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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.
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Laurie C. Alexander, Ken M. Fritz, Kate A. Schofield, Bradley C. Autrey, Julie E. DeMeester, Heather E.
Golden , David C. Goodrich, William G. Kepner, Hadas R. Kiperwas, Charles R. Lane, Stephen D. LeDuc,
Scott G. Leibowitz, Michael G. McManus , Amina I. Pollard, Caroline E. Ridley, Melanie K. Vanderhoof, and
Parker J. Wigington, Jr.
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, protect-
ing 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 estu-
aries. 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 longi-
tudinal, 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.
(KEY TERMS: ecological integrity; river networks; streams; wetlands; floodplains; riparian areas; watersheds;
U.S. Clean Water Act.)
Alexander, Laurie C., Ken M. Fritz, Kate A. Schofield, Bradley C. Autrey, Julie E. DeMeester, Heather E.
Golden, David C. Goodrich, William G. Kepner, Hadas R. Kiperwas, Charles R. Lane, Stephen D. LeDuc, Scott
G. Leibowitz, Michael G. McManus, Amina I. Pollard, Caroline E. Ridley, Melanie K. Vanderhoof, and Parker J.
Wigington, Jr., 2018. Featured Collection Introduction: Connectivity of Streams and Wetlands to Downstream
Waters. Journal of the American Water Resources Association (JAWRA) 54(2): 287297.
Paper No. JAWRA-17-0107-P of the Journal of the American Water Resources Association (JAWRA). Received July 24, 2017; accepted
January 22, 2018. ©2018 American Water Resources Association. This article is a U.S. Government work and is in the public domain in the
USA. Discussions are open until six months from issue publication.
National Center for Environmental Assessment (NCEA) (Alexander, Schofield, DeMeester, LeDuc, Ridley), and Office of Water (Kiperwas
[formerly], Pollard), U.S. Environmental Protection Agency (USEPA), Washington, D.C., USA; National Exposure Research Laboratory
(NERL) (Fritz, Autrey, Golden, Lane), and NCEA (McManus), USEPA, Cincinnati, Ohio, USA; Southwest Watershed Research Center (Good-
rich), USDA-Agricultural Research Service, Tucson, Arizona, USA; NERL (Kepner), USEPA, Las Vegas, Nevada, USA; National Health and
Environmental Effects Research Laboratory (Leibowitz, Wigington [retired]), USEPA, Corvallis, Oregon, USA; and Geosciences and Environ-
mental Change Science Center (Vanderhoof), U.S. Geological Survey, Denver, Colorado, USA (Correspondence to Alexander:
The principal objective of the U.S. Clean Water
Act (CWA) is to “restore and maintain the chemical,
physical, and biological integrity of the Nation’s
waters” (33 U.S.C. §1362(7)). This objective explic-
itly establishes the central role of ecological (i.e.,
chemical, physical, and biological) integrity to the
attainment of clean water. Connectivity is a key
component of ecological integrity, and has long been
a central tenet in aquatic ecosystem research. Con-
cepts and definitions of connectivity have evolved
over the past several decades (Taylor et al. 2006) as
have metrics for quantifying it (Leibowitz et al.
2018). For the purposes of this featured collection,
we define connectivity as follows: Connectivity is the
degree to which components of a watershed are
joined and interact by transport mechanisms that
function across multiple spatial and temporal scales,
and is determined by the characteristics of both the
physical landscape and the biota of the specific sys-
tem. Here, “physical landscape” refers to abiotic fea-
tures of the landscape, i.e., the scalable habitat
template established by climate, geology, landform,
and human activities (Southwood 1988). Within the
abiotic template, connections established by
exchanges of matter, energy, and living organisms
are influenced by the spatial structure and arrange-
ment of habitats and land uses (Turner and Gardner
2015; Leibowitz et al. 2018). This definition of con-
nectivity reflects a systems perspective of watersheds
as heterogeneous mosaics of interacting ecosystems
in which variations in the duration, magnitude, fre-
quency, timing, and stability of flows form dynamic,
spatiotemporal continua of connectivity (Figure 1).
These gradients of connectivity, which vary in
degree from highly isolated to highly connected, sup-
port the wide range of ecosystem functions needed
to maintain the chemical, physical, and biological
integrity of the nation’s waters, and are the focus of
this featured collection.
The papers in this featured collection review the
results of 40+years of scientific research on the
chemical, physical, and biological connectivity of
streams and wetlands to larger, downstream waters,
such as rivers, lakes, and coastal waters (hereafter
collectively referred to as downstream waters). They
synthesize the substantial body of scientific evidence
on the ecological effects of source waters and in
particular, small or temporary streams and nontidal
wetlands on the ecological integrity of downstream
waters and, as a collection, summarize the state-of-
the-science on the interrelatedness of these diverse
aquatic ecosystems.
The reviews in this collection were originally devel-
oped as a report (USEPA 2013, 2015) that provided
the scientific basis for a 2015 rulemaking by the U.S.
Environmental Protection Agency (EPA) and the U.S.
Army Corps of Engineers (Corps) to clarify the defini-
tion of “waters of the United States,” which determi-
nes the scope of CWA jurisdiction. The resulting
regulation, titled the Clean Water Rule (FR 80 FR
page-37054) went into effect in most U.S. states in
August 2015, but was stayed nationwide by the U.S.
Court of Appeals for the Sixth Circuit in October
2015 pending the outcome of litigation. At the time of
this writing, the 2015 regulation is in review by the
issuing agencies under direction of an Executive
Order, issued in February 2017, to rescind or revise
it (FR 82-42, 12532;
The need for rulemaking to clarify CWA scope
arose from three Supreme Court cases in 1985, 2001,
and 2006 that created uncertainty about the regula-
tory status of some types of waters. In 1985, the
Court’s unanimous decision in United States v. River-
side Bayview Homes (474 U.S. 12) upheld the agen-
cies’ long-standing practice of regulating “adjacent”
wetlands, defined as wetlands that are “bordering,
contiguous, or neighboring” to a “navigable water.”
(Note: Regulatory and legal terms are shown in quo-
tation marks to avoid confusion with other usages.)
