147
It is not known if any invasive species have been introduced by the movement of
drill rigs and associated equipment from place to place across the country. Although
this site-to-site movement happens all the time, during the shale boom it was much
more frantic, and crews were being less careful about how equipment was cleaned
and inspected before traveling to a new geographic area. Since invasive species
often take years to decades to become established and noticeable, it may be some
time yet before we know if this is a problem.
A final issue related to fracking and terrestrial ecosystems is known as “ecological succession.” This is essentially how an ecosystem rebuilds to infill an area that
had been cleared by fire, bulldozers, or other means. There are two types of succession: primary and secondary. Primary succession occurs on entirely new habitat that
has never before been colonized, like a freshly quarried rock face or sand dunes.
Secondary succession refers to the process of ecosystem rebuilding in previously
occupied habitat that has been disturbed or damaged, for example by clearcutting
timber or by a forest fire.
Drill pads designed for shale wells and fracking are typically constructed by
clearing topsoil from approximately five acres (2 hectares) of land, laying down a
heavy, impervious “geomembrane” to prevent any leaks or spills from infiltrating
into the ground, and then covering the geomembrane with a layer of gravel nearly a
foot (30 cm) thick. Any ecosystem attempting to re-colonize this constructed, unoccupied surface area would essentially be undergoing a primary succession.
The process of re-colonization results in the organisms interacting with and
affecting the physical and chemical environment. As the environment changes, the
species in the area gradually change with it. Because each species is adapted to
thrive under a specific set of environmental conditions, if these change a different
set of species that are better adapted will out-compete the existing species.
Succession passes through a number of stages known as “seres.” Each sere merges
gradually into the next until the final stage, called the climax community, is reached.
This is the end of the succession. Succession occurs on many different timescales,
ranging from a few days to hundreds of years. Even in the climax community, things
are not static. When trees die and fall, for example, new openings are created for
secondary succession to occur.
The question related to fracking is how do drill pads, roads, and pipeline access
rights-of-way affect succession? If left alone, a drill pad will become overgrown
with grass, brush, and finally trees over a period of months to years. However, if the
production site remains active, the ecology will not re-establish. Shale wells drilled
along the south shore of Lake Erie in the nineteenth century to supply individual
farms produced natural gas for decades, and some even remained productive for a
century or longer (Soeder 2017). It is not known how this might apply to modern
horizontal shale wells, but it is possible they could be productive for a long time.
The need for continuous, periodic visits to the pad for maintenance and other
activities will require that at least some of the cleared area be kept clear, and will
preclude succession. It may be possible to substantially shrink the initial five-acre
(2 hectare) pad size down to just those areas needed to provide access for production
and maintenance activities like the wellheads, produced water tanks, compressor,
8.2 Terrestrial Ecosystems
It is not known if any invasive species have been introduced by the movement of
drill rigs and associated equipment from place to place across the country. Although
this site-to-site movement happens all the time, during the shale boom it was much
more frantic, and crews were being less careful about how equipment was cleaned
and inspected before traveling to a new geographic area. Since invasive species
often take years to decades to become established and noticeable, it may be some
time yet before we know if this is a problem.
A final issue related to fracking and terrestrial ecosystems is known as “ecological succession.” This is essentially how an ecosystem rebuilds to infill an area that
had been cleared by fire, bulldozers, or other means. There are two types of succession: primary and secondary. Primary succession occurs on entirely new habitat that
has never before been colonized, like a freshly quarried rock face or sand dunes.
Secondary succession refers to the process of ecosystem rebuilding in previously
occupied habitat that has been disturbed or damaged, for example by clearcutting
timber or by a forest fire.
Drill pads designed for shale wells and fracking are typically constructed by
clearing topsoil from approximately five acres (2 hectares) of land, laying down a
heavy, impervious “geomembrane” to prevent any leaks or spills from infiltrating
into the ground, and then covering the geomembrane with a layer of gravel nearly a
foot (30 cm) thick. Any ecosystem attempting to re-colonize this constructed, unoccupied surface area would essentially be undergoing a primary succession.
The process of re-colonization results in the organisms interacting with and
affecting the physical and chemical environment. As the environment changes, the
species in the area gradually change with it. Because each species is adapted to
thrive under a specific set of environmental conditions, if these change a different
set of species that are better adapted will out-compete the existing species.
Succession passes through a number of stages known as “seres.” Each sere merges
gradually into the next until the final stage, called the climax community, is reached.
This is the end of the succession. Succession occurs on many different timescales,
ranging from a few days to hundreds of years. Even in the climax community, things
are not static. When trees die and fall, for example, new openings are created for
secondary succession to occur.
The question related to fracking is how do drill pads, roads, and pipeline access
rights-of-way affect succession? If left alone, a drill pad will become overgrown
with grass, brush, and finally trees over a period of months to years. However, if the
production site remains active, the ecology will not re-establish. Shale wells drilled
along the south shore of Lake Erie in the nineteenth century to supply individual
farms produced natural gas for decades, and some even remained productive for a
century or longer (Soeder 2017). It is not known how this might apply to modern
horizontal shale wells, but it is possible they could be productive for a long time.
The need for continuous, periodic visits to the pad for maintenance and other
activities will require that at least some of the cleared area be kept clear, and will
preclude succession. It may be possible to substantially shrink the initial five-acre
(2 hectare) pad size down to just those areas needed to provide access for production
and maintenance activities like the wellheads, produced water tanks, compressor,
8.2 Terrestrial Ecosystems