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Biotic impacts of energy development from shale: Research priorities and knowledge gaps


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Although shale drilling operations for oil and natural gas have increased greatly in the past decade, few studies directly quantify the impacts of shale development on plants and wildlife. We evaluate knowledge gaps related to shale development and prioritize research needs using a quantitative framework that includes spatial and temporal extent, mitigation difficulty, and current level of understanding. Identified threats to biota from shale development include: surface and groundwater contamination; diminished stream flow; stream siltation; habitat loss and fragmentation; localized air, noise, and light pollution; climate change; and cumulative impacts. We find the highest research priorities to be probabilistic threats (underground chemical migration; contaminant release during storage, during disposal, or from accidents; and cumulative impacts), the study of which will require major scientific coordination among researchers, industry, and government decision makers. Taken together, our research prioritization outlines a way forward to better understand how energy development affects the natural world.
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330 © The Ecological Society of America
Rapid development of fossil-fuel resources has the
potential to transform landscapes and biological
communities before the resulting impacts are fully under-
stood. In the US, the extraction of gas and oil reserves
trapped in shale rock (known as “shale-gas” and “tight
oil”, respectively) through hydraulic fracturing (also
called “fracking” or “hydrofracking”) has grown exponen-
tially since 2007 (Figure 1; EIA 2011). Such technology
exploits previously inaccessible natural gas reserves
through the deep injection of high-pressure aqueous
chemicals into shale rock to create fractures, releasing
trapped gas (Figure 2; see “Additional references” section
in the web-only materials [WOM]). Although this tech-
nology is well studied (with >1000 peer-reviewed publi-
cations), surprisingly little research has focused on the
biotic impacts of shale development. While the biologi-
cal effects of other methods for extracting fossil fuels are
better understood, these studies generally lack clear
mechanistic links to fuel extraction and are limited to a
small number of species, countries, and ecoregions
(Northrup and Wittemyer 2012). Moreover, shale devel-
opment differs from other forms of fossil-fuel extraction
in multiple ways, including a broad and diffuse geo-
graphic footprint and an extremely high water demand.
Therefore, many of the biotic impacts of shale develop-
ment are unique and cannot be inferred from knowledge
of other forms of oil and natural gas extraction.
Understanding the impacts of shale development is
essential because many shale basins, particularly those in
the eastern US, occur in regions of exceptional biological
diversity (Figure 3); for instance, the most rapidly growing
source of natural gas in the US (ie the Marcellus Shale in
the Appalachian Basin) underlies one of the country’s
highest diversity areas for amphibians and freshwater fish
(Collen et al. 2013). In the US and Europe (Figure 4),
shale basins often overlap with areas already experiencing
severe threats to freshwater resources. In conjunction with
other anthropogenic activities, environmental change
associated with shale operations may cumulatively affect
living organisms in unknown, potentially calamitous, ways.
Here, we identify and prioritize research needs related
to shale development using a quantitative framework. We
consider the entire process of shale development, exam-
ining the threats to animals and plants from site develop-
ment and maintenance, water sourcing, well operation
and fracturing, and storage and disposal of injection fluids
(Figure 2). We classify impacts as probabilistic (ie
Biotic impacts of energy development from
shale: research priorities and knowledge gaps
Sara Souther1*, Morgan W Tingley2, Viorel D Popescu3,4, David TS Hayman5,6,7, Maureen E Ryan3,8,
Tabitha A Graves9, Brett Hartl10, and Kimberly Terrell11
Although shale drilling operations for oil and natural gas have increased greatly in the past decade, few studies
directly quantify the impacts of shale development on plants and wildlife. We evaluate knowledge gaps related
to shale development and prioritize research needs using a quantitative framework that includes spatial and tem-
poral extent, mitigation difficulty, and current level of understanding. Identified threats to biota from shale
development include: surface and groundwater contamination; diminished stream flow; stream siltation; habitat
loss and fragmentation; localized air, noise, and light pollution; climate change; and cumulative impacts. We
find the highest research priorities to be probabilistic threats (underground chemical migration; contaminant
release during storage, during disposal, or from accidents; and cumulative impacts), the study of which will
require major scientific coordination among researchers, industry, and government decision makers. Taken
together, our research prioritization outlines a way forward to better understand how energy development affects
the natural world.
Front Ecol Environ 2014; 12(6): 330–338, doi:10.1890/130324
In a nutshell:
Exploitation of oil and gas reserves trapped in shale rock,
including the extraction process known as “fracking”, poses
substantial and unexplored risks to living creatures
Understanding the biotic impacts of operations that fracture
shale to access reserves is hindered by the unavailability of
high-quality data about fracturing fluids, wastewater, and
spills or violations
The risks of chemical contamination from spills, deep well
failures, storage leaks, and underground fluid migration are
top research priorities
Cumulative effects of shale development may represent the
most severe threats to plants and animals, but are particularly
challenging to study
1Department of Botany, University of Wisconsin, Madison,
Madison, WI *(; 2Woodrow Wilson School,
Princeton University, Princeton, NJ; 3Earth to Ocean Research
Group, Department of Biological Sciences, Simon Fraser
University, Burnaby, Canada (continued on p 338)
S Souther et al. Research priorities for shale development
© The Ecological Society of America
unplanned or accidental) or deterministic (ie planned or
unavoidable) following the structure developed by Rahm
and Riha (2012). Our focus is on biota because plants,
animals, and other living organisms have largely been
omitted from other reviews, which tend to emphasize abi-
otic effects (eg Entrekin et al. 2011; Howarth et al.
2011a), and because shale formations often lie beneath
global hotspots of species diversity. Our goal is to improve
research of the biotic impacts associated with shale devel-
opment by prioritizing research needs and highlighting
associated challenges.
nPrioritization scheme
We assessed potential effects of shale development on liv-
ing organisms based on four criteria: current understand-
ing, spatial extent, temporal extent, and mitigation diffi-
culty (Table 1). For each impact, we ranked current
understanding as low, medium, or high and assigned a cor-
responding value of 3, 2, or 1 (where 3 is low understand-
ing, suggesting high research needs) based on the number
of relevant studies (additional methods provided in
WebPanel 1). The three remaining risk-based criteria were
assigned values of 1, 2, or 3, corresponding to low, medium,
or high ratings (where 3 represents high risk to biota for a
criterion). For each impact, the research priority was calcu-
lated by averaging criteria values, where current under-
standing was weighted by a factor of 3 to reflect the impor-
tance of existing scientific information in determining
research needs. Average values corresponded to final rank-
ings as follows: low (1.0–1.5), medium-low (1.6–1.9),
medium (2), medium-high (2.1–2.5), and high (>2.5).
nProbabilistic impacts
Probabilistic impacts to biota from shale development do
not occur as an unavoidable outcome of development but
do occur with a certain frequency. Although some of
these impacts may be rare occurrences (ie the result of
“unexpected” events), because most relate to the release
of potentially toxic chemicals into the environment, the
possibility of biotic harm can be great.
