Early fish growth varies in response to components of the flow regime in a temperate floodplain river

1. The biological productivity of floodplain rivers is intimately related to their flow regimes and it has been proposed that fish production should be linked to components of the flow regime in productivity models. To assess applicability of existing models of productivity in floodplain rivers, we tested predictions about growth during the early life stages of a common, short‐lived fish (Australian smelt Retropinna semoni) in a non‐flow‐altered, temperate Australian floodplain river. 2. The morphometric condition of larval and juvenile fish measured over a five‐year period was positively related to annual discharge, but the highest average seasonal growth rates occurred in two years of contrasting hydrology, one with early spring flooding and the other with predominantly low flows and a late season (within channel) flow pulse. 3. Analysis of daily growth measures indicated that timing, river height, the duration of in‐channel flow events and antecedent flood events are all significant factors influencing the early growth of Australian smelt. The flexible manner in which fish growth responds to these factors appears to be an effective early life history strategy for a short‐lived species occupying a highly variable environment. 4. Growth rates conformed to some predictions of the Flood Pulse Concept (in particular the Extended Flood Pulse Concept), but specific growth responses suggest that the Riverine Productivity Model and tenets of the Low Flow Recruitment Hypothesis best describe the production of Australian smelt in this system. We suggest that none of the existing conceptual models adequately describes fish productivity in temperate Australian floodplain rivers but that aspects of each are likely to be relevant under different flow conditions.     

Ecosystem-level effects of re-oligotrophication and N:P imbalances in rivers and estuaries on a global scale

Trends and ecological consequences of phosphorus (P) decline and increasing nitrogen (N) to phosphorus (N:P) ratios in rivers and estuaries are reviewed and discussed. Results suggest that re-oligotrophication is a dominant trend in rivers and estuaries of high-income countries in the last two–three decades, while in low-income countries widespread eutrophication occurs. The decline in P is well documented in hundreds of rivers of United States and the European Union, but the biotic response of rivers and estuaries besides phytoplankton decline such as trends in phytoplankton composition, changes in primary production, ecosystem shifts, cascading effects, changes in ecosystem metabolism, etc., have not been sufficiently monitored and investigated, neither the effects of N:P imbalance. N:P imbalance has significant ecological effects that need to be further investigated. There is a growing number of cases in which phytoplankton biomass have been shown to decrease due to re-oligotrophication, but the potential regime shift from phytoplankton to macrophyte dominance described in shallow lakes has been documented only in a few rivers and estuaries yet. The main reasons why regime shifts are rarely described in rivers and estuaries are, from one hand the scarcity of data on macrophyte cover trends, and from the other hand physical factors such as peak flows or high turbidity that could prevent a general spread of submerged macrophytes as observed in shallow lakes. Moreover, re-oligotrophication effects on rivers may be different compared to lakes (e.g., lower dominance of macrophytes) or estuaries (e.g., limitation of primary production by N instead of P) or may be dependent on river/estuary type. We conclude that river and estuary re-oligotrophication effects are complex, diverse and still little known, and in some cases are equivalent to those described in shallow lakes, but the regime shift is more likely to occur in mid to high-order rivers and shallow estuaries.     

Spatial and Temporal Trade-Offs by Bluegills in Floodplain River Ecosystems

Ecological trade-offs by organisms to minimize mortality and maximize growth is a foundational theme in ecology. Yet, these trade-offs are rarely examined within spatially complex, temporally variable ecosystems, such as floodplain rivers. Here, we evaluate ecological trade-offs across space and time for the bluegill (Lepomis macrochirus) in two unregulated river ecosystems in southeastern USA. Life-history differences among spatially segregated main channel and floodplain lake populations were used to assess effects of habitat type on bluegill fitness. Growth, condition, and gonadal somatic index were all significantly enhanced in floodplain lakes relative to the main channel. Furthermore, stomach fullness was significantly higher, and predator densities significantly lower in floodplain lakes thereby providing an ecological explanation for the life-history plasticity observed across the riverscape. However, historical observations suggested that although floodplain lakes are highly productive for bluegills, they are also prone to complete desiccation by drought approximately every 5 years, revealing the ultimate value of channel habitat, which does not dry, as desiccation refugia. Bluegills are faced with a balancing act associated with variation in foraging opportunities, and risks to predation and desiccation, that change in both the temporal and the spatial dimensions of floodplain rivers. The differential responses to these opportunities and risks help to explain why both habitats remain actively populated by bluegills, as well as many other organisms, in these and many other natural rivers.     

