Want to prevent California’s looming flood disaster? Grow a marsh.

Something is amiss on Sherman Island, a whale-shaped swath of
farm and grazing land at the confluence of the Sacramento and San
Joaquin rivers. If you don’t know what ails the place, it might
be hard to pinpoint the problem. The island, in the Sacramento
Delta, is roughly 16 square miles. Its asphalt roads, cracked and
sagging at the edges, look like cheese melted over a lumpy pizza.
The telephone poles, many of them kept erect by taut guy-wires,
stand conspicuously at non-right angles. The landscape feels Dr.
Seussian — a wacky, slightly absurdist version of farmland, right
down to the exaggerated industrial backdrop: a steady stream of
cars driving past on State Highway 160, which traverses the island;
steaming smokestacks from the power plant across the river; the
Antioch Bridge arcing dramatically over the San Joaquin River;
enormous wind turbines turning lazily on a hill to the
northwest.

What’s wrong?

“We’re standing 10 feet below sea level,” Bryan Brock, an
engineer with California’s Department of Water Resources, told me
during a visit in May. Brock, who has a white-blond goatee
sprouting from his chin like tuft grass, evinced supreme calm as he
explained: “None of these people realize it driving past, but
they’re below sea level. And that’s a problem.”

The land here, and hundreds of thousands of acres elsewhere in
the delta, began to sink in the late 1800s as people started
draining the region’s vast wetlands. As they walled off rivers
and created dry islands from what was previously soggy marsh, they
discovered incredibly rich soil. In contrast to other fertile
regions like Iowa, where topsoil two feet deep was considered
bounteous when farmers began plowing it in the 19th century, delta
peat soils — created over thousands of years, by wetland plants
growing and dying and not quite decomposing — could be 50 feet
deep. No one foresaw that this very bounty — soil rich with
organic material — would, over time, become a curse of sorts.

River and marsh bottoms typically have low oxygen levels, which
slows the decomposition of organic material that collects there.
That organic material contains copious amounts of carbon. Once the
waterlogged delta soils dried out, microbes began to consume the
organic detritus, transforming it into gas. Millions of tons of
solid ground started going up into the air as microbial
exhaust.

And the land began to sink.

In some places, including parts of Sherman Island, the land has
now subsided 25 feet since the late 1800s — and continues to sink
between half an inch and 1.5 inches yearly.

These “islands” aren’t really islands at all anymore,
Brock told me, but empty bathtubs whose bottoms are receding. The
deepening cauldrons, now sitting well below sea level, are creating
a situation that grows more precarious with each passing year. The
more the islands sink, the greater the pressure on the aging
mounded dirt levees that keep the water back, and the greater the
likelihood that they’ll fail.

Sherman Island Cross Road
is warping due to subsidence near its junction with State Highway
160. Jonno Ratman / Bay Nature

This situation, called subsidence, worries the California
Department of Water Resources and many others, not just because
farmers could lose pasture and farmland, but because much of the
water that irrigates the Central Valley, and that many Californians
depend on for drinking water, is pumped through a sprawling network
of canals from the delta. A large enough breach of those levees —
especially if it affected many of the delta’s 57 islands
simultaneously — could hamper the flow of fresh water to the
Central Valley, leaving huge swaths of the state without usable
water for months, even years.

Brock describes the mechanics of the threat as the “big
gulp.” Water in the 1,100-square-mile delta — nearly the size
of Rhode Island — sits at sea level. Only the pressure of the
fresh water flowing down the leveed Sacramento and San Joaquin
rivers prevents salt water from the San Francisco Bay from pushing
inland. If many levees fail at once, the fresh water that otherwise
keeps the salt water away would rush to fill all those empty
bathtubs. Brackish water from San Francisco Bay would then flow
inland. The water used to irrigate the Central Valley and its $17
billion agricultural economy, and the drinking water for about 25
million people, could become salty and unusable.

“It’s Katrina on steroids,” Dennis Baldocchi, a professor
of biometeorology at UC Berkeley who studies the delta, told me.
“We’re a $4 trillion economy. Think of shutting down water for
30 million Californians.”

Because the region is prone to earthquakes — and because
faults pass right through the delta region — an earthquake that
could trigger a catastrophic levee failure, defined as 20 islands
flooding at once, has a 62 percent chance of occurring in the next
two decades if subsidence isn’t addressed, DWR’s own analysis
suggests. The event would likely incur tens of billions of
dollars’ worth of damage and could take a year and a half to
repair. Nor is the flooding of delta islands unprecedented. When
Jones Tract, a delta island, flooded in 2004, the damage cost $90
million to fix. In earlier times, several islands that were
inundated were simply abandoned: Google Maps reveals lakes — the
Mildred Tract, Franks Tract — where farmland once existed,
discernible by the ring-shaped remains of levees rising, like coral
atolls, from the delta water.