Underground migration of contaminants
During well fracturing, chemicals suspended in an aque-
ous medium are injected under high pressure into shale to
release natural gas. Fracturing fluid generally includes a
mix of acids, biocides, friction-reducing agents, and other
chemicals to facilitate gas retrieval (Vidic et al. 2013).
Many of the chemicals (eg methanol, xylene, naphtha-
lene, hydrochloric acid, toluene, benzene, and formalde-
hyde) are regulated in the US by the Safe Drinking Water
Act, the Clean Water Act (40 CFR Section 401.15), or
the Clean Air Act (US EPA 2012) and have been linked
to negative health effects in humans (Colborn et al.
2011). Releases of fracking fluid into streams have
resulted in direct mortality and stress of fish and aquatic
invertebrates (Papoulias and Velasco 2013). A propor-
tion of this fluid – the amount varies substantially among
geologic formations, but can be as high as 90% – remains
underground after its application (Entrekin et al. 2011;
Vidic et al. 2013). The fate and potential biotic impacts of
unrecovered fracturing fluids are highly uncertain.
Due to the depth of most hydraulically fractured shale-gas
formations (900–2800 m; Vidic et al. 2013), the contamina-
tion of groundwater by subsurface migration of fracturing
fluid is considered unlikely (Engelder 2011; Vidic et al.
2013). Nevertheless, geologic pathways for chemical migra-
tion have been identified (Warner et al. 2012). Moreover,
drinking water contamination with fracturing chemicals
and/or methane (CH4) has been reported (DiGiulio et al.
2011; Osborn et al. 2011; Jackson et al. 2013), although
some of these studies have been criticized as providing
insufficient evidence to attribute water contamination to
shale development (eg Davies 2011). Future research must
determine whether hydraulic fracturing causes CH4conta-
mination and whether, in the absence of equipment failure
and accidents, chemicals do migrate from fractured shale
beds. Given the limited understanding (WebTable 1) of the
likelihood, frequency, and spatiotemporal extent of such
contamination events, and the few options for mitigation,
this is a high research priority (Table 1).
Contamination from equipment failure, illegal
activities, and accidents
In addition to chemical migration from fractured shale,
freshwater contamination may result from well blowouts,
casing failures, illegal discharge, and spills during fluid
transport and storage (Figure 2). Many such contamina-
tion events involve the release of recovered fluid (called
“produced water”), which consists of fracturing fluid and
salts, heavy metals, hydrocarbons, and radioactive material
accumulated from natural underground sources (Howarth
et al. 2011a). The high saline content of recovered fluid
Figure 1. Proliferation of natural gas wells in the Jonah Field,
Wyoming, US. Inset: historical and predicted natural gas
production in the US. Data from EIA (2011).
Research priorities for shale development S Souther et al.
332 © The Ecological Society of America
alone poses risks to biota, given that increases in salinity
of as little as 1 g L–1 can harm or kill aquatic plants and
invertebrates (Hart et al. 1991).
Currently, the frequency and extent of freshwater contam-
ination due to spills, accidents, and violations is poorly quan-
tified. Of the 24 US states with active shale gas reservoirs,
only Pennsylvania, Colorado, New Mexico, Wyoming, and
Texas maintain public records of spills or violations for oil
and gas drilling operations. We examined the frequency and
nature of violations in the Pennsylvania Department of
Environmental Protection’s (PADEP’s) oil and gas manage-
ment compliance-reporting database (data analyzed in
WebTable 2). A total of 523 violations at 279 permitted wells
were detected in 2013, representing ~2.5% of inspections
(12 452 total) and 5% of wells (5580 total). The three most
common violations included: failure to properly store, trans-
port, process, or dispose of residual waste (n= 85); failure to
adopt required or prescribed pollution prevention measures
(n= 48); and failure to plug a well upon abandonment (n=
43). Spills were detected at 37% of wells found in violation
and were generally small (median = 265 L; range = 4–43 000
L), although there were nine spills of over 3500 L. Spills typ-
ically occurred on the well pad, with nearly
20% of reports documenting contamina-
tion of land or surface water. Location (on-
pad versus off-pad) was specified in fewer
than half of the reports (42%), and spatial
extent of contamination was rarely (5%)
described. The time between the spill and
reporting was noted in <10% of cases
(median = 5.75 hours; range = 1 hour to 6
weeks). In addition to the lack of data
describing the nature and extent of spills,
spill frequency was probably underesti-
mated. Many reports were ambiguous, and
companies routinely violated Pennsylva-
nia’s reporting requirement (only 59% of
documented spills were reported by the
drilling company). Collectively, poor data
quality and lack of consistent reporting
represent a major obstacle to understand-
ing the impacts of chemical contamina-
tion from shale development. Ecological
impacts of spills and accidents are also a
high research priority, given the limited
knowledge, the potential for lasting and
widespread adverse environmental con-
sequences, and the difficulty in mitigating
such contamination events.
Release of contaminants during
waste storage and disposal
As in the case of contamination from
spills and accidents, lack of data on
wastewater disposal impedes environ-
mental assessment. Waste volume, com-
position, and fate vary among drilling companies, states,
and geologic formations (Entrekin et al. 2011; Rozell and
Reaven 2011; Rahm and Riha 2012; Rahm et al. 2013).
Industry-reported data from PADEP revealed a 570%
increase in wastewater production since 2004 from devel-
opment of the Marcellus Shale (Maloney and Yoxtheimer
2012; Lutz et al. 2013). Drill cuttings were principally dis-
posed of in landfills, and wastewater (ie recycled fluid) was
most frequently treated at industrial facilities or injected
into deep wells (a large proportion of wastewater was re-
used prior to disposal; Maloney and Yoxtheimer 2012).
Risk of waste migration from deep injection wells to fresh-
water aquifers is poorly understood and, notably, deep well
injection has been linked to increased seismic activity
(Frohlich et al. 2011). Containment ponds frequently serve
as temporary wastewater storage at drilling sites, and these
vary substantially in structural integrity. Inadequately
designed ponds can overflow during heavy rain, may leak
as liners degrade, are accessible to wildlife, and are poten-
tial sources of air pollution as chemicals volatilize
(Entrekin et al. 2011). While the frequency of con-
tainment pond failure has not been quantified, our in-
Figure 2. Shale development includes multiple processes focused around natural gas
extraction via hydraulic fracturing. Impacts of shale development on biota can
include probabilistic (1, 6, 7, 8) and deterministic (2, 3, 4, 5, 9) effects of these
various processes. Contamination of aquatic and terrestrial systems may occur due to
spills, leaks, or accidents during hydraulic fracturing (6), waste storage (1, 8), and
transport (5). Permanent removal of water from the hydrologic cycle and subsequent
effects on water quality (9), habitat loss and fragmentation (4), and air (2) and
noise and light (3) pollution are unavoidable consequences of shale development,
although technological advances and appropriate planning can minimize biotic effects.
