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In-Depth Information
l uvial material. Low topographic relief with a
slope of 0.3 to 0.5 m/km from east to west
and between 0.03 to 0.15 m/km from north to
south ensures slow surface water l ows across
the Pantanal (Franco and Pinheiro 1982 in
Alho 2005). Since the Late Pleistocene, these
processes have built geographically expansive
l uvial fans, which form a distinctive geomor-
phological feature of the Pantanal (Assine and
Silva 2009). A Moderate Resolution Imaging
Spectroradiometer (MODIS) image from 16 June
2003 shows one of the largest l uvial fans quite
distinctly in the center of the image, while
smoke from agricultural i res in the vicinity
provide the image a hazy appearance (Fig. 15-
9). Pantanal's lakes are clearly visible to the
north and west of the alluvial fan as black dots
of variable size. The Brazilian landscape to the
east and north of the fan indicates agricultural
activities. Healthy vegetative cover is observed
in Bolivia to the west of the Pantanal.
The region experiences typically tropical
climate, with average annual temperatures at
25 °C and distinct seasonal rainfall during the
summer months. Rain-fed l oodwaters in the
northern upper reaches of the Paraguay River
system as well as region-wide seasonal precipi-
tation provide the key drivers for life across the
region. Rainfall occurs between November and
March and ranges between 1200 and 1300 mm
per year. Low-slope conditions allow water to
overl ow river banks starting in the northern
reaches and can l ood extensive portions of the
Pantanal.
The timing, amount of land inundated, and
the length of inundation are generally dictated
by the level of the river and precipitation pat-
terns. A l ood pulse starts across the upper Pan-
tanal in February with southern downstream
regions observing delayed l oods as late as May
and June. As l oodwaters recede between August
and September during the dry season, isolated
pools, watering holes and lakes may retain
water for variable amounts of time depending
on their depth and evapotranspiration rates.
These ephemerally wet areas are also inter-
spersed by narrow rivers and streams and serve
as important forage sites for birds and refuges
for i sh and other mammals during the dry
Figure 15-8.
Map of the Pantanal wetlands and
surrounding region of South America. Produced by A.
Dailey. Map made with data from Natural Earth, Global
Administrative Areas, and World Wildlife Fund
Terrestrial Ecoregions Database (Olson et al. 2001).
Accessed online
<
www.naturalearthdata.com
>
<
http://
www.gadm.org/
http://www.worldwildlife.org/
science/data/item6373.html
>
February 2011.
>
and
<
and permanently l ooded lakes and lowland
regions across the countries of Bolivia, Brazil
and Paraguay (Keddy et al. 2009). The Pantanal
is located between 15° S to 22° S latitude and
54° W to 58° W longitude within the upper Para-
guay River basin. Roughly two-thirds of the wet-
lands fall within the country of Brazil with the
remaining distributed between Bolivia and Para-
guay. As a point of comparison, the Pantanal at
the height of the wet season may extend over
an area the size of the state of Georgia in the
United States.
The wetlands and seasonally l ooded grass-
lands are located within a shallow geographic
depression i lled in with sediments eroded from
surrounding plateaus and highlands since the
Quaternary period (Alho 2005). Moreover, as the
rivers and tributaries of the Paraguay, which
l ow across the region, enter the low-relief
plains they deposit large quantities of eroded
