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Temporary streams in temperate zones: recognizing, monitoring and restoring transitional aquatic‐terrestrial ecosystems

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Temporary streams are defined by periodic flow cessation, and may experience partial or complete loss of surface water. The ecology and hydrology of these transitional aquatic‐terrestrial ecosystems have received unprecedented attention in recent years. Research has focussed on the arid, semi‐arid, and Mediterranean regions in which temporary systems are the dominant stream type, and those in cooler, wetter temperate regions with an oceanic climate influence are also receiving increasing attention. These oceanic systems take diverse forms, including meandering alluvial plain rivers, ‘winterbourne’ chalk streams, and peatland gullies. Temporary streams provide ecosystem services and support a diverse biota that includes rare and endemic specialists. We examine this biota and illustrate that temporary stream diversity can be higher than in comparable perennial systems, in particular when differences among sites and times are considered; these diversity patterns can be related to transitions between lotic, lentic, and terrestrial instream conditions. Human impacts on temperate‐zone temporary streams are ubiquitous, and result from water‐resource and land‐use‐related stressors, which interact in a changing climate to alter natural flow regimes. These impacts may remain uncharacterized due to inadequate protection of small temporary streams by current legislation, and hydrological and biological monitoring programs therefore require expansion to better represent temporary systems. Novel, temporary‐stream‐specific biomonitors and multi‐metric indices require development, to integrate characterization of ecological quality during lotic, lentic, and terrestrial phases. In addition, projects to restore flow regimes, habitats, and communities may be required to improve the ecological quality of temporary streams. WIREs Water 2017, 4:e1223. doi: 10.1002/wat2.1223

Examples of temporary streams in oceanic (Cfb) environments: (a) a snow‐covered mountain stream, Scotland, UK; (b) a ponded peatland tributary of Green Field Beck, England, UK; (c) the bedrock‐dominated channel of Deepdale Gill, England, UK; (d) the alluvial plain River Orari, New Zealand; (e) the forested Lerderderg River, Australia; (f) the winterbourne headwaters of the chalk River Till, England, UK; and (g) the karst River Manifold, England, UK. Photo credits: A. Youngson (a); L. Brown (b); J. Clift (c); F. Burdon (d); A. Boulton (e); A. House (f); R. Stubbington (g).
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In chalk streams including the River Misbourne (England, UK), macrophyte communities are characterized by longitudinal zonation during the summer months, and differ between sites with (a) perennial flow, (b) shorter (typically 2‐4 month) and (c) longer (typically 4‐8 month) annual dry periods, as described by Westwood et al.. Photo credits: J. England (a); N. Holmes (b‐c).
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Turnover of lotic, lentic, and terrestrial taxa during (a) flowing, (b) pool, and (c) dry habitat phases in a temporary stream reach. Arrows indicate a typical annual cycle of environmental changes; reversals (e.g., transitions from pool to flowing conditions) and omissions (e.g., flowing‐dry‐flowing or flowing‐pool‐flowing transitions) may also occur. Taxonomic patterns are those observed and hypothesized for invertebrate communities, with some plant community data suggesting comparable patterns.
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Typical patterns of alpha (α), beta (β), and gamma (γ) diversity of communities in (a) a temporary stream network and (b) a perennial stream network, at multiple sites during flowing phases (blue lines), and at one site during an annual cycle (black circles). The size of blue, filled symbols allows comparison of panes (a) and (b) and is proportional to diversity, i.e., larger symbols indicate higher diversity at temporary or perennial sites; symbol sizes should not be compared within a pane. Shapes indicate differences in community composition. Abbreviations: stβ, ttβ and vβ, spatial turnover, temporal turnover, and variation β‐diversity, respectively. Superscript letters allow comparison of (a) and (b). Definitions of diversity measures are provided in Box and patterns are described in Box .
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Concepts of diversity illustrated using a theoretical stream network: (a) α‐diversity; (b) variation β‐diversity; and (c) turnover β‐diversity along simplified two‐site (S1, S2) and two‐time (T1, T2) ‘gradients’. Small filled symbols indicate different ‘types,’ e.g., taxa or traits, their size representing their relative abundance; larger circles and semi‐circles indicate sampling units; blue lines represent a plan view of the stream network. In each theoretical case, the left‐hand side of the network (as viewed) has higher diversity than the right‐hand side; the patterns observed in temporary streams are described in Box .
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Science of Water > Water Extremes
Water and Life > Nature of Freshwater Ecosystems
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