Shale development contributes to climate change in various ways, including CH4
release during well venting (2) as well as fossil-fuel use during site development, well
fracturing, and waste disposal (eg 5).
S Friedrich
S Souther et al. Research priorities for shale development
© The Ecological Society of America
vestigation of Pennsylvania’s
2013 well inspection data
(described above) detected
numerous violations (eg 27
violations citing “Pit and
tanks not constructed with
sufficient capacity to contain
pollutional substances”), indi-
cating that some containment
facilities fail to prevent escape
of contaminants. Inappropri-
ate management of waste
products, including the direct
discharge of industrial waste
into streams, comprised 34%
of the total violations issued
by PADEP (WebTable 2).
There is virtually no empir-
ical information about the
biotic risks associated with
disposal of produced water
and drill cuttings (WebTable
1). Given this paucity of data,
the unquantified spatial and
temporal extent of contami-
nation, and few mitigation
options, the pathways and
consequences of environmen-
tal contamination from waste
storage and disposal represent
high research priorities (Table
1). A critical first step in this
research is improving basic
reporting to generate accurate
data describing waste compo-
sition and fate. For each
method of wastewater dis-
posal, future research should
determine the concentration
of toxins released into the
environment, exposure duration and potential pathways
(eg ingestion, inhalation, or contact), and the effects on
aquatic and terrestrial biota. A general evaluation of cur-
rent above- and belowground remediation strategies is
needed to address whether current technologies are capa-
ble of removing contaminants and what site characteristics
enhance or preclude effective remediation.
Disclosure of fracturing chemicals
Although not a biotic impact on its own, the lack of disclo-
sure regarding many fracturing chemicals can hamper the
ability of researchers to understand, predict, and mitigate
adverse environmental effects. Certain chemicals in frac-
turing fluids are classified as confidential business informa-
tion under Section 14(c) of the US Toxic Substances
Control Act (US EPA 2012). Many companies have vol-
untarily disclosed non-proprietary fluid components, and
ten states currently participate in the FracFocus
( national registry as a means of chemi-
cal disclosure. We investigated the proportion of propri-
etary components for 150 randomly selected wells repre-
senting three of the top producing states (ie Texas,
Pennsylvania, and North Dakota) in the registry (data
presented in WebTable 3). Overall, 67% of wells in our
sample were fractured with fluid containing at least one
undisclosed chemical, and 37% were fractured with five or
more undisclosed chemicals. Some wells (18%) were frac-
tured with a complex fluid containing 10 or more undis-
closed components. Importantly, many disclosed chemi-
cals lacked Chemical Abstracts Service (CAS) numbers
or concentration values. Most wells (82%) were fractured
with fluid containing either undisclosed components or
disclosed chemicals lacking this information. Chemical
Table 1. Research priorities based on the relative extent, difficulty mitigating, and
current understanding of potential impacts
Source of ecological Type of Spatial Temporal Mitigation Current Research
impact occurrence*extent** extent difficulty
Underground Unknown Unknown High Low High
migration of Probabilistic (3) (3) (3) (3) (3.0)
Contamination of
surface water from Unknown Unknown High Low High
equipment failure, Probabilistic (3) (3) (3) (3) (3.0)
illegal activities,
and accidents
Release of
contaminants during Unknown Unknown High Low High
waste storage or Probabilistic (3) (3) (3) (3) (3.0)
Cumulative impacts Unknown Unknown Unknown Low High
Probabilistic (3) (3) (3) (3) (3.0)
Land application of Deterministic Low Medium Medium Low Medium-High
wastewater (1) (2) (2) (3) (2.3)
Climate-change Deterministic High High High High Medium
contribution (3) (3) (3) (1) (2)
Habitat Deterministic High High Medium High Medium-Low
loss/fragmentation (3) (3) (2) (1) (1.8)
Diminished stream Deterministic Medium Medium Low Medium Medium-Low
flow (2) (2) (1) (2) (1.8)
Air pollution Low Low Medium Medium Medium-Low
Deterministic (1) (1) (2) (2) (1.7)
Siltation Medium Medium Medium High Low
Deterministic (2) (2) (2) (1) (1.5)
Noise pollution Low Low Low High Low
Deterministic (1) (1) (1) (1) (1.0)
Light pollution Low Low Low High Low
Deterministic (1) (1) (1) (1) (1.0)
Notes: *Following Rahm and Riha (2012). **Values in parentheses correspond to numerical rankings, as explained in text. Box
color reflects the severity of each criterion, from minor (blue) to severe (orange). †Weighted by a factor of 3 to reflect impor-
tance of current knowledge in determining research priorities. ‡Final rankings in parentheses correspond to weighted average
of individual rankings.
Research priorities for shale development S Souther et al.
334 © The Ecological Society of America
information was sometimes omitted for “non-hazardous”
components, but chemicals that are innocuous to humans
(eg some salts) can be lethal to freshwater organisms. No
chemical information was provided for produced water,
making it impossible to formulate these reclaimed fluids
for experimental research. A centralized source of chemi-
cal information would greatly facilitate research. The cur-
rent FracFocus registry has major limitations, including:
incomplete state participation; failure to consistently pro-
vide concentrations and CAS numbers for disclosed
chemicals; and non-disclosure of a substantial proportion
of chemicals. Because compounds in mixtures can have
synergistic or antagonistic effects (Altenburger et al.
2003), full chemical disclosure of fracturing fluid and
wastewater is essential for understanding the associated
risks to biota, including the effects of leaks, spills, and
direct terrestrial or aquatic application.
Cumulative impacts
The biological impacts of shale energy development are
numerous, and include water scarcity, habitat loss, and
various forms of pollution (see “Deterministic impacts”
section below). Many of these threats (Figure 2) cross ter-
restrial and aquatic boundaries, extend beyond the imme-
diate footprint of the operation, and may interact to
affect ecosystems in unexpected ways. Given that the
overall impact of shale development will likely outweigh
that of any individual stage of the process, risk assess-
ments should incorporate cumulative impacts on biota.
Importantly, this assessment framework should be
extended to consider the contributions of unrelated but
co-occurring stressors (eg resource extraction or residen-
tial development).