In a 2001 case, Solid Waste Agency of Northern Cook
County (SWANCC) v. U.S. Army Corps of Engineers
(531 U.S. 159), the Court decided 5-4 that use by
migratory birds was not, by itself, sufficient for CWA
jurisdiction over intrastate, nonnavigable, isolated
waters, including the many ponds and wetlands along
common flyways and overwintering areas. Most
recently, in 2006, the Supreme Court heard Rapanos
v. United States, 547 U.S. 715, a case challenging the
inclusion of nonnavigable tributaries and their “adja-
cent” wetlands in CWA jurisdiction. The Court’s split
(4-1-4) ruling in Rapanos yielded multiple, conflicting
opinions with no majority decision. Justice Scalia and
three other Justices argued that the scope of the
CWA includes only “relatively permanent, standing or
flowing bodies of water” and wetlands with a “contin-
uous surface connection” to such waters. Justice Ken-
nedy concurred with Scalia et al. that Rapanos
should be remanded to the lower courts, but dis-
agreed with their standard of relative permanence for
jurisdiction. In a separate opinion, Justice Kennedy
wrote that tributaries, wetlands, and open waters
must “possess ‘significant nexus’ to waters that are or
were navigable in-fact or that could reasonably be so
made.” He argued that a water body has “significance
nexus” if, “either alone or in combination with simi-
larly situated lands in the region, [it] significantly
affect[s] the chemical, physical, and biological integ-
rity of other covered waters more readily understood
as ‘navigable.’” In a third, dissenting opinion, Justice
Stevens and three other Justices agreed with the reg-
ulatory agencies that the waters at issue were juris-
dictional under the CWA, and that the Corps’
decision to assert jurisdiction over the particular wet-
lands in question was both “reasonable” and “permis-
sible.” The dissenting Justices also stated that the
multiple standards issued in these Court opinions
“can only muddy the jurisdictional waters.” For a
more complete history of the CWA and legal chal-
lenges to its jurisdiction, see Downing et al. (2003),
Downing et al. (2007), Nadeau and Rains (2007), and
Adler (2013, 2015).
While the uncertainties raised by these court cases
cannot be resolved by science alone (Adler 2015;
Alexander 2015; Hawkins 2015), the available scien-
tific literature provides a large body of evidence on
the connectivity and ecological functions of water bod-
ies in question primarily, small or temporary
streams and nontidal wetlands that can influence the
chemical, physical, or biological integrity of large riv-
ers, lakes, and coastal waters. The authors of this
introduction and featured collection worked together
on a five-year interdisciplinary review of literature on
watershed connections that have potential wide-
spread relevance to CWA programs. In September
2013, a draft of the EPA report (USEPA 2013) was
released for public comment and independent peer
review. The peer review (20132014) was conducted
by a panel of 27 experts nominated by the public and
convened by EPA’s Science Advisory Board (SAB). All
SAB panel meetings are open to the public, and all
SAB documents including comments, meeting
notes, and draft and final reports are available on
the SAB’s website. The proceedings of this SAB
Water table level
Groundwater flow through local and larger scale aquifers
Overland and interflow
Streamflow and transport of materials, organisms
Overbank flow and transport of materials, organisms
Bank storage
Hyporheic flow and surface-subsurface exchange of water, materials, organisms
Stream and wetland recharge of
local and regional aquifers
Perennial stream
Ephemeral stream
Intermittent stream
Atmospheric losses
(e.g., evapotranspiration, volatilization, denitrification)
Wetland (dry period)
Open-water (dry period)
Active floodplain: Expansion and overbank flow into floodplain
and overflow of wetlands and open-waters during wetter periods
Unsaturated zone
Saturated zone
Local aquifer and hyporheic zone
Confining layer
FIGURE 1. Hydrologic flow paths. Arrows are representative of surface water and groundwater flows occurring throughout a watershed.
Subsurface flows are shown within the cross section, and by faded arrows outside the cross section. Source: USEPA (2015).
review, and the panel’s final report to EPA’s adminis-
trator, can be found at
TableRow=2.3#2. Comments from this SAB panel’s
report (USEPA 2014) were incorporated into EPA’s
final report (USEPA 2015) and were further consid-
ered while writing the papers in this featured
Collectively, the papers presented here provide a
synthesis of evidence pertaining to the interrelated-
ness of freshwater ecosystems, emphasizing what is
known about the watershed-scale functions of
streams, wetlands, and open waters whose jurisdic-
tional status under the CWA have been called into
question by the three U.S. Supreme Court cases sum-
marized briefly above. While relevant to regulatory
decisions under the CWA, these papers are technical
reviews of peer-reviewed scientific literature. As such,
they do not consider or establish EPA policy and do
not consider or propose legal standards for CWA
Because the original intent of these reviews was to
inform the 2015 regulation clarifying the definition of
“waters of the United States,” the papers in this col-
lection address three charge questions that were
developed in 2010 for that effort (Table 1). These
questions were formulated through iterative dia-
logues between scientists in EPA’s Office of Research
(ORD), attorneys and policy specialists in EPA’s
Office of Water, and EPA’s Office of General Counsel
(OGC) to identify the specific nature of the policy
needs, and to determine, within that scope, which
questions could be informed by a formal review of sci-
entific (ORD) or legal (OGC) knowledge. Policy ques-
tions expressed in terms of CWA regulations (which
include categories such as “adjacent waters,” “tradi-
tional navigable waters,” and “other waters”) were
translated into terms that could be used to search the
literature (Table 1). For example, “adjacent” waters
were translated into “wetlands and open waters in
riparian areas and floodplains.” The regulatory term
“traditional navigable waters” is derived from the
statutory term “navigable waters” (Downing et al.
2003) and serves as a reference for many CWA juris-
dictional determinations. It includes large streams
and rivers, lakes, reservoirs, coastal waters, but is
not limited to water bodies that are “navigable-in-
fact” (Downing et al. 2003; Adler 2015). For the pur-
poses of these reviews, we use the term “downstream
waters” as a flexible surrogate for “traditional naviga-
ble waters” (Table 1).
This introductory paper describes the featured col-
lection, briefly reviews the concept of connectivity in
freshwater science, and summarizes major conclu-
sions across the papers in the collection. Leibowitz
et al. (2018) provide a framework to understand
hydrological, chemical, and biological connectivity,
focused on the mechanisms by which wetlands and
headwater streams connect to and contribute to riv-
ers. Fritz et al. (2018) review evidence of the physical
and chemical connections by which streams and asso-
ciated riparian and floodplain wetlands influence the
structure and function of downstream waters (i.e.,
the fluvial hydrosystem; Figure 1). Lane et al. (2018)
review the functions and effects of diverse wetland
and open-water systems occurring outside of riparian
areas and floodplains on downstream waters (Fig-
ure 1). Schofield et al. (2018) review the literature on
how movements of aquatic and semiaquatic biota con-
nect freshwater habitats over various temporal and
spatial scales (Figure 2). Finally, Goodrich et al.
(2018) present a regionally focused case study on the
connections and effects of the intermittent and
ephemeral streams and rivers that dominate the arid
southwestern U.S. Each review also considers biotic
and abiotic factors that influence connectivity, and
synthesizes information on ecosystem functions
TABLE 1. Translating connectivity-related questions between regulatory policy and science. This table crosswalks regulatory and scientific
questions that determined the scope of the reviews in this featured collection. Regulatory and legal terms are shown in quotation marks to
avoid confusion with other usages. Modified from USEPA (2015).
Regulatory question Review question Featured papers
What tributaries have a “significant
nexus” to
“traditional navigable waters”?
What are the connections to and effects of
ephemeral, intermittent, and perennial streams
on downstream waters?
Leibowitz et al. (2018)
Fritz et al. (2018)
Schofield et al. (2018)
Goodrich et al. (2018)
What “adjacent” waters have a “significant
nexus” to
“traditional navigable waters”?
What are the connections to and effects of riparian
or floodplain wetlands and open waters on
downstream waters?
Leibowitz et al. (2018)
Fritz et al. (2018)
Schofield et al. (2018)
What categories of “other waters” have a “significant
nexus” to “traditional navigable waters”?
