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The current erosion of biodiversity is a major concern that threatens the ecological integrity of ecosystems and the ecosystem services they provide. Due to global change, an increasing proportion of river networks are drying and changes from perennial to non‐perennial flow regimes represent dramatic ecological shifts with potentially irreversible alterations of community and ecosystem dynamics. However, there is minimal understanding of how biological communities respond functionally to drying. Here, we highlight the taxonomic and functional responses of aquatic macroinvertebrate communities to flow intermittence across river networks from three continents, to test predictions from underlying trait‐based conceptual theory. We found a significant breakpoint in the relationship between taxonomic and functional richness, indicating higher functional redundancy at sites with flow intermittence higher than 28%. Multiple strands of evidence, including patterns of alpha and beta diversity and functional group membership, indicated that functional redundancy did not compensate for biodiversity loss associated with increasing intermittence, contrary to received wisdom. A specific set of functional trait modalities, including small body size, short life span and high fecundity, were selected with increasing flow intermittence. These results demonstrate the functional responses of river communities to drying and suggest that on‐going biodiversity reduction due to global change in drying river networks is threatening their functional integrity. These results indicate that such patterns might be common in these ecosystems, even where drying is considered a predictable disturbance. This highlights the need for the conservation of natural drying regimes of intermittent rivers to secure their ecological integrity. [ABSTRACT FROM AUTHOR]

Conceptual models underpin river ecosystem research. However, current models focus on continuously flowing rivers and few explicitly address characteristics such as flow cessation and drying. The applicability of existing conceptual models to nonperennial rivers that cease to flow (intermittent rivers and ephemeral streams, IRES) has not been evaluated. We reviewed 18 models, finding that they collectively describe main drivers of biogeochemical and ecological patterns and processes longitudinally (upstream‐downstream), laterally (channel‐riparian‐floodplain), vertically (surface water‐groundwater), and temporally across local and landscape scales. However, perennial rivers are longitudinally continuous while IRES are longitudinally discontinuous. Whereas perennial rivers have bidirectional lateral connections between aquatic and terrestrial ecosystems, in IRES, this connection is unidirectional for much of the time, from terrestrial‐to‐aquatic only. Vertical connectivity between surface and subsurface water occurs bidirectionally and is temporally consistent in perennial rivers. However, in IRES, this exchange is temporally variable, and can become unidirectional during drying or rewetting phases. Finally, drying adds another dimension of flow variation to be considered across temporal and spatial scales in IRES, much as flooding is considered as a temporally and spatially dynamic process in perennial rivers. Here, we focus on ways in which existing models could be modified to accommodate drying as a fundamental process that can alter these patterns and processes across spatial and temporal dimensions in streams. This perspective is needed to support river science and management in our era of rapid global change, including increasing duration, frequency, and occurrence of drying. This article is categorized under:Water and Life > Nature of Freshwater EcosystemsWater and Life > Stresses and Pressures on EcosystemsScience of Water > Hydrological Processes [ABSTRACT FROM AUTHOR]

Streamflow observations can be used to understand, predict, and contextualize hydrologic, ecological, and biogeochemical processes and conditions in streams. Stream gages are point measurements along rivers where streamflow is measured, and are often used to infer upstream watershed‐scale processes. When stream gages read zero, this may indicate that the stream has dried at this location; however, zero‐flow readings can also be caused by a wide range of other factors. Our ability to identify whether or not a zero‐flow gage reading indicates a dry fluvial system has far reaching environmental implications. Incorrect identification and interpretation by the data user can lead to inaccurate hydrologic, ecological, and/or biogeochemical predictions from models and analyses. Here, we describe several causes of zero‐flow gage readings: frozen surface water, flow reversals, instrument error, and natural or human‐driven upstream source losses or bypass flow. For these examples, we discuss the implications of zero‐flow interpretations. We also highlight additional methods for determining flow presence, including direct observations, statistical methods, and hydrologic models, which can be applied to interpret causes of zero‐flow gage readings and implications for reach‐ and watershed‐scale dynamics. Such efforts are necessary to improve our ability to understand and predict surface flow activation, cessation, and connectivity across river networks. Developing this integrated understanding of the wide range of possible meanings of zero‐flows will only attain greater importance in a more variable and changing hydrologic climate. This article is categorized under:Science of Water > MethodsScience of Water > Hydrological ProcessesWater and Life > Conservation, Management, and Awareness [ABSTRACT FROM AUTHOR]

