Protecting hydrologic connectivity of freshwater ecosystems is fundamental to ensuring species persistence, ecosystem integrity, and human well-being. More frequent and severe droughts associated with climate change are poised to significantly alter flow intermittence patterns and hydrologic connectivity in dryland streams of the American Southwest, with deleterious effects on highly endangered fishes. By integrating local-scale hydrologic modeling with emerging approaches in landscape ecology, we quantify fine-resolution, watershed-scale changes in habitat size, spacing, and connectance under forecasted climate change in the Verde River Basin, United States. Model simulations project annual zero-flow day frequency to increase by 27% by midcentury, with differential seasonal consequences on continuity (temporal continuity at discrete locations) and connectivity (spatial continuity within the network). A 17% increase in the frequency of stream drying events is expected throughout the network with associated increases in the duration of these events. Flowing portions of the river network will diminish between 8% and 20% in spring and early summer and become increasingly isolated by more frequent and longer stretches of dry channel fragments, thus limiting the opportunity for native fishes to access spawning habitats and seasonally available refuges. Model predictions suggest that midcentury and late century climate will reduce network-wide hydrologic connectivity for native fishes by 6-9% over the course of a year and up to 12-18% during spring spawning months. Our work quantifies climate-induced shifts in stream drying and connectivity across a large river network and demonstrates their implications for the persistence of a globally endemic fish fauna.fragmentation | temporary streams | barriers | groundwater extraction R epresenting one of the most critically imperiled environments in the world (1), virtually every drop of water is managed, accounted for, and allocated for human use in arid ecosystems of the American Southwest (2). Ephemeral and intermittent streams (hereafter called "dryland streams") that fluctuate between drying and wetting are a distinguishing characteristic of these ecosystems and are associated with a range of important ecological and societal values (3). From a landscape perspective they provide essential hydrologic connectivity during bouts of stream inundation by linking a patchwork of perennial habitats over space and in time. Hydrologic connectivity-here referring to the upstream-downstream longitudinal connection of surface water-is widely recognized as a primary driver of freshwater ecosystem structure and function (3, 4) and is considered fundamental to organic matter and nutrient transport and the persistence of aquatic species by facilitating the repeated recolonization of motile and drifting organisms from isolated stream pools (refuges) to rewetted channel reaches that are intermittently dispersed throughout the river network (5, 6).Prospects of a rapidly changing climate that ...

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.

Wood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel-, valley-and watershed-scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non-randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non-randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range.

Electrical resistance sensors are used as a novel approach to quantify streamflow continuity (continuous through time) and longitudinal connectivity (continuous through space) across watersheds in south‐eastern Arizona, USA. We demonstrate this approach by reporting on a spatial array of 21 sensors installed in streams supporting naturally perennial, intermittent and ephemeral flow on the US Army Garrison, Fort Huachuca. Continuity and connectivity were quantified based on a strict interpretation of continuous flow at an individual sensor (strict continuity) or simultaneous streamflow at multiple sensors (strict connectivity). In addition, we evaluated continuity and connectivity to include periods (<48 h) when in‐channel refuges may exist between streamflow events (refuge‐maintained continuity and connectivity). Continuous streamflow in intermittent reaches accounted for 34% of the 121‐day monitoring period (15 April–13 August 2010) and 28% of the summer monsoon period (1 July–13 August 2010). Streamflow in ephemeral reaches accounted for 1.5% and 2.3% of the entire monitoring and monsoon period, respectively. Canyon‐wide longitudinal connectivity was rare (<1%); however, substantial longitudinal connection occurred along extensive portions of individual canyons. The refuge‐maintained criteria increased continuity 2–8%, with less influence on connectivity (e.g. <3% increase in only some portions of canyons). Despite this result, the refuge‐maintained concept remains important because of its broad applicability to refuge persistence across aquatic species and hydro‐climatic regimes. The approach presented in this study supports the growing scientific research on the influence of longitudinal hydrologic connectivity on population dynamics and ecological processes in dendritic river networks. Copyright © 2011 John Wiley & Sons, Ltd.

The natural wood regime forms the third leg of a tripod of physical processes that supports river science and management, along with the natural flow and sediment regimes. The wood regime consists of wood recruitment, transport, and storage in river corridors. Each of these components can be characterized in terms of magnitude, frequency, rate, timing, duration, and mode. We distinguish the natural wood regime, which occurs where human activities do not significantly alter the wood regime, and a target wood regime when management emphasizes wood recruitment, transport, and storage that balance desired geomorphic and ecological characteristics with mitigation of wood-related hazards. Wood regimes vary across space and through time, but can be inferred and quantified via direct measurements, reference sites, historical information, and numerical modeling. Classifying wood regimes with respect to wood process domains and quantifying the wood budget are valuable tools for assessing and managing rivers.