What are the connections to and effects of
wetlands and open waters in nonfloodplain
settings on downstream waters?
Leibowitz et al. (2018)
Lane et al. (2018)
Schofield et al. (2018)
“Significant,” as used here, is a policy determination informed by science; it does not refer to statistical significance.
associated with different types and degrees of connec-
tivity (Figure 3).
The primary pathways of aquatic connectivity con-
sidered here are surface water flows, shallow ground-
water flows, and movements of aquatic and
semiaquatic organisms, all of which connect water-
sheds in four dimensions (Table 2).
Key considerations in our synthesis of aquatic con-
nectivity are ecosystem functions within watershed
components (e.g., streams, wetlands) that alter fluxes
of materials or movements of organisms between
them (Leibowitz et al. 2018). These functions are
broadly categorized into source, sink, refuge, lag, and
transformation (Leibowitz et al. 2018).
In this collection, the term “connectivity”
which has many contexts and definitions in the lit-
erature is shorthand for the complex interactions
of landscape, climate, and biota that support ecolog-
ical integrity (Figure 3). Our reviews focus on con-
nections of potential relevance to CWA programs,
but draw from the rich history of research (next
section) that built the foundation for current under-
standing of the role of connectivity in maintaining
the integrity and resilience of downstream waters
(Figure 3).
Connectivity has long been central to the study of
freshwater ecology, hydrology, biogeochemistry, and
geomorphology. The River Continuum Concept (RCC)
(Vannote et al. 1980) portrayed the stream network,
from the headwaters to the river mouth, as a complex
hydrologic gradient with predictable longitudinal pat-
terns of ecological structure and function. The key to
the RCC pattern is that downstream communities are
organized, in large part, by upstream communities
and their processes (Vannote et al. 1980; Battin et al.
2009). The Serial Discontinuity Concept (Ward and
Stanford 1983) built on the RCC to further under-
stand how dams and impoundments disrupt the lon-
gitudinal patterns of ecological function in flowing
waters with predictable downstream effects. The Spi-
raling Concept (Webster and Patten 1979; Newbold
et al. 1981; Elwood et al. 1983) described how river
network connectivity can be conceptualized and mea-
sured as materials cycle from dissolved forms to tran-
siently stored forms in living organisms, then back to
dissolved forms, as they are transported downstream.
Water table level
Aquatic transport or movement
Overland transport or movement (aerial or terrestrial)
Surface-subsurface exchange of water, materials, organisms
Biochemical transformation and transport (e.g., nutrient spiraling)
Perennial stream
Ephemeral stream
Intermittent stream
Wetland (dry period)
Open-water (dry period)
Active floodplain: Expansion and overbank flow into floodplain
and overflow of wetlands and open-waters during wetter periods
Unsaturated zone
Saturated zone
Local aquifer and hyporheic zone
Confining layer
FIGURE 2. Biological pathways. Arrows are representative of biological pathways occurring throughout a watershed.
This figure also includes representative biogeochemical pathways occurring in streams and floodplains. Source: USEPA (2015).
Habitat quality
Water quality
Community structure
Indicator species
Functional groups
Population attributes
Annual water surplus
Rainfall intensity
Soil type
Aquifer permeability
Spatial distribution
Life cycle
Dispersal capability
Dispersal cues
Dispersal behavior
Stream and wetland
FIGURE 3. The role of connectivity in maintaining the integrity of water. Climate, landscape, species’ traits, and human activities (Influencing
Factors) interact to form Connections (hydrologic, chemical, and biological) between ecosystems throughout and across watersheds. Fluxes of
materials and energy, and movements of living organisms, are enabled, inhibited, or modified by functions within watershed components (e.g.,
streams, wetlands) that modify the timing of transport and the quantity and quality of resources available to downstream communities (Effects).
Monitoring programs have developed metrics for assessing physical habitat, water quality, and biological assemblages as indicators of the
ecological (i.e., physical, chemical, and biological) integrity of downstream waters (Assessment Endpoints and Metrics). Source: USEPA (2015).
TABLE 2. Dimensions of watershed connectivity. Modified from USEPA (2015).
Dimension Examples and pathways
(Alexander et al. 2007; Freeman et al. 2007) Streamflow and downstream transport of materials, organisms (Figure 1)
Hyporheic flow (Figure 1)
Groundwater flow through local and large-scale aquifers (Figure 1)
Aquatic or overland movement of organisms in or along stream channels (Figure 2)
Biogeochemical transport and transformation (Figure 2)
(Ward 1989; Stanford and Ward 1993) Overbank flow and transport from channels into banks, floodplains, and riparian
areas (Figure 1)
Spillage and transport from wetlands and open waters into streams (Figure 1)
Overland flow and interflow (Figure 1)
Groundwater recharge from streams and wetlands (Figure 1)
Bank storage (Figure 1)
Transport or movement of organisms between streams and wetlands or open
waters (Figure 2)
(Amoros and Bornette 2002; Banks et al. 2011) Surface-subsurface exchange of water, materials, organisms (Figures 2 and 3)
Groundwater recharge from streams and wetlands (2)
Atmospheric exchanges (Figure 1)
(Hewlett and Hibbert 1967; Bohonak and
Jenkins 2003; Zedler 2003)
Variable source area (Figure 1)
Seasonal cycles of wetland inundation and outflow to streams (Figure 1)
Migration by aquatic organisms (Figure 2)
Dormancy of aquatic organisms (Figure 2)
These conceptual frameworks focused on the longitu-
dinal connections of river ecosystems, whereas the
subsequent Flood Pulse Concept (Junk et al. 1989)
examined the importance of lateral connectivity
between river channels and floodplains, including
wetlands and open waters, through seasonal expan-
sion and contraction of river networks. Ward (1989)
summarized the significance of connectivity to lotic
ecosystems across four dimensions: longitudinal,
lateral, vertical (surfacesubsurface), and temporal
connections; he concluded that running water
ecosystems are open systems because they are highly
interactive with both contiguous habitats and other
ecosystems in the surrounding landscape (Figure 1).
Stanford et al. (2005) related the flows of water and
materials through channels and into floodplains to
dynamic and interconnected habitats (shifting habitat
mosaics) that enable diverse assemblages of aquatic
species to coexist (Figures 1 and 2). As these concep-
tual frameworks illustrate, scientists have long recog-
nized the dynamic hydrologic connectivity that the
physical structure of river networks represents.
More recently, scientists have incorporated this
network structure into conceptual frameworks
describing ecological patterns in river ecosystems and
the processes linking them to other watershed compo-
nents, including wetlands and open waters (Power
and Dietrich 2002; Benda et al. 2004; Nadeau and
Rains 2007; Rodriguez-Iturbe et al. 2009). The net-
work dynamic hypothesis (Benda et al. 2004) is a
physically-based framework for predicting patterns of
habitat heterogeneity along rivers, based on dynam-
ics that generate potential biological “hotspots” at
tributary confluences. It reflects a more realistic river
network perspective through remixing the earlier,
more linearly driven frameworks with frameworks
describing the patchy and stochastic nature of lotic
ecosystems (e.g., Resh et al. 1988; Townsend 1989;
Rice et al. 2001). Bunn and Arthington (2002) identi-
fied natural flow variability and associated lateral
and longitudinal connectivity of stream channels and
floodplains as two principal mechanisms linking
hydrology to aquatic biodiversity of riverine species
(also Leigh et al. 2010). In their review of integrative
research on river corridors, Harvey and Gooseff
(2015) highlight quantification of connectivity from
river-reach to regional scales in terms of “hydrologic
exchange flows” that bring downstream flows into
contact with hyporheic, riparian, and floodplain envi-
ronments, where many biogeochemical reactions and
contaminant filtration occur.