The few studies that consider cumulative impacts sug-
gest that shale-gas development will affect ecosystems on
a broad scale (Kiesecker et al. 2009; Jones and Pejchar
2013; Evans and Kiesecker 2014). For example, Evans and
Kiesecker (2014) found that energy development – pri-
marily from shale – in a large portion of the Marcellus
Shale could result in the construction of >500 000 ha of
impervious surface, leaving >400 000 ha of affected forest.
Given the overall absence of knowledge regarding cumu-
lative impacts, and the potential for synergistic, negative
interactions of shale-gas development impacts on ecosys-
tems, this area represents another high research priority
(Table 1). Using a cumulative-impacts framework,
researchers should specifically address how the density and
spatial configuration of shale wells interact with the tim-
ing and frequency of drilling operations (eg water with-
drawals or site clearing) to develop strategies for minimiz-
ing negative biological impacts. As cumulative impacts’
methodology and knowledge improve, research should
move toward detecting synergies between shale develop-
ment and other likely drivers of extinction, such as cli-
mate change, as site-specific or single variable risk assess-
ments likely underestimate threats to ecological health.
nDeterministic impacts
Most of the foreseeable ecological impacts of shale devel-
opment (eg pollution, habitat loss, siltation) are also asso-
ciated with other forms of anthropogenic disturbance.
While much knowledge can (and should) be drawn from
other disciplines, certain aspects of shale development
have unique temporal, geographic, spatial, and/or mecha-
nistic attributes. The challenge for the scientific commu-
nity is to determine what new information is needed to
understand and mitigate these impacts in the specific
context of shale development.
Siltation and diminished stream flow
Only 21% of river and stream length in the US is in “good
biological condition”, and major threats to freshwater
biota include siltation and water extraction (US EPA
2013b). Quantifying the effect of shale development on
siltation is difficult, but the factors that determine siltation
(eg well density and proximity to surface waters) are rela-
tively well studied. In the US, more than 6000 rivers are
impaired as a result of sediment pollution (US EPA 2014),
and the causes, consequences, and mitigation of siltation
have been studied for decades (Berkman and Rabeni 1987;
Donohue and Garcia Molinos 2009; Gellis and Mukundan
2013). The contribution of shale development to sediment
load will vary geographically, depending on local hydrol-
ogy, geology, and existing forms of land disturbance. In the
Marcellus region, habitats affected by shale development
are likely to include lower-order (eg headwater) streams
with relatively little sediment input from other sources
(Olmstead et al. 2013). Given the extensive amount of rel-
evant scientific literature about stream siltation
(WebTable 1), the moderate spatial and temporal extent of
this problem, and the existence of well-developed mitiga-
tion strategies as compared with other impacts, this threat
is a low research priority (Table 1).
While many forms of land use contribute to siltation,
shale development consumes an exceptionally large
quantity of fresh water. An average of nearly 20 million L
of water is required to fracture a shale well over its life-
time (Entrekin et al. 2011; Howarth et al. 2011a). Given
this massive water demand, well pads are typically con-
structed near freshwater sources. As of September 2010,
more than 750 shale wells had been drilled within 100 m
of rivers and streams in five eastern US states (Entrekin et
al. 2011), and nearly 4000 wells drilled within 300 m of
these freshwater habitats (Entrekin et al. 2011). The close
proximity of well sites to freshwater sources exacerbates
the risk of chemical contamination and sedimentation of
aquatic ecosystems (Gregory et al. 2011). Water extrac-
tion can substantially alter local hydrology by reducing
stream water levels and flow rates, which can result in
warmer water temperatures, increased concentrations of
pollutants, and less dissolved oxygen for aquatic life.
Certain aspects of freshwater removal for hydraulic frac-
S Souther et al. Research priorities for shale development
turing are unique (ie volume and geographic
pattern of water withdrawals). Although in-
stream flow is well studied in other contexts,
there is virtually no relevant empirical data
for shale development (WebTable 1). Given
the modest level of scientific understanding,
potential ease of mitigation (eg by restricting
water withdrawals), and relatively moderate
spatial and temporal extent, this threat repre-
sents a medium to low priority for research
(Table 1). The minimum stream flow rates
and water volumes necessary to sustain bio-
logical function will vary among habitats and
life stages, and should be studied at fine spa-
tial scales.
Habitat loss and fragmentation
Construction of wells and associated infra-
structure (eg access roads, pipelines) disrupts
habitat. On average, 1.5–3.1 ha of vegetation
are cleared during the development of a sin-
gle well pad (Entrekin et al. 2011). Although
this footprint is relatively small, the vast
number of shale wells equates to considerable
habitat loss. Furthermore, the amount of land
cleared for pipelines and other infrastructure
can far exceed that of the well pad
(Slonecker et al. 2012). In Pennsylvania’s
Bradford and Washington counties (together
representing ~280 000 ha of forest), shale-
drilling operations disturbed nearly 2500 ha
of land between 2004 and 2010, and dispro-
portionally affected the interior forests that
provide important habitat for rare species
(Slonecker et al. 2012); in the Susquehanna
River basin, more than one-quarter of shale
well pads were constructed in previously
intact forest habitat (Drohan et al. 2012). In
the western US, natural gas development has
decreased secure habitat for pronghorn
(Antilocapra americana; Bechmann et al.
2012) and mule deer (Odocoileus hemionus;
Sawyer et al. 2009), and disrupted breeding
sagebrush bird communities (Gilbert and
Chalfoun 2011) including greater sage-
grouse (Centrocercus urophasianus; Webb et al. 2012).
Well pads and infrastructure result in major habitat frag-
mentation. Shale development in known basins (Figures 3
and 4) threatens to disrupt ~500 natural corridors in west-
ern North America (Theobald et al. 2012). Such corridors
are crucial to maintaining healthy wildlife populations in a
changing climate (Lawler et al. 2013). While fragmentation
effects of shale development have been poorly studied
(Northrup and Wittemyer 2012), fragmentation from any
source can reduce dispersal, foraging, and mating success,
thereby increasing species’ risk of local extinction (Aguilar
© The Ecological Society of America
et al. 2006; Fischer and Lindenmayer 2007). The resulting
edge habitat generally benefits common and generalist
species at the expense of rare and more vulnerable species
(Ries et al. 2004). Opening of formerly remote areas can
facilitate poaching of imperiled and sensitive species, serve
as a conduit for invasive and non-native species (including
pathogens), and provide a gateway to further and more per-
manent development (Fahrig 2003). Although habitat loss
and fragmentation occur on broad scales and are moder-
ately difficult to mitigate, these processes are relatively well
studied (WebTable 1) and represent a medium-low research
Figure 3. Freshwater biodiversity in relation to the extent of shale gas basins:
normalized species richness (a) globally and (b) within the US; US-only (c)
amphibian species richness, (d) crayfish species richness, and (e) fish species richness.