Abstract: Streams, riparian areas, floodplains, alluvial aquifers, and downstream waters (e.g., large rivers, lakes, and oceans) are interconnected by longitudinal, lateral, and vertical fluxes of water, other materials, and energy. Collectively, these interconnected waters are called fluvial hydrosystems. Physical and chemical connectivity within fluvial hydrosystems is created by the transport of nonliving materials (e.g., water, sediment, nutrients, and contaminants) which either do or do not chemically change (chemical and physical connections, respectively). A substantial body of evidence unequivocally demonstrates physical and chemical connectivity between streams and riparian wetlands and downstream waters. Streams and riparian wetlands are structurally connected to downstream waters through the network of continuous channels and floodplain form that make these systems physically contiguous, and the very existence of these structures provides strong geomorphologic evidence for connectivity. Functional connections between streams and riparian wetlands and their downstream waters vary geographically and over time, based on proximity, relative size, environmental setting, material disparity, and intervening units. Because of the complexity and dynamic nature of connections among fluvial hydrosystem units, a complete accounting of the physical and chemical connections and their consequences to downstream waters should aggregate over multiple years to decades. [ABSTRACT FROM AUTHOR]

Abstract: Connectivity is a fundamental but highly dynamic property of watersheds. Variability in the types and degrees of aquatic ecosystem connectivity presents challenges for researchers and managers seeking to accurately quantify its effects on critical hydrologic, biogeochemical, and biological processes. However, protecting natural gradients of connectivity is key to protecting the range of ecosystem services that aquatic ecosystems provide. In this featured collection, we review the available evidence on connections and functions by which streams and wetlands affect the integrity of downstream waters such as large rivers, lakes, reservoirs, and estuaries. The reviews in this collection focus on the types of waters whose protections under the U.S. Clean Water Act have been called into question by U.S. Supreme Court cases. We synthesize 40+ years of research on longitudinal, lateral, and vertical fluxes of energy, material, and biota between aquatic ecosystems included within the Act's frame of reference. Many questions about the roles of streams and wetlands in sustaining downstream water integrity can be answered from currently available literature, and emerging research is rapidly closing data gaps with exciting new insights into aquatic connectivity and function at local, watershed, and regional scales. Synthesis of foundational and emerging research is needed to support science‐based efforts to provide safe, reliable sources of fresh water for present and future generations. [ABSTRACT FROM AUTHOR]

Abstract: Freshwater ecosystems are linked at various spatial and temporal scales by movements of biota adapted to life in water. We review the literature on movements of aquatic organisms that connect different types of freshwater habitats, focusing on linkages from streams and wetlands to downstream waters. Here, streams, wetlands, rivers, lakes, ponds, and other freshwater habitats are viewed as dynamic freshwater ecosystem mosaics (FEMs) that collectively provide the resources needed to sustain aquatic life. Based on existing evidence, it is clear that biotic linkages throughout FEMs have important consequences for biological integrity and biodiversity. All aquatic organisms move within and among FEM components, but differ in the mode, frequency, distance, and timing of their movements. These movements allow biota to recolonize habitats, avoid inbreeding, escape stressors, locate mates, and acquire resources. Cumulatively, these individual movements connect populations within and among FEMs and contribute to local and regional diversity, resilience to disturbance, and persistence of aquatic species in the face of environmental change. Thus, the biological connections established by movement of biota among streams, wetlands, and downstream waters are critical to the ecological integrity of these systems. Future research will help advance our understanding of the movements that link FEMs and their cumulative effects on downstream waters. [ABSTRACT FROM AUTHOR]

