Content uploaded by Kristin L Jaeger
Author content
All content in this area was uploaded by Kristin L Jaeger on Oct 17, 2018
Content may be subject to copyright.
This article has been accepted for publication and undergone full peer review but has not been
through the copyediting, typesetting, pagination and proofreading process which may lead to
differences between this version and the Version of Record. Please cite this article as doi:
10.1002/eco.1712
This article is protected by copyright. All rights reserved.
Understanding controls on flow permanence in intermittent rivers to aid ecological research:
Integrating meteorology, geology and land cover
Katie H. Costigan1,2; Kristin L. Jaeger1; Charles W. Goss1; Ken M. Fritz3; P. Charles Goebel1
1School of Environment and Natural Resources
Ohio Agricultural Research & Development Center
The Ohio State University
1680 Madison Ave.,
Wooster, Ohio 44691
2Current address:
School of Geosciences
University of Louisiana at Lafayette,
611 McKinley Street,
Lafayette, Louisiana 70504
3Ecological Exposure Research Division
National Exposure Research Laboratory
Environmental Protection Agency,
26 W. Martin Luther King Jr. Dr.,
Cincinnati, OH 45268
Running head: Integrating science to understand flow intermittence.
This article is protected by copyright. All rights reserved.
Abstract
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 due 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
spatiotemporal 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.
Keywords: temporary streams, flow cessation, network expansion, connectivity, continuity
This article is protected by copyright. All rights reserved.
INTRODUCTION
Intermittent rivers are those fluvial landforms that periodically cease to flow and include
temporary, ephemeral, seasonal, and episodic streams and rivers in defined channels. The
character of surface water presence in intermittent rivers – here referred to as flow
permanence – encompasses a wide range of spatiotemporal patterns in timing, frequency, and
duration that defines streamflow continuity through time and connectivity across space from
the mesohabitat to network spatial scales (Jaeger et al., 2014; Jaeger and Olden, 2012).
Estimates of total length and discharge of intermittent rivers are difficult to determine but
conservative estimates suggest that intermittent rivers constitute more than 30%, and
reasonably can be extended to >50%, of the total length and discharge of the global river
network (Datry et al., 2014). Intermittent rivers drain all terrestrial biomes and can occur due
to natural (figure 1a, b, c) or anthropogenic (figure 1d, e) drivers in all areas of the river
network continuum from small headwater to large mainstem rivers (Kennard et al., 2010).
The prevalence of intermittent rivers is likely to increase in regions subject to water resources
development and/or climate shifts (Rupp et al., 2008; Stanley et al., 1997; Larned et al.,
2010b). For example, networks with shifts towards increased aridity or snow-to-rain
dominated events will likely be unable to support current or historic flows (Buttle et al.,
2012).
Intermittent rivers, like all rivers, possess geomorphic features that reflect the
dominance of erosion by moving water that include defined banks, presence of scour, and,
generally, convergence of channels. However, intermittent rivers demonstrate greater
variation between and within rivers in the size of their drainage areas and characteristics of
their hydrology, morphology, and substrate (Buttle et al., 2012; Adams and Spotila, 2005;
Tooth and Nanson, 2011) relative to perennial rivers (figure 2). For example, discontinuous
channels and downstream hydraulic geometry relationships that are different from perennial
systems can occur as a result of downstream decreases in streamflow volume from
This article is protected by copyright. All rights reserved.
transmission losses or the combined effect of variable discharges, erodible substrate, and
large amounts of bedload, particularly in drier systems (Tooth, 2000; Merritt and Wohl,
2003). Intermittency can occur in narrow, steep rivers with coarse grains (figure 2(a)) as well
as in wider, gradual, alluvial rivers with fine grains (figure 2(b)).
The recognized prevalence of intermittent rivers and their expected extension due to
climatic shifts and/or water resources development have resulted in a growing awareness of
the ecological importance of these systems (Datry et al., 2014; Larned et al., 2010b; Acuna et
al., 2014; Datry et al., 2014; Datry et al., 2011; Larned et al., 2011). Intermittent river
systems undergo periodic transitions between aquatic and terrestrial phases (figure 3, 4),
potentially enabling them to support a high level of biodiversity when both wet and dry
habitats (e.g., lentic, lotic, and terrestrial) are collectively taken into account (Datry et al.,
2014; Allen et al., 2013). Aquatic taxa of intermittent rivers possess traits enabling them to
persist in these harsh environments (e.g., high dispersal ability, rapid development, dormant
stages) (Williams 2006). This typically results in lower aquatic species richness when
compared to more perennial systems (Datry et al., 2014; Arscott et al., 2010) supporting the
notion that stream drying (i.e., the loss of surface water) is a principal driver of community
structure in river networks. Terrestrial/riparian taxa have life histories, strategies, and
adaptations to take advantage of limiting resources, avoid and/or endure hydrological
changes, in particular inundation and current forces when flow returns to intermittent streams
(Lambeets et al., 2008; O'Callaghan et al., 2013; McCluney and Sabo, 2014). The faunal
composition of assemblages that colonize intermittent stream beds can change markedly
within and between years (wet-dry cycles) and include taxa distinct from those in perennially
flowing stream beds or adjacent terrestrial habitats (Stromberg et al., 2009; Dell et al., 2014;
Steward et al., 2011) but the effect of drying on adjacent riparian communities may not be as
distinct (Corti and Datry, 2014).Only those taxa that have adaptations enabling them to
This article is protected by copyright. All rights reserved.
tolerate harsh drying conditions or exploit newly available aquatic habitat (e.g., burrowing or
dormant stages) can persist locally (Williams 2006). Organisms inhabiting historically
perennial rivers that become intermittent may not possess adaptations that enable them to
persist in intermittent systems.
Intermittent rivers function differently from their perennial counterparts with respect
to biogeochemical fluxes and may have substantial impacts on carbon and nutrient fluxes at
the network, regional, and global scales (Datry et al., 2014; Pisani et al.). The periodic
transitions between aquatic and terrestrial phases in intermittent river beds, particularly
immediately at their transitions have been identified as hot spots and hot moments for
biogeochemistry (McClain et al., 2003) and have been further described as “punctuated
biogeochemical reactors” (Larned et al., 2010b). The physiochemical changes stemming
from changes in water availability, including redox state, temperature, and retention are key
in controlling the sequence of biogeochemical functions (Ademollo et al., 2011). During the
dry phase, processing is slow, and materials accumulate and transform through
photodegradation, evaporation, and desorption (McLaughlin, 2008; Dieter et al., 2013; Kerr
et al., 2010). The nature of the rewetting will largely determine the subsequent function.
When flow resumes through advancing fronts much of the stored material (leaf litter,
dissolved nutrients, terrestrial organisms) is transported downstream (Obermann et al., 2009).
During the recession or where flow resumes gradually (upwelling groundwater) local
material processing is fast (Tzoraki and Nikolaidis, 2007; Gallo et al., 2013). As flow
contracts, isolated pools can lead to further biogeochemical heterogeneity controlled by
factors at smaller scales (Fellman et al., 2013).
Despite the recognized importance of their character on river-riparian ecosystem
structure and function, a fundamental and largely overlooked component of intermittent river
ecology is a quantitative understanding of the controls on wetting and drying cycles. The
This article is protected by copyright. All rights reserved.
strong longitudinal, vertical, and lateral shifts in hydrologic connectivity associated with
these cycles affect movement of organisms and exchange of materials and energy across
aquatic habitats and aquatic-terrestrial interfaces (i.e., riparian areas). Flow attributes,
including antecedent conditions, duration, magnitude, frequency, and rate of change (Poff et
al., 1997), can be used to describe discharge patterns and spatiotemporal variations during
low flow conditions. Recent ecological research has developed principles of low-flow
conditions that describe how these flow attributes influence river ecosystems (Rolls et al.
