No abstract

A matéria orgânica (MO) encontrada no solo pode ser uma ferramenta auxiliar na identificação de uma vegetação remota. Na Floresta Nacional do Araripe e circunvizinhança, na Chapada do Araripe, realizou-se o presente estudo, em que as medidas de d13C e d15N da MO dos solos foram utilizadas para: (i) avaliar os valores atuais desses parâmetros; (ii) analisar a variabilidade natural do d13C no solo de diferentes formações florestais e (iii) indicar o declínio de florestas. Verificou-se que os solos das áreas hoje preservadas e cuja MO na superfície mostra d13C tipo C3, da vegetação atual, e uma mistura C3-C4 em profundidade, correspondem a ecossistemas antropizados no passado por uso agrícola; já os solos que mantiveram o d13C tipo C3 em todo o perfil se referem a ecossistemas antropizados, porém por uso não agrícola. Na caatinga, o perfil do d15N indicou um solo mais mineralizado e com menos MO. As áreