Amazon basin
5
The mighty Amazon
The most
powerful river,
one of the longest,
and the
largest
drainage basin
The sources of the Amazon tumble
down from the Andes, falling from
an altitude of 5,000 m to 300 m over
just a few hundred kilometres.
Across South America, the Amazon’s
climate is influenced by the Atlantic
and Pacific oceans, which regulate
the Amazon’s tropical rains.
In the lowlands, the flow of water
and sediment, as well as the shallow
slope, create form numerous meanders
and secondary branches. Downstream,
the river basin is subject to
the Amazon’s high water season,
which causes seasonal flooding.
The heavy precipitations,
which move from East to West until
they are blocked by the Andes,
are regularly supplemented
by evapotranspiration from the trees
of the Amazon rainforest.
in the world -
DID YOU KNOW?
the Amazon
is certainly a
record-breaking
river.
The Amazon drainage basin covers almost half of South America.
More than 500 rivers discharge their waters into it.
The Amazon’s discharge is 5 times higher
than the second most powerful river
in the world, the Congo. Two of the
Amazon’s tributaries, the Rio Madeira and
the Rio Negro, are also some of the most
powerful rivers on the planet.
IDENTITY CARD
Source: the Andes
Mouth: Atlantic Ocean
Length: between 6,300 and 6,800 km
Discharge at mouth: 206,000 m3/s
Surface of drainage basin:
6 million km²
Countries: Venezuela, Colombia,
Ecuador, Peru, Bolivia, Brazil,
Guyana.
20 % of freshwater which flows
into the world’s oceans comes
from the Amazon basin.
There is a significant reduction
in seawater salinity at the river
mouth and the sediment carried
by the river can be seen
by satellites.
The river levels in the Central Amazon can vary by 20 m from
high to low water periods.
The waters of the Solimões River (full of fertile clay sediment)
meet the dark Rio Negro (full of dissolved organic matter) at Manaus.
The Amazon can reach a depth
of 110 m and a width of 2-10 km
depending on the scale of flooding
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Amazon basin
Torrential rains,
extreme droughts
Researchers can use various
techniques to measure this, in order
to understand and prevent these
phenomena affecting the population
of several South American countries.
Exceptional low water levels - 2005,
2010 - and floods - 1999, 2009, 2012,
and 2014 - have affected the Amazon and
its confluences; this has been monitored
via local measuring stations. Thanks
to the space altimetry, researchers have
had access to more reliable and regular
data on river levels since 2002.
The results show that in recent years,
extreme events have become more
common and more powerful.
The influence of climate phenomena
over the Pacific and Atlantic oceans
is the main cause. Local factors
can amplify these extreme periods:
for example, deforestation reduces the
available moisture during droughts and
increases surface runoff in rainy seasons.
As a result, fish stocks are reduced
and the main urban centres are negatively
affected. In Bolivia in 2014, 56 people
were killed and 58,000 families were
affected by the catastrophic flooding
of the Madeira River. In Brazil, floods
and low waters disrupt transport along
watercourses, the only transport means
for the majority of Amazonian inhabitants.
RESEARCH
Since 2003, scientists from the Observation Service
at (SO)HYBAM have been monitoring the main rivers
of the Amazon basin to measure and understand the impact
of climate variation on hydrology, soil erosion and aquatic
chemistry. This data is available to the scientific community
online at www.ore-hybam.org
Over the last
15 years,
the Amazon
basin is facing
a succession
of exceptional
high and low
water levels
as a result
of climate
variation and
environmental
changes on
a regional scale.
In Peru, the three highest Amazon water levels in the past 40 years was recorded in 2009,
2012 and 2014 while the lowest are for 2005 and 2010. Flooding in 2012 in the city of Iquitos.
In 2014, in Porto Velho in Brazil, the Madeira
River reached its highest level ever recorded.
The discharge was considerably higher
than historical maximums and caused
significant damage from Peru to Brazil.
