In the State of Pará, mangroves occur in the transition between terrestrial and marine environments, subject to two daily tides, between 5-7 m high, from a hydrological complex, in a very rainy humid tropical climate (2,800 mm). Although with low diversity of plant species (biogeographic region ACEP), with Rbizophora mangle L. (Rhizophoraceae), Atncennia germinans (L.) Stearn (verbenaceae) and Laguncularia racemosa (L.) Gaertn (Combretaceae), have high adaptability to the variability of soil attributes, such as pH (Rhizophora), cation exchange capacity (Avicennia) and salinity (Laguncularia). Considering the presence of adult mangrove vegetation on muddy substrate, four sampling sites were selected, with three soil profiles collected in each, along the Marapanirn River estuary, starting 50 meters from the river bank. The samples were described and chemically analyzed, according to the usual methods employed for mangrove soil analysis, to determine the macronutrient content (C, N, Ca, Mg, Na, Ke P), Al+3 content, expressed in cmol.Kg', associated with in situ pH, pH in H, O, Eh, and salinity. High in situ pH values (6-7) differed strongly from pH values in H20 (2-3). The carbon values at all four collection points indicate a strong concentration of plant remains (roots, twigs and leaves). The soils also have a high absorption capacity for cations, particularly magnesium, abundant in seawater, as well as sodium and calcium, while potassium is comparatively lower. Phosphorus is probably fixed by aluminum and iron, due to the strong acidity of the soil. The contents of carbon (18.64 to 25.88), nitrogen (2.72 to 3.40), sodium (03.94 to 14.81), magnesium (18.58 to 30.65) and potassium (0.29 to 1.32) decrease gradually from point p4 (montande) to point PI (iusante), different from calcium (9. 15 to 3.40) and aluminum (13.53 to 10.64), whose values are lower at points P3 and P4 and higher at points P1 and P2, probably linked to the sand fraction. The values of macronutrients found do not differ from other mangroves. This knowledge is useful in the use/preservation and conservation planning of this fragile and at the same time important ecosystem, in terms of productivity, ecological and socioeconomic value.
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