Biodiversity data (a–d) were derived from Collen et al. (2013); data in (e) were
derived from Hoekstra et al. (2010; downloaded from and used
under a Creative Commons Attribution 3.0 License, http://creativecommons.
org/licenses/by/3.0). All freshwater biodiversity data are shown in relation to the
extent of shale gas basins assessed by the US Energy Information Administration
( and represent known extents as of May 2011; countries/regions
included in the global shale gas assessment are: Mexico, Canada, Colombia,
Venezuela, Argentina, Chile, Uruguay, Paraguay, Bolivia, Brazil, Algeria,
Tunisia, Libya, South Africa, France, Germany, Netherlands, Norway, Denmark,
Sweden, the UK, Poland, Ukraine, Lithuania, Romania, Bulgaria, Hungary,
China, India, Pakistan, Turkey, and Australia.
(b) (c)
(d) (e)
Research priorities for shale development S Souther et al.
336 © The Ecological Society of America
priority (Table 1). Notably, however, new extraction tech-
niques have made it economical to develop historically
unprofitable gas reserves, threatening terrestrial biota in for-
merly intact areas (Northrup and Wittemyer 2012).
Moreover, the diffuse, branching pattern of habitat loss asso-
ciated with hydraulic fracturing distinguishes it from other
forms of land-use change (Northrup and Wittemyer 2012).
Light, noise, and air pollution
Shale operations create light, noise, and air pollution.
Anthropogenic light and noise can negatively affect fitness
across a broad group of species, including mammals, amphib-
ians, birds, insects, and aquatic invertebrates (see “Addi-
tional references” in the WOM). Noise pollution generated
by natural gas extraction causes some avian species to avoid
breeding sites (Blickley et al. 2012), resulting in reduced bird
abundance (Bayne et al. 2008). Shale operations emit nitro-
gen oxides (NOx), sulfur dioxide (SO2), carbon monoxide
(CO), volatile organic compounds (VOCs), and particulate
matter, each of which is harmful to biota (see “Additional
references” in the WOM). In addition to their
direct toxicity, NOxand VOCs contribute to
ozone (O3) formation. Natural gas operations
emit nearly 30 times the VOCs as compared
with coal operations, primarily during extrac-
tion and transport (US EPA 2013a). Ground-
level O3is a strong pulmonary and respiratory
irritant in mammals (Watkinson et al. 2001)
and negatively affects growth, reproduction,
and survival of plants (Karnofsky et al. [2005]
and references within). Dangerous concentra-
tions of surface O3have been detected near
large oil and gas operations (Martin et al. 2011),
including in winter (Carter and Seinfeld 2012).
As O3pollution is normally a warm-weather
problem, its potential impacts on animals and
plants as a year-round phenomenon are entirely
Given the limited scale of noise and light
pollution, along with the ease of mitigation
and relatively well-developed state of knowl-
edge, these threats are low research priorities
(Table 1). Air pollution is a slightly higher
(medium to low) research priority because it is
more challenging to mitigate; thus, aspects
unique to shale development warrant further
study (eg wintertime O3).
Climate-change contribution
Shale development will affect biota indirectly,
but substantially, through climate change.
These impacts occur primarily through the
routine venting of CH4during well fracturing,
but also from the release of carbon dioxide
(CO2) and other greenhouse gases during site
development, fracturing, and waste disposal (Howarth et
al. 2011b, 2012; Petron et al. 2012). Climate change poses
one of the greatest global threats to biota (Thomas et al.
2004), has spatially and temporally expansive impacts, and
is extremely challenging to mitigate. However, because
greenhouse gases and the chemical basis for climate change
are well understood (WebTable 1), we rank this threat as a
medium research priority in the context of shale develop-
ment (Table 1).
Land application of wastewater
As of 2011, certain states – including West Virginia,
Arkansas, and Colorado – permitted wastewater disposal via
direct application to land or roadways, often as a de-icing
agent (Adams 2011). Direct land application guarantees
immediate and widespread contamination of ecosystems.
Land application of wastewater has caused rapid, complete
mortality of vegetation and 56% mortality of trees within 2
years (Adams 2011). Other research supports these findings
and indicates that even low concentration of wastewater
Figure 4. (a) Global and (b) US distribution of pre-existing threats to freshwater
biodiversity in relation to the extent of shale gas basins. The Incident Biodiversity
Threat index for freshwater biodiversity was derived by Vörösmarty et al. (2010;
downloaded from and used under a Creative Commons
Attribution 3.0 License,, and ranges
from 0 (lowest threat) to 1 (highest threat). Areas in white denote regions with an
average annual runoff <10 mm (see supplementary materials from Vörösmarty
et al. [2010] for full description).
S Souther et al. Research priorities for shale development
© The Ecological Society of America
can alter species composition (DeWalle and Galeone 1990).
Because current understanding of this threat is limited, miti-
gation is difficult, and impacts can persist for several years
(Adams 2011), the impact of wastewater application is a
medium-high research priority (Table 1).
As the development of shale energy reserves continues to
expand, substantial knowledge gaps remain regarding
effects of these activities on plants and animals. Using
criteria related to the environmental risks and current
understanding of these impacts, we suggest that top
research priorities are related to probabilistic events that
lead to contamination of fresh water, such as equipment
failure, illegal activities, accidents, chemical migration,
and wastewater escape, as well as cumulative ecological
impacts of shale development (Table 1). Although other
threats are considered lower priorities, these rankings are
relative, general, and dependent on the scarce peer-
reviewed literature pertaining directly to shale develop-
ment (WebTable 1). Certain components of relatively
low-ranking threats (eg winter O3, air pollution) may
warrant greater prioritization, especially in particular
regions or ecosystems. Furthermore, these rankings are
based on the assumption that feasibility of mitigation
translates to effective mitigation. For example, water
scarcity has documented negative effects on aquatic
organisms, and can be avoided by managing water with-
drawals. Nevertheless, water management continues to
be a major conservation issue in water-limited ecosys-
tems. When the ecological consequences of shale devel-
opment are easily foreseeable (ie deterministic), research
focused on mitigation is generally a higher priority than
determining basic effects on biota. In other cases (eg land
application of wastewater), the need for research may be
circumvented by a change in state or federal regulation.
Given the rapid expansion of shale development, the
scientific community should prioritize research to exam-
ine threats with the greatest potential for biotic harm.
