Spatial evolution of supramareal hypersaline plans associated with mangrove forests: anthropic and natural factors on the Todos os Santos bay, northeast coast of Brazil

Abstract

‘Apicuns’, on Portuguese, are transitional flat and hypersaline environments associated with mangroves. In Todos os Santos Bay (TBS), mangroves and apicuns occupy 177.6 km2 and 10.2 km2 respectively. The aim of this study was to analyze the spatio-temporal variation of apicuns in TBS, between 1954 and 2015, based on aerial photographs from the years 1954, 1989, 2010 and satellite images from the year 2015. Four municipalities were studied along the TBS coast: Madre de Deus (MD) to the north, Saubara (SB) to the northwest, Vera Cruz (VC) to the midwest and Jaguaripe (JP) to the southwest. The apicuns areas in the different years were digitized based on visual interpretation and corrected from field truth and in situ analysis. The total area of apicuns calculated for 1954, in the four study regions, was 805 hectares (ha), while in 2015 it was 618 ha, indicating a reduction of 23% in the occupied area. This reduction is not homogeneous, as a decrease in the apicuns of MD (-72.6%), JP (-21%) and VC (-25.2%) and a stabilization in SB (+ 5%) were identified. In VC and MD, the advance of urban occupation over apicuns occurred through landfills. Apart from anthropogenic changes, the formation of apicuns was observed from the closure of mangrove fringes. In most areas, there was an advance of mangroves over the apicuns, which can result from greater rainfall in relation to evaporation, weather tides or sea level variation.