ANALYSIS OF THE PROCESS OF ENVIRONMENTAL DEGRADATION OF AREAS OF SWAMP IN THE REGION NORTH OF MINAS GERAIS FROM TEMPORAL SERIES OF IMAGES

Environmental studies to characterize the process of environmental degradation of different ecosystems are extremely complex. In recent years, satellite images have become a great ally in these types of study, since they have the advantage of allowing the joint analysis of different variables, especially when associated with the temporal series. In this perspective, the study aimed to analyze the process of environmental degradation in areas of meadows, at the southern end of the basin of the Urucuia river, situated in the North of the state of Minas Gerais, from LANDSAT5/TM images. Characterized by a transition region between the biomes savanna and caatinga, areas of meadows suffer strong anthropogenic pressures that are promoting major disturbances and disfiguration of the entire ecosystem. For the analysis were studied images of months more dry (July and August) for the years 1984, 1990, 2000 and 2010. The areas of meadows have been identified and mapped and then there was an automatic segmentation and analysis of the NDVI (Normalized Difference Vegetation Index) to study the dynamics of this environment. The results showed that during the period analyzed, these areas fell by around 9.61 times, mainly due to silting. The NDVI showed behavior similar to those observed in areas of paths, i.e. there was a change on the surface of the water for values corresponding to areas of exposed soil in the advanced stage of deterioration. The greatest period of degradation was observed between the decades of 1980’s and 1990’s with reduction in these areas around 88.29 %.


Introduction
In the Northern region of the state of Minas Gerais the savanna biome represents the greatest treasure of natural heritage, and the anthropic activities are its main instrument of environmental degradation, since this biome is still seen as available land and fuel reserve.
Environments more sensitive as subecossistema of savanna, paths present a great ecological significance especially in the lowest areas which when formed by interconnected ponds are also called Swamp.
Second Aguiar & Camargo (2004) the paths, This will serve as a subsidy for the development of research in the region, and the results generated can be used in search of mitigating actions and decision making processes.

Study Area
The study area is located in the extreme north of Minas Gerais along the Urucuia river that covers several areas of ecological interest being considered one important nurseries for fish of the Sao Francisco river along with the River cornets.01), therefore very susceptible to erosion processes that subsequently ends up culminating in silting of lower areas and sensitive as the area in question.

Selection and georeferenced images of LANDSAT-5/TM
To analyze the process of degradation of the areas of meadows along the temporal series, were used images from LANDSAT-

Atmospheric images
Has been performed radiometric and atmospheric corrections for bands 3, 4 LANDSAT-5/TM images.The refletance and radiance are calculated by Equations 1 and 2, respectively.
Were: Lrad and the spectral radiance in band i in Wm-2sr-1 µm-1 ;Li,max and Li,min values of radiance maximum and minimum in band i, respectively, and NCi the level of ash in band i.
Were, Li and the spectral radiance of each band (Wm i Lλ -2 sr -1 μm -1 ); Ki and the solar irradiance of spectral band at the top of the atmosphere (Wm i Kλ -2 μm -1 ); Z and the overhead angle solar; dr, and the square of the ratio between the average distance earth sun (r0) and the distance earth-sun (r 0 ) in a given day of the year (DJ).For the atmospheric correction, the values of irradiance measurements were converted to a by the method of (Dark Object Subtraction), using the histogram of band 1, as reference for the selection the pixel darker second methodology proposed by (Gürtler et al., 2005).The atmospheric correction allows mitigate the combined effects of absorption, scattering and atmospheric, caused by the presence of various gases, water vapor and particles that interact with the electromagnetic radiation as (Rodrigues et al., 2010).

Segmentation
From the images pre-processed were performed compositions color RGB-453 and then the classification non-supervised by kmeans algorithm.The automatic segmentation was performed to delimit the areas of meadows of spatial area.The polygons resulting from the segmentation were quantified, to study the behavior of the advance of degraded areas throughout the series.

Calculating the NDVI
The NDVI was calculated by the  reflectance of red (band 3).

Statistical Analysis
The statistical analysis of the results was performed using a regression analysis used the computer program SAS (Statistical Analysis System) version 9.1.river.In the period there was an increase 390 hectares (Figure 3b), irrigated area.

