Sensoriamento remoto e sistemas de informações geográficas aplicados ao mapeamento dos manguezais na região do baixo sul da Bahia

Abstract

Brazilian mangroves occupy an area equivalent to 25,000 km2 and are found along almost all 8,000 km of the Brazilian coast. In Bahia, it is estimated that the mangrove occupies an area around 1.000 km2. In Bahia, the high light is for the Baixo Sul region, where the largest forests are located between the municipalities of Valença and Maraú. The mangroves are of fundamental economic importance for the support of the regional fishing communities. The objective of the study was to map and analyze the spatial and temporal variation of the mangrove cover areas in the Southern Bahia, through a mapping using Remote Sensing techniques and the Geographic Information System. Landsat 5, 8 sensor images from the years 1994 and 2017 were used by supervised classification using the MAXVER method and high resolution images of Google Earth to the identification and mapping of the main vectors responsible for the suppression of mangrove areas. A Subsequently, the data wereconvertedto vector format (shapefile) and quantified. It wasconsiderednecessarytomapandanalyzethe classes of use andcoverageofthecoastal zone ofthestudyarea, toidentifythefactorsthataffecttheintegrityof mangroves. The use of high resolutionimagesof Google Earth allowedustoidentifyeightmain classes of use andcoverage: mangrove, restinga, denseombrophilousvegetation, shrimpfarming, allotments, shrimpfarming, urbanareaandwaterbodies. In theanalyzedperiod (1994-2017), three principal vectorsresponsible for mangrove suppressionwereidentified: urbanexpansion, excavationofshrimpponds, andtheadvanceof apicum areas. The urbanexpansionhasreachedmainlythe mangroves ofthemunicipalityof Valença; theadvanceofshrimpfarminghasbeenplace in themunicipalityof Nilo Peçanha, specifically in thecommunitiesof São Francisco and Barra dos Carvalhos; whileCairuisthemunicipalitywiththegreatestreductionofthe mangrove areabyapparently natural processofadvancementof apicuns. It isnoteworthythatthe total areaof mangroves in thecoastal zone ofthemunicipalityof Nilo Peçanha suffered a reductionofapproximately 18% ofthe natural cover observed in 2002 (4.31km2), remaining in 2017 only 3.53 km2 of mangroves. In thesameperiod, thereisanexpansionofshrimpfarmingareas (ponds) five times greaterthanthatobserved in 2002. Theseshrimpponds are located in PermanentProtectionAreas (APP), within a state Environmental ProtectionArea (APA ofPratigi), where it isprohibitedthesuppressionofnativevegetationwithoutdueprocessofenvironmentallicensing. In general, thesupervisedclassificationwassatisfactory for theobjectivesproposed in thestudy. The use of Remote SensingandGeographicInformation System tools were fundamental in identifyingthevectorsresponsible for thesuppressionof mangrove areas in thestudyarea. The analysisoftheimagesof Google Earth allowedtolocateand follow thevariationofthe mangrove cover areasandthe classes of use andoccupationoftheestuarinecoastal zone, in excellentdetailsandquality, allowingthesubstitutionfromremotesensing, oftheaccessin loco in areasofdifficultaccessorthatexposetheresearchertorisks, as demonstrated in thisstudy.Besides the mapping of the mangrove, it was necessary to map, analyze and understand the other classes of use and coverage of the Coastal Zone of the study area. The vectors identified, responsible for the suppression of the mangroves in the region were: apicum, shrimp farming and urbanization. Shrimpfarming is the main vector responsible for the suppression of mangroves in the municipality of NiloPeçanha, between the communities of São Francisco and Barra dos Carvalhos