Vegetation coverage usually features as a major concern when it comes to the topic Legal Amazon....

Vegetation coverage usually features as a major concern when it comes to the topic Legal Amazon. Nevertheless, the environmental heritage of this part of the Brazilian territory goes far beyond the forest and other types of vegetation. It includes, for instance, an underground area formed by rocks with a high potential for the storage and transfer of potable water and a soil with an amount of carbon which, if released into the atmosphere, may affect the balance of greenhouse gases.

These and other treasures are presented by “Geostatistics of the Legal Amazon’s Natural Resources”, a publication which gathers information about natural resources in the region – vegetation and land coverage; relief; soils; and rocks and mineral resources – many of which may become useful indicators for systematic monitoring of the use and conservation status of these resources.

The selected statistics are generated using the Environmental Information Database (BDIA), maintained by IBGE, which presents information obtained by the RADAMBRASIL Project, in the 1970’s and 1980’s, and also more recent data, of 2002. The vegetation and relief data of the Legal Amazon, as well as part of those relative to soils and geology, are already available on the IBGE web site (ftp://geoftp.ibge.gov.br/mapas/banco_dados_georeferenciado_recursos_naturais/ ).

The goal for the remaining part of the Brazilian territory is to have data available up to 2014. Although the information from BDIA are not intended for the real-time monitoring of land coverage changes in the Legal Amazon, they help understand how these processes occur and predict medium and long-term trends. 

The Legal Amazon covers 5,016,136,3 km2, which correspond to about 59% of the Brazilian territory. It is inhabited by about 24 million persons, according to the 2010 Census, distributed in 775 municipalities in the states of Acre, Amapá, Amazonas, Mato Grosso, Pará, Rondônia, Roraima, Tocantins (98% of the total state area), Maranhão (79%) and Goiás (0.8%). Besides presenting 20% of the cerrado, the region encompasses the longest of the Brazilian biomes, which corresponds to 1/3 of the tropical rainforests on the planet and holds the greatest biodiversity, the major gene bank and 1/5 of the world’s potable water availability.

See below the main highlights of “Geostatistics of the Legal Amazon’s Natural Resources”, which is fully available at https://www.ibge.gov.br/home/geociencias/recursosnaturais/diagnosticos_levantamentos/default.shtm

Legal Amazon concentrates about 45% of the potable  groundwater in the country

The knowledge about the distribution and frequency at which minerals and rocks occur in the Legal Amazon make it possible to evaluate, for instance, the production potential of ground water (water potential); fossil fuels (petroleum, for example); and the formation of concentrations of valuable ore in the area. A total 14 indicators about this topic have been investigated. 

Sedimentary rocks, originated from rock alteration, erosion, transportation and deposition of any other types of rock, form 66.8% of the Legal Amazon area. They lead to the formation of porous aquifers, a type of underground reservoir, able to store water enough to be used as a supply source. It is estimated that 91% of the ground water in Brazil is in porous aquifers, being 49.45% of them in the Legal Amazon, that is, this area comprises about 45% of all the ground water in the country.

The participation of porous aquifers in relation to the total aboveground area (surface, except for the rivers) of the Legal Amazon is 68.3%, and there are three main provinces, or big areas, of sedimentary rocks: the Amazon river, the Parnaíba river or the Middle-North and the Paraná-Parecis, which, together with the smallest reserves, make up a total 101,920 km3 of fresh water.

The biggest areas of porous aquifers can be found in the Amazon River (1,344,201,7 km2), in Mato Grosso (677,135,1 km2) and in Pará (513,818,9 km2). Acre and Maranhão have the highest participation indexes, above 90%, which means a soil almost completely formed by sedimentary rocks. Roraima (33.8%) and Amapá (33.2%) present the lowest percentages, although porous aquifers have significant extension in both states.

Since it is predominantly formed by sedimentary rocks, the Legal Amazon subsoil is also appropriate for the exploration of fossil fuels, what can be confirmed by the petroleum and gas fields of Urucu, in Amazonas. There are good prospects for the accumulation of these substances in the sedimentary rocks of coastal basin in Maranhão, Pará and Amapá, besides natural gas reserves in the municipality of Capinzal do Norte (MA).

Also in sedimentary rock areas, it is also possible to find limestone deposits, useful both for agriculture and cement production; rock-salt and gypsum, sources of plaster for medicine and construction; and anhydrite, a source of sulfate and calcium. Despite their lower metallic potential, minerals of this kind and precious stones can be found in the region. Gold deposits, cassiterite and diamonds are common ones.

More than half of the rocks that can form noble metal deposits are in Pará

Igneous rocks (15.1% of the Legal Amazon), resulting from the solidification of magma (molten rock material present inside the earth), and metamorphic rocks (16.1%), resulting from the alteration of other types of rocks as a result of chemical or physical changes (such as in temperature and pressure, for instance), present a higher mineral potential.

Igneous rocks tend to form deposits of noble metals such as gold; rocks formed by industrial minerals, such as cassiterite, are more concentrated in the Central Amazon, in an almost continuous strip that goes from the southeast of Pará to the North of Roraima and the northwest of Amazonas (see the map on the previous page). Pará encompasses 51.9% of the igneous rocks in the Legal Amazon, being followed by Mato Grosso, with 14.2%. Acre has the longest relative extension of this kind of rock, occupying less than 0.01% of the state territory.

Besides precious metals igneous rocks also present groundwater potential, with the occurrence of the so-called fractured aquifers, with accumulation of water in the fractures of rocks. They represent a total 10,080 km3 of fresh water in Brazil, out of which an estimated 6,048 km3, at least, can be found in the Legal Amazon.