“We’re not paying attention,” Baldocchi told me; the
disaster-in-waiting, he asserts, has not drawn the concern it
deserves. Action to address the problem has been stymied for years
by, in part, the sheer number and variety of agencies, sometimes
with competing agendas, operating in the delta. Interagency rivalry
and distrust have yielded what Ray Seed, a UC Berkeley professor of
environmental engineering and an expert on the delta, once
described as a “60- to 70-year stalemate” in which “we will
all lose together.”

“It’s truly a wicked problem,” agrees Campbell Ingram,
head of the Delta Conservancy, a state agency tasked with ecosystem
restoration in the area. Yet for the first time in his 13-plus
years working on the issue, he says, the majority of stakeholders
now concur that the subsidence issue needs to be addressed
urgently. “We’re kind of in this weird space where we
simultaneously can’t prevent the delta from failing, and we
can’t allow it to fail,” he adds.

One solution is for the landowners, with some state funding, to
keep repairing the levees, building them higher and wider. But as
sea levels rise and the islands continue to subside, the costs of
fortifying and maintaining the structures may exceed the value of
the land and agricultural production behind them, says Alf Brandt,
counsel to the State Assembly Speaker Anthony Rendon. For some of
the deepest islands, the conclusion of that cost-benefit analysis
already looks unfavorable, he says.

For decades, DWR has been working on another more
ecosystem-based fix. Since the 1990s, the agency has experimentally
re-flooded pieces of land in the delta, with the goal of
reestablishing wetlands like those that created the soil in the
first place. The reasoning is that once wet, the land will stop
losing carbon and the sinking will come to a halt. Even if that
doesn’t entirely resolve the problem, Ingram says, it prevents
the situation from getting worse. And over the long term, marsh
plants may, through photosynthesis, capture enough carbon from the
atmosphere that the ground begins rising again.

It’s through this last mechanism — plants’ ability to pull
carbon from the atmosphere — that a project originally conceived
to protect California’s water infrastructure has, over the years,
evolved into something more interdisciplinary, and of potentially
greater importance. Although they can produce powerful greenhouse
gases, wetlands can also sequester and store immense quantities of
carbon. Policymakers have historically ignored these places in
discussions about greenhouse gas emissions, but that’s now
changing as they come to appreciate the huge stores of carbon that
wetlands already contain — and the large quantities of greenhouse
gases they release when destroyed.

An expanding body of research has prompted land managers to
consider, for the first time, creating wetland carbon credits that
might be traded in carbon markets. In California, at least, efforts
to address one worsening disaster could enable prevention of
another. Mounting anxiety over global heating may be what spurs
creation of carbon credits that, by providing funding for delta
wetland restoration, also produce badly needed funds to protect
California’s water infrastructure. “It would have been great to
have done this 30 or 40 years ago,” Kristopher Tjernell, deputy
director of DWR’s Integrated Watershed Management Program, told
me. “But you know, it wasn’t ripe. And it’s ripe now.”

Bryan Brock, an engineer
with DWR. Jonno Rattman / Bay Nature

“Blue carbon” refers to carbon momentarily trapped — or
slowed down, really — in waterlogged ecosystems. Because the
microbes that break down carbon in wet conditions work much more
slowly than those in more aerated environs and through different
biochemical pathways, wetland ecosystems can accumulate and store
far more carbon per acre than forests and savannas can. Scientists
have known this in a roundabout way for a long time: After all, the
coal and oil deposits that have fueled civilization since the
Industrial Revolution come from ancient marsh and marine ecosystems
that, after accumulating huge quantities of carbon, were buried and
fossilized over millions of years. Fossil fuels, you might say, are
an aged form of blue carbon.

Historically, policymakers and scientists have been daunted by
the many variables involved in calculating the amount of carbon
held in wetlands and, more broadly, in the web of living things we
call the biosphere, according to Stephen Crooks, cofounder of
Silvestrum Climate associates in San Francisco. It’s far more
complicated than quantifying how much comes out of smokestacks and
tailpipes, he says: “It was seen as more challenging and somewhat
scary to include.” But the omission has always been, in his view,
untenable.

Worldwide, about 450 million tons of carbon dioxide enter the
atmosphere yearly from wetland degradation — destroyed mangrove
forests, drained marshes, and smothered seagrass beds. That’s
equal to the yearly human-caused greenhouse gas emissions of
France, the U.K., or California. “When your emissions are the
size of California’s economy and you weren’t counting it,” he
told me, “that’s a very big surprise.”

