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GIS and Spatial Decision Support System for Environmental Degradation Monitoring
1. Introduction
The Taquari river is a major contributor to the Brazilian Pantanal hydrological system. Its
watershed covers approximately 80,000 km 2 of land, being approx. 30,000 km 2 located in the
highlands of the Paraguay river basin. The lowlands have been occupied during the last 200 years by
extensive cattle grazing on natural pastures, an economic activity that did not reduce significantly the
Pantanal’s luxuriant biodiversity.
On the other hand, occupation during the last 30 years of the Cerrados in the highlands
amplified degradation of soil and water resources, to a point that it is considered the principal menace
to the Pantanal’s integrity. Substitution of the Cerrado vegetation in the Taquari watershed highlands 34 - 2
by pastures (mainly in sandy soils) and cash crops correlates with increased sediment deposition in the
Taquari river bed.
As a result, at least 400,000 ha of native grazing pasture of the Pantanal lowlands have been
lost, due to flooding. This has driven local farmers to abandon their lands or remove vegetation in
upper strips of land, which are being transformed into exotic pastures. The combination of flooding
and deforestation is leading to transformation of the landscape, and reduction of terrestrial
biodiversity. Other negative environmental and economic impacts are:
- Increasing magnitude, duration and unpredictability of floods;
- Changes in land use by farmers (eg. introduction of buffalo);
- Construction of polders and dams;
- Difficulties to navigation;
- Alterations in the ecology of the floodplains.
The topography and characteristics of most of the soils in the region make them highly or very
highly susceptible to erosion, being therefore unsuitable for agricultural use. Potential erosion rates
may vary from 600 to 950 MT/Ha/year. Considering the lack of planning of agricultural land use,
aided by bad design of rural roads, lack of soil conservation practices, and destruction of river bank
vegetation, the Taquari river carries a sediment load of 491 Mg/Lt. Deposition in the Pantanal
lowlands occur at rates higher than 100MT/Ha/year, resulting in flood events that, every year, increase
their spatial and temporal significance.
In order to unravel the complexity of the Taquari issue we adopted a problem-oriented
approach. What is considered a major problem to people located in the lowlands (siltation and floods,
for example) may not be considered of utmost importance to those in the highlands (soil erosion). In
order to streamline our problem analysis, we considered the highland portion of the Taquari watershed
in our studies.
We propose a model that explains the Upper Taquari watershed land degradation problem and
will feed a Spatial Decision Support System.
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