In addition, application of metapopulation theory
and population genetic theory to natural populations
has greatly improved our understanding of the role of
dispersal and migration in the demographic persis-
tence, community assembly, and evolution of aquatic
species (Figure 2) (Hastings and Harrison 1994; Pan-
nell and Charlesworth 2000; Fagan 2002; Bohonak
and Jenkins 2003; Waples 2010; Bauer and Hoye
2014). Sheaves (2009) emphasized the key ecological
connections which include process-based connec-
tions that maintain habitat function (e.g., nutrient
dynamics, trophic function) and movements of indi-
vidual organisms throughout a complex of inter-
linked freshwater, tidal wetland, and estuarine
habitats as critical to the persistence of aquatic spe-
cies, populations, and communities over the full
range of time scales.
Based on the review and synthesis of more than
four decades of scientific research into aquatic ecosys-
tem connectivity, the papers in this collection found
strong evidence supporting the critical role of chemi-
cal, physical, and biological connectivity of streams,
wetlands, and open waters in maintaining the struc-
ture, function, and overall ecological (chemical, physi-
cal, and biological) integrity of downstream waters
(e.g., rivers, lakes, estuaries, and oceans) (Figure 3).
Watersheds are integrated at multiple spatial and
temporal scales by flows of surface water and ground-
water, transport and transformation of physical and
chemical materials, and movements of organisms,
which establish varying degrees of connection and
isolation among freshwater habitats in space and
The literature unequivocally demonstrates that
perennial, intermittent, and ephemeral streams, indi-
vidually or cumulatively, exert a strong influence on
the integrity of downstream waters (Fritz et al. 2018;
Goodrich et al. 2018) (Figure 1). The existence of a
continuous bed and bank structure in river networks
is strong geomorphologic evidence for longitudinal
connectivity; lateral connections maintain the struc-
ture of floodplains and riparian areas via recurrent
inundation and deposition of materials during peak
and recession flows (Fritz et al. 2018). Perennial,
intermittent, and ephemeral headwaters make up the
majority of stream channels in most river networks
and cumulatively supply most of the water in rivers
(Fritz et al. 2018). Flows from ephemeral streams are
a major driver of the dynamic hydrology, geomorphol-
ogy, and biogeochemistry of southwestern rivers,
where approximately 80% or more of streams by
southwestern state are ephemeral or intermittent
(Goodrich et al. 2018). Intervening channels connect
headwaters structurally and functionally to large
inland or coastal waters via channels, wetlands, and
alluvial deposits where water and other materials are
concentrated, mixed, transformed, and stored or
transported (Fritz et al. 2018).
Wetlands located outside of floodplains and ripar-
ian areas (hereafter, nonfloodplain wetlands) are
abundant in some regions and perform many of the
same functions as wetlands in floodplains and ripar-
ian areas. These functions include recharge of
groundwater that sustains river baseflows; retention
and transformation of nutrients, metals, sediment,
and pesticides; export of organisms or propagules to
downstream waters; storage and subsequent release
of floodwaters; and provision of protective habitats
for stream species (Lane et al. 2018). However, the
mechanisms by which nonfloodplain wetlands are
hydrologically connected to downstream waters differ
fundamentally from those for riparian and floodplain
wetlands, and their effects on downstream waters
can be more challenging to detect and quantify (Lane
et al. 2018). Nonfloodplain wetlands can and typi-
cally do remain chemically and biologically con-
nected, even in the absence of hydrologic connections,
by overland or aerial movements of aquatic and semi-
aquatic organisms and the materials that they trans-
port (Lane et al. 2018; Schofield et al. 2018)
(Figures 1 and 2).
There is robust evidence that the movement of
organisms between streams, wetlands, open waters,
and downstream waters is an integral component of
the river food webs that support aquatic life. Streams
and wetlands serve numerous functions for down-
stream waters and their populations, by acting as
sources of colonists, food, and genetic diversity; as
refuges from adverse abiotic and biotic conditions;
and as complementary or obligate habitats for the
maturation and reproduction of fish, amphibians, and
invertebrates (Schofield et al. 2018). Because many
aquatic species are capable of moving overland (e.g.,
by active flight, walking, wind dispersal), biological
connections can be more widespread, complex, and
variable than hydrologic connections, and habitats
that seem to be hydrologically isolated are often
highly connected by movements of aquatic biota (Fig-
ure 2). For practical reasons, research into biological
connectivity is often conducted in single systems, for
example, looking at individual species, assemblages,
or ecosystem types. In reality, biological connectivity
is best assessed as the cumulative effects of multiple
species moving, via multiple pathways and across
multiple habitat types, to make use of the full range
of resources found in spatially and temporally vari-
able wetlands, streams, rivers, lakes, ponds, and
other freshwater habitats found throughout water-
sheds (Schofield et al. 2018).
Natural variation in degrees of connectivity arises
from differences in local and regional climate,
landscape, and biotic factors (i.e., connectivity gradi-
ents), and is needed to support the range of functions
by which streams and wetlands maintain down-
stream water integrity (Figure 3). For example,
whereas large stream channels are highly efficient
transport mechanisms for water and other materials,
smaller tributaries and riparian or floodplain wet-
lands provide optimal environments for functions
associated with water storage and material transfor-
mation (e.g., flood control, denitrification) (Fritz et al.
2018). Therefore, variation in the types and degrees
of connectivity enables different ecosystem functions,
and its quantification is central to our understanding
of how streams and wetlands influence the integrity
of downstream waters. In addition, the incremental
effects of individual streams and wetlands accumu-
late throughout (and across) watersheds and must be
evaluated in context with other streams and wet-
lands, as downstream water quality reflects the com-
bined effects of the functions (e.g., of biogeochemical
cycling) and connections (e.g., transport of nutrients)
of all watershed components (Fritz et al. 2018; Good-
rich et al. 2018; Lane et al. 2018; Leibowitz et al.
Due to the variable functions and aggregate effects
of tributaries and wetlands, the size, number, and spa-
tial distribution of streams and wetlands in a water-
shed are important factors governing the integrity of
downstream waters (Fritz et al. 2018; Lane et al.
2018; Schofield et al. 2018). For example, while the
probability of a large-magnitude transfer of sediment
or organisms from any given headwater stream in a
given year might be low (i.e., a low-frequency connec-
tion when each stream is considered individually),
headwater streams are the most abundant type of
stream in most watersheds. The actual probability of a
large-magnitude transfer in a given year is therefore
much higher when the cumulative contributions are
considered. Similarly, nonfloodplain wetlands can
store large proportions of snowmelt runoff (30%60%)
and precipitation (11%20%) received by a watershed,
and that storage could be increased by wetland
restoration (Lane et al. 2018). Similarly, cumulative
export of invertebrates from headwater to downstream
waters can be substantial, especially in intermittent
and ephemeral streams, as terrestrial invertebrates
accumulate in these channels during dry periods and
are then transported downstream in wet periods (Scho-
field et al. 2018).
