chapter - Atmospheric and Oceanic Science

Physiography and Hydrology
tion of the Mata Atlantica, ecosystem that covers the basin of the High Paraná, the
area with the largest and most intense precipitation. In this ecosystem, its forest-like
covering decreased from 58% to 8% in Sao Paulo' state in the last century, and in
the state of Paraná it went from 85% of its covered surface to current 5%.
Something similar happens in Paraguay, with a quicker process by the end of the
century but with the same path. Soils are uncovered and are incorporated to agriculture,
leaving soil more compacted and increasing the water erosion whose consequences
are both the increase and acceleration of the superficial runoffs toward
the courses of water, the rise of peak flows, its occurrence in shorter periods, the
increment of the sedimentation of the rivers and reservoirs, affecting its navigability
and accelerating the turbidity of the reservoirs (with the consequent loss of its
potential energy) and less feeding to the aquifers.
In the Pampas, due to economic conditions the pastures are being replaced by
cultivations due to their more favorable prices compared to the cattle rising. For
example, in the Province of Buenos Aires the areas under cultivation were
increased in 40% between 1988 and 1993. These changes have pressed the opening
of the agricultural frontier toward marginal soils of the Pampas ecosystem itself as
well as the Chaco, which implies larger deforestation required by an escalation of
the production systems and raw material, increasing the risk of degradation in areas
with desertification processes.
Deforestation of the natural forests of the Paraguay has accelerated, going
from 200 to 400 thousand annual hectares during the last 50 years; thus, the probability
of maintaining areas with forest-like coverings is small. With the loss of the
forests biodiversity is suffering, with the consequent disappearance of important
genetic resources. In the Oriental Region between 1945 at 1991, the forest covering
went from 8805000 to 2403000 hectares. It has to be highlighted that most of
the reduction of the forest surface was verified in the last 20 years. To this situation
contributed the combined actions of the following main factors: the expansion of
the agricultural border, the lack of policies on use of the land, the scarce appraisement
of the forests, and the loan policy that has fomented the expansion of the agricultural
frontier in detriment of the forests.
The affectation of the aquatic ecosystems deserves special attention in the
whole La Plata basin, characterized as one of the basins of larger continental aquatic
diversity of the world, in particular the sub-basins of the Paraná and Paraguay
rivers (Pantanal) and of its marine front. At the moment these ecosystems are constantly
and mainly affected by: I) the increments of sediments, II) the modifications
in the contribution of nutrients to the waters, III) the obstruction that present the
dams and the proliferation of reservoir constructions that are particularly important
in the High Paraná and in the Uruguay River, IV) the punctual and diffuse pollution
of certain water courses, added to the lack of an appropriate handling of the difficulties
associated to the trans-boundary character of the issue, V) the handling of
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