Processos dinÃmicos e evolutivos da zona costeira de Itamaracà por sensoriamento remoto e medidas in situ

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The coastal zone of Itamaracà is like a highly dynamic environment where land and oceanic processes interact altering frequently coastal characteristics. In this context, this current study examines the responsible processes of such changes from the development and application of methodologies, which includes digital image processing and the obtaining of in situ data. At the first stage, remote sensing and GIS (Geographic Information System) were used in order to analyze mangrove distribution of the estuarine system of Itamaracà as well as identify the changes in the vegetation from 1974 to 2001. The approach used to estimate the mangrove changes is based at the supervised classification method from multispectral and multi-temporal SPOT/HRV and Landsat7/ETM+ images. As result, preserved areas of mangrove forest (4,118.01 ha), salt flat (397.28 ha), mud flat (464.77 ha) and shrimp farms (484.05 ha) were computed from ETM+ (2001) images in ItamaracÃ, Goiana, Itapissuma and Igarassu. Temporal analysis was done in 64% of the estuarine system total area and around 11% of mangrove forest reduction was computed in 27 years (1974- 2001). The annual rate of mangrove deforestation was 0.42% (1974-1996) and 0.28% (1996-2001). Otherwise, areas of shrimp farms increased 394% (1996-2001). The kappa coefficient and the global accuracy of the thematic map produced by the classification method were, respectively, of 0.97 and 98.56% (ETM+) and of 0.95 and 97.38% (SPOT). Results obtained from this research pointed out the carcinoculture activity as one responsible for the mangrove forest deforestation and also proved it interfered in the sediment distribution at the Santa Cruz Channel (SCC). The second stage of this study is based on the premise that circulation is the main responsible for the control and distribution of sediment particles and the characterization of its pattern may contribute to the understanding of depositional processes. The spatial and seasonal analyses of the circulation (currentmetry), thermohaline parameters (CTD â Conductivity-Temperature-Depth) and suspended sediment presence (OBS â Optical Backscatterance Sensor) were executed at the southern branch of SCC during a whole tidal cycle. The thermohaline parameters in the surface layer of SCC presented small variation at the end of the cycle. However, a seasonal variability was observed with mean values of temperature and salinity, respectively, at 30ÂC and 36 (dry period), and 27ÂC and 25 (wet period), when highest values of suspended material (OBS=88) were registered. In both periods, there was no stratification in the water column in relation to temperature and salinity showing that circulation at the south branch of SCC is predominantly ruled by the tidal forcing. Afterwards, ADCP (Acoustic Doppler Current Profiler) data were collected in order to analyze the horizontal and vertical circulation at the SCCâs and Timbà Riverâs entrances. Current intensity and direction maps were produced at surface, middle and close to the bottom of the water column. Highest current value was observed during the ebb tide and presented a mean of 0.93 m s-1 at the SCCâs entrance, and 0.68 m s-1 at Timbà Riverâs mouth. The vertical distribution obtained from ADCP identified specific sites along the depth where current components flow against the water stream. The flow direction of the residual circulation influenced the sedimentation pattern in the study area during dry and rainy seasons pointing out a seasonal variability. The current intensity and the calculated flow proved scientifically the occurrence of âhydraulic jettyâ at the southern mouth of SCC, which works as a boundary to the coastal drift. The third stage contemplates the understanding about the processes of sediment transport and deposition associated to the local hydrodynamics through the extraction of depositional features. It also presented a methodology that uses operators for the edge detection at the band 1 of the SPOT5/HRG (2003) and IKONOS (2005) images in order to identify base features in shallow coastal water. The results were obtained from the Compass-gradient Prewitt operator, which provided images with sediment features caused by hydrodynamics (sand waves, swash-bar, marginal dike, transversal banks, flow channels) and banks algal reefs. This study pointed out that data from passive remote sensors and field campaigns contributed efficiently for analyzing the changes in the depositional features of Itamaracà coastal zone.

ASSUNTO(S)

hidrodinÃmica termohalinos parameters directional operators hydrodynamics itamaracà gis brazil circulaÃÃo residual oceanografia mangroves manguezais hydraulic jetty oceanografia sensoriamento remoto remote sensing residual circulation

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