CHARACTERIZATION AND CLASSIFICATION OF FLOODPLAIN SOILS IN THE PORTO ALEGRE METROPOLITAN REGION, RS, BRAZIL

Luís De França Da Silva Neto,Elvio Giasson,Catiline Schmitt,Nilton Curi,Alberto Vasconcellos Inda,Paulo César Do Nascimento

doi:10.1590/s1413-70542015000500001

Abstract

ABSTRACTIn the Porto Alegre metropolitan region (PAMR) there are a significant proportion of floodplain soils, mainly Planosols and Gleysols, in relation to upland soils. This study aimed to evaluate the morphological, chemical and physical characteristics, and to classify floodplain soils in the PAMR. Six soil profiles were evaluated under different sedimentary lithologies and drainage classes, and samples were collected for chemical and physical analyzes. Two orders of mineral soils (Planosols and Gleysols) and one order of organic soil (Organosols) were identified. The soils were moderately deep to deep and stratified. In mineral soils hue ranged between 7.5YR and 2.5Y, with the occurrence of Bg, Btg or Cg gley horizons, while in organic soil the colors were neutral. Sand and silt were the predominant particle sizes according to the origin sedimentary deposits. The organic carbon content was negatively related to soil density and positively related to soil specific surface area and with soil cation exchange capacity. Soil chemical characterization showed expressive variation in bases, aluminum and sodium saturation. Ki index and Fe(CBD)/Fe(H2SO4) ratio indicated a low soil weathering degree. The different sedimentary lithologies and the soil hydromorphism degree were the main factors related to differences in morphological, physical and chemical characteristics of soils in the PAMR.

Highlights

Floodplain soils are considered the soils found along the plains of rivers, lakes and lagoons, where they develop in sediments from various sources under various drainage classes often with hydromorphic conditions
In Rio Grande do Sul, the floodplain soils occupy an area of approximately 53,000 km2 (19% of the territory)
The greater influence of the water table due to the proximity of water bodies limited the differentiation of characteristics, such as structure, as well as the development of other pedogenic processes besides hydromorphism and paludization

Summary

Introduction

Floodplain soils are considered the soils found along the plains of rivers, lakes and lagoons, where they develop in sediments from various sources under various drainage classes often with hydromorphic conditions. In Rio Grande do Sul, the floodplain soils occupy an area of approximately 53,000 km (19% of the territory) This proportion changes significantly in the Porto Alegre metropolitan region (PAMR), where the floodplain soils occupy about 60% of the area. Urbanization pressure has increased recently, which can result in important changes in local environment These soils are part of intermediate ecosystems between the highlands and aquatic ecosystems, with environmental importance for the conservation of water resources and the maintenance of fauna and flora. In this sense, it is important that the use of floodplain

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