2012). For example, particular characteristics of flow conditions in all rivers, but especially
intermittent rivers, impacts the extent and quality of available aquatic habitat and the
connectivity and exchange of materials through a river network (Jaeger et al., 2014) with
implications for metacommunity and metaecosystem dynamics (Larned et al., 2010b;
Whitney et al., 2015).
Seminal work in fluvial geomorphology occurred in intermittent, dryland systems of
the American Southwest (e.g., Bull, 1997; Schumm, 1979), but the emphasis did not extend
to controls on flow permanence. More recent hydrologic and geologic research on
intermittent rivers has largely been constrained to identifying physical indicators of
intermittent rivers (Fritz et al., 2008; Snelder et al., 2013), with few exceptions that address
mechanisms driving flow permanence (Godsey and Kirchner, 2014). The scarcity of research
that integrates meteorologic, geologic, land cover, and biologic processes (Allen et al., 2014)
may be attributed to the challenge of integrating different disciplines that maintain specific
research methodologies, timescales, and spatial extents of interest.
There is a need for ecologists to recognize the broader and more holistic freshwater
and terrestrial context in which intermittent rivers function (Datry et al., 2014). This
understanding requires an even broader integration beyond ecology that includes hydrologic
and geologic disciplines in order to identify and quantify the mechanisms and thresholds in
This article is protected by copyright. All rights reserved.
hydrologic response that drive spatiotemporal patterns of flow permanence. Although there is
growing recognition of the importance of intermittent rivers from scientific (e.g., Datry et al.,
2014; Jaeger et al. 2014) and policy (e.g., the US Environmental Protection Agency’s Clean
Water Rule; http://www2.epa.gov/cleanwaterrule) perspectives, implementations of
management objectives are still subject to key knowledge gaps that leave rivers vulnerable to
further degradation and misuse (Acuña et al. 2014). Consequently, there is an urgency to
understand the mechanisms controlling flow permanence in order to predict anthropogenic
impacts on intermittent river ecological processes, including their resiliency, responses to
climatic shifts, and other ongoing water-resource pressures (Leibowitz et al., 2008; Doyle
and Bernhardt, 2010). While other recent reviews include or can be extended to intermittent
rivers (e.g., Tooth 2000, Smakhtin 2001; Gomi et al. 2002, Levick et al. 2008; McDonough et
al 2011; Bracken et al. 2013), the present work integrates the full suite of meteorologic,
geologic, and land-use processes across spatiotemporal scales within a context pertinent to
biological applications. In addition, we provide research priorities for intermittent river
science that will elucidate the relative controls of meteorology, geology, and land cover on
flow permanence.
METEOROLOGIC, GEOLOGIC, AND LAND COVER INFLUENCES ON FLOW
PERMANENCE.
Particularly characteristic of river networks are expansion and contraction cycles in response
to variations in the amount of available water, which are most extreme for intermittent rivers,
oscillating between terrestrial and aquatic states. River networks expand when moisture
conditions increase and more of the network supports streamflow; networks contract when
moisture reserves are depleted (figure 4; Stanley et al., 1997; Godsey and Kirchner, 2014).
Figure 4 may be modified or adapted for those systems that are supported by hydrologic
processes other than a fluctuating water table, like the humid region, or by upstream
streamflow generation that outpaces downstream losses, like the arid region. In particular,
This article is protected by copyright. All rights reserved.
some systems rapidly transition from completely dry to fully inundated (i.e., flash flood)
where surface flows can be connected because surface water volumes exceed losses to the
subsurface. This example may not have any effect on water table elevations so may not
include all steps within the illustrated sequence of wetting and drying. In addition, the
patterns described here may be interrupted or initiated at any time in the sequence, as
indicated by the arrows. For example, short dry spells interrupted by precipitation events can
transition from contraction to expansion before a channel reaches the completely dry state.
The proximate cause of intermittent streamflow in those channels with more
persistent flows is, generally, water table fluctuations relative to riverbed elevation; flows
occur when water tables intersect riverbeds and cease when the water table drops below the
riverbed (Konrad 2006b, Larned et al. 2010a, von Schiller et al. 2011). Rivers may be
perennially flowing with no connection to groundwater if the upstream flow generation
volumes exceed losses to groundwater, which may be the case for dryland, mountainous
rivers (Larned et al., 2011; Larned et al., 2007) but may occur in alpine, tropical, and
temperate regions as well (Steward et al., 2012). Drying processes at all spatiotemporal scales
may be interrupted at any stage by rewetting associated with precipitation and runoff (Stanley
et al. 1997). Network expansion and contraction cycles in intermittent river networks can
range in complexity, that result in dynamic spatiotemporal gradients of flow continuity (i.e.,
continuous flow at a specific location through time) and flow connectivity (i.e., continuous
flow across space and time) (Jaeger and Olden, 2012). The dynamic spatiotemporal patterns
of flow continuity and connectivity create mosaics of aquatic and terrestrial habitats that
influence physical, chemical, and biological processes in rivers (Larned et al., 2010b). Those
channels having streamflow generated only from overland flow or direct channel interception
will generally have lower flow permanence (Gomi et al. 2002) and therefore may not
experience the complexity of network expansion described above.
This article is protected by copyright. All rights reserved.
Flow permanence reflects the interactions between inputs of water and the basin
conditions that mediate how water moves to and through the river network (Montgomery,
1999). River networks are nested, hierarchically organized systems (Frissell et al., 1986).
Patterns of streamflow are at least partially controlled by processes acting at small
spatiotemporal time scales (Snelder et al., 2013; Fleckenstein et al., 2006; Dodds, 1997). It is
important to look at the full range spatiotemporal conditions and the interactions between
spatiotemporal scales to understand patterns of streamflow. Water inputs and basin
conditions, including geologic and land cover characteristics, interact across spatiotemporal
scales that range from the watershed to sub-meter and millennia to hours.
Here we propose a framework that describes the three dominant controls on flow
permanence – meteorology, geology, and land cover – across spatiotemporal scales that we
consider pertinent to biological processes in intermittent rivers systems (figure 5). We
introduce the framework at the broadest scale, recognizing that broad-scale structure controls
finer scale processes (Montgomery, 1999; Frissell et al., 1986) that affect flow permanence.
The spatio-temporal (e.g., x-axis) scale should be interpreted as nested hierarchical levels and
the tendency towards intermittent or perennial flow (e.g., y-axis) should be interprested that
those with a larger arrow have a greater influence than those with a smaller arrow.
Hydrologic processes at the hillslope are applicable and can be extended to understanding
mechanisms driving flow permanence in intermittent rivers and can be coupled with
conventional catchment hydrology. Therefore, we apply hillslope and catchment hydrology in
addition to studies on perennial rivers and a few well studied intermittent rivers. We build
upon and expand on previous work with attention to spatiotemporal scales that transcend
hydroclimatic regimes and are meaningful to biological research. We do this by applying
knowledge obtained through hillslope and watershed hydrology work as the foundation to our
assertions, coupled with the few well-studied intermittent rivers. Our goals are to: (1) provide
This article is protected by copyright. All rights reserved.
a conceptual framework that appropriately describes flow permanence and (2) provide a
foundation to evaluate anticipated changes in flow permanence under climate change and/or
water resources development scenarios.