Here, we identify four high-priority research areas, but
acknowledge that these priorities are likely to change as
scientific understanding, government regulations, and
mitigation strategies develop. Rather than a rigid guide-
line, the approach presented here is a call to action for
scientists, industry leaders, and decision makers. We must
actively cooperate to understand the ecological risks asso-
ciated with shale energy development and work to mini-
mize its impacts on natural systems.
We received support from the David H Smith Fellowship
program, administered by the Society for Conservation
Biology and funded by the Cedar Tree Foundation. BH was
supported by a Policy Fellowship from the Wilburforce
Foundation to the Society for Conservation Biology. An
early version of this manuscript was sent as a letter to the
US Geological Survey, the Environmental Protection
Agency, and the US Department of the Interior; we thank
these agencies for their review and assistance in improving
the manuscript. We also thank M Böhm and B Collen for
providing the freshwater species richness data, and S
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4Centre for Environmental Research, University of Bucharest,
Bucharest, Romania; 5Department of Biology, Colorado State
University, Fort Collins, CO; 6Department of Biology, University
of Florida, Gainesville, FL; 7mEpiLab, Massey University,
Palmerston North, New Zealand; 8School of Environmental and
Forest Sciences, University of Washington, Seattle, WA;
9Department of Fish, Wildlife, and Conservation Biology, Colorado
State University, Fort Collins, CO; 10Society for Conservation
Biology, Washington, DC; 11Center for Species Survival,
Smithsonian Conservation Biology Institute, Front Royal, VA
... Expanding energy development is a primary source of human disturbance to wildlife worldwide (Allred et al., 2015;Copping et al., 2014;Northrup & Wittemyer, 2013;Trainor et al., 2016), altering habitat use and recruitment in rangeland species (Gamo & Beck, 2017;Sawyer et al., 2002;Sawyer & Lindzey, 2004;Sawyer et al., 2006;Sawyer et al., 2009). Energy development alters habitat composition by changing soil and vegetation structure, increasing habitat fragmentation, and altering natural vegetation (Naugle et al., 2011;Northrup & Wittemyer, 2013;Souther et al., 2014;Walker et al., 2019). The effect of disturbance associated with energy development is most significant for habitat specialists and area-sensitive species that require large expanses of intact habitat (e.g., Brittingham et al., 2014;Walker et al., 2019). ...
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Wildlife population dynamics are modulated by abiotic and biotic factors, typically climate, resource availability, density-dependent effects, and predator-prey interactions. Understanding whether and how human-caused disturbances shape these ecological processes is helpful for the conservation and management of wildlife and their habitats within increasingly human-dominated landscapes. However, many jurisdictions lack either long-term longitudinal data on wildlife populations or measures of the interplay between human-mediated disturbance, climate, and predator density. Here, we use a 50-year time series (1962-2012) on mule deer (Odocoileus hemionus) demographics, seasonal weather, predator density, and oil and gas development patterns from the North Dakota Badlands, USA, to investigate long-term effects of landscape-level disturbance on mule deer fawn fall recruitment, which has declined precipitously over the last number of decades. Mule deer fawn fall recruitment in this study represents the number of fawns per female (fawn:female ratio) that survive through the summer to October. We used this fawn recruitment index to evaluate the composite effects of interannual extreme weather conditions, energy development, and predator density. We found that density-dependent effects and harsh seasonal weather were the main drivers of fawn fall recruitment in the North Dakota Badlands. These effects were further shaped by the interaction between harsh seasonal weather and predator density (i.e., lower fawn fall recruitment when harsh weather was combined with higher predator density). Additionally, we found that fawn fall recruitment was modulated by interactions between seasonal weather and energy development (i.e., lower fawn fall recruitment when harsh weather was combined with higher density of active oil and gas wells). Interestingly, we found that the combined effect of predator density and energy development was not interactive but rather additive. Our analysis demonstrates how energy development may modulate fluctuations in mule deer fawn fall recruitment concurrent with biotic (density-dependency, habitat, predation, woody vegetation encroachment) and abiotic (harsh seasonal weather) drivers. Density-dependent patterns emerge, presumably due to limited quality habitat, being the primary factor influencing fall fawn recruitment in mule deer. Secondarily, stochastic weather events periodically cause dramatic declines in recruitment. And finally, the additive effects of human disturbance and predation can induce fluctuations in fawn fall recruitment. Here we make the case for using long-term datasets for setting long-term wildlife management goals that decision makers and the public can understand and support.
... Os impactos da produção de petróleo e gás não convencionais sobre a biodiversidade já são analisados em diversos estudos (BAMBERGER; OSWALD, 2015;KIVIAT, 2013;SOUTHER et al., 2014) apresentando os riscos ao funcionamento dos ecossistemas e à conservação de espécies da fauna e flora de uma maneira geral. As questões ambientais devem ser analisadas dentro de um arcabouço legislativo federal e estadual onde cada ator possui claramente seu papel bem delimitado, bem como sua competência de legislar e jurisdicionar em cada esfera. ...
A extração do gás de folhelho ocorre no mundo de diversas formas, avançando sobre novos territórios e utilizando técnicas cada vez mais agressivas como o fracking ou o fraturamento hidráulico. O objetivo deste trabalho é discutir as potenciais consequências ambientais de sua extração no Brasil apresentando as políticas relativas à sua exploração e as implicações legais que norteiam a discussão no Brasil. Trata-se de uma pesquisa básica de abordagem qualitativa e exploratória apoiada principalmente na literatura internacional sobre o tema. Os resultados apontaram que existe um alto grau de risco ambiental com o fraturamento hidráulico podendo contaminar o solo, lençóis freáticos e aquíferos, contudo no Brasil não existe uma lei que proíba a exploração. Conclui que diante da iminente busca por energias limpas e renováveis, a demanda por combustível fóssil não justifica a extração do gás de folhelho tanto ambientalmente, como comercialmente.