Assessments of the functional, watershed-scale
effects of nonfloodplain wetlands on downstream
waters can be especially challenging, as temporal and
spatial gradients of connectivity of this diverse group
of wetlands (e.g., many prairie potholes, vernal pools,
playa lakes) are particularly dynamic (Lane et al.
2018; Leibowitz et al. 2018). Recent research has
quantified the connectivity and cumulative effects of
many individual nonfloodplain wetlands within
watersheds. For example, landscape-scale analysis of
inundation from satellite imagery and watershed
modeling of groundwater flow paths have shown that
apparently “isolated” wetlands can be hydrologically
connected seasonally, cyclically, or continuously over
long (>30 km) distances, via surface water and
groundwater flows that contribute to river baseflow
(Lane et al. 2018; Leibowitz et al. 2018). Data from
these and other studies provide strong evidence that
functions of these wetlands act at multiple spatial
and temporal scales to affect hydrologic and chemical
fluxes or transfers of water and materials to down-
stream waters.
The overall objective of the U.S. CWA to restore
and maintain the chemical, physical, and biological
integrity of the nation’s waters acknowledges the
critical role of ecological processes in the attainment of
clean water. Interim goals of the CWA related to water
quality, populations of shellfish, fish and wildlife, and
societal needs (e.g., water for human consumption and
recreational uses) recognize the need for advancing the
scientific understanding of aquatic ecosystems with
authorizations to fund “basic research into the struc-
ture and function of fresh water aquatic ecosystems,
and to improve understanding of the ecological charac-
teristics necessary to the maintenance of the chemical,
physical, and biological integrity of fresh-water aquatic
ecosystems” (33 U.S.C. §1254). The ultimate and
interim goals of the CWA are inextricably intercon-
nected. Societal needs for safe drinking water, for
example, are highly dependent on surface water
ecosystem integrity. In an analysis of water use in the
U.S. in 2005, the U.S. Geological Survey found that
77% of the total freshwater used and 67% of the
public drinking water used came from surface
waters (U.S. Geological Survey, Surface Water Use in
the United States, 2005. Accessed June 30, 2017, In addition, an
analysis by EPA in 2009 found that intermittent,
ephemeral and perennial-headwater streams are
major sources of water for public water supplies (U.S.
Environmental Protection Agency, Section 404 of the
Clean Water Act. Accessed July 21, 2017, https://
This study found that a total of 357,404 miles
(575,186 km) of streams in the continental U.S. are
located within “source protection areas” of public
drinking water intakes that have been identified by
state and local governments. Of these stream miles,
the majority (58%) are intermittent, ephemeral, or
perennial headwaters (207,476 miles or 333,900 km).
In the year of that study (2009), approximately one-
third of the U.S. population (~117,000,000 people)
received their drinking water from public sources that
are supplied entirely or in part by freshwater intermit-
tent, ephemeral, or perennial headwater streams (U.S.
Environmental Protection Agency, Section 404 of the
Clean Water Act. Accessed July 21, 2017, https://
These estimates are conservative, due to the underrep-
resentation of small streams in the nationally avail-
able hydrographic maps (Fritz et al. 2018) used in
these analyses.
As demands on surface water sources continue to
grow, the need for up-to-date scientific information on
natural and anthropogenic controls of freshwater
ecosystem integrity is even greater than it was when
the CWA was enacted in 1972. The literature reviews
in this collection provide a unique synthesis of evi-
dence from the rich history of foundational research
into connectivity, much of which was motivated by
CWA objectives, and from exciting, new studies that
have advanced our scientific understanding of ecologi-
cal connectivity in terms of scale, precision, and com-
plexity. Current research is closing data gaps
identified in this collection and showing promise for
near-term improvements in our ability to assess con-
nectivity and integrity. Examples include network-
based methods for multiscale, multispecies, and mul-
tilevel assessments of ecological networks (Br
et al. 2013; Malvadkar et al. 2015; Engelhard et al.
2016; Rayfield et al. 2016; Pilosof et al. 2017); empiri-
cal observations of spatial and temporal surface wet-
land-stream hydrodynamics at field (Brooks et al.
2018) and landscape scales (Vanderhoof et al. 2016);
models that integrate observational data into mecha-
nistic simulations of hydrologic function (Evenson
et al. 2016; Ameli and Creed 2017; Golden et al.
2017) or integrate those data with network-based geo-
statistical analysis (McGuire et al. 2014); and biologi-
cal connectivity (Bauer and Klaassen 2013). Many
questions about the effects of streams and wetlands
on downstream water integrity can be answered from
the literature reviewed in this featured collection.
Emerging research is rapidly closing existing data
gaps with new insights into aquatic ecosystem con-
nectivity and function at local, watershed, and regio-
nal scales. The syntheses of foundational and
emerging research in this collection provide a
resource for science-based efforts to restore and main-
tain safe, reliable sources of fresh water for present
and future generations.
We thank Rose Kwok for her excellent comments on all manu-
scripts in this featured collection. We also thank Dan Auerbach and
three anonymous reviewers for comments that improved this intro-
duction to the collection. Lastly, we again thank the 47 peer review-
ers acknowledged in USEPA (2015), whose contributions to that
assessment also improved the papers in this featured collection.
Although this work has been reviewed by the USEPA and approved
for publication, it does not necessarily reflect Agency policy.
Former JAWRA editor Kenneth J. Lanfear served as acting edi-
tor in chief for all articles in this featured collection. Parker J. Wig-
ington, Jr., an author on some of the collection papers and who
was JAWRA editor in chief at the time the collection was submit-
ted, had no role in the review or editorial decisions for any part of
the collection.
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... With the constant siltation experienced by dams, their storage capacity is gradually reduced and the hydrological dynamics of the floodplains are progressively resumed. Anthropic adjustment of rivers has changed the natural flow regime in many rivers in the world, decreasing the supply of ecosystem services (Alexander et al. 2018;Poff et al. 2007). Consequently, there is a reduction in the connectivity of floodplains and their associated benefits (Alexander et al. 2018). ...
... Anthropic adjustment of rivers has changed the natural flow regime in many rivers in the world, decreasing the supply of ecosystem services (Alexander et al. 2018;Poff et al. 2007). Consequently, there is a reduction in the connectivity of floodplains and their associated benefits (Alexander et al. 2018). ...
