Changes of Estuarine Sedimentation Patterns by Urban Expansion: The Case of Middle Capibaribe Estuary, Northeastern Brazil

摘要

The aim of this study is to describe the sedimentary evolution occurred during the last 200-years in the middle Capibaribe Estuary by mean of the sedimentary analysis (magnetic susceptibility, grain size, calcium carbonate, total organic matter—TOM) and geochemical parameters (sedimentation rates, heavy metal concentrations, enrichment and contamination factor) along a core. The core recorded four units and the measured sedimentation rate was 0.52 cm cm·y﹣1. The first unit, dating before 1812, showed environmental characteristics of mangrove with predominance of fine sediments, high total organic matter percentages and heavy metal concentrations probably from natural sources. The second unit, from 1812 to 1937, showed a slight increase in sand percentages and decrease in fine fraction, TOM contents and heavy metals concentrations. These characteristics may be associated with the urban expansion processes and the presence of monoculture of sugar cane occurred in the middle Capibaribe Estuary. The third unit, from 1937 to 2004, showed the highest sand percentages of the core, characterizing a unit exclusively of sand with low fine fractions percentages, total organic matter contents and heavy metals concentrations. This unit represented the intensification of the urban processes expansion of Recife City. The fourth unit showed increases in fine fraction sedimentation, TOM contents and heavy metals concentrations. This new change in sedimentation probably is consequence of rebirth of marginal estuarine banks by mangrove vegetation, due to environmental projects carried out by Recife Prefecture in the early 2000’s. It was not possible to register the anthropic contamination to middle estuary area probably due to the Barreiras Formation influences in the metal concentration records, masking the anthropic contamination inputs in estuarine region. Although, lead and arsenic showing an enrichment level indicating anthropic contamination.