Long-term effects of oil pollution in mangrove forests (Baixada Santista, Southeast Brazil) detected using a GIS-based multitemporal analysis of aerial photographs

Oil spills are potential threats to the integrity of highly productive coastal wetlands, such as mangrove forests. In October 1983, a mangrove area of nearly 300 ha located on the southeastern coast of Brazil was impacted by a 3.5 million liter crude oil spill released by a broken pipeline. In order to assess the long-term effects of oil pollution on mangrove vegetation, we carried out a GIS-based multitemporal analysis of aerial photographs of the years 1962, 1994, 2000 and 2003. Photointerpretation, visual classification, class quantification, ground-truth and vegetation structure data were combined to evaluate the oil impact. Before the spill, the mangroves exhibited a homogeneous canopy and well-developed stands. More than ten years after the spill, the mangrove vegetation exhibited three distinct zones reflecting the long-term effects of the oil pollution. The most impacted zone (10.5 ha) presented dead trees, exposed substrate and recovering stands with reduced structural development. We suggest that the distinct impact and recovery zones reflect the spatial variability of oil removal rates in the mangrove forest. This study identifies the multitemporal analysis of aerial photographs as a useful tool for assessing a system's capacity for recovery and monitoring the long-term residual effects of pollutants on vegetation dynamics, thus giving support to mangrove forest management and conservation. Vazamentos de petróleo s o potenciais amea as à integridade de ecossistemas costeiros. Em outubro de 1983, devido ao rompimento de um oleoduto, um manguezal com cerca de 300 ha, localizado na costa sudeste do Brasil foi impactado por 3.5 milh es de litros de petróleo. Visando avaliar os efeitos de longo prazo do petróleo sobre a vegeta o do manguezal, foi realizada uma análise multitemporal (1962, 1994, 2000 e 2003) de fotografias aéreas em SIG. Fotointerpreta o, classifica o visual, quantifica o de áreas, dados de campo e dados estruturais da vegeta o foram utilizados na avalia o. Antes do vazamento, a vegeta o exibia dossel homogêneo elevado desenvolvimento estrutural. Mais de dez anos após o derrame, a vegeta o apresentou três zonas distintas, com diferentes impactos decorrentes do derrame de petróleo. A zona mais impactada (10.5 ha) apresentou árvores mortas, substrato exposto e bosques em recomposi o com reduzido desenvolvimento estrutural. Os resultados indicam que os distintos impactos e recomposi o refletem a variabilidade espacial da taxa de remo o do petróleo em cada zona do manguezal. A análise multitemporal de aerofotografias se reve