Normally used to study oceans,
the radar equipment on satellites Jason 2
and Saral are now carrying out altimeter
measurements of river water levels.
In 2010 in Iquitos - Peru, the Amazon reached
its lowest level since 45 years, after a long
absence of rain and a period of high
temperatures.
Temperature variations in the Atlantic and
Pacific oceans are the main cause of reduced
rainfall over the Amazon rainforest.
The rains have suffered
an overall reduction of 9% in 40 years
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Amazon basin
Exceptional
biodiversity
The Amazon and its tributaries play host
to almost 20% of the planet’s freshwater
fish species, including the famous
piranhas, electric eels and giant catfish.
Up until now, the basin has remained
relatively well-preserved compared
to some other world’s large watercourses.
Human activities in constant development
as fishing, dam building and deforestation,
could accelerate species’ natural
extinction rates. Instead, researchers have
recently demonstrated that the effects of
climate change will only marginally increase
extinction rates.
The Arapaima gigas, one of the most iconic
species of the basin, can reach 4 metres
in lenght and 200 kg. It lives in the natural
lagoons and small streams of Amazonian
rivers. Its tasty and almost boneless meat
makes it a valuable fish and a victim
of overfishing. To cope with the decline
in catches, fish farms have been set up
in Colombia, Peru and Brazil.
RESEARCH
The LMI EDIA*, created in 2011 by the IRD and the IIAP**,
brings together scientists from France, Germany, and the main
Amazon countries. Its scientific programme is based around
understanding the diversity of the natural fish populations
in the Amazon, their evolution, their life history strategies
and the development of sustainable fish farming.
* Laboratoire mixte international « Évolution et Domestication de l’Ichtyofaune Amazonienne» (International Joint Laboratory on ‘Evolution and Domestication
of Amazon Fish Fauna’). ** Peruvian Amazon Research Institute.
From the Andes
to the vast
tropical forest
plains, the
Amazon basin
is home
to an incredible
diversity of
aquatic systems
inhabited by
more than
2000 species
of freshwater
fish.
The pacu (Colossoma macropomum)
is a fish that can reach 30 kg and its meat
is highly prized. It is caught in the wild
or raised in fish farms.
Piranhas are the iconic fish species
of Amazon Basin Rivers.
A general characteristic of tropical freshwater
fish fauna is the abundance of extremely small
fish (20 to 40 mm), such as Hyphessobrycon
eques.
The arapaima’s scales are coated
with a thick and extremely hard
collagen layer. This ‘armour’
protects it against piranha attacks
and other threats.
The waters of the Amazon basin are also
home to two freshwater dolphin species,
Inia geoffrensis and Inia boliviensis.
Since 1975, the arapaima has been listed
on Appendix II of CITES*: it is not currently
threatened with extinction but may become
so unless trade is strictly controlled.
* Convention on International Trade in Endangered Species
of Wild Fauna and Flora.
Arapaima farming is highly profitable since
the reproduction rate is significant and the fish
can reach 10 kg in a year.
The Arapaima is one
of the Amazonian species victims
of overfishing
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Amazon basin
When water become
a threat
In the Amazon, around 300,000 cases
of malaria occur each year. In some regions,
the mosquitoes which transmit the disease
are more common from June to September,
during the «dry» season.
During this period, the river levels are
no longer high, leading to areas of land
being exposed where stagnant lakes may
form, creating potentially favourable
conditions for high density of mosquitoes.
Transmission can also take place
throughout the year, when environmental
conditions are favourable.
Mercury, which is found naturally
in the soil, can in some areas is a public
health problem due to the double impact
of human activity and the climate.
The Amazonia
Mines, agriculture, gold mining
and deforestation destabilise and leave
the soil exposed, allowing nutrient
leaching. This becomes worse with rain,
which is more and more abundant
in certain regions. The mercury then flows
into watercourses, contaminating
fish as well as the populations
who eat them.
health
problems
RESEARCH
Among its activities, the UMR ESPACE-DEV conducts
research on “Environment, Society and Health Risks» (ESOR).