Results and Discussion
Corresponding author: crisrodnas@gmail.com.typical environments of the savanna are located near the springs and act as drainage ways, contributing to the continued existence and regularity of water courses, since that act as collecting basins.However, with the economic development and agricultural expansion, these areas have been experiencing a series of degradation over time causing a rapid deterioration of these environments and so the need to understand the temporal dynamics of this process.In this context the basin of the Urucuia river which covers the Northern region of Minas Gerais is of great importance, because it is one of the basins of the middle São Francisco that has expressive contribution socio-environmental and economic.In the extreme south of the basin is large areas of swamp that form an environment with characteristics quite particular and even studied very little, but it is essential to the revitalization of the São Francisco River.The area form a kind of Swamp because the marginal lagoons that makes an environment very conducive to procreation of fish of the São Francisco River.These areas present characteristics quite peculiar, especially as to its geographical location, as they are inserted in regions of transition between the biomes savanna and caatinga, surrounded by subecossistema paths.However with the strong anthropic intervention these areas suffer from strong changes in the scheme of flood being perceived mainly by decrease of flooded areas over the years.Second Melack & Hess (2004) information about the location, extent and other basic features that characterize the area, are scarce in the literature, mainly due to the difficulty of monitoring of those areas.In this context, the monitoring itself is of fundamental importance, since, changes in the schemes of floods cause changes in plant cover, which, therefore, change the whole ecosystem.The orbital remote sensing becomes an important tool in this process, since it provides a better assessment, management, management, and management of natural resources, such as water, soil and vegetation.The satellite images allow the generation of maps that show the conditions that the system is submitted to the course of time, provided that they are carried out analyzes temporal.Another important issue concerns the analysis of these environments that normally considers only the two extreme phases (flood and ebb tides), which has just disregarding a great diversity of scenarios intermediaries, with ecological implications distinct.From time series of satellite images is possible to perform analyzes between intermediate levels and correlating the data of different times and by establishing direct relations with different variables.In this perspective, the study aimed to analyze the process of environmental degradation of the areas of meadows on the south end of the basin of the Urucuia river through temporal series of LANDSAT-5/TM images in four different time periods: 1984, 1990, 2000 and 2010, corresponding to a period of twenty-six years.To characterize and quantify the changes in the area were analyzed NDVI images, corresponding to the years analyzed.
equation (3).They were then selected 100 points randomly distributed in the areas of meadows, along the rivers tambourines and San Francisco, taking as reference the year of 1984, considered the initial period of evaluation of the process of environmental degradation.From the analysis of points of control was possible to assess the fluctuation in the NDVI values, and correlate them with the changes of coverage in the areas studied as a function of time.Were, NIR  reflectance near infrared (band 4) and RED

Figure 1
Figure 1 represents the composition color RGB-453 and automatic segmentation of the areas of meadows, the initial period and end of the temporal series, respectively representing the 1984 and 2010.Figure 2 shows the total of degraded area versus % decrease in function of decades analyzed, is it

Figure 2 .
Figure 2. Degraded area in hectares (%) decrease of polygons of meadows in function of years analyzed, taking as reference 1984.

Figure 4 .
Figure 4. Graph of monthly average of rainfall and average maximum temperatures for their four years of the series.

Figure 5 .
Figure 5. Statistical analysis of the points of NDVI acquired throughout the series.

Figure 6
Figure 6 shows the NDVI in the whole series analyzed where you can check the variation and the dynamics of their values also changes in coverage and use of the soil.As the area in question is located in environment formed by vast paths in an advanced stage of disruption because these practices, the training of plant substratum differentiated in the areas of swamp is associated with the loss of soil moisture appearing as well an environment more conducive to species more resistant and more rustic and/or adapted to these conditions, influencing the response of the index.The NDVI proved to be favorable to the type of

Figure 6 .
Figure 6.Image NDVI from 1984 (a), 1990 (b), 2000 (c) and 2010 (d) of the areas of meadows in the north of Minas Gerais.

Table 01 .
Comparison of the soil loss for the Basin of the Urucuia river between 1987 and 2007.
driest time of the region.The images, acquired from the National Institute for Space Research/INPE, were selected by eliminating

Table 2 .
Average variation in the values of NDVI in the period analyzed.