Full-text available
Floodplains cover only 6% of the Earth’s surface. Connectivity occurs in multidirectional patterns in riverbeds, throughout both the drainage paths of the tributaries and the areas contiguous to the riverbed. This study discusses the variations in the levels of the water table as a component of a spatiotemporal representation for evaluating the importance of floodplains as hydric regulatory elements, and the application of this knowledge for developing techniques for the renaturalization of water functions to produce ecosystem services. We measured the variation in the water table level in a floodplain of the Paraiba do Sul River (southeastern Brazil), whose 77 floodplains occupy only 3.87% of the basin and present a high potential for the renaturalization of their water functions. The litho-structural control point (LSCP) is situated in the river channel and mark the end of the floodplain. Areas near the LSCP remain continually saturated, storing water and contributing to dry-season hydrographs. Areas up to 4400 m away from the LSCP perform hydric regulation, storing water from floods of the riverbed and reducing its flow downstream. Areas up to 7500 m away from the LSCP have an increased absorption potential. These three areas operate differently and integrally in absorbing floodwaters and recharging the water table, influencing the increase in minimum flows in the riverbed. The understanding of the functions of these sectors enables the design of objective measures that safeguard and increase the likelihood of the renaturalization of the hydrological functions of floodplains.
... In engineering studies such as the traffic predictions, studies (Cui et al., 2019) used at most 3-hop neighborhoods in their studies since the traffic congestion is mainly a short-term issue and it is very rare to have traffic congestion over 100 kilometers. However, in hydrology, precipitation that falls over land runs off into streams, which would affect downstream regions (Alexander et al., 2018). Thus, it is very critical to take all the rainfall in the watershed into account to make it physically meaningful. ...
Recent studies using latest deep learning algorithms such as LSTM (Long Short-Term Memory) have shown great promise in time-series modeling. There are many studies focusing on the watershed-scale rainfall-runoff modeling or streamflow forecasting, often considering a single watershed with limited generalization capabilities. To improve the model performance, several studies explored an integrated approach by decomposing a large watershed into multiple sub-watersheds with semi-distributed structure. In this study, we propose an innovative physics-informed fully-distributed rainfall-runoff model, NRM-Graph (Neural Runoff Model-Graph), using Graph Neural Networks (GNN) to make full use of spatial information including the flow direction and geographic data. Specifically, we applied a time-series model on each grid cell for its runoff production. The output of each grid cell is then aggregated by a GNN as the final runoff at the watershed outlet. The case study shows that our GNN based model successfully represents the spatial information in predictions. NRM-Graph network has shown less over-fitting and a significant improvement on the model performance compared to the baselines with spatial information. Our research further confirms the importance of spatially distributed hydrological information in rainfall-runoff modeling using deep learning, and we encourage researchers to incorporate more domain knowledge in modeling.
... While the implementation of effective conservation actions is always challenging (Beatty et al., 2014;Collier, 2011;Esselman & Allan, 2011;Hermoso et al., 2018), the design of protected river networks can now benefit from insights and tools provided by a long experience in conservation planning of terrestrial and marine systems (Margules & Pressey, 2000;Watson et al., 2014). Likewise, more recent advances and developments of conservation prioritization methods have been dedicated to running waters (Alexander et al., 2018;Hermoso et al., 2012Hermoso et al., , 2016Moilanen et al., 2008). ...
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Aim Estimate the current and future distribution of brown trout and identify priority areas for conservation of the species. Location Rhône River basin and Mediterranean streams. Methods We first developed a spatially explicit species distribution model to estimate the current and future distribution of brown trout for three time horizons (2030, 2055 and 2080) and two climate change scenarios (RCP 4.5 and RCP 8.5). We then performed a prioritization analysis to identify priority areas for brown trout conservation, accounting for: (a) spatial dependencies along the riverine system, (b) several sources of uncertainty arising from climate-related forecasts and (c) different protected area scenarios by comparing hypothetical, optimal protected networks to an actual protected network designed by regional fish experts. Results Future projections of brown trout densities exhibited a general trend towards a gradual range contraction, with a significant risk of extirpation across mountainous regions of low to mid-elevation. Overall, the projected current and future distributions were well-covered by the existing protected network. In addition, up to 70% of the river reaches included in this expert-based protection network were also priorities in the optimal priority set (e.g. the best set of areas to maximize biodiversity protection). Finally, a large proportion of these reaches were invariably identified regardless of climate change scenarios and uncertainties or spatial dependencies. Main conclusions Our analytical approach highlighted priority areas for brown trout conservation which were robust to a set of climate and connectivity assumptions. This core priority network could be further refined by taking into account key fine-scale processes like thermal refugia. Therefore, we advocate for combining computational and expert-based approaches in conservation planning of riverine ecosystems to achieve a relevant consensus between regional-scale management and fine-grain ecological knowledge.
... Recent U.S. policy debate has centered on the question of whether waters that dry on a regular basisnon-perennial streams and wetlands-are sufficiently critical to the integrity of downstream perennial waters that they should receive the same federal protections (Alexander et al 2018, Sills et al 2018, Walsh and Ward 2019, Sullivan et al 2020. The Rapanos v. US (2006) Supreme Court decision addressed which waters would receive federal protections under the Clean Water Act and urged regulatory agencies to issue clear guidance. ...
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Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the three intermittency signatures, and changes in no-flow duration were most pervasive (41% of gages). Changes in intermittency were substantial for many streams, and 7% of gages exhibited changes in annual no-flow duration exceeding 100 days during the study period. Distinct regional patterns of change were evident, with widespread drying in southern CONUS and wetting in northern CONUS. These patterns are correlated with changes in aridity, though drivers of spatiotemporal variability were diverse across the three intermittency signatures. While the no-flow © 2021 The Author(s). Published by IOP Publishing Ltd Environ. Res. Lett. 16 (2021) 084033 S C Zipper et al timing and duration were strongly related to climate, dry-down period was most strongly related to watershed land use and physiography. Our results indicate that non-perennial conditions are increasing in prevalence over much of CONUS and binary classifications of 'perennial' and 'non-perennial' are not an accurate reflection of this change. Water management and policy should reflect the changing nature and diverse drivers of changing intermittency both today and in the future.
... Elementos fundamentais na estrutura da paisagem (e ligadas ao seu funcionamento geoecológico), as AUs apresentam grande relevância na articulação entre recursos hídricos superficiais e superficiais (PHILLIPS, 1989). Assim, consideram-se as AUs como contribuintes para a formação e manutenção de nascentes e canais fluviais (através da infiltração de água, sua estagnação e eventual exfiltração), e também entrando no funcionamento do ciclo hidrológico (ALEXANDER et al., 2018;TUNDISI, 2003) e alimentando-o (sob a ótica de diversas escalas). ...