Fish mediate high food web connectivity in the lower reaches of a tropical floodplain river

High levels of hydrological connectivity during seasonal flooding provide significant opportunities for movements of fish between rivers and their floodplains, estuaries and the sea, possibly mediating food web subsidies among habitats. To determine the degree of utilisation of food sources from different habitats in a tropical river with a short floodplain inundation duration (~2 months), stable isotope ratios in fishes and their available food were measured from three habitats (inundated floodplain, dry season freshwater, coastal marine) in the lower reaches of the Mitchell River, Queensland (Australia). Floodplain food sources constituted the majority of the diet of large-bodied fishes (barramundi Lates calcarifer, catfish Neoarius graeffei) captured on the floodplain in the wet season and for gonadal tissues of a common herbivorous fish (gizzard shad Nematalosa come), the latter suggesting that critical reproductive phases are fuelled by floodplain production. Floodplain food sources also subsidised barramundi from the recreational fishery in adjacent coastal and estuarine areas, and the broader fish community from a freshwater lagoon. These findings highlight the importance of the floodplain in supporting the production of large fishes in spite of the episodic nature and relatively short duration of inundation compared to large river floodplains of humid tropical regions. They also illustrate the high degree of food web connectivity mediated by mobile fish in this system in the absence of human modification, and point to the potential consequences of water resource development that may reduce or eliminate hydrological connectivity between the river and its floodplain.     

Biodiversity: towards a unifying theme for river ecology

1. A broadened concept of biodiversity, encompassing spatio‐temporal heterogeneity, functional processes and species diversity, could provide a unifying theme for river ecology. 2. The theoretical foundations of stream ecology often do not reflect fully the crucial roles of spatial complexity and fluvial dynamics in natural river ecosystems, which has hindered conceptual advances and the effectiveness of efforts at conservation and restoration. 3. Inclusion of surface waters (lotic and lentic), subsurface waters (hyporheic and phreatic), riparian systems (in both constrained and floodplain reaches), and the ecotones between them (e.g. springs) as interacting components contributing to total biodiversity, is crucial for developing a holistic framework of rivers as ecosystems. 4. Measures of species diversity, including alpha, beta and gamma diversity, are a result of disturbance history, resource partitioning, habitat fragmentation and successional phenomena across the riverine landscape. A hierarchical approach to diversity in natural and altered river‐floodplain ecosystems will enhance understanding of ecological phenomena operating at different scales along multidimensional environmental gradients. 5. Re‐establishing functional diversity (e.g. hydrologic and successional processes) across the active corridor could serve as the focus of river conservation initiatives. Once functional processes have been reconstituted, habitat heterogeneity will increase, followed by corresponding increases in species diversity of aquatic and riparian biota.     

Landscape-Scale Hydrologic Characteristics Differentiate Patterns of Carbon Flow in Large-River Food Webs

Efforts to conserve, restore, or otherwise manage large rivers and the services they provide are hindered by limited understanding of the functional dynamics of these systems. This shortcoming is especially evident with regard to trophic structure and energy flow. We used natural abundances of carbon and nitrogen isotopes to examine patterns of material flow in ten large-river food webs characterized by different landscape-scale hydrologic characteristics (low-gradient river, high-gradient river, river stretches downstream of reservoirs, and reservoirs), and tested predictions from three ecosystem concepts commonly applied to large-rivers: The River Continuum Concept, The Flood Pulse Concept and the Riverine Productivity Model. Carbon derived from aquatic C₃ plants and phytoplankton were the dominant energy sources supporting secondary consumers across the ten large-river food webs examined, but relative contributions differed significantly among landscape types. For low-gradient river food webs, aquatic C₃ plants were the principal carbon source, contributing as much as 80% of carbon assimilated by top consumers, with phytoplankton secondarily important. The estimated relative importance of phytoplankton was greatest for food webs of reservoirs and river stretches downriver from impoundments, although aquatic C₃ plants contributed similar amounts in both landscape types. Highest 99th percentile source contribution estimates for C₄ plants and filamentous algae (both approximately 40%) were observed for high-gradient river food webs. Our results for low-gradient rivers supported predictions of the Flood Pulse Concept, whereas results for the three other landscape types supported the Riverine Productivity Model to varying degrees. Incorporation of landscape-scale hydrologic or geomorphic characteristics, such as river slope or floodplain width, may promote integration of fluvial ecosystem concepts. Expanding these models to include hydrologically impacted landscapes should lead to a more holistic understanding of ecosystem processes in large-river systems.     