Meteorologic
Climate, multi-annual phenomena, weather, and events are the meteorologic processes that
govern inputs of precipitation and energy, which are first-order controls on streamflow
(figure 5a). Climate is the longer term (>100 years) averages of environmental conditions
(e.g., precipitation, temperature, and humidity). Multi-annual phenomena are the inter-annual
or decadal variability in climate. Weather is the inter- and intra-annual variations in
environmental conditions. Events are unique occurrences of rain, snowstorm, or meltwater at
a discrete location and point in time.
Proximity of the river channel to the water table is a control in determining the
spatiotemporal pattern of streamflow in intermittent rivers (Larned et al., 2010a; Konrad,
2006; Von Schiller et al., 2011; Goulsbra et al., 2014). All of the meteorologic scales
(climate, multi-annual phenomena, weather, and event) presented here influence the location
of the water table. Shallow water table depths occur under wetter antecedent conditions;
depth to water table increases under drier antecedent conditions. While the location of the
water table is a key control on streamflow, groundwater resources must be of sufficient size
and have the hydraulic properties that are conducive to contribute to streamflow (Smakhtin,
2001).
The climatic regime, juxtaposed against evapotranspiration (ET) demands, is the
overarching control on the occurrence of intermittent rivers. Precipitation can exceed or be
exceeded by ET, depending on availability of solar radiation within the system. Arid and
semi-arid biomes have low but highly variable precipitation that is often exceeded by
potential ET due to high energetic inputs that result in both a higher proportion of and higher-
This article is protected by copyright. All rights reserved.
ordered intermittent rivers (Snelder et al., 2013; Levick et al., 2008). Conversely, temperate
or humid regions are characterized with higher and more consistent mean annual precipitation
that is not often exceeded by ET resulting in decreased frequency of and generally lower-
ordered intermittent rivers. Multi-annual phenomena have oscillations that strongly influence
inter- and intra-annual patterns in precipitation and ET. Multi-annual phenomena influence
average flow permanence patterns that extend over multiple years or decades. Drought
periods extending over several years may result in increased drying and reduced flow
permanence. Perennial rivers may transition to intermittent rivers under prolonged and/or
intense droughts (e.g., the Arkansas River at Great Bend, KS, figure 1d). Ecological
responses to potentially catastrophic disturbances (Beisner et al., 2003) such as drought can
include fundamental and sustained changes to community composition (e.g., Bêche et al.,
2009), which in turn will influence how the broader ecosystem functions (Leberfinger et al.,
2010; Bruder et al., 2011). Over large spatial scales, the filtering effects of drought results in
more homogeneous community composition among different locations (Chase, 2007).
The finer scales of weather and event influence the immediate duration, timing, and
frequency of continuity and connectivity of streamflow. Weather patterns of precipitation,
meltwater, ET, and aquifer recharge influence streamflow and water table relationships
(Konrad, 2006; Doering et al., 2007). Intermittency occurs if there are sufficient precipitation
deficits (Buttle et al., 2012) and can manifest as changes in the spatial extent of streamflow as
a consequence of decreased precipitation between years (Jaeger et al., 2007). Variations in
weather (e.g., energy inputs) control meltwater generation, which will control the timing and
magnitude of water delivery to the channels draining areas with snowpack and/or glaciers.
The character of individual precipitation or meltwater events will determine flow continuity
and connectivity at the shortest temporal scale but can affect both small and intermediate
spatial scales (Jaeger and Olden, 2012). Precipitation events of higher frequencies, higher
This article is protected by copyright. All rights reserved.
intensities, and longer durations promote flow permanence compared to those of low
frequency, low intensity, and shorter durations. During prolonged dry periods, the channel
will require longer and higher intensity precipitation events to support streamflow compared
to instances when time periods between precipitation events are short and antecedent
moisture conditions are wet (Zimmerman et al. 2014).
Geologic
River networks are multi-scaled, non-linear, hierarchically nested systems that may be
organized geologically, at a coarse scale, by watershed, reach, functional set, and mesohabitat
(Frissell et al., 1986). The watershed, reach, functional set, and mesohabitat scales are useful
scales because they are often the scales over which various fluvial geomorphic and river
ecologic research is conducted. Watersheds are the areas draining to a specific point in a river
network. Reaches are large lengths of rivers with integrated geologic units with generally
similar characteristics of valley confinement and channel sinuosity. Functional sets are
hydromorphologic units or bedform combinations with characteristic channel dimension and
hydraulic relationships (pool-riffle, step-pool, etc.) as a function of flow depth, velocity, and
bed material. Mesohabitats are discrete bedforms or patches within the functional set (e.g., an
individual pool or riffle) with relatively homogenous flow depth, velocity, and bed material.
Watersheds are fixed at the broadest spatiotemporal level, barring instances of low frequency,
extreme magnitude events (e.g., tectonic uplift, volcanism, sudden climatic shifts); whereas,
at the finest level, mesohabitats are highly dynamic.
Lithology governs the types of rock and soils that develop at the watershed scale,
which exerts critical controls on hillslope water movement, to and through the subsurface,
and its eventual delivery to the river. Permeable soils and preferential flowpaths facilitate
rapid water delivery to channels and rapid expansion and contraction cycles (Doering et al.,
2007). Highly permeable surficial geology and soils with rapid infiltration enhance flow
This article is protected by copyright. All rights reserved.
permanence whereby water infiltrates during wet periods and re-emerges to contribute to
streamflow during drier periods (Jencso and McGlynn, 2011). Impermeable bedrock mantled
by a thin layer of permeable surficial geology and soil results in insufficient storage to sustain
flows and thus reduced flow permanence. Transitions in surficial geology alter subsurface
storage capabilities (Payn et al., 2009) that can either promote or reduce hydrologic
connectivity and flow permanence (Jencso and McGlynn, 2011). Basin shape will also
influence flow permanence. For example, small, elongated watersheds with steep slopes tend
to more often support intermittent flows as a consequence of rapid water delivery to (e.g.,
short flowpath distances) and processing through rivers (Snelder et al., 2013).
Local slope influences river-aquifer exchanges, which promotes flow intermittency or
permanence at the reach and functional set scales (Goulsbra et al., 2014). Incising rivers with
slopes steeper than the regional groundwater table slope induce hydraulic gradients that drive
groundwater towards the river (Konrad, 2006). Aggrading reaches with riverbed elevations
above the regional water table produce hydraulic gradients that force surface water from the
river into the aquifer (Konrad, 2006), promoting drying and decreased flow permanence.
Preferential flow paths are, potentially, key controls on flow permanence (Payn et al., 2012)
and the spatiotemporal variability in water sources (Payn et al., 2009). Springs and seeps that
flow along fractures can serve as dominant and consistent sources of streamflow (Payn et al.,
2012), which promotes flow permanence. Soil macropores are preferential flow paths that
develop by action of soil fauna and plant roots, physical or chemical weathering of materials,
and/or by subsurface flows or piping (Beven and Germann, 1982). Macropores can
temporarily but fundamentally alter the hillslope-river hydrologic relationships by producing
a desynchronization between streamflow and precipitation that will vary inter- and intra-
annually and can promote or diminish flow permanence (Zimmermann et al., 2014; Costigan
et al., 2015)).
This article is protected by copyright. All rights reserved.