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As áreas úmidas (AUs) ou wetlands são sistemas hidrogeomorfológicos saturados de água (permanentemente ou temporariamente) durante um período de tempo suficiente para o desenvolvimento de ecossistemas ímpares, em contextos geomorfológicos e pedológicos específicos. Devido à grande relevância ambiental que possuem, são objetos de diversas pesquisas, as quais normalmente preconizam áreas úmidas de grande porte. Diante da necessidade de conhecimento sobre as pequenas áreas úmidas que ocorrem no domínio dos Mares de Morro, o presente trabalho visa compreender a distribuição espacial e classificar tais sistemas no contexto da bacia hidrográfica de contribuição da Represa de São Pedro, em Juiz de Fora-MG. O recorte estudado apresenta nove áreas úmidas (0,7 por km²), classificadas como 'fluviais" e "de depressão", com ocorrência frequente em cabeceiras de drenagem com controle estrutural associado a falhamentos em rochas pré-cambrianas. A dinâmica híbrida de alimentação entre águas pluviais, fluviais e subsuperficiais foi notória, estando atualmente em processo de alteração por pressões humanas, o que levanta questionamentos acerca da integridade desses sistemas na manutenção de suas funções ecológicas. Palavras-chave: Hidrossistemas; hidromorfismo; brejo. Abstract Wetlands are hydrogeomorphological systems saturated by water long enough (permanent or temporary) to develop particular ecosystems into specific geomorphological and pedological contexts. Due to their vast environmental relevance, they are subject of several research that usually emphasize large wetlands. Facing the lack of knowledge about small wetlands that are common in the Mares de Morro domain, this work aims to comprehend the spatial distribution and to classify the wetlands from São Pedro Dam watershed, in Juiz de Fora, Minas Gerais state, Brazil. We notice nine wetlands (0,7 per km²), classified as "fluvial" and "depressional". They are frequent on headwaters with structural control from faults associated with Precambrian rocks. They have hybrid hydrodynamics with influence of pluvial, fluvial, and underground waters, but we can see an increasing human pressure over the studied wetlands, which raises doubts about their systems integrity and ecological functions.
Lakes are important inland surface water resources and have great influence on the ecological environment as well as the surrounding residential life. However, global lake water resources showed a depleting tendency over the past decades because of the climate change and human activities. To mitigate the drought of lakes linked to a regulated main river, this study proposes an integrated scheduling–assessing system (ISAS) based on the machine learning methodology for a large river–lake system controlled by upstream reservoirs. Closely calibrated to observational data, the ISAS was applied to the middle Yangtze River to mitigate the Poyang Lake drought. The results show that the drought situation in the downstream lake could be improved through the reservoir optimal operation. For the Poyang Lake case, the lowest lake level is not obviously improved, while the starting data of the drought could be delayed by 12, 11, and 17 days, comparing to the conventional scheme in typical dry, normal, and wet years, respectively. Moreover, the duration of the drought could be 20, 19, and 21 days less. It is illustrated that accelerating the reservoir filling speed and decelerating the emptying speed is beneficial to alleviate the drought situation of downstream river-connected lakes.
Currently, only about 40% of European surface waters achieve good ecological status; for floodplains, the European Environment Agency even assumes that about 70 to 90% of these areas have been degraded and altered by human activities (EEA, 2020). One of the most effective measures and an important basis for addressing these challenges are planning instruments at catchment level. Appropriate approaches enable targeted management that brings together water management issues in the context of an ecosystem approach while taking the different environmental objectives, society and also economic activities into account. With the River Development and Risk Management Concepts (GE-RM), corresponding approaches should be established in the planning practice of the Austrian water management. In the first section, the article discusses the importance of a catchment-based perspective, then presents the approach in the GE-RM in this context and concludes by presenting the first findings of ongoing planning on pilot rivers from the LIFE IP IRIS project. First experiences show that the instrument enables a combination of flood risk management and water ecology measures as well as a broad coordination of interests.
Technical Report
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Wetlands provide critical wildlife habitat, improve water quality, and mitigate the impacts of floods, droughts, and climate change. Yet, they are drained, filled, dredged, and otherwise altered by humans, all of which contribute to their high susceptibility to plant invasions. Given the societal significance of wetlands and the disproportionately large amount of time and money spent controlling invaders in remaining wetlands, a fundamental shift must occur in how we approach restoration of plant-invaded wetlands. The need for more research is often used as an excuse for a lack of progress in invader management but, in fact, constraints to invader management are spread across the science, management, and stakeholder engagement domains. At their intersection are “implementation gap” constraints where the monumental efforts required to bridge the gap among scientists, managers, and community stakeholders are often unassigned, unrewarded, and underestimated. Here we synthesize and present a portfolio of broad structured approaches and specific actions that can be used to advance restoration of plant-invaded wetlands in a diversity of contexts immediately and over the long-term, linking these solutions to the constraints they best address. These solutions can be used by individual managers to chart a path forward when they are daunted by potentially needing to pivot from more familiar management actions to increase efficiency and efficacy in attaining restoration goals. In more complex collaborations with multiple actors, the shared vocabulary presented here for considering and selecting the most appropriate solution will be essential. Of course, every management context is unique (i.e., different constraints are at play) so we advocate that involved parties consider a range of potential solutions, rather than either assuming any single solution to be universally optimal or relying on a solution simply because it is familiar and feasible. Moving rapidly to optimally effective invasive plant management in wetlands may not be realistic, but making steady, incremental progress by implementing appropriate solutions based on clearly identified constraints will be critical to eventually attaining wetland restoration goals.
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Extreme climatic conditions likely caused a massive fish mortality during the summer of 2001 in the St. Lawrence River. To corroborate this hypothesis, we used a physical habitat simulation approach incorporating hydraulic and water temperature models. Spawning Habitat Suitability Indices (HSI) for common carp (Cyprinus carpio) were developed using fuzzy logic and applied to the model outputs to estimate habitat weighted usable area during the event. The results revealed that areas suitable for common carp spawning (HSI > 0.3) were severely reduced by high water temperatures, which exceeded 28 °C during the mortality event. During the mortality event, the amount of suitable habitat was reduced to <200 ha/day, representing less than 15% of the maximum potential suitable habitat in the study reach. In addition, the availability of cooler habitats that could have been used as thermal refuges was also reduced. These results indicate that the high water temperature in spawning areas and reduced accessibility to thermal refuge habitats exposed the carp to substantial physiological and environmental stress. The high water temperatures were highly detrimental to the fish and eventually led to the observed mortalities. This study demonstrates the importance of including water temperature in habitat suitability models.
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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.
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Interest in connectivity has increased in the aquatic sciences, partly because of its relevance to the Clean Water Act. This paper has two objectives: (1) provide a framework to understand hydrological, chemical, and biological connectivity, focusing on how headwater streams and wetlands connect to and contribute to rivers; and (2) briefly review methods to quantify hydrological and chemical connectivity. Streams and wetlands affect river structure and function by altering material and biological fluxes to the river; this depends on two factors: (1) functions within streams and wetlands that affect material fluxes; and (2) connectivity (or isolation) from streams and wetlands to rivers that allows (or prevents) material transport between systems. Connectivity can be described in terms of frequency, magnitude, duration, timing, and rate of change. It results from physical characteristics of a system, e.g., climate, soils, geology, topography, and the spatial distribution of aquatic components. Biological connectivity is also affected by traits and behavior of the biota. Connectivity can be altered by human impacts, often in complex ways. Because of variability in these factors, connectivity is not constant but varies over time and space. Connectivity can be quantified with field-based methods, modeling, and remote sensing. Further studies using these methods are needed to classify and quantify connectivity of aquatic ecosystems and to understand how impacts affect connectivity.