Morphological and biomechanical responses of floodplain willows to tidal flooding and salinity

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区县尺度下的河流生态系统健康评价——以北京房山区为例

伴随郊区城市化的快速发展,高强度人工管控对河流生态系统产生持续胁迫作用,河流生态系统健康受到严重威胁甚至损害。以北京房山区河流水系为例,于2016—2017年在区域内的31处样点进行野外调查。选取河流的水环境功能、防洪效益功能、生态效益功能和支持利用功能4方面16个具体评价指标,并通过层次分析法计算权重,构建区县尺度下的河流生态系统健康评价指标体系,并进行健康状况评价。结果表明:房山区河流的防洪效益功能与生态效益功能中"健康与亚健康"状态比例分别为58.0%与41.9%,而水环境功能与和支持利用功能中"较差与差"状态比例为71.0%与41.9%;河流生态系统健康整体水平较差,勉强满足河流生态系统一般需求。同时,房山区境内的拒马河与小清河的河流生态系统健康状态远优于大石河与永定河。河流生态基流是影响河流生态系统健康的关键因素,适当释放库区截留水量与调配区外清洁水体,已成为恢复房山区河流生态系统健康的前提与基础。     

Impact of habitat fragmentation on genetic population structure of roach, Rutilus rutilus, in a riparian ecosystem

During the last 200 years, the riparianecosystem along major rivers has been reducedto a few scattered remnants. Important elementsof the riparian ecosystem are water bodieswhich were originally connected to the mainriver channel by annual floodings. Due to riverregulations many of these remnants are nowvirtually isolated. In an allozyme analysisusing roach, Rutilus rutilus, as a studyspecies we demonstrate that the geneticdiversity (number of alleles per locus,expected heterozygosity) of populations livingwithin floodplain water bodies is not severelyimpoverished compared to the genetic diversitywithin the main river channel. However, wefound slight differences in the allelefrequencies of flood plain water bodies and themain river channel. Nevertheless, fishpopulations in floodplain water bodies mayserve as reservoirs of autochthonous geneticmaterial for restoration of fish populations inthe main river channel after populationextinction due to catastrophic accidents (e.g.industrial pollution).     

Hyporheic rehabilitation in rivers: restoring vertical connectivity

1. The hyporheic zone below the channel and banks of many rivers where surface water and ground water exchanges plays a crucial functional role in the biogeochemical transformation of water, mediated by active microbial biofilms. This zone also harbours assemblages of invertebrates that graze biofilms, contribute to secondary production, and can alter the porosity of the hyporheic zone through their movement or burrowing activities. 2. Many human activities cause interstitial sedimentation or disrupt surface–groundwater hydrological linkages, impacting upon ecological processes in the hyporheic zone. However, strategies for river rehabilitation seldom explicitly consider the hyporheic zone or seek to restore lost vertical linkages with groundwater. Instead, restoration goals target surface, riparian or floodplain features even though current river ecosystem theory emphasises the three dimensions of hydrological connectivity. To guide effective, holistic river restoration, scientists and managers therefore need information on the mechanisms by which energy and material are transferred in the hyporheic zone and which ecosystem services are thus provided. 3. Other gaps in our understanding of hyporheic zone rehabilitation include recruitment processes of the hyporheos and the relative importance of groups of hyporheic invertebrates in rivers differing in substratum size, disturbance frequency and groundwater linkages. Carefully designed experiments that assess responses to hyporheic rehabilitation strategies will provide valuable data at varying scales (e.g. distribution of hyporheic habitat types at the reach scale) for management as well as providing insights into the mechanisms controlling hyporheic invertebrate assemblages and ecological processes. Fully successful river rehabilitation must include restoration of vertical linkages between the river and its shallow groundwater aquifers.     