Riverbed permeability is a primary control on flow permanence at the functional set
and mesohabitat scales. The residence time of water in intermittent rivers is brief over
permeable substrates (Bull, 1997) as a consequence of higher transmission losses to
groundwater (Levick et al., 2008). The relative importance of transmission losses in
governing streamflow is largely unknown (Smakhtin, 2001) but likely plays a substantial role
in the persistence of local surface water (Buttle et al., 2012). Local hydraulic gradients
attributed to local changes in bed slope variations occur within and between mesohabitats
(e.g., pool, riffle, run) and will drive the movement of surface water into and out of rivers
(Stanley et al., 1997; Konrad, 2006). For example, streamflow goes subsurface at the
downstream extent of pools and upstream extent of riffles and resurfaces at the downstream
extent of riffles. At the mesohabitat scale, as water vacates the channel the tops of rocks are
the first to dry and the last to become wet when the water returns to the channel.
Land cover
Land cover is the material that covers the surface of the Earth and reflects the interactions
between meteorologic, geologic, ecologic, and anthropogenic activities on that landscape. We
organize land cover as a function of distance from the river into biome, land use, riparian
zone, and in-channel engineered structures (figure 5c). At the broadest levels, climate and
lithology regulate the natural biome of the region. The natural biome of a region will, in part,
determine the particular land uses that may occur, the composition and structure of riparian
zones that can include engineering activities, and the types of engineered structures present
within the river. Land use is the anthropogenic management and modification of natural
biomes. Riparian zones are the interface between terrestrial and aquatic systems, which can
include substantial anthropogenic activities such as levee construction, mining, and other
activities across the floodplain and adjacent terraces and hillslopes. In-channel engineered
infrastructure involve direct river manipulations (e.g., dams, culverts, weirs).
This article is protected by copyright. All rights reserved.
Intermittency occurs in all terrestrial biomes but is more likely to occur in dryland
areas such as grasslands (figure 1a), deserts (figure 1b), and tundra (Dodds, 1997; Poff,
1996). The agent, severity, and frequency of land cover disturbances, both natural and
anthropogenic, will influence flow permanence at the biome, land use, and riparian zone
levels. Understanding these natural as well as anthropogenic influences is critical to
understand how human related activities will change these systems. Land-cover disturbances
influence streamflow (or change hydrologic regime) by altering infiltration capacity, ET, and
canopy interception of water. Intermittent headwaters have, in particular, been extensively
disturbed by anthropogenic actives such as being filled or diverted to support development
activities (Roy et al., 2009). Large-scale timber harvesting or large stand-replacing wildfires
will lower ET losses, which promote perennial flow; whereas, large-scale afforestation will
raise ET losses, which promote intermittent flows. Impervious surfaces from urban land use
can decrease flow permanence by reducing groundwater recharge (due to reduced infiltration
capacity); however, leaky infrastructure and increased riverbed incision as a consequence of
alterations in runoff and streamflow patterns may sustain surface flows in urban intermittent
rivers (Fritz et al., 2013; Lerner, 2002). For example in the southwestern US, the duration and
number of flow events in urbanized areas were greater than in less disturbed areas, which was
attributed to reductions in infiltration capacities and subsequent increases in runoff events
within the watershed (Gungle, 2006). Urbanization causes increases in impervious surface
covers that reduce groundwater recharge and infiltration, which has resulted in intermittent
rivers having particularly flashy hydrographs (Rheinhardt et al., 2009). Water is routed to and
through the river more rapidly when impervious surfaces comprise riparian zones or roads
intersecting the river. Soil compaction associated with large-scale anthropogenic activities
(e.g., surface and subsurface mining, heavy machinery traffic) changes the natural
meteorologic and geologic structure and results in rapid delivery of water to rivers, which can
This article is protected by copyright. All rights reserved.
either promote or reduce flow permanence (Peirce and Lindsay, 2015). Groundwater
extraction promotes intermittency by depleting aquifers.
Water resource development at the land use and riparian zone scales alter
streamflows. Perennial rivers may transition to an intermittent regime if there is substantial
drawdown of an aquifer (Falke et al., 2011). For instance, the Arkansas River, which flows
across the Ogallala Aquifer, has sections that have recently gone dry (figure 1d) as a result of
extensive and intensive irrigation practices (Falke et al., 2011). Anthropogenic delivery
systems (e.g., tile drainage systems, sewers, irrigation systems) can usurp catchment
characteristics in controlling the patterns of water delivery to rivers (Helton et al., 2010). A
common agricultural practice is artificial subsurface drainages systems (e.g., tile drainage)
that remove of near-surface soil moisture that can rapidly deliver water to the channel
(Schilling and Helmers, 2008; Klaus et al., 2013).
In-channel structures, whether natural (e.g., large wood) or engineered, mediate
whether or not water is able to persist in the river at the smallest spatiotemporal scales. Direct
importation or exportation of water via inter-basin transfers can substantially restructure
natural flow regimes (Larned et al., 2010b; Steward et al., 2012). Diversion structures, weirs,
and dams intercept flows and inundate upstream sections and may cause downstream portions
of streams to become intermittent (Steward et al., 2012; Caruso and Haynes, 2011). In cases
where dam releases are consistent and constant or when water is discharged from mining or
sewage treatment facilities intermittent rivers may transition to perennial (Steward et al.,
2012; Hassan and Egozi, 2001).
RESEARCH PRIORITIES
Understanding meteorologic, geologic, and land-cover controls of intermittency has
significant implications for the ecology and management of intermittent networks (Allen et
al., 2014). Here we identify critical knowledge gaps in our understanding of the controls of
This article is protected by copyright. All rights reserved.
flow permanence and provide practical and field-based approaches to strengthen insights on
the relative importance of meteorologic, geologic, and land cover controls on intermittency
by linking information across multiple spatiotemporal scales. Many of the controls on flow
permanence were inferred from the literature of perennial river systems; intermittent river-
targeted research is necessary to test and validate these assertions.
There have been numerous studies on hillslope and watershed hydrology. The key to
understanding intermittent streams is to identify the threshold behavior of channelized
surface flow generation and the patterns in space and time of when that threshold is crossed.
Future studies investigating the influence of surface-groundwater interactions on flow
permanence are especially important since transmission losses, infiltration, and effluence are
primary controls on streamflow in those intermittent rivers influenced by water table
fluctuations (Shanafield and Cook, 2014). Applying what we know about boundary
conditions from streamflow generation (i.e., hillslope/watershed hydrology) studies to new
research on alluvial systems that focuses on understanding the threshold behavior of surface
water flow in the channel is necessary in order to gain new insight into predicting the
spatiotemporal patterns of intermittent flow. Future research addressing the timing and
pathways of water within intermittent rivers will be of particular importance.
Effects of urban land use on flow permanence represent another area of needed
research given the extent and continued increase of urbanization and the confounding
interactions and inconsistent directionality of streamflow changes in response to urbanization
(Fritz et al., 2013). Lag times may hinder the ability to detect the effects of recent land-use
change on river morphology because intermittent rivers may only flow briefly (Miller and
Doyle, 2014; Benda et al., 2005; Rendell and Alexander, 1979). Concurrent research on the
influence of natural disturbances on flow permanence is also necessary to disentangle the
complexity associated with the effects of human land use, particularly as water resources are
This article is protected by copyright. All rights reserved.
managed more intensively. With projected growing demand on water resources, other land-
use activities such as inter-basin transfers may play an increasing role and could have
substantial impact on larger rivers from which water is being transferred, as well as the
receiving channel (Larned et al., 2010b; Steward et al., 2012).