Urban streams are degraded by a suite of factors, including burial beneath urban infrastructure, such as roads or parking lots, which eliminates light and reduces direct organic matter inputs to streams from riparian zones. These changes to stream metabolism and terrestrial carbon contribution will likely have consequences for organic matter metabolism by microbes and dissolved organic matter ( DOM) use patterns in streams. Respiration by heterotrophic biofilms drives the nitrogen and phosphorus cycles, but we lack a clear understanding of how stream burial and seasonality affect microbial carbon use., We studied seasonal changes (autumn, spring, and summer) in organic matter metabolism by microbial communities in open and buried reaches of three urban streams in Cincinnati, OH. We characterised DOM quality using fluorescence spectroscopy and extracellular enzyme profiles, and we measured the respiration response to carbon supplements in nutrient diffusing substrata ( NDS). We hypothesised: (1) that algal production would lead to higher quality DOM in spring compared to other seasons and in open compared to buried reaches, (2) lower reliance of microbial respiration on recalcitrant carbon sources in spring and in open reaches, and (3) that microbial respiration would increase in response to added carbon in autumn and in buried reaches., Several fluorescence metrics showed higher quality DOM in spring than autumn, but only the metric of recalcitrant humic compounds varied by reach, with more humic DOM in open compared to buried reaches. This likely reflected open reaches as an avenue for direct terrestrial inputs from the riparian zone., Extracellular enzyme assays showed that microbes in buried reaches allocated more effort to degrade recalcitrant carbon sources, consistent with a lack of labile carbon compounds due to limited photosynthesis. Nitrogen acquisition enzymes were highest in autumn coincident with riparian leaf inputs to the streams. Buried and open reaches both responded more strongly to added carbon in autumn when terrestrial leaf inputs dominated compared to the spring when vernal algal blooms were pronounced., Our data show that stream burial affects the quality of the DOM pool with consequences for how microbes use those carbon sources, and that heterotrophic respiration increased on carbon-supplemented NDS in buried and open stream reaches in both seasons. Different carbon quality and use patterns suggest that urban stream infrastructure affects spatiotemporal patterns of bacterial respiration, with likely consequences for nitrogen and/or phosphorus cycling given that carbon use drives other biogeochemical cycles. Management actions that increase light to buried streams could shift the balance between allochthonous and autochthonous DOM in urban streams with consequences for spatiotemporal patterns in bacterial metabolism. [ABSTRACT FROM AUTHOR]

Intermittent rivers, those channels that periodically cease to flow, constitute over half of the total discharge of the global river network and will likely increase in their extent owing to climatic shifts and/or water resources development. Burgeoning research on intermittent river ecology has documented the importance of the meteorologic, geologic and land-cover components of these ecosystems on structuring ecological communities, but mechanisms controlling flow permanence remain poorly understood. Here, we provide a framework of the meteorologic, geologic and land-cover controls on intermittent streamflow across different spatio-temporal scales and identify key research priorities to improve our understanding of intermittent systems so that we are better able to conserve, manage and protect them. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Supreme Court cases have questioned if jurisdiction under the Clean Water Act extends to water bodies such as streams without year-round flow. Headwater streams are central to this issue because many periodically dry, and because little is known about their influence on navigable waters. An accurate account of the extent and flow permanence of headwater streams is critical to estimating downstream contributions. We compared the extent and permanence of headwater streams from two field surveys with values from databases and maps. The first used data from 29 headwater streams in nine U.S. forests, whereas the second had data from 178 headwater streams in Oregon. Synthetic networks developed from the nine-forest survey indicated that 33 to 93% of the channel lacked year-round flow. Seven of the nine forests were predicted to have >200% more channel length than portrayed in the high-resolution National Hydrography Dataset ( NHD). The NHD and topographic map classifications of permanence agreed with ~50% of the field determinations across ~300 headwater sites. Classification agreement with the field determinations generally increased with increasing resolution. However, the flow classification on soil maps only agreed with ~30% of the field determination despite depicting greater channel extent than other maps. Maps that include streams regardless of permanence and size will aid regulatory decisions and are fundamental to improving water quality monitoring and models. [ABSTRACT FROM AUTHOR]