Fluvial landscape ecology: addressing uniqueness within the river discontinuum

1. As rivers and streams are patchy and strongly hierarchical systems, a hierarchical patch dynamics perspective can be used as a framework for visualising interactions between structure and function in fluvial landscapes. The perspective is useful for addressing fundamental attributes of lotic ecosystems, such as heterogeneity, hierarchy, directionality and process feedback occurring across spatial scales and for illustrating spatio‐temporal linkages between disparate concepts in lotic system ecology such as the River Continuum Concept, the Serial Discontinuity Concept, the Flood Pulse Concept and the Hyporheic Corridor Concept. 2. At coarse spatial scales, the hierarchical patch dynamics perspective describes each river network as a unique, patchy discontinuum from headwaters to mouth. The discontinuum is comprised of a longitudinal series of alternating stream segments with different geomorphological structures. Each confluence in the steam network further punctuates the discontinuum because the sudden change in stream characteristics can create a `gap' in the expected pattern of downstream transitions. The discontinuum view recognises general trends in habitat characteristics along the longitudinal profile, but creates a framework for studying and understanding the ecological importance of each stream's individual pattern of habitat transitions along longitudinal, lateral or vertical vectors at any scale. 3. Object‐oriented modelling and programming techniques provide a means for developing robust, quantitative simulation models that describe the dynamic structure of patch hierarchies. Such models can simulate how the structure and function of lotic ecosystems are influenced by the landscape context of the system (the ecological conditions within which the system is set) and the metastructure (structural characteristics and juxtaposition) of finer‐scale patches comprising the system. 4. A simple object‐oriented, multiscale, discontinuum model of solute transformation and biological response along a stream channel illustrates how changing the branching pattern of a stream and the arrangement of its component patches along the downstream profile will result in substantial changes in predicted patterns of solute concentration and biotic community structure. 5. The importance of context, structure, and metastructure in determining lotic ecosystem function serves to underscore 27 ) concept that `every stream is likely to be individual.' Advancing the discipline of fluvial landscape ecology provides an excellent opportunity to develop general concepts and tools that address the individual character of each stream network and integrate the concept of `uniqueness within the river discontinuum' into our ecological understanding of rivers and streams.     

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.     

Productivity and Connectivity in Tropical Riverscapes of Northern Australia: Ecological Insights for Management

Flow regimes are fundamental to sustaining ecological characteristics of rivers worldwide, including their associated floodplains. Recent advances in understanding tropical river–floodplain ecosystems suggest that a small set of basic ecological concepts underpins their biophysical characteristics, especially the high levels of productivity, biodiversity and natural resilience. The concepts relate to (1) river-specific flow patterns, (2) processes ‘fuelled’ by a complex of locally generated carbon and nutrients seasonally mixed with carbon and nutrients from floodplains and catchments, (3) seasonal movements of biota facilitated by flood regimes, (4) food webs and overall productivity sustained by hydrological connectivity, (5) fires in the wet/dry tropical floodplains and riparian zones being major consumers of carbon and a key factor in the subsequent redistribution of nutrients, and (6) river–floodplains having inherent resilience to natural variability but only limited resilience to artificial modifications. Understanding these concepts is particularly timely in anticipating the effects of impending development that may affect tropical river–floodplains at the global scale. Australia, a region encompassing some of the last relatively undisturbed tropical riverine landscapes in the world, provides a valuable case study for understanding the productivity, diversity and resilience of tropical river–floodplain systems. However, significant knowledge gaps remain. Despite substantial recent advances in understanding, present knowledge of these highly complex tropical rivers is insufficient to predict many ecological responses to either human-generated or climate-related changes. The major research challenges identified herein (for example, those related to food web structure, nutrient transfers, productivity, connectivity and resilience), if accomplished in the next decade, will offer substantial insights toward assessing and managing ecological changes associated with human alterations to rivers and their catchments.     

Marine angiosperm indices used to assess ecological status within the Water Framework Directive and South African National Water Act: Learning from differences and common issues

This paper reviews and discusses the methods and metrics used for the assessment of the ecological status of marine angiosperms comparing the European with the South African situation. In Europe salt marsh and seagrasses are an important biological element for establishing the ecological quality status of transitional waters and in South Africa changes over time in the salt marsh and submerged macrophyte habitats (species richness, abundance and community composition) is used nationally to assess the health of estuaries. In Europe several studies have developed metrics that include salt marsh species composition and community structure to assess the ecological quality status. Deviation of taxonomic composition and abundance from a reference situation is investigated. Multi-metric approaches have been shown to provide a more holistic view of the ecological status of the ecosystem. Many indices are highly dependent on historical data to assess the deviation from reference conditions. Within the WFD spirit one widely used approach for salt marsh assessment, the Best’s method, the baseline can be determined based on the first sampling effort, by the largest previously recorded size of the salt marsh or using the “maximum potential size” of the salt marsh from habitat prediction models. In South Africa all habitat below the 5 m contour line is considered estuary habitat and any land occupied here by agricultural or other developments is considered as a loss of habitat from the reference condition. For seagrasses European metrics are based on attributes from the community (e.g., taxonomic composition, epiphytes), the population (e.g., bed extent, shoots density), but also quantified at individual species (e.g., leaves length) or physiological levels (e.g., stable isotopic signatures). Seagrass habitats in South African estuaries are highly dynamic in response to floods and an understanding of this is needed before present ecological status can be assessed.     