Models and remote sensing are also frontiers in hydrologic sciences that have
considerable potential when the cost for widespread, long-term monitoring becomes
prohibitive. Field data are necessary to build and validate models and remote sensing. Two
methods for future field research that we believe will help elucidate the complex interaction
of meteorology, geology, and land cover include: (1) use of environmental tracers and
isotopes for identifying age, sources, and pathways of water within a riverscape that includes
both the aquatic and associated terrestrial regions of a river network and (2) monitoring
networks for assessing spatiotemporal patterns of flow within intermittent river networks.
Meteorologic, geologic, and land cover watershed characteristics interact in complex ways
which influence flow pathways and how water is routed through landscapes. Isotopes (e.g.,
18O, 2H, 3H) provide information about transit time and environmental tracers (e.g., Si, Ca, F)
provide information about the sources of water and flow pathways of hydrologic systems
(McDonnell et al., 2010). Multi-tracer approaches are necessary to fully characterize the
sources and timing of water intermittent rivers. The use of environmental tracers and isotopes
to assess hydrological characteristics of a system is particularly beneficial, requiring less a
priori information, and can integrate heterogeneity within the system (Bracken et al., 2013).
Environmental tracers used in conjunction with isotopes are able to integrate small-scale
hydrological processes and large-scale catchment responses (Soulsby et al., 2006).
Traditional gages (e.g., located at a single station) are unlikely to capture the
spatiotemporal variability of intermittent rivers (Snelder et al., 2013). Field mapping of
expansion and contraction has been conducted (Godsey and Kirchner, 2014; Day, 1978; Day,
This article is protected by copyright. All rights reserved.
1980; Turner and Richter, 2011) but the accuracy is limited by subjectivity of interpretation
and the frequency of site visits. Electrical resistivity (ER) sensors are increasingly used to
characterize the spatiotemporal dynamics of flow connectivity and continuity of intermittent
rivers. ER sensors provide a low cost, high performance, and minimal data interpretation
method to monitor intermittent river spatiotemporal dynamics (Chapin et al., 2014). Aspects
other than timing, duration, and frequency of flow such as the resumption (i.e., advancing)
and recession (i.e., retreating) rates or magnitudes can be characterized with ER sensor arrays
(Jaeger et al., 2014; Goulsbra et al., 2014; Peirce and Lindsay, 2015; Chapin et al., 2014;
Blasch et al., 2002; Goulsbra et al., 2009; Bhamjee and Lindsay, 2010; Adams et al., 2006;
Bhamjee et al., 2015) or other instrumentation (e.g., video, photographs, audio, temperature;
Larned et al., 2010a; Gungle, 2006; Constantz et al., 2001; Spence and Mengistu, 2015;
Quinlan et al., 2015). A combined approach of instrumentation with piezometers to
determine groundwater table elevations, soil water probes, and ER sensor arrays would
facilitate an understanding of expansion and contraction cycles at an unprecedented
resolution over large spatial scales. However, ER sensors and piezometers alone are only able
to determine presence/absence of water and cannot provide information about the source of
water within a network, which would require tracer methods. Integrating piezometers, soil
water probes, and ER sensors remain intellectual and practical issues in translating massive
datasets in to scientific knowledge (Porter et al., 2012). Using field-based measurements of
flow permanence in conjunction with model simulations may provide valuable insight into
how flow continuity and connectivity may change as a function of climatic shifts (Jaeger et
al., 2014).
Quantifying characteristics of streamflow continuity and connectivity are important
for understanding ecological responses to this hydrologic disturbance. The degree of
continuity will influence the ability of aquatic and riparian zone biota to endure and/or avoid
This article is protected by copyright. All rights reserved.
a drying disturbance (i.e., resistance). Connectivity will influence the ability of biota
dependent on water to recolonize from refuges (e.g., perennial reaches, groundwater, isolated
pools) when water returns (i.e., resilience). Variability of flow permanence characteristics
within and among networks may influence the harshness of meteorologic, geologic, and land-
cover conditions at local and regional scales, constraining the diversity of aquatic organisms
that can persist at a given locality and the overall pool of species available to recolonize after
drying. Hydrologic variation can be better characterized by using recently developed tools
such as ER sensors that would enhance our ecological understanding of these transient
systems and enable better predictions of ecological dynamics across a range of
spatiotemporal scales.
Bridging disciplinary-specific methods and spatiotemporal scales of studies to
produce a more consistent, synthetic understanding of intermittency is a primary challenge of
studying intermittent rivers. Intermittent rivers are complex systems with various influences
on the manner through which flow is distributed over time and space. Integrating
environmental tracers, isotopes, piezometers, and ER sensors provides an exciting
opportunity to gain a comprehensive understanding of the timing, pathways, and sources of
water and the expansion and contraction cycles that are exemplified in intermittent rivers. If
this integrated methodological approach is deployed long-term with high spatiotemporal
resolution, we can more thoroughly understand the meteorology, geology, and land-cover
characteristics that give rise to the presence and source of water within intermittent river
networks.
CONCLUSIONS
The conceptual models and future research directions described in this paper are aimed at
moving us toward a more comprehensive understanding of the complex
hydromorphodynamics of intermittent rivers. Research focusing on intermittent rivers has
This article is protected by copyright. All rights reserved.
increased rapidly with respect to the number of published studies and the maturity of the
science within the last decade. We have classified research around intermittent rivers into
three primary controls that represent distinct disciplines with discipline-specific concepts,
methods, and spatiotemporal scales of study. It is timely for researchers to begin unifying
research on the meteorologic, geologic, and land-cover aspects of intermittent rivers with
biological studies of intermittent rivers across spatial and temporal scales that range from the
watershed to sub-meter and millennial to hours.
Research design approaches that capture the structure as well as the functions that
control the presence and absence of surface water and/or groundwater in intermittent river
networks will contribute substantially to this field of study. Research integration from the
fields of meteorology, geology, and ecology will provide exciting opportunities for exploring
the interactions of multiple spatiotemporal controls on intermittency and their implications
for river ecosystems. An understanding of each scale of influence on the character of flow
permanence provides a useful framework to appropriately describe flow permanence and
better anticipate hydrological and ecological responses under changing climate change
scenarios and/or water resources development. Coupling surface-water monitoring using ER
sensors and piezometers with the use of environmental tracers and isotopes are necessary
tools to assess intermittent rivers resulting in information gained that is a high research
priority for the hydrological and ecological community. The temporal resolution and storage
capacity of the latest generation of ER sensors enable long term (i.e., multiple years)
deployment and capture of network expansion and contraction dynamics. The conceptual
models and future research directions described here are aimed at moving us toward a more
comprehensive understanding of the complex hydromorphodynamics of intermittent river
networks.
This article is protected by copyright. All rights reserved.
ACKNOWLEDGEMENTS
Support for this research was provided by The Ohio State University’s Climate, Water, and
Carbon Program. Joshuah Perkin provided thoughtful ideas for figure generation. Although
this work was reviewed by USEPA and approved for publication, it might not necessarily
reflect official Agency policy. This manuscript was improved by the thoughtful comments of
Robert Payn and four anonymous reviewers.
This article is protected by copyright. All rights reserved.
REFERENCES
Acuna V, Datry T, Marshall J, Barcelo D, Dahm CN, Ginebreda A, McGregor G, Sabater S,
Tockner K, Palmer MA. 2014. Conservation. Why should we care about temporary
waterways?. Science (New York, N.Y.) 343: 1080-1081.
Adams EA, Monroe SA, Springer AE, Blasch KW, Bills DJ. 2006. Electrical resistance
sensors record spring flow timing, grand canyon, arizona. Groundwater 44: 630-641.