Wetland ecosystems comprise just 5 to 8 percent of the
planet’s land area but contain between 20 and 30 percent of the
world’s soil carbon. “When you destroy a wetland, you can
release thousands of years of carbon in just a few decades,”
Crooks says. On the flip side, by preserving wetlands, you can
protect millennia’s worth of accumulated carbon with, in theory,
relatively little effort. The Sacramento Delta, the largest estuary
along the western edge of the Americas, has become a test case for
this idea.

The delta may have once held the largest freshwater wetland
carbon reserves on the West Coast. Since it was drained over a
century ago, it has released an amount of carbon equal to
one-quarter of California’s forests — all the redwoods, pines,
and oaks in the nation’s third-largest state, according to
Baldocchi and his colleagues. And it’s still emitting carbon.
Although it comprises less than 1 percent of the state’s
cropland, every year the delta releases a quantity of carbon equal
to one-quarter of all plant-related agriculture — all the
tractors, plows, and combine harvesters operated in the state.
“I’ve been making measurements my whole career, and I’ve
never seen fluxes as large as what’s happening from these peat
soils,” Baldocchi told me. The near-term goal in the delta, and
in any degraded wetland really, is to stop subsidence and
emissions. The longer-term goal is to reverse them.

DWR measures the CO2 and
methane emissions from the wetlands it created on Sherman Island.
Jonno Rattman / Bay Nature

Crossing over the blue-gray San Joaquin River on the Antioch
Bridge, you can just glimpse the glittering wetlands to the west on
Sherman Island. They’re easy to miss at 60 miles an hour. But as
I stood with Brock on a wooden walkway a few feet above them in
May, the low roar of the semi-industrial landscape — cars
speeding over the bridge and boats motoring by on the other side of
the levee — receded as I watched birds flit acrobatically among
the rustling tule reeds and dragonflies hover over the dark water.
The wetlands, hemmed in as they are by levees, roads, and fields of
grazing cows, look remarkably healthy. They represent the
implementation phase of DWR’s ongoing project, which seeks to
shore up the threatened levees by creating wetlands on their
subsided “bathtub” sides.

“Isn’t it beautiful,” Brock said, looking out over the
reeds. “Sometimes nature can do things better than humans.”
Which is not to say the DWR restoration project was as easy as
opening the floodgates and watching the cattails return. Before
water was allowed back, he explained, the land had to be carefully
sculpted to ensure the optimal water depth for marsh plants to
grow.

Brock’s predecessors created the first experimental wetlands,
on nearby Twitchell Island, in the 1990s. Not only did bringing
water back halt the loss of carbon from the soil and stop
subsidence, experts discovered, but the wetland plants grew so
rapidly that, as they died and left tangled masses of roots and
stalks, they raised the elevation of ground at an average rate of 4
centimeters per year. A common assertion among soil scientists is
that an inch of topsoil takes a century to accumulate, maybe
longer. But these wetland plants were turning carbon dioxide into
solid earth at a rate observable by humans from one year to the
next.

Even so, given the magnitude of the subsidence problem, that
rate of soil accretion can seem sorely inadequate. It will take
roughly 150 years to get the most sunken areas of these islands
back to sea level, Baldocchi told me. “People have trouble
thinking in 100-year time scales,” he said. “We can’t get
bored with these projects in 15 years.”

Yet the long-term time frame doesn’t mean we have to wait till
the end for the project to bear fruit. Campbell Ingram of the Delta
Conservancy emphasizes the importance of “stopping increased
risk” — of halting subsidence. What’s key to understand, he
says, is that the risk of levee breach does not increase linearly
with subsidence, but exponentially. So by halting subsidence, you
prevent the ballooning probability of catastrophic failure.

And if the ground regains just a few feet over the years, the
risk of catastrophe declines non-linearly as well. Meaning you
don’t need to grow the ground back to sea level to dramatically
reduce the possibility of a calamitous breach. Some modeling
suggests that just gaining half the lost ground back — about 50
to 75 years as opposed to 150 — could bring the likelihood of
widespread failure to nearly zero.

Even so, the major challenge facing the project is how to reach
a scale of wetland restoration that’s meaningful for the greater
Sacramento Delta. DWR has so far flooded about 1,700 acres in four
separate wetlands. But altogether there are about 250,000 acres of
deeply subsided land in the delta, most of it owned by farmers. So
success depends in part on convincing farmers to forgo cash crops
and flood their land instead, something that’s unlikely to happen
without adequate monetary incentive.

Ideally, Ingram says, the state would pay farmers to convert
cropland to wetland. (There is also an intermediate option, a
wetland that sustains a crop: rice in flooded fields. In
experiments, rice paddies stopped subsidence, but they didn’t
reverse it.)

California does have a relatively new program, called the
Healthy Soils Initiative, whereby state money goes to farmers who
implement practices thought to benefit soil health. It’s a model
of what’s possible, Ingram says, but regrettably no such program
exists for Sacramento Delta wetlands. Marsh provides critical
habitat for various species, so other income sources for farmers
might include duck clubs or federal and state programs that pay for
creation of endangered-animal habitat. But for now Ingram is
betting on carbon markets, particularly California’s
cap-and-trade system.

“We want to get to a point where a farmer wakes up and says,
‘I can earn more flooding my land than growing corn,’” Ingram
told me.

Established in 2006 by the law AB32, the cap-and-trade system
seeks to reduce the state’s greenhouse gas emissions by
harnessing market forces. The state establishes an upper limit on
greenhouse gas pollution — the cap — and then gives polluters a
certain number of allowances to emit the offending gases. The
quantity of allowances given out declines over time, forcing
polluters to either clean up their operations or to purchase
allowances from polluters who have a surfeit. Polluters can also
buy a certain number of offset carbon credits from projects that
either prevent the emission of greenhouse gases or remove them from
the atmosphere. This is where restored delta marshes might come in
— as a source of offset credits for purchase.

Ingram and Steve Deverel — one of the scientists who, when
with USGS, conducted the original pilot projects on reversing
subsidence in the delta and is now with the consulting firm
Hydrofocus — developed a delta wetland carbon protocol that the
American Carbon Registry approved in 2017. Meaning that they can
sell offsets in the voluntary carbon market.

Approval for the state’s cap-and-trade system, where offset
credits now trade for roughly double the rate seen on the voluntary
market and might actually compete with earnings from crops, is
likely a year and a half away, Ingram says.

And these are complicated carbon offsets. Freshwater wetland
plants can pull carbon from the atmosphere at a spectacular rate
— about 5.7 tons per acre per year in the delta — but
freshwater wetlands also emit the greenhouse gas methane, which has
about 30 times the warming potential of carbon dioxide. According
to Baldocchi, the warming caused by the methane released from delta
wetlands about equals, in the short term, the cooling potential of
the carbon dioxide removed from the atmosphere.

Why go through all the trouble, then, if we end up right where
we started? Think of it as preventive medicine. By re-flooding one
acre of peatland in the Sacramento Delta, you prevent between 10
and 20 tons of carbon dioxide from entering the atmosphere — via
the organic material that microbes would have turned into gas if
the land remained dry. That’s equivalent to between two and four
years of driving your average car. In addition, you prevent
worsening of the subsidence problem and its threat to the state’s
water supply.

Lisamarie Windham-Myers, a scientist with USGS, thinks she may
eventually be able to improve the climate-cooling potential of
these wetlands by emulating what happens in certain marshes that
don’t produce greenhouse gases. Saltwater and brackish marshes
don’t release nearly as much methane as freshwater wetlands, she
explains. That’s because ocean water contains sulfate, which
changes the biochemical pathways available to microbes that break
down organic material. With sulfate present, instead of creating
methane as a byproduct, microbes produce sulfide, which isn’t a
greenhouse gas.

Windham-Myers studies the Suisun marshes, not far from Sherman
Island. She’s found that even trace amounts of sulfate in the
water prevent those counterproductive methane emissions. In Suisun,
the sulfate comes from the small quantity of seawater that pushes
into the system from San Francisco Bay. But even freshwater
systems, she emphasizes, can contain trace amounts of sulfate —
or iron, which also prevents methane production. In fact, she has
observed that methane emissions from different parts of the
restored DWR wetlands vary greatly, likely because of how water
moves through them — carrying tiny concentrations of sulfate or
iron to some areas, but not to others. Once scientists better
understand such dynamics, they may be able to control the flow of
water through resurrected wetlands in a way that limits methane,
increases the net climate benefit, and raises the value of the
carbon credit sold against restored delta wetlands.

“The role of hydrology is definitely emerging as a knob we can
turn,” Windham-Myers told me. “Let’s fine-tune these wetlands
to make them as amazing as possible.”

This story was originally published by Grist with the headline
Want to prevent California’s looming flood disaster? Grow a
marsh.
on Oct 9, 2019.

Source: FS – All – Science – News
Want to prevent California’s looming flood disaster? Grow a marsh.