Delta Life Nr. 3 February 2015

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CO2-GUZZLERS,
NURSERIES, WATER
TREATMENT PLANTS,
BREAKWATERS
■ ■ Wetlands includemangrove forests, seagrass pastures,
salt marshes and flood plains. World-famous wetlands
include the Okavango Delta in Botswana, Bank d’Arguin
near Mauritania, the Sundarbans in Bangladesh and the
Mississippi Delta.
■ ■ Seagrass (Posidonia oceanica) propagates itself mainly
bymeans of shoots and rhizomes. In 2006, Portuguese
researchers discovered a seagrass pasture to the south of
Ibiza that was more than 10,000 years old. This colony is
the oldest living organismon the planet.
■ ■ In the past century, the total wetlands surface area has
beenmore than halved. That area is still diminishing an-
nually by between two and five per cent as a result of drai-
nage, land reclamation, mining, unregulated fish farming
and pollution, but also as a result of rivers being dammed,
preventing river sediment reaching the wetlands.
■ ■ The Ramsar convention of 1971 protects more than
2000 wetland areas that together make up more than
200million hectares. That is an area as big as Mexico,
but still a fraction of the total area worldwide.
■ ■ Mangroves are genuine CO2 guzzlers: every square
metre retains 3 to 4 times more carbon in the soil
than tropical rainforests. So preserving and restoring
wetlands is an important asset in the trade of carbon
credits.
■ ■ The wetlands in the USA alone provide natural
protection against hurricanes worth 20 billion dollars.
■ ■ Plants in wetlands purify the water. The city authorities
of New York found out that they could save 3 to 8
billion dollars on investments in sewage treatment
by investing 1.5 billion dollars in purchasing and
protecting wetlands surrounding water reservoirs.
■ ■ Restoring the subtle interaction between plant growth,
sediment supplies and waves is not straightforward. In
most traditional cultivation projects, less than 20% of
the seagrass survives the first year.
WETLANDS:
■ ■ Young mangrove or seagrass plants will not survive if the
type of plant is not appropriate for the local conditions. A
common error is therefore attempting to make the leap to
the final goal for the vegetation in the system in a single
step.
■ ■ Restoring the favourable natural boundary conditions,
using seeds that are naturally available locally, and being
patient for a minimum of five to ten years will often be
more effective than large-scale planting campaigns that
claim to be successful within a year.
■ ■ Different interests need not be conflicting interests.
Studies are being conducted in the Mississippi delta to see
whether changes in the upper reaches of the Mississippi
can encourage the sediment supply without affecting the
local oyster farms.
For more information:
, Bregje.vanWesenbeeck@
deltares.nl, , Ellis.Penning@
deltares.nl
Wetlands aren’t just beautiful.
They also protect our coasts,
purify our water and help in the
fight against climate change.
Unfortunately, more than half
of our wetlands have now been
lost. Restoring them can be
fraught with difficulties and
setbacks. BY MEINTE BLAAS