Adams RK, Spotila JA. 2005. The form and function of headwater streams based on field and
modeling investigations in the Southern Appalachian Mountains. Earth Surface
Processes and Landforms 30: 1521-1546.
Ademollo N, Capri S, Patrolecco L, Puddu A, Polesello S, Rusconi M, Valsecchi S,
Froebrich J. 2011. Fate and monitoring of hazardous substances in temporary rivers.
TrAC Trends in Analytical Chemistry 30: 1222-1232.
Allen DC, Cardinale BJ, Wynn-Thompson T. 2014. Toward a better integration of ecological
principles into ecogeoscience research. Bioscience 64: 444-454.
Allen DC, McCluney KE, Elser SR, Sabo JL. 2013. Water as a trophic currency in dryland
food webs. Frontiers in Ecology and the Environment 12: 156-160.
Arscott DB, Larned S, Scarsbrook MR, Lambert P. 2010. Aquatic invertebrate community
structure along an intermittence gradient: Selwyn River, New Zealand. Journal of the
North American Benthological Society 29: 530-545.
Bêche LA, Connors PG, Resh VH, Merenlender AM. 2009. Resilience of fishes and
invertebrates to prolonged drought in two California streams. Ecography 32: 778-788.
Beisner BE, Haydon DT, Cuddington K. 2003. Alternative stable states in ecology. Frontiers
in Ecology and the Environment 1: 376-382.
Benda L, Hassan MA, Church M, May CL. 2005. Geomorphology Of Steepland Headwaters:
The Transition From Hillslopes To Channels1. Journal of the American Water
Resources Association 41: 835-851.
Beven K, Germann P. 1982. Macropores and water flow in soils. Water Resources Research
18: 1311-1325.
Bhamjee R, Lindsay J. 2010. Ephemeral stream sensor design using state loggers. Hydrology
and Earth System Sciences Discussions 7: 6381-6405.
Bhamjee R, Lindsay JB, Cockburn J. 2015. Monitoring ephemeral headwater streams: a
paired‐sensor approach. Hydrological Processes.
Blasch KW, Ferré T, Christensen AH, Hoffmann JP. 2002. New field method to determine
streamflow timing using electrical resistance sensors. Vadose Zone Journal 1: 289-
299.
Bracken L, Wainwright J, Ali G, Tetzlaff D, Smith M, Reaney S, Roy A. 2013. Concepts of
hydrological connectivity: Research approaches, pathways and future agendas. Earth-
Science Reviews 119: 17-34.
Bruder A, Chauvet E, Gessner MO. 2011. Litter diversity, fungal decomposers and litter
decomposition under simulated stream intermittency. Functional Ecology 25: 1269-
1277.
Bull WB. 1997. Discontinuous ephemeral streams. Geomorphology 19: 227-276.
Buttle J, Boon S, Peters D, Spence C, van Meerveld H, Whitfield P. 2012. An overview of
temporary stream hydrology in Canada. Canadian Water Resources Journal 37: 279-
310.
Caruso BS, Haynes J. 2011. Biophysical‐Regulatory Classification and Profiling of Streams
Across Management Units and Ecoregions1. JAWRA Journal of the American Water
Resources Association 47: 386-407.
This article is protected by copyright. All rights reserved.
Chapin TP, Todd AS, Zeigler MP. 2014. Robust, low‐cost data loggers for stream
temperature, flow intermittency, and relative conductivity monitoring. Water
Resources Research 50: 6542-6548.
Chase JM. 2007. Drought mediates the importance of stochastic community assembly.
Proceedings of the National Academy of Sciences of the United States of America
104: 17430-17434.
Constantz J, Stonestorm D, Stewart AE, Niswonger R, Smith TR. 2001. Analysis of
streambed temperatures in ephemeral channels to determine streamflow frequency
and duration. Water Resources Research 37: 317-328.
Corti R, Datry T. 2014. Drying of a temperate, intermittent river has little effect on adjacent
riparian arthropod communities. Freshwater Biology 59: 666-678.
Costigan KH, Daniels MD, Dodds WK. 2015. Fundamental spatial and temporal
disconnections in the hydrology of an intermittent prairie headwater network. Journal
of Hydrology 522: 305-316.
Datry T, Larned S, Fritz K, Bogan M, Wood P, Meyer E, Santos A. 2014. Broad‐scale
patterns of invertebrate richness and community composition in temporary rivers:
effects of flow intermittence. Ecography 37: 94-104.
Datry T, Arscott DB, Sabater S. 2011. Recent perspectives on temporary river ecology.
Aquatic Sciences-Research Across Boundaries 73: 453-457.
Datry T, Larned ST, Tockner K. 2014. Intermittent Rivers: A Challenge for Freshwater
Ecology. Bioscience 64: 229–235.-DOI:10.1093/biosci/ bit027.
Day D. 1978. Drainage density changes during rainfall. Earth surface processes 3: 319-326.
Day DG. 1980. Lithologic controls of drainage density: A study of six small rural catchments
in New England, NSW. Catena 7: 339-351.
Dell AI, Alford RA, Pearson RG. 2014. Intermittent pool beds are permanent cyclic habitats
with distinct wet, moist and dry phases.
Dieter D, Frindte K, Krüger A, Wurzbacher C. 2013. Preconditioning of leaves by solar
radiation and anoxia affects microbial colonisation and rate of leaf mass loss in an
intermittent stream. Freshwater Biology 58: 1918-1931.
Dodds WK. 1997. Distribution of runoff and rivers related to vegetative characteristics,
latitude, and slope: a global perspective. Journal of the North American Benthological
Society: 162-168.
Doering M, Uehlinger U, Rotach A, Schlaepfer D, Tockner K. 2007. Ecosystem expansion
and contraction dynamics along a large Alpine alluvial corridor (Tagliamento River,
Northeast Italy). Earth Surface Processes and Landforms 32: 1693-1704.
Doyle MW, Bernhardt ES. 2010. What is a stream?. Environmental science & technology 45:
354-359.
Falke JA, Fausch KD, Magelky R, Aldred A, Durnford DS, Riley LK, Oad R. 2011. The role
of groundwater pumping and drought in shaping ecological futures for stream fishes
in a dryland river basin of the western Great Plains, USA. Ecohydrology 4: 682-697.
Fellman JB, Petrone K, Grierson P. 2013. Leaf litter age, chemical quality, and
photodegradation control the fate of leachate dissolved organic matter in a dryland
river. Journal of Arid Environments 89: 30-37.
Fleckenstein JH, Niswonger RG, Fogg GE. 2006. River‐aquifer interactions, geologic
heterogeneity, and low‐flow management. Groundwater 44: 837-852.
Frissell CA, Liss WJ, Warren CE, Hurley MD. 1986. A hierarchical framework for stream
habitat classification: viewing streams in a watershed context. Environmental
management 10: 199-214.
Fritz KM, Hagenbuch E, D'Amico E, Reif M, Wigington PJ, Leibowitz SG, Comeleo RL,
Ebersole JL, Nadeau T. 2013. Comparing the Extent and Permanence of Headwater
This article is protected by copyright. All rights reserved.
Streams From Two Field Surveys to Values From Hydrographic Databases and Maps.
JAWRA Journal of the American Water Resources Association 49: 867-882.
Fritz KM, Johnson BR, Walters DM. 2008. Physical indicators of hydrologic permanence in
forested headwater streams. Journal of the North American Benthological Society 27:
690-704.
Gallo EL, Brooks PD, Lohse KA, McLain JE. 2013. Temporal patterns and controls on
runoff magnitude and solution chemistry of urban catchments in the semiarid
southwestern United States. Hydrological Processes 27: 995-1010.