The decay rate of cellulose filters and associated chemical and biological characteristics were compared with those of white oak ( Quercus alba) leaves to determine whether cellulose filters could be a suitable standardized material for assessing deciduous leaf breakdown in headwater streams. The comparison was done across reaches draining mixed deciduous forest and post-coal mining catchments, in natural and constructed channels, and ranged in flow duration from ephemeral to perennial. Decay rates of leaves and filters were predicted to differ at a given site, but the decay rates and associated characteristics of leaf and filter litterbags would be positively related. Filter decay rates did not differ across channel type or flow permanence class. Oak leaves decayed ca 2·5× faster than cellulose filters and there was no relationship between decay rates ( R = 0·02). Ergosterol concentration, total invertebrate density, shredder density, total invertebrate biomass and taxa richness were significantly higher in oak litterbags than in filter litterbags across four sampling dates over 306 days. The biomass of invertebrate shredders colonizing litterbags did not differ between the substrate types. The C:N content was higher for filters than for oak leaves, but the mean difference between substrates decreased by ∼10-fold over the 306-day study. In contrast, mean differences in ergosterol concentration between substrates increased threefold over the study. Although characteristics associated with filter litterbags were positively related to those of oak leaf litterbags, most relationships had low explanatory power ( R⩽0·3); however, stronger relationships existed for total invertebrate density, shredder density and taxa richness ( R = 0·78). Although a standardized material would be useful for incorporating litter breakdown in stream assessments, because of the strong differences in decay rate and associated characteristics, we cannot recommend cellulose filters as a suitable substrate to represent the natural breakdown of leaf material. Published in 2010. This article is a US Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

The article presents a study which determines the contaminated aquatic subsidies in riparian zones in Lake Harwell in Clemson, South Carolina. It states that the study analyzes the condition of riparian araneid spiders, terrestrial insects, and aquatic insects using stable isopotes and polychlorinated biphenyls (PCB). The result of the study illustrate the importance of emergent insects as drivers of contaminant transfer from lake sediments to riparian food webs.

The article presents a stream subsidy research which looks into the relationships between the aquatic resource utilization and the contaminant exposure of the riparian predators, like spiders and herptiles, in a polychlorinated biphenyls contaminated stream in the U.S. According to the study, the energy subsidy of the riparian has a huge impact on the behavior, production, as well as diversity of the species. With this, identifying and validating the ecological tracers of the stream subsidy relevant to the stream conditions are believed necessary.

Summary 1. Patches of stable substratum in streams may be important refugia for benthic organisms during scouring floods. Streambed stone stability, packing and embeddedness were assessed within and adjacent to beds of the macrophyte Justicia americana in five Alabama streams. 2. The force needed to dislodge stones and embeddedness was about two times lower outside Justicia beds than within them. Significant positive correlations between stone stability and (i) degree of embeddedness, and (ii) the abundance of binding rhizomes and the presence of attached roots indicate that Justicia may physically modify the local streambed, indirectly enhancing substratum stability and reducing flow, thereby increasing sand deposition. 3. Despite higher stability (i.e. physical refugia during bed-moving spates) within Justicia beds, the abundance of epilithic plants (moss and Podostemum ceratophyllum ) and pleurocerid snails (Elimia spp.) was similar both inside and outside the macrophyte beds. Several physical characteristics within macrophyte beds, such as low light, reduced current and increased sand intrusion, may create suboptimal conditions for benthic organisms in these habitats. 4. Additional work is needed to determine if Justicia biogenically enhances substratum stability or if its presence merely reflects patches of stable substratum within the streambed. Regardless of the mechanism, there is an association between Justicia beds and streambed characteristics. [ABSTRACT FROM AUTHOR]

Headwater ephemeral tributaries are interfaces between uplands and downstream waters. Terrestrial coarse particulate organic matter (CPOM) is important in fueling aquatic ecosystems; however, the extent to which ephemeral tributaries are functionally connected to downstream waters through fluvial transport of CPOM has been little studied. Hydrology and deposition of leaf and wood, and surrogate transport (Ginkgo biloba leaves and wood dowels) were measured over month‐long intervals through the winter and spring seasons (6 months) in 10 ephemeral tributaries (1.3–5.4 ha) in eastern Kentucky. Leaf deposition and surrogate transport varied over time, reflecting the seasonality of litterfall and runoff. Leaf deposition was higher in December than February and May but did not differ from January, March, and April. Mean percent of surrogate leaf transport from the ephemeral tributaries was highest in April (3.6% per day) and lowest in February (2.5%) and May (2%). Wood deposition and transport had similar patterns. No CPOM measures were related to flow frequency. Ephemeral tributaries were estimated to annually contribute 110.6 kg AFDM·km−1·yr−1 of leaves to the downstream mainstem. Ephemeral tributaries are functionally connected to downstream waters through CPOM storage and subsequent release that is timed when CPOM is often limited in downstream waters. [ABSTRACT FROM AUTHOR]