Análise dos Elementos Traços (Ni, Pb, Zn, Cd, Cr e Cu) em Solos de Manguezais do Estuário do Rio Marapanim-PA

Abstract

Mangroves constitute authentic coastal forests, whose structure and diversity of plant species is highly adapted to the topographic and geomorphologic differences of the environment, to saline fluctuations and tidal amplitudes. The present study was carried out in the coastal plain of the municipality of Marapanim-PA, bounded by the geographic coordinates 00° 32'30" S/ 00° 52' 30" S and 47° 28' 45" W /47" 45' 00" W. The study area is subjected to semi-diurnal macro-tides, with heights between 5 - 7 meters, a humid tropical climate, of the Awi Kôppen type, mean annual precipitation of 2,800 mm, mean annual temperature of 27.7 °C, mean annual thermal amplitude of 6.5 °C, and mean annual relative air humidity around 80%. Collections were carried out at 4 sites, P4-ContactMangue Várzea (upstream), P3-Ilha do Bombeiro, P2-Lóbulo and PI-Sul de Algodoal (downstream), in March 12003, along the Marapanim River estuary, with a mud auger extending up to 3 m, in 3 contiguous botanical plots, 20 m X20 m, each. The analysis for trace element levels (Ni, Pb, Zn, Cd, Cr and Cu), were based on usual methods, with triacid attack and reading by atomic absorption spectrophotometer, in the Atomic Absorption Laboratory of MPEG and correlated to pH, Eh and salinity. The soils have no developed structure, with a predominance of the clay fraction, whose proportions are in the following order: clay-silt-fine sand. The Copper, Nickel and Chromium contents gradually decrease from P4 (upstream) to PI (downstream), while the Zinc contents reach high values at P4, decreasing at P3 and increasing again at PI and P2, probably associated with the high amount of Iron oxide. The Cadmium and Lead elements were not detected, as they were below the detection limit of the device. The accumulation of heavy metals in mangrove sediments may be a function of chemical and physical conditions such as particle size, concentration and type of organic matter, salinity, pH, and redox potential. There was no increase in the levels of the trace elements analyzed with depth for all points, presenting low concentrations, except for zinc.