a plastic sheet lined with neoprene and a por-
table gas analyzer to measure emissions from
dead trees. The goal is to see whether the
skeletal tree trunks serve as chimneys, pip-
ing methane and CO 2 up into the atmosphere
from the soil microbes, or as plugs, keeping
the gases in the ground. So far, Ardón says,
the preliminary data point to the dead trees
as plugs that minimize the emission of green-
house gases into the atmosphere.^1
Still, greenhouse gases can leak into the
atmosphere directly from the soil. Under
normal conditions, forested wetlands con-
stantly give off methane due to the high
numbers of methane-producing bacteria
that thrive in the water-soaked habitats,
says Martinez, and repeated inundation
with salty water may affect the soil microbi-
ome composition and emissions.
In 2011, the University of Connecti-
cut’s Ashley Helton, then a postdoc in Ber-
nhardt’s lab at Duke, collected soil sam-
ples in PVC pipes from Timberlake and
brought them back to the lab, where she
regularly measured their greenhouse gas
emissions as they were subjected to dif-
ferent treatments: irreversible inundation
with salt or fresh water, or being left to dry
out between floodings with salt water once
a week for 20 weeks. Separately, the team
started dumping water with various salt
concentrations into PVC pipes pushed
down into the ground at different spots
around Timberlake, then measuring the
soil’s emissions in the field.
Based on past research suggesting that
adding moisture to the soil could speed the
decomposition of roots and stems of dead
plants in forested wetlands and thereby
accelerate the flux of greenhouse gases
into the atmosphere,^2 Bernhardt’s group
had predicted that CO 2 emissions would
increase. But the opposite happened: in
both the lab and field experiments, upping
the salt reduced CO 2 emissions by almost
half. Methane emissions also dropped in
permanently saltwater-flooded soils. But
when the soils switched back and forth
between being dry and wetted with salty
water, they spouted methane, releasing
double the amount exuded by untreated
soils or soils intermittently flooded with
freshwater.^3 Bernhardt notes that similar
studies have shown conflicting results, so
it’s not exactly clear how flooding affects
a forest’s soil-to-atmosphere greenhouse
gas emissions.
Repeated influxes of saltwater are
exactly what is expected as strong hurricanes
and storm surges increase in frequency.
“Sunshine flooding,” where higher tides, as
a result of rising seas, leave standing water
in inland regions independent of precipita-tion, is also expected to become more com-
mon. And as lower-lying lands become fully
inundated with saltwater, the land farther
inland will begin to experience this inter-
mittent flooding. If this type of flooding does
increase methane emissions, it could exacer-
bate climate change.
To complicate matters further, farm-
ers in near-coastal areas can control how
water flows to their fields and adjoin-LOSING LAND
While some plants and animals living in ever-saltier landscapes seem to be capable of
adapting, it’s the people there who are going to be displaced, notes Erin Seekamp, who
develops models of climate adaptation planning at North Carolina State University.
Near Taylors Island, west of the Blackwater National Wildlife Refuge in eastern Mary-
land, saltwater marshes have already begun to infiltrate residential backyards and are
encroaching on a historic graveyard. South of the refuge, in Somerset County, residents
are selling their homes as the invasive saltmarsh reed Phragmites australis advances
deeper into their lots.
Part of the land being left fallow is farmland. Monitoring abandoned fields as salty
water periodically makes its way inland, coastal marine ecologist Keryn Gedan of
George Washington University in Washington, DC, and biologist Eduardo Fernández-
Pascual of the University of Oviedo in Spain found that these regions are producing a
new and diverse set of plant communities not seen in traditional wetlands, suggesting
the fields may respond to salty conditions differently than natural marshes. They may
be dominated by marsh shrub species, rather than reed species, and have a greater
resilience to P. australis (J Veg Sci, 30:1007–16, 2019).
That transition of farmland and residential land to marsh is happening predomi-
nantly in low-lying, rural communities that are already economically disadvantaged.
These communities typically lack the funds to pay for infrastructure—such as seawalls
seen in China, dikes in the Netherlands, or even elaborate pumping systems used on
large-scale farms—that could help to mitigate saltwater intrusion and later sea level
rise. On the Albemarle-Pamlico Peninsula in North Carolina, for example, it took nearly
20 years for the town of Swanquarter to raise the funds to build a dike system to pre-
vent storm flooding. The cost of that project means that strategy is now likely “off the
table” for other communities that have begun to be affected by saltwater intrusion,
Seekamp says.
“We’re not really talking about how human communities are affected by ghost for-
ests,” she says. “But as ghost forests form and marshes migrate, we’re going to see
loss of land.... We’re going to be faced with really hard decisions about what people
should do, and how our current federal policies and state level policies can help these
communities.”
Resettling communities farther inland is an option—one that’s being tried in Louisi-
ana with residents of Isle de Jean Charles. The narrow ridge of land, inhabited mostly by
people with American Indian ancestry, is being swallowed by the Gulf of Mexico, with
the salty water infiltrating the remaining oak forests and transforming them into grave-
yards of tree skeletons. The state government has allocated funds to relocate residents,
but many aren’t willing to leave. “There’s this really important aspect of people’s connec-
tions to place,” Seekamp says. “It’s hard to hold a community together if that place con-
nection doesn’t exist.”