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Shale gas development occurs in forests of the Appalachian Basin within breeding habitat for forest songbirds. Development requires linear infrastructure (e.g., pipelines, gas access roads) that fragments habitat and reduces core forest. Collocation is a mitigation practice that sites new pipelines adjacent to existing surface disturbance such as forest roads; it reduces core forest loss but may have associated ecological costs, defined as negative effects on native species and ecosystems. We conducted a paired sampling design between forest roads and collocated pipelines (expanded gas access roads collocated with pipelines) to evaluate ecological costs to forest songbirds in 2013 in Pennsylvania, USA. We surveyed 4 focal songbird species: 3 territorial species that varied in habitat requirements and the non‐territorial brown‐headed cowbird ( Molothrus ater ), an obligate brood parasite. We used spot mapping to survey focal species within linear corridors and the adjacent mature forest. Territory density of forest interior ovenbirds ( Seiurus aurocapilla ) was significantly lower on collocated pipelines (5.1 fewer territories per 10 ha) compared to forest road sites. We found no effect of collocation on territory density for the early successional species, eastern towhee ( Pipilo erythrophthalmus ) and chestnut‐sided warbler ( Setophaga pensylvanica ). Territories of all 3 territorial focal species crossed collocated pipeline sites less frequently than forest roads (ovenbird: 16%, eastern towhee: 14%, chestnut‐sided warbler: 31%) and the barrier effect increased with increasing corridor width. In contrast, brown‐headed cowbird abundance was 15 times greater at collocated pipelines compared to forest roads, suggesting that wider gas corridors provide enhanced access routes for cowbirds. Our study indicates the expansion of forest roads to collocated pipelines exacerbates the negative ecological effects already present with the existing road including increased edge avoidance by a forest interior species, greater barrier effects for all 3 territorial forest songbirds, and increased access for brown‐headed cowbirds into core forest. We support collocation as a mitigation strategy but emphasize restricting overall corridor width to reduce the additional ecological costs associated with this practice.
The development of unconventional oil and gas shales using hydraulic fracturing and directional drilling is currently a focal point of energy and climate change discussions. While this technology has provided access to substantial reserves of oil and gas, the need for large quantities of water, emissions, and infrastructure raises concerns over the environmental impacts. Written by an international consortium of experts, this book provides a comprehensive overview of the extraction from unconventional reservoirs, providing clear explanations of the technology and processes involved. Each chapter is devoted to different aspects including global reserves, the status of their development and regulatory framework, water management and contamination, air quality, earthquakes, radioactivity, isotope geochemistry, microbiology, and climate change. Case studies present baseline studies, water monitoring efforts and habitat destruction. This book is accessible to a wide audience, from academics to industry professionals and policy makers interested in environmental pollution and petroleum exploration.
Developments in shale oil production technologies made the US, already the most important oil consumer, an important oil producer and exporter. This paper examines the response of shale oil production across eight production basins in the US to both US domestic and foreign oil demand shocks. The empirical evidence reveals that shale oil production in the Permian basin responds to PADD 3 Exports shocks faster, and Western/Eagle Ford responds more rapidly to Refinery Utilization Rate shocks. On the other hand, the Appalachian basin responses to PADD 3 Exports and Refinery Utilization Rate shocks are slower/weaker than other basins. Moreover, basins closer to the PADD 3 region have stronger responses, whereas basins farther from the PADD3 have weak ones.
Climate change poses innumerable threats to economic, social, and environmental systems. Despite our best efforts, emerging research indicates that mitigation and adaptation efforts must incorporate technologies such as carbon capture and storage (CCS) to draw carbon dioxide from the atmosphere and store it elsewhere. This study examines how psychological distance and perceived risk pertaining to climate change influence Texans’ support for CCS through perceived CCS costs/benefits and affect. Overall, the results indicate that perceived psychological distance of climate change influences support for CCS through risk perception about local climate change impacts, perceived CCS benefits, and affective evaluation. Political partisanship moderates the relationship between psychological distance and climate change risk perception, but not the relationship between psychological distance and support for CCS.
The development of unconventional oil and gas shales using hydraulic fracturing and directional drilling is currently a focal point of energy and climate change discussions. While this technology has provided access to substantial reserves of oil and gas, the need for large quantities of water, emissions, and infrastructure raises concerns over the environmental impacts. Written by an international consortium of experts, this book provides a comprehensive overview of the extraction from unconventional reservoirs, providing clear explanations of the technology and processes involved. Each chapter is devoted to different aspects including global reserves, the status of their development and regulatory framework, water management and contamination, air quality, earthquakes, radioactivity, isotope geochemistry, microbiology, and climate change. Case studies present baseline studies, water monitoring efforts and habitat destruction. This book is accessible to a wide audience, from academics to industry professionals and policy makers interested in environmental pollution and petroleum exploration.
Full-text available
diverged in similarity downstream compared to upstream of impacts in the first and last years of the study when SGD activity was elevated. Assemblage divergence was related to variation in water quality. Indicator species analysis linked a few key taxa to un-impacted conditions in the first year of the study; tolerant taxa were indicators for impacted conditions later in the study. Our study links SGD to weak negative changes in water quality and benthic macroin-vertebrates, which may have negative consequences to food quality for wildlife that rely on aquatic prey within forested systems.
We already know that the construction of shale gas extraction infrastructure exacerbates soil erosion in vulnerable areas. We are not clear however, about whether the completed well pads and pipelines continue to influence soil erosion after the construction is completed. We applied high-resolution remote sensing images and DEM data from 2014 and 2017 and the Revised Universal Soil Loss Equation (RUSLE) model to calculate how the layout of the well pads and pipelines in a shale gas development area affected soil erosion. We used Geodetector to analyze the factors that affected the soil erosion intensity around the well pads. The results showed that about 0.02% and 0.12% of the total erosion in the shale gas development zone was directly caused by the completed well pads and pipelines in 2014 and 2017, respectively. Most of the erosion was related to the completed pipelines. The completed shale gas well pads affected the soil erosion intensity up to 90 and 60 m from the pads in 2014 and 2017, respectively. The soil erosion around the completed pipelines was mainly from the soil surface over the pipeline and had little effect on the surroundings. The main influences on the soil erosion intensity at different distances from the well pads were land use and slope, and the interactions between them. We suggest that, when developing new shale gas extraction facilities, gas pipelines should be arranged in gently sloping areas, and vegetation should be planted on the bare soil over the pipelines to reduce soil erosion.
Increased salinity (sodium chloride; NaCl) is a prevalent and persistent contaminant that negatively affects freshwater ecosystems. Although most studies focus on effects of salinity from roads salts (primarily NaCl), high‐salinity wastewaters from energy extraction (wastewaters) could be more harmful because they contain NaCl and other toxic components. Many amphibians are sensitive to salinity and their eggs are thought to be the most sensitive life history stage. However, there are few investigations with salinity that include eggs and larvae sequentially in long‐term exposures. We investigated the relative effects of wastewaters from a large energy reserve, the Williston Basin (USA), and NaCl on northern leopard (Rana pipiens) and boreal chorus (Pseudacris maculata) frogs. We exposed eggs and tracked responses through larval stages (for 24 days). Wastewaters and NaCl caused similar reductions in hatching and larval survival, growth, development, and activity while also increasing deformities. Chorus frog eggs and larvae were more sensitive to salinity than leopard frogs, suggesting species‐specific responses. Contrary to previous studies, eggs of both species were less sensitive to salinity than larvae. Our ecologically relevant exposures suggest that accumulating effects can reduce survival relative to starting experiments with unexposed larvae. Alternatively, egg casings of some species may provide some protection against salinity. Notably, effects of wastewaters on amphibians were predominantly due to NaCl rather than other components. Therefore, findings from studies with other sources of increased salinity (e.g., road salts) could guide management of wastewater‐contaminated ecosystems, and vice versa, to mitigate effects of salinization. This article is protected by copyright. All rights reserved.