Metamorphic rocks have a potential as sources of primary gold. They are also appropriate for the formation of mineral deposits for industrial use, especially of iron and manganese, and copper, plumb and zinc sulfides. They also provide material for civil construction, such as grit and ornamental rocks.  Pará has 37.7% of this type of rock in the Legal Amazon, whereas Acre (with a percentage close to zero) and Maranhão (0.8%) have little significant proportions.

Carbon stored in the soil is bigger than in the atmosphere

The information provided by the five indicators gathered in the topic soil is useful for the understanding of relevant topics for the Legal Amazon, such as agricultural development and the preservation of risk areas.

In the terrestrial ecosystem, the soil is a key element in the process of greenhouse gas emission, because it has a big amount of carbon. The soil holds, in the first meter depth, about twice the amount of gas found in the atmosphere.

It is estimated that, in Brazil, 75% of the CO2 emissions come from changes in land use, due either to erosion and decomposition of organic matter or to the conversion of forests and other forms of natural vegetation into forms for agricultural use. These factors explain the relevance of carbon stocks for the balance of greenhouse gases in the atmosphere.

On average, the soil in the Legal Amazon has, on its surface horizon (a maximum depth of 50 cm, with average width of 30 cm) a stock of 55.7 hectares of organic carbon per hectare, but this concentration is not uniform and ranges between 0.1 and 208.7 metric tons per hectare, with a predominance of the class of 40 to 60 metric tons/hectare.

By considering up to one meter depth, the average figure for carbon stock increases to 95.7 metric ton/hectare, and may reach a maximum figure of 250 metric tons/hectare, with a predominance of the class of 80 to 100 metric ton/hectare. The map below indicates, in the Legal Amazon, the carbon concentration areas with up to one meter depth.

Vegetation is fundamental for the balance of erosion processes in the Legal Amazon 

The knowledge of relief is extremely important to the organization, planning and management of the territory, since it exerts great influence on the distribution of population and, to a certain extent, links economic activities to the structuring of the roads network. Five indicators about the topic have been analyzed.

In the Legal Amazon, there is a predominance of a hilly, or slightly wavy relief, mostly covered with dense vegetation, the maintenance of which is fundamental for the balance of erosion processes. The maintenance of vegetation also plays an important role in the areas subject to floods, which correspond to 12.4% of the Legal Amazon territory, such as river, sea and lake plains.

The areas with most uneven relief, with dissection intensity classes classified as “high” (12.4% of the area) ad “very high” (11.0% of the area), are more concentrated in the west end of the Legal Amazon, in the states of Acre and Amazonas, in the west of Amapá, the northwest of Pará and Roraima and the north of Mato Grosso. These areas are extremely weak in environmental terms, especially because they have been affected by man’s action in roads that knocked forests down and contributed to the acceleration of erosion processes, with damage to passageways and the sale of production.

The total anthropic areas (where original vegetation has been replaced by another type of coverage due to man’s action) in the Legal Amazon corresponds to 752,202 km² or 15% of the total surface in 2002. In absolute figures, the states that have the biggest areas changed by man are: Maranhão, with 139,239 km2, representing 53% of its total area; Mato Grosso, with 233,416 km2 or 25.8% of the total; and Pará, with 203,606 km2 or 16.3% of the total. In the states of Amazonas, Amapá, Roraima and in the western part of Pará and Acre, occupation is more rarefied and occur by in passageways such as rivers or open roads in natural vegetation areas.

Historical balance of deforestation: 2.6 billion trees eliminated up to 2002

Being divided into 16 indicators, the topic vegetation and land coverage shows, among others, the historical effects of man’s action on the forest and on other types of vegetation of the Legal Amazon. About four million square kilometers of the Brazilian Amazon were originally covered by forests and, up to 2002, the deforested area was about 15.3% of the total vegetation – a percentage which has increased since then. The deforestation process became more intense in the last four decades, being concentrated in the south and east ends of the Legal Amazon (deforestation arc). 

Up to 2002, the area had been affected by the elimination of 2.6 billion trees, what corresponded to approximately 13% of all the trees with a diameter above 33 cm in forests. In terms of volume, 4.7 billion cubic meters of wood had been eliminated by deforestation in the forest formations of the Legal Amazon up to the aforementioned year.

Deforestation accounted for the elimination of approximately 23 billion metric tons (12.7%) of biomass, or organic matter of vegetal origin, and 6.6 billion metric tons of carbon (12.7%) of the Legal Amazon forest formations up to 2002. It is estimated that, in the aforementioned year, there were, in the same place, about 157 million metric tons of biomass and 45 billion metric tons of carbon left.

In 2002, land use affected 15.3% of the Legal Amazon vegetation

In 2002, anthropic changes, or the change of land coverage caused by human action, due to deforestation and fires, reached 15.3% of the primary vegetation area of the Legal Amazon.

Livestock is a highlight as the main use that changes land coverage, representing 51.7% of the vegetation affected by human action in the Legal Amazon, whereas the secondary vegetation (that appears naturally after areas previously used by men are abandoned) corresponds to 32.1%, and agriculture, 15.2%.

In the states of Maranhão, Goiás, Tocantins, Mato Grosso and Rondônia less than 20% of the vegetation had undergone anthropic changes in vegetation. Considering the part of the territory of Maranhão included in the Legal Amazon, 54% of the primary vegetation had been affected by such changes in 2002. Amazonas had been the least affected state, with only 1.5% of its vegetation changed.