Disentangling and ranking the influences of multiple environmental factors on plant and soil-dwelling arthropod assemblages in a river Rhine floodplain area

Floodplains of large rivers are among the most dynamic and diverse, yet most threatened ecosystems on earth. For a solid underpinning of river conservation and rehabilitation measures, it is critical to unravel the influences of the multiple stressors affecting floodplain ecosystems. Using canonical correspondence analysis with variance partitioning, we disentangled and ranked the influences of three floodplain ecosystem stressors (land use, flooding and soil contamination) on terrestrial plant and soil-dwelling arthropod assemblages in a floodplain area along the river Rhine in The Netherlands. We included five biotic assemblages: plant species (73 taxa), ground beetle species (57 taxa), ground beetle genera (29 taxa), beetle families (32 taxa) and arthropod groups at taxonomic levels from family to class (10 taxa). Plant and arthropod assemblages were primarily related to land use, which explained 19–30% of the variation in taxonomic composition. For plant species composition, flooding characteristics were nearly as important as land use. Soil metal contamination constituted a subordinate explanatory factor for the plant assemblages only (3% of variation explained). We conclude that the taxonomic composition of terrestrial plant and arthropod assemblages in our study area is related to land use and flooding rather than soil metal contamination.     

A critical analysis of regulated river ecosystem responses to managed environmental flows from reservoirs

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Effects of hydromorphological integrity on biodiversity and functioning of river ecosystems

River channels tend to a dynamic equilibrium driven by the dynamics of water and sediment discharge. The resulting fluctuating pattern of channel form is affected by the slope, the substrate erodibility, and the vegetation in the river corridor and in the catchment. Geomorphology is basic to river biodiversity and ecosystem functioning since the channel pattern provides habitat for the biota and physical framework for ecosystem processes. Human activities increasingly change the natural drivers of channel morphology on a global scale (e.g. urbanization increases hydrological extremes, and clearing of forests for agriculture increases sediment yield). In addition, human actions common along world rivers impact channel dynamics directly, e.g. river regulation simplifies and fossilizes channel form. River conservation and restoration must incorporate mechanisms of channel formation and ecological consequences of channel form and dynamics. This article (1) summarizes the role of channel form on biodiversity and functioning of river ecosystems, (2) describes spatial complexity, connectivity and dynamism as three key hydromorphological attributes, (3) identifies prevalent human activities that impact these key components and (4) analyzes gaps in current knowledge and identifies future research topics.     

An Ecosystem View of the Restoration of the Kissimmee River

Restoration of the Kissimmee River and floodplain ultimately will involve restoring 70 km of river channel and riparian zone and 11,000 ha of wetland over a period of two decades. Restoring ecosystem integrity is a crucial goal of the project, and the evaluation program is designed to assess the success of this endeavor. Major components of the riverine and floodplain ecosystem will be evaluated, guided by conceptual models of their structure and function. These studies will be referenced to historic conditions of the past and to present-day conditions in the channelized system. Enhanced connectivity and interactions between the river and floodplain, the interplay of abiotic and biotic variables, and interactions between trophic levels will restructure the channelized river and the largely drained floodplain that now exist. The key to evaluating the success of this ambitious project will be selecting measurements of the structure and function of the river and floodplain ecosystems that are responsive to this large-scale manipulation. The timing and duration of floodplain inundation, improved dissolved oxygen conditions, germination and establishment of wetland vegetation, and enhancement and expansion of rheophilic benthic invertebrate populations are critical initial elements of restoration. Further expected outcomes are an increase in the primary productivity of the ecosystem, expansion of the fish community into the reopened channels and onto the reflooded floodplain, and improved visitation and use by waterbirds in the restored regions. We highlight predictions of some of these key linkages and primary structural and functional attributes of the restored river and floodplain that should be measured.     

河流沉积物氮循环主要微生物的生态特征

微生物驱动的氮循环过程是全球生物地球化学循环的重要组成部分,由于人类活动的影响,氮循环负荷加剧,氮素的生态平衡和微生物的功能特征也相应地受到干扰。河流生态系统是陆地与海洋联系的纽带,因人类活动过量活性氮的输入导致水体富营养化,明显影响着河流的生态功能以及河口沿岸海洋生态系统的平衡。富含微生物的沉积物对氮素的转化和去除起着至关重要的作用。本文主要介绍河流沉积物氮循环主要功能微生物,包括氨氧化细菌、氨氧化古菌、亚硝酸盐氧化菌、反硝化细菌和厌氧氨氧化细菌的群落特征和生态功能,总结氮相关营养盐、溶氧和季节变化等环境因子,以及河道控制管理措施和污水处理厂扰动等条件下氮循环过程主要功能类群的生态特征和响应关系。指出还需深入全面地研究河流沉积物生态系统氮循环过程的驱动机制和微生物的贡献效率,加强城市河流沉积物微生物功能作用的研究及河道生物修复技术的开发。