sons, Ltd.     

HYDROLOGICAL CONNECTIVITY OF ABANDONED CHANNEL WATER BODIES ON A COASTAL PLAIN RIVER

Oxbow lakes, sloughs and other floodplain depressions associated with former channel positions are critical elements of floodplain hydrology, geomorphology and ecology. They comprise key elements of wetland and aquatic habitats and have important influence on the storage and routing of floodwaters. The hydrological connectivity between active river channels and floodplain depressions varies considerably in a qualitative sense, even within a single fluvial system. Several oxbows, sloughs and paleochannels were examined on the lower Sabine River, Texas/Louisiana, during a period of high but sub‐bankfull flow as well as at lower flows. Six different types of surface water connectivity with the main, active channel were identified: (i) flow through—a portion of the river flow regularly passes through the feature and returns to the main channel; (ii) flood channel—there is no hydraulic connection at normal flows, but at high flows the channels convey discharge, at least part of which returns to the main channel; (iii) fill and spill—the features fill to a threshold level at high flows and then overflow (mainly via ephemeral channels) into flood basins; (iv) fill and drain—the features fill at high river discharges but do not (except in large floods) overflow because as river discharge declines, water drains back to the river; (v) tributary occupied—tributaries draining to the abandoned channel continue to occupy it, flowing through it to the active channel; and (vi) disconnected—no flow is exchanged except during large floods. The age or stage of infilling and the relative elevation of abandoned channels are important first‐order controls of hydrological connectivity, but the lateral distance from the active channel is poorly related. Other critical controls are whether the cutoff section receives tributary input and whether a tie channel forms. The alluvial valley geomorphic context—specifically the presence of a meander belt ridge and flood basins—is also critical. Copyright © 2011 John Wiley & Sons, Ltd.     

HYDROLOGICAL GRADIENT AND SPECIES TRAITS EXPLAIN GASTROPOD DIVERSITY IN FLOODPLAIN GRASSLANDS

Floodplains are characterized by high spatial and temporal heterogeneity. Despite low active mobility, Central European floodplain gastropod communities show a high species diversity. They are supposed to have developed a large range of resistance and/or resilience strategies to survive in the highly variable and frequently disturbed floodplain habitats. Relating gastropod diversity and species traits to hydrological conditions, we tested how different groundwater and flood regimes affect gastropod diversity and identified the main species traits favouring their survival in highly dynamic floodplain grasslands. Species richness, species diversity and functional diversity peaked at intermediate flood disturbance and moisture levels. Harsher environmental conditions in either dryer or frequently flooded habitats restricted the gastropod communities to a few specialized species. Morphological and life‐history traits showed significant variations along the hydrological gradient. Shell character and mode of reproduction proved to be important functional determinants for gastropod community composition. Species with strongly calcified shells, which limit the risk of injuries in case of dislodgment, were more often found in flood prone sites. Uniparental reproduction dominated in the driest as well as in highly flood‐disturbed habitats, providing reproductive assurance where harsh environmental conditions may reduce the number of potential mates. Intermediate disturbance and moisture levels favoured local gastropod diversity whereas dryer or highly flood‐disturbed habitats sheltered specialized species. Therefore, the maintenance of areas with different disturbance and moisture levels is of major importance in favouring taxonomical and functional mollusc diversity across the whole floodplain. Copyright © 2011 John Wiley & Sons, Ltd.