These investigations aim to define, explain and establish patterns
of spatial health inequalities. The UMR three teams are also
responsible for training researchers from southern hemisphere
countries. A team from the GET Joint Research Unit is developing
a new geochemical tool which allows mercury sources from
gold mining to be traced and quantified in the environment,
from rivers to the Amerindian populations exposed to
the neurotoxin (ANR RIMNES).
records numerous
closely related
to the presence
of water.
This is the case of
malaria, caused
by a parasite
and transmitted by
some mosquitoes,
mercury
pollution.
and
Climate and
Stilt houses in the Brazilian Amazon
during a flood. The house is surrounded
by water, which can be a breeding site
for mosquitoes.
In French Guiana, unlike in the Amazon
basin, a significant amount of mercury
contamination is due to gold-mining activities,
which use mercury to separate gold
from deposits.
environment in
Mercury is transformed into methylmercury,
one of its most toxic chemical forms for bacteria
found in sediment on flooded plains
and on aquatic plant biofilms.
general play a
key role in its
dissemination.
Lakes forming
after floodwaters
recede near Manaus
are ideal locations
for mosquitoes
to reproduce.
The proximity
of a city worsens
the spread
of malaria.
Piscivorous fish contain much higher mercury
contamination levels than herbivorous fish,
up to 5 times the World Health Organisation
limit values.
Collecting hair for analysis. Populations can present
significantly higher mercury levels than the thresholds
set by the WHO. This causes developmental delay
in foetuses and young children, as well as neurological
damage in adults.
The main carrier of malaria
in the Amazon is the mosquito
Anopheles darlingi.
Soil in the Amazon contains
10 times more mercury
than soils in mild climates
9
Amazon basin
Ancient variations
To study climates from the past, scientists
study archives and natural environmental
markers: fossilised pollen grains, lake
sediment, charcoal or speleothems mineral deposits taken from caves.
Analysing fossilised pollen grains
and lake sediment allows scientists
to reconstruct the climate which existed
6000 years ago, for example. Much drier
than today, it caused a significant reduction
in the area covered by the Amazon
rainforest. In addition, discoveries
of micro-charcoal layers - an indicator
of ancient fires - in lake sediment and soil
demonstrate the extremely low atmospheric
humidity at the time.
These findings are also confirmed by oxygen
isotope value trends, which indicate lower
precipitation levels.
All these changes indicate that this
dry phase is due to a decreased isolation
caused by a weakening of the South
American monsoon. Reconstructing ancient
climates provides better understanding
of the consequences of current change
and improve climate prediction models.
The Amazon
has experienced
significant
variation
in its climate,
environment
and hydrology
RESEARCH
The International Joint Laboratory «PALEOTRACES»,
founded in 2009, brings together multidisciplinary
teams from Brazil, Chile and France, who work
on palaeoclimates in South America, from the Middle
Holocene to the present day. They work from lake
and ocean sedimentary records, corals
and speleothems.
over the last
10,000 years.
Researchers
are recreating
these past
changes
to gain better
understanding
Fossilised pollen grains prove that
at a given time and place certain plants
were growing, indicating a certain climate.
Byrsonima pollen reveals a savannah
environment marked by fires.
4,000 years ago, the dry period gradually
gave way to conditions in which forests
and the network of watercourses we know
today could develop.
Thin section of lake sediment. Black
micro-charcoal can be seen in the layers
of sand and silt.
Sedimentary core showing various strata:
light (sand) and dark (clay). These markers
provide precious information about
the successive states of the atmosphere,
biodiversity, and watercourses.
of the current
changes.
Archive and marker research can provide more accurate simulations of the impact of climate
change on water resources, crop and livestock production and food security.
The calcareous concretions of caves
are markers
of ancient climates
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