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Climate
Change is Pushing Lake Okeechobee’s Water Levels Higher — And
that’s Bad News For Algae Blooms, Flood Risk
11
July, 2016
More
powerful storms. Heavier extreme rainfall events. Storms with higher
potential energy. These are the result of a human-forced warming of
the Earth’s atmosphere. And South Florida finds itself sandwiched
between heavier evaporation flows streaming off the Gulf of Mexico, a
more volatilely stormy North Atlantic, and large rivers of moisture
streaming in from the Southeast Pacific.
(Atmospheric
water vapor levels over South Florida during late June of 2016. South
Florida sits between numerous heavily laden atmospheric moisture
flows. As human forced warming increases evaporation, these moisture
flows expand, resulting in heavier rainfall potentials during storms
over South Florida. This climate change dynamic is increasing
over-topping flood risks for Lake Okeechobee even as the added heat
and rainfall run-off enhances the potential for toxic algae blooms
like the one now afflicting South Florida. Image source: Earth
Nullschool).
And
as these moisture-enhanced storms of climate change dump heavier and
heavier rains over South Florida’s Lake Okeechobee, the choice
appears to be one between flood risk or toxic algae blooms.
*****
Flood
Risk Worsens With Climate Change
Lake
Okeechobee sits at the heart of South Florida. Covering
730 square miles,
the lake is bounded on the north, east, and west by farms. Run-off
from these farms streams into the lake, feeding the growth of algae
blooms. As the Earth’s atmosphere and ocean warmed due to human
greenhouse gas emissions, rainfall events over South Florida have
grown more intense. This trend increases run-off from pesticide,
phosphorous, and nitrogen rich soils which then swell the lake with
these chemicals and compounds — many of which promote the growth of
cyanobacteria (or blue-green algae).
The
increasingly heavy rains also force lake levels higher. During Winter
of 2016, the
wettest January in South Florida’s climate record pushed Lake
Okeechobee’s water levels to 16.4 feet above sea level by February.
November through May is South Florida’s dry season. So abnormally
wet conditions during a typically dry period greatly increased flood
risk for communities surrounding the lake as South Florida entered
its June through October wet season.
Heavy
rains have continued through recent months and, in order to mitigate
the heightened flood risk, the US Army Corp of Engineers has been
pumping large volumes of the run-off enhanced, nutrient-rich waters
out of the lake in order to relieve pressure on the Hoover Dike. The
Dike, for its part, is
a 132 mile system of levees surrounding the lake and preventing its
waters from flooding local communities during heavy rainfall events.
(Lake
Okeechobee [upper right of frame] and the algae-laden coastal waters
of South Florida as seen in this June 26 LANCE
MODIS satellite
shot.)
Paul
Gray, a scientist with Audubon Florida and Lake Okeechobee
expert recently
noted:
“One big storm would be a bad situation, really bad. We are nearing the heart of the tropical season and the corps knows they are one storm away from levels they are not comfortable with.”
To
reduce pressure on the Dike, the Corps likes to keep Lake Okeechobee
in a range of 12.5 to 15.5 feet above sea level. This creates a
buffer zone to allow for the impacts of unexpectedly strong storms —
like tropical cyclones — which can alone produce enough rainfall to
push lake water levels between 1-4 feet higher.
At
around 18.5 to 19.5 feet above sea level, the Hoover Dike system is
under high risk of a breach or of over-topping. An event which would
flood thousands of homes and businesses with 1-5 feet of water and
generate a serious risk of loss of life.
So
this year, with the dry season acting like the rainy season and with
the rainy season now underway, the US Army Corps of Engineers has
been releasing much larger volumes from the Lake in what some could
call a frantic effort to keep water levels there in the safe range.
These efforts, as of Thursday, July 7 produced
a Lake Okeechobee water level of 14.93 feet —
which was at the top edge of the safe zone. But the effort came at
the cost of flushing nutrient rich waters into South Florida’s
rivers and estuaries.