Godsey S, Kirchner J. 2014. Dynamic, discontinuous stream networks: hydrologically driven
variations in active drainage density, flowing channels and stream order. Hydrological
Processes 28: 5791-5803.
Goulsbra C, Evans M, Lindsay J. 2014. Temporary streams in a peatland catchment: pattern,
timing, and controls on stream network expansion and contraction. Earth Surface
Processes and Landforms 39(6): 790–803.
Goulsbra C, Lindsay J, Evans M. 2009. A new approach to the application of electrical
resistance sensors to measuring the onset of ephemeral streamflow in wetland
environments. Water Resources Research 45: W09501.
Gungle B. 2006. Timing and duration of flow in ephemeral streams of the Sierra Vista
subwatershed of the Upper San Pedro Basin, Cochise County, southeastern Arizona.
US Geological Survey.
Hassan MA, Egozi R. 2001. Impact of wastewater discharge on the channel morphology of
ephemeral streams. Earth Surface Processes and Landforms 26: 1285-1302.
Helton AM, Poole GC, Meyer JL, Wollheim WM, Peterson BJ, Mulholland PJ, Bernhardt
ES, Stanford JA, Arango C, Ashkenas LR. 2010. Thinking outside the channel:
modeling nitrogen cycling in networked river ecosystems. Frontiers in Ecology and
the Environment 9: 229-238.
Jaeger K, Olden J. 2012. Electrical resistance sensor arrays as a means to quantify
longitudinal connectivity of rivers. River Research and Applications 28: 1843-1852.
Jaeger KL, Montgomery DR, Bolton SM. 2007. Channel and perennial flow initiation in
headwater streams: management implications of variability in source-area size.
Environmental management 40: 775-786.
Jaeger KL, Olden JD, Pelland NA. 2014. Climate change poised to threaten hydrologic
connectivity and endemic fishes in dryland streams. Proceedings of the National
Academy of Sciences of the United States of America 111: 13894-13899.
Jencso KG, McGlynn BL. 2011. Hierarchical controls on runoff generation: Topographically
driven hydrologic connectivity, geology, and vegetation. Water Resources Research
47: W11527.
Kennard MJ, Pusey BJ, Olden JD, MacKay SJ, Stein JL, Marsh N. 2010. Classification of
natural flow regimes in Australia to support environmental flow management.
Freshwater Biology 55: 171-193.
Kerr JG, Burford M, Olley J, Udy J. 2010. The effects of drying on phosphorus sorption and
speciation in subtropical river sediments. Marine and Freshwater Research 61: 928-
935.
Klaus J, Zehe E, Elsner M, Külls C, McDonnell J. 2013. Macropore flow of old water
revisited: experimental insights from a tile-drained hillslope. Hydrology and Earth
System Sciences 17: 103-118.
Konrad CP. 2006. Location and timing of river-aquifer exchanges in six tributaries to the
Columbia River in the Pacific Northwest of the United States. Journal of hydrology
329: 444-470.
This article is protected by copyright. All rights reserved.
Lambeets K, Vandegehuchte ML, Maelfait J, Bonte D. 2008. Understanding the impact of
flooding on trait‐displacements and shifts in assemblage structure of predatory
arthropods on river banks. Journal of Animal Ecology 77: 1162-1174.
Larned ST, Arscott DB, Schmidt J, Diettrich JC. 2010a. A Framework for Analyzing
Longitudinal and Temporal Variation in River Flow and Developing Flow‐Ecology
Relationships1. JAWRA Journal of the American Water Resources Association 46:
541-553.
Larned ST, Datry T, Arscott DB, Tockner K. 2010b. Emerging concepts in temporary‐river
ecology. Freshwater Biology 55: 717-738.
Larned ST, Datry T, Robinson CT. 2007. Invertebrate and microbial responses to inundation
in an ephemeral river reach in New Zealand: effects of preceding dry periods. Aquatic
Sciences 69: 554-567.
Larned ST, Schmidt J, Datry T, Konrad CP, Dumas JK, Diettrich JC. 2011. Longitudinal
river ecohydrology: flow variation down the lengths of alluvial rivers. Ecohydrology
4: 532-548.
Leberfinger K, Bohman I, Herrmann J. 2010. Drought impact on stream detritivores:
experimental effects on leaf litter breakdown and life cycles. Hydrobiologia 652: 247-
254.
Leibowitz SG, Wigington Jr PJ, Rains MC, Downing DM. 2008. Non-navigable streams and
adjacent wetlands: addressing science needs following the Supreme Court's Rapanos
decision. Frontiers in Ecology and the Environment 6: 364-371.
Lerner DN. 2002. Identifying and quantifying urban recharge: a review. Hydrogeology
Journal 10: 143-152.
Levick L, Fonseca J, Goodrich D, Hernandez M, Semmens D, Stromberg J, Leidy R, Scianni
M, Guertin D, Tluczek M. 2008. The ecological and hydrological significance of
ephemeral and intermittent streams in the arid and semi-arid American southwest. US
Environmental Protection Agency and USDA/ARS Southwest Watershed Research
Center. ARS Southwest Watershed Research Center.
McClain ME, Boyer EW, Dent CL, Gergel SE, Grimm NB, Groffman PM, Hart SC, Harvey
JW, Johnston CA, Mayorga E. 2003. Biogeochemical hot spots and hot moments at
the interface of terrestrial and aquatic ecosystems. Ecosystems 6: 301-312.
McCluney KE, Sabo JL. 2014. Sensitivity and Tolerance of Riparian Arthropod Communities
to Altered Water Resources along a Drying River.
McDonnell J, McGuire K, Aggarwal P, Beven K, Biondi D, Destouni G, Dunn S, James A,
Kirchner J, Kraft P. 2010. How old is streamwater? Open questions in catchment
transit time conceptualization, modelling and analysis. Hydrological Processes 24:
1745-1754.
McLaughlin C. 2008. Evaporation as a nutrient retention mechanism at Sycamore Creek,
Arizona. Hydrobiologia 603: 241-252.
Merritt DM, Wohl EE. 2003. Downstream hydraulic geometry and channel adjustment during
a flood along an ephemeral, arid-region drainage. Geomorphology 52: 165-180.
Miller BW, Doyle MW. 2014. Rangeland management and fluvial geomorphology in
northern Tanzania. Geomorphology 214: 366-377.
Montgomery DR. 1999. Process domains and the river continuum. Journal of the American
Water Resources Association 35: 397-410.
Obermann M, Rosenwinkel K, Tournoud M. 2009. Investigation of first flushes in a medium-
sized mediterranean catchment. Journal of Hydrology 373: 405-415.
O'Callaghan MJ, Hannah DM, Boomer I, Williams M, Sadler JP. 2013. Responses to river
inundation pressures control prey selection of riparian beetles. PloS one 8.
This article is protected by copyright. All rights reserved.
Payn R, Gooseff M, McGlynn B, Bencala K, Wondzell S. 2012. Exploring changes in the
spatial distribution of stream baseflow generation during a seasonal recession. Water
Resources Research 48: W04519.
Payn R, Gooseff M, McGlynn B, Bencala K, Wondzell S. 2009. Channel water balance and
exchange with subsurface flow along a mountain headwater stream in Montana,
United States. Water Resources Research 45: W11427.
Peirce SE, Lindsay JB. 2015. Characterizing ephemeral streams in a southern Ontario
watershed using electrical resistance sensors. Hydrological Processes 29: 103–111.
Pisani O, Dodds WK, Jaffé R. Characterizing organic matter inputs to sediments of small,
intermittent, prairie streams: a molecular marker and stable isotope approach. Aquatic
Sciences: 1-12.
Poff N. 1996. A hydrogeography of unregulated streams in the United States and an
examination of scale‐dependence in some hydrological descriptors. Freshwater
Biology 36: 71-79.
Poff NL, Allan JD, Bain MB, Karr JR, Prestegaard KL, Richter BD, Sparks RE, Stromberg
JC. 1997. The natural flow regime. Bioscience: 769-784.
Porter JH, Hanson PC, Lin C. 2012. Staying afloat in the sensor data deluge. Trends in
ecology & evolution 27: 121-129.
Quinlan E, Gibbins C, Batalla R, Vericat D. 2015. Impacts of Small Scale Flow Regulation
on Sediment Dynamics in an Ecologically Important Upland River. Environmental
management 55: 671-686.
Rendell H, Alexander D. 1979. Note on some spatial and temporal variations in ephemeral
channel form. Geological Society of America Bulletin 90: 761-772.
Rheinhardt RD, McKenney‐Easterling M, Brinson MM, Masina‐Rubbo J, Brooks RP,
Whigham DF, O’Brien D, Hite JT, Armstrong BK. 2009. Canopy Composition and
Forest Structure Provide Restoration Targets for Low‐Order Riparian Ecosystems.
Restoration Ecology 17: 51-59.
Roy AH, Dybas AL, Fritz KM, Lubbers HR. 2009. Urbanization affects the extent and
hydrologic permanence of headwater streams in a midwestern US metropolitan area.
Journal of the North American Benthological Society 28: 911-928.
Rupp DE, Larned ST, Arscott DB, Schmidt J. 2008. Reconstruction of a daily flow record
along a hydrologically complex alluvial river. Journal of hydrology 359: 88-104.
Schilling KE, Helmers M. 2008. Effects of subsurface drainage tiles on streamflow in Iowa
agricultural watersheds: Exploratory hydrograph analysis. Hydrological Processes 22:
4497-4506.
Shanafield M, Cook PG. 2014. Transmission losses, infiltration and groundwater recharge
through ephemeral and intermittent streambeds: A review of applied methods.
Journal of Hydrology 511: 518-529.
Smakhtin V. 2001. Low flow hydrology: a review. Journal of hydrology 240: 147-186.
Snelder TH, Datry T, Lamouroux N, Larned ST, Sauquet E, Pella H, Catalogne C. 2013.
Regionalization of patterns of flow intermittence from gauging station records.
Hydrology & Earth System Sciences Discussions 17: 2685–2699.
Soulsby C, Tetzlaff D, Rodgers P, Dunn S, Waldron S. 2006. Runoff processes, stream water
residence times and controlling landscape characteristics in a mesoscale catchment:
An initial evaluation. Journal of Hydrology 325: 197-221.
Spence C, Mengistu S. 2015. Deployment of an unmanned aerial system to assist in mapping
an intermittent stream. Hydrological Processes.
Stanley EH, Fisher SG, Grimm NB. 1997. Ecosystem expansion and contraction in streams.
Bioscience 47: 427-435.
This article is protected by copyright. All rights reserved.
Steward AL, Marshall JC, Sheldon F, Harch B, Choy S, Bunn SE, Tockner K. 2011.
Terrestrial invertebrates of dry river beds are not simply subsets of riparian
assemblages. Aquatic Sciences 73: 551-566.
Steward AL, von Schiller D, Tockner K, Marshall JC, Bunn SE. 2012. When the river runs
dry: human and ecological values of dry riverbeds. Frontiers in Ecology and the
Environment 10: 202-209.
Stromberg JC, Hazelton AF, White MS, White JM, Fischer RA. 2009. Ephemeral wetlands
along a spatially intermittent river: temporal patterns of vegetation development.
Wetlands 29: 330-342.
Tooth S. 2000. Process, form and change in dryland rivers: a review of recent research.
Earth-Science Reviews 51: 67-107.
Tooth S, Nanson GC. 2011. Distinctiveness and diversity of arid zone river systems. Arid
Zone Geomorphology: Process, Form and Change in Drylands, Third Edition: 269-
300.
Turner DS, Richter HE. 2011. Wet/dry mapping: using citizen scientists to monitor the extent
of perennial surface flow in dryland regions. Environmental management 47: 497-
505.
Tzoraki O, Nikolaidis NP. 2007. A generalized framework for modeling the hydrologic and
biogeochemical response of a Mediterranean temporary river basin. Journal of
Hydrology 346: 112-121.
Von Schiller D, Acuña V, Graeber D, Martí E, Ribot M, Sabater S, Timoner X, Tockner K.
2011. Contraction, fragmentation and expansion dynamics determine nutrient
availability in a Mediterranean forest stream. Aquatic Sciences 73: 485-497.
Whitney JE, Gido KB, Martin EC, Hase KJ. 2015. The first to arrive and the last to leave:
colonisation and extinction dynamics of common and rare fishes in intermittent
prairie streams. Freshwater Biology.
Zimmermann B, Zimmermann A, Turner BL, Francke T, Elsenbeer H. 2014. Connectivity of
overland flow by drainage network expansion in a rain forest catchment. Water
Resources Research 50: 1457-1473.
This article is protected by copyright. All rights reserved.
Fig. 1. Examples of intermittency patterns for natural (left column) and anthropogenically
altered (right column) rivers in the USA. The grey area represents the 95% confidence
intervals on mean daily discharge from 1980-2009 and the black line represents mean daily
discharge from 2012. Area is provided by the USGS but is unavailable for Willow Creek
Floodway Channel.
This article is protected by copyright. All rights reserved.
Fig. 2. Examples of the highly variable morphologic forms among intermittent rivers: (A)
small, steep, cobble- and gravel-bed river, (B) large, gradual, sand-bed river. Approximate
coordinates of where the photos were taken are given in the figure. Photograph A was taken
by Katie Costigan of an unnamed river in the Killbuck River watershed, Ohio, USA. Joshuah
Perkin provided photograph B of the Salt Fork Arkansas River, Kansas, USA.
This article is protected by copyright. All rights reserved.
Fig. 3. An example of an intermittent river during (A) terrestrial and (B) aquatic states. The
white arrows in the photo mark the same location. Approximate coordinates of where the
photos were taken are given in the figure. The photo was taken by Ken Fritz of Sycamore
Branch, Hoosier National Forest, Indiana, USA.
This article is protected by copyright. All rights reserved.
Fig. 4. Expansion and contraction cycles of intermittent rivers at the mesohabitat, functional
set, and network scales. Flow is from left to right in the functional set and longitudinal profile
and top to bottom in the network scale. The insets at the mesohabitat and functional set scale
are planviews of a pool and of pool-riffle sequence, respectively. We have included the
location of the insets in the network scale for arid and humid regions. This figure is adapted
after Datry et al. 2014b, McDonough et al. 2011, and Stanley et al. 1997.
This article is protected by copyright. All rights reserved.
Fig. 5. Spatiotemporal hierarchy of the (a) meteorologic, (b) geologic, and (c) land-cover
characteristics that control streamflow regimes. The direction of influence are assigned, either
promoting intermittent flow (upper half with black arrows) or perennial (lower half with grey
arrows), with the understanding that alternative cases exist as well as unknown directions of
influence, which are denoted in text along the center line of the graph where arrows radiate
from. The x-axis is hierarchically nested. The tendency towards promoting perennial or
intermittent flows is along the y-axis.
