On much of the world's coast, salt
marshes provide an important first line
of defense against coastal erosion and
flooding but vast areas of these valuable coastal buffer zones are
rapidly changing around the world.
We are a team of geographers and geologists and
for the past two years we have worked
hard to figure out just how stable these
salt marshes; formed of plants and
sediment, are. To be prepared for the next
big storm we need to understand whether a severe storm may destroy these
valuable natural features. When they are
gone our homes cities and infrastructure
become a lot more vulnerable.
To find out what controls their likely
response to future storms, we have put
intact soil columns from a muddy marsh
on the east coast of the UK and a sandier
marsh from the west coast into a CT
scanner to see what the soil and roots
look like inside. We then carefully cut
one side open and put them into a giant
wave flume to let waves crash into and
over them, and we use digital imaging
techniques to map areas of the soil that
eroded and washed away, and other areas
that swelled under the water. We also
studied the composition of the soil; how
much organic matter, the type and size of
particles, and what type of roots it
contained. Our results show that
particular species of plants, and
particular types of particles, caused the
soil to bind together more than others.
"We use medical CT scanning to look at
what is under the marsh in three
dimensions and study the structure of
roots and voids. Our CT images show
that the shape and distribution of roots
and voids varies with vegetation and
sediment type". "In field and lab tests we
find that both the sediment type and the
vegetation type have an important effect
on the resistance of the marsh. In the
flume we see more erosion in the sandy
sediments than the muddy ones, but in
both cases we see most erosion close to
where we see roots and voids". We can map
what is on the ground from above using
drones and satellite images. In this way
we can map how the soil structure and
its possible response to the influence
of waves and tides varies across an area. "The images we can get from the drone are
great for measuring erosion but we can
also use them to map different plant
species and infer their effect on
sediment stability". "Salt marshes play a
very important role in the context of
climate change, they reduce the impact of
storms and they take carbon from the
atmosphere. By better understanding
mechanisms of erosion we can help to
protect these important environments and
plan for the future". A future in which sea levels are rising, and storms may be
increasing in frequency and magnitude,
and a future in which we are becoming
increasingly reliant on our natural
surroundings for protecting us, and
everything we do, from the impact of a changing climate. "The great thing about
the resist project is that it's shown
us that natural coastal features form
extremely strong natural defenses that
self-repair and grow with rising sea
levels.
They also safeguard our fisheries, they
give us beautiful spaces to enjoy, they
store carbon, and they increase
biodiversity. Now that we know all this
we need to continuously monitor them and
we need to recognize them within our
policy and planning frameworks". "Here at
BGF we have to try and understand the
vulnerability of our coastline in
England and Wales to erosion overtopping
by waves and storm surges. Working with the
RESIST team has really helped us to
understand how we score the
vulnerability in low-lying land,
particularly with salt marshes. By
understanding salt marshes much, much
better we're improving our data project
and we're also able to improve our
support to local authorities with their
shoreline management plans."