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Ephemeral and intermittent streams are abundant in the arid and semiarid landscapes of the Western and Southwestern United States (U.S.). Connectivity of ephemeral and intermittent streams to the relatively few perennial reaches through runoff is a major driver of the ecohydrology of the region. These streams supply water, sediment, nutrients, and biota to downstream reaches and rivers. In addition, they provide runoff to recharge alluvial and regional groundwater aquifers that support baseflow in perennial mainstem stream reaches over extended periods when little or no precipitation occurs. Episodic runoff, as well as groundwater inflow to surface water in streams support limited naturally occurring riparian communities. This paper provides an overview and comprehensive examination of factors affecting the hydrologic, chemical, and ecological connectivity of ephemeral and intermittent streams on perennial or intermittent rivers in the arid and semiarid Southwestern U.S. Connectivity as influenced and moderated through the physical landscape, climate, and human impacts to downstream waters or rivers is presented first at the broader Southwestern scale, and secondly drawing on a specific and more detailed example of the San Pedro Basin due to its history of extensive observations and research in the basin. A wide array of evidence clearly illustrates hydrologic, chemical, and ecological connectivity of ephemeral and intermittent streams throughout stream networks.
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Understanding hydrologic connectivity between wetlands and perennial streams is critical to understanding the reliance of stream flow on inputs from wetlands. We used the isotopic evaporation signal in water and remote sensing to examine wetland-stream hydrologic connectivity within the Pipestem Creek watershed, North Dakota, a watershed dominated by prairie-pothole wetlands. Pipestem Creek exhibited an evaporated-water signal that had approximately half the isotopic-enrichment signal found in most evaporatively enriched prairie-pothole wetlands. Groundwater adjacent to Pipestem Creek had isotopic values that indicated recharge from winter precipitation and had no significant evaporative enrichment, indicating that enriched surface water did not contribute significantly to groundwater discharging into Pipestem Creek. The estimated surface water area necessary to generate the evaporation signal within Pipestem Creek was highly dynamic, varied primarily with the amount of discharge, and was typically greater than the immediate Pipestem Creek surface water area, indicating that surficial flow from wetlands contributed to stream flow throughout the summer. We propose a dynamic range of spilling thresholds for prairie-pothole wetlands across the watershed allowing for wetland inputs even during low-flow periods. Combining Landsat estimates with the isotopic approach allowed determination of potential (Landsat) and actual (isotope) contributing areas in wetland-dominated systems. This combined approach can give insights into the changes in location and magnitude of surface water and groundwater pathways over time. This approach can be used in other areas where evaporation from wetlands results in a sufficient evaporative isotopic signal. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.
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Hydrologic connectivity among wetlands is poorly characterized and understood. Our inability to quantify this connectivity compromises our understanding of the potential impacts of wetland loss on watershed structure, function and water supplies. We develop a computationally efficient , physically based subsurface–surface hydrologic model to characterize both the subsurface and surface hydrologic connectivity of " geographically isolated " wetlands and explore the time and length variations in these connections to a river within the Prairie Pothole Region of North Amer-ica. Despite a high density of geographically isolated wetlands (i.e., wetlands without surface inlets or outlets), mod-eled connections show that these wetlands are not hydrologically isolated. Subsurface connectivity differs significantly from surface connectivity in terms of timing and length of connections. Slow subsurface connections between wetlands and the downstream river originate from wetlands throughout the watershed, whereas fast surface connections were limited to large events and originate from wetlands located near the river. This modeling approach provides first ever insight on the nature of geographically isolated wetland subsurface and surface hydrologic connections to rivers, and provides valuable information to support watershed-scale decision making for water resource management.
We reviewed the scientific literature on non-floodplain wetlands (NFWs), freshwater wetlands typically located distal to riparian and floodplain systems, to determine hydrological, physical, and chemical functioning and stream and river network connectivity. We assayed the literature for source, sink, lag, and transformation functions, as well as factors affecting connectivity. We determined NFWs are important landscape components, hydrologically, physically, and chemically affecting downstream aquatic systems. NFWs are hydrologic and chemical sources for other waters, hydrologically connecting across long distances and contributing compounds such as methylated mercury and dissolved organic matter. NFWs reduced flood peaks and maintained baseflows in stream and river networks through hydrologic lag and sink functions, and sequestered or assimilated substantial nutrient inputs through chemical sink and transformative functions. Landscape-scale connectivity of NFWs affects water and material fluxes to downstream river networks, substantially modifying the characteristics and function of downstream waters. Many factors determine the effects of NFW hydrological, physical, and chemical functions on downstream systems, and additional research quantifying these factors and impacts is warranted. We conclude NFWs are hydrologically, chemically, and physically interconnected with stream and river networks though this connectivity varies in frequency, duration, magnitude, and timing.
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.
Wetlands across the globe provide extensive ecosystem services. However, many wetlands – especially those surrounded by uplands, often referred to as geographically isolated wetlands (GIWs) – remain poorly protected. Protection and restoration of wetlands frequently requires information on their hydrologic connectivity to other surface waters, and their cumulative watershed-scale effects. The integration of measurements and models can supply this information. However, the types of measurements and models that should be integrated are dependent on management questions and information compatibility. We summarize the importance of GIWs in watersheds and discuss what wetland connectivity means in both science and management contexts. We then describe the latest tools available to quantify GIW connectivity and explore crucial next steps to enhancing and integrating such tools. These advancements will ensure that appropriate tools are used in GIW decision making and maintaining the important ecosystem services that these wetlands support.
Connectivity is regarded globally as a guiding principle for conservation planning, but due to difficulties in quantifying connectivity empirical data remain scarce. Lack of meaningful connectivity metrics are likely leading to inadequate representation of important biological connections in reserve networks. Identifying patterns in landscape connectivity can, theoretically, improve the design of conservation areas. 2.We used a network model to estimate seascape connectivity for coral reef-associated fishes in a subtropical bay in Australia. The model accounted for two scales of connectivity: i) within mosaics at a local scale and ii) among these mosaics at a regional scale. Connections among mosaics were modelled using estimations of post-larval small and intermediate movement distances represented by home ranges of two fish species. 3.Modelled connectivity patterns were assessed with existing data on fish diversity. For fishes with intermediate home ranges (0 to 6 km), connectivity (quantified by the index Probability of Connectivity (dPC)) explained 51– 60% of species diversity. At smaller home ranges (0 to 1 km) species diversity was associated closely with intra-mosaic connectivity quantified by the index dPCintra. 4.Mosaics and their region-wide connections were ranked for their contribution to overall seascape connectivity, and compared against current positions and boundaries of reserves. Our matching shows that only three of the ten most important mosaics are at least partly encompassed within a reserve, and only a single important regional connection lies within a reserve. 5.Synthesis and applications. Notwithstanding its formal recognition in reserve planning, connectivity is rarely accounted for in practice, mainly because suitable metrics of connectivity are not available in planning phases. Here, we show how a network analysis can be effectively used in conservation planning by identifying biological connectivity inside and outside present reserve networks. Our results demonstrate clearly that connectivity is insufficiently represented within a reserve network. We also provide evidence of key pathways in need of protection to avoid nullifying the benefits of protecting key reefs. The guiding principle of protecting connections among habitats can be achieved more effectively in future, by formally incorporating our findings into the decision framework. This article is protected by copyright. All rights reserved.