Mitigate
Flood Risk and Toxic Algae Blooms Result
During
recent years, heavy use of fertilizers has loaded up farmland soils
surrounding Lake Okeechobee with phosphorous and nitrogen. As
human-forced climate change has produced more extreme rainfall events
over lands surrounding the lake, greater runoff of these
nutrient-rich soils and chemicals into the lake has resulted.
Phosphorous
levels, which government regulators like to keep in the range of 40
parts per billion in lake waters, has risen to 100 to 200 parts per
billion. That’s 2.5 to 5 times the safe allowable level. And as the
Army Corps of Engineers ramped up lake water outflows into the St.
Lucie and Caloosahatchee rivers during recent months, this influx of
high nutrient lake waters helped to spur the large algae blooms now
afflicting the region.
John
Campbell, a spokesperson for the US Army Corps of Engineers recently
noted that people often ask:
“‘Why didn’t you release more water?’ Well, this is what releasing more water looks like.”
Due
to the increased water outflows from Lake Okeechobee, high nutrient
levels hit river systems warmed to bacterial growth enhancing
temperatures by climate change. Cyanobacteria (blue-green algae)
populations in these river and estuary systems then exploded. Goo
painted waterways green, putrescent mats of algae formed in calmer
waters, and airs smelling of rotten eggs wafted up from the
suffocating rivers. These explosive and toxic bacterial growths
prompted a
declaration of a state of emergency by Governor Rick Scott as
four South Florida counties were heavily impacted by the algae
blooms.
(Toxic
algae blooms like this one have resulted in beach closures across
South Florida. Human-caused climate change spurs an increasing
incidence of such toxic algae blooms by increasing water
temperatures, which enhances algae growth, and by spurring more
extreme heavy rainfall events — which generates increased nutrient
influx into rivers, lakes, and oceans. Image source:Surfrider.)
Directly,
cyanobacteria can produce a number of toxins capable of harming
animal and human organ systems. Most common toxins are neurotoxins
and toxins that impact the gastrointestinal track — particularly
the liver. In addition, large blooms can deprive waterways of
life-giving oxygen. Such anoxic conditions spur fish kills and mass
production of hydrogen-sulfide generating organisms — a powerful
toxin which generates the sulfuric rotten eggs smell that many South
Florida locations are now reporting.
Indirectly,
the blooms are unpleasant, unsightly and result in beach closures.
And since the blooms became widespread, South Florida has experienced
losses to its tourist industry (see toxic algae chokes business) — one of the biggest revenue producers for the State. Yet one more example of how human-forced warming not only harms the health of the natural world, but also harms human systems that rely on such natural wealth and beauty to function.
(Large
algae blooms spurred by rising water outflows from an increasingly
flood-stressed Lake Okeechobee resulted in tourism industry losses
during the Fourth of July weekend of 2016. However, residents are
rightfully concerned over long-term health risks due to the algae
blooms. Note that purple water in gaps between the algae as well as
reports of ‘rotten eggs’ smell is circumstantial evidence of
increasing concentrations of hydrogen sulfide producing bacteria that
tends to thrive in the anoxic dead zones produced by the algae. Video
Source: CBS
Youtube.)
Conditions
in Context
The
US Army Corps of Engineers is now reducing Lake Okeechobee water
outflows in an effort to limit harmful algae blooms over South
Florida waterways and estuaries. Outflow levels, as of June 30 were
cut by 35 percent. As a result, some of the nutrients feeding algae
blooms will be removed from waterways. But it’s questionable if the
large algae blooms can be entirely halted by this mitigation.
Warmer
than normal temperatures and heavier than normal rains are expected
over this region during the coming weeks and months and these
conditions will add to bloom promotion even without a larger pulse of
water coming from Lake Okeechobee. In addition, reducing water flows
from the lake will again push the lake to rise. And that puts South
Florida one large storm away from risking an over-topping of the
Hoover Levee System.
Climate
change, in this context, has therefore put South Florida in a tough
bind between worsening algae blooms over its waterways or worsening
flood threats from a swelling Lake Okeechobee. A more immediate
problem juxtaposed to the longer term risk of sea level rise — a
human-forced ocean invasion which could flood the whole of South
Florida by or before the end of this Century.
Links:
Hat
tip to Colorado Bob
Hat
tip to DT Lange
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