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Fracking fluids were released into Acorn Fork, KY, a designated Outstanding State Resource Water, and habitat for the threatened Chrosomus cumberlandensis (Blackside Dace). As a result, stream pH dropped to 5.6 and stream conductivity increased to 35,000 µS/cm, and aquatic invertebrates and fish were killed or distressed. The objective of this study was to describe post-fracking water quality in Acorn Fork and evaluate if the changes in water quality could have extirpated Blackside Dace populations. Semotilus atromaculatus (Creek Chub) and Lepomis cyanellus (Green Sunfish) were collected from Acorn Fork a month after fracking in lieu of unavailable Blackside Dace. Tissues were histologically analyzed for indicators of stress and percent of fish with lesions. Fish exposed to affected Acorn Fork waters showed general signs of stress and had a higher incidence of gill lesions than unexposed reference fish. Gill lesions observed were consistent with exposure to low pH and toxic concentrations of heavy metals. Gill uptake of aluminum and iron was demonstrated at sites with correspondingly high concentrations of these metals. The abrupt and persistent changes in post-fracking water quality resulted in toxic conditions that could have been deleterious to Blackside Dace health and survival.
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Global demand for energy has increased by more than 50 percent in the last half-century, and a similar increase is projected by 2030. This demand will increasingly be met with alternative and unconventional energy sources. Development of these resources causes disturbances that strongly impact terrestrial and freshwater ecosystems. The Marcellus Shale gas play covers more than 160,934 km(2) in an area that provides drinking water for over 22 million people in several of the largest metropolitan areas in the United States (e.g. New York City, Washington DC, Philadelphia & Pittsburgh). Here we created probability surfaces representing development potential of wind and shale gas for portions of six states in the Central Appalachians. We used these predictions and published projections to model future energy build-out scenarios to quantify future potential impacts on surface drinking water. Our analysis predicts up to 106,004 new wells and 10,798 new wind turbines resulting up to 535,023 ha of impervious surface (3% of the study area) and upwards of 447,134 ha of impacted forest (2% of the study area). In light of this new energy future, mitigating the impacts of energy development will be one of the major challenges in the coming decades.
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Extraction of natural gas from hard-to-reach reservoirs has expanded around the world and poses multiple environmental threats to surface waters. Improved drilling and extraction technology used to access low permeability natural gas requires millions of liters of water and a suite of chemicals that may be toxic to aquatic biota. There is growing concern among the scientific community and the general public that rapid and extensive natural gas development in the US could lead to degradation of natural resources. Gas wells are often close to surface waters that could be impacted by elevated sediment runoff from pipelines and roads, alteration of streamflow as a result of water extraction, and contamination from introduced chemicals or the resulting wastewater. However, the data required to fully understand these potential threats are currently lacking. Scientists therefore need to study the changes in ecosystem structure and function caused by natural gas extraction and to use such data to inform sound environmental policy.
Conference Paper
Striking similarities have been observed in a number of extrapulmonary responses of rodents to seemingly disparate ambient pollutants. These responses are often characterized by primary decreases in important indices of cardiac and thermoregulatory function, along with secondary decreases in associated parameters. For example, when rats are exposed to typical experimental concentrations of ozone (O-3), they demonstrate robust and consistent decreases in heart rate (HR) ranging from 50 to 100 beats per minute, whereas core temperature (T-infinity) often falls 1.5-2.5 degreesC. Other related indices, such as metabolism, minute ventilation, blood pressure, and cardiac output, appear to exhibit similar deficits. The magnitudes of the observed decreases may be modulated by changes in experimental conditions and appear to vary inversely with both ambient temperature and body mass. More recent studies in which both healthy and compromised rats were exposed to either particulate matter or its specific components yielded similar results. The agents studied included representative examples of ambient, combustion, and natural source particles, along with individual or combined exposures to their primary metallic constituents. In addition to the substantial decreases in HR and T-CO, similar to those seen with the O-3-exposed rats, these animals also displayed numerous adverse changes in electrocardiographic waveforms and cardiac rhythm, frequently resulting in fatal outcomes. Although there is only limited experimental evidence that addresses the underlying mechanisms of these responses, there is some indication that they may be related to stimulation of pulmonary irritant receptors and that they may be at least partially mediated via the parasympathetic nervous system.
Landscape modification and habitat fragmentation are key drivers of global species loss. Their effects may be understood by focusing on: (1) individual species and the processes threatening them, and (2) human-perceived landscape patterns and their correlation with species and assemblages. Individual species may decline as a result of interacting exogenous and endogenous threats, including habitat loss, habitat degradation, habitat isolation, changes in the biology, behaviour, and interactions of species, as well as additional, stochastic threats. Human-perceived landscape patterns that are frequently correlated with species assemblages include the amount and structure of native vegetation, the prevalence of anthropogenic edges, the degree of landscape connectivity, and the structure and heterogeneity of modified areas. Extinction cascades are particularly likely to occur in landscapes with low native vegetation cover, low landscape connectivity, degraded native vegetation and intensive land use in modified areas, especially if keystone species or entire functional groups of species are lost. This review (1) demonstrates that species-oriented and pattern-oriented approaches to understanding the ecology of modified landscapes are highly complementary, (2) clarifies the links between a wide range of interconnected themes, and (3) provides clear and consistent terminology. Tangible research and management priorities are outlined that are likely to benefit the conservation of native species in modified landscapes around the world.
Protecting the worlds freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the worlds population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.
Widespread human modification and conversion of land has led to loss and fragmentation of natural ecosystems, altering ecological processes and causing declines in biodiversity. The potential for ecosystems to adapt to climate change will be contingent on the ability of species to move and ecological processes to operate across broad landscapes. We developed a novel, robust modeling approach to estimate the connectivity of natural landscapes as a gradient of permeability. Our approach yields a map capable of prioritizing places that are important for maintaining and potentially restoring ecological flows across the United States and informing conservation initiatives at regional, national, or continental scales. We found that connectivity routes with very high centrality intersected proposed energy corridors in the western United States at roughly 500 locations and intersected 733 moderate to heavily used highways (104–106 vehicles per day). Roughly 15% of the most highly connected locations are currently secured by protected lands, whereas 28% of these occur on public lands that permit resource extraction, and the remaining 57% are unprotected. The landscape permeability map can inform land use planning and policy about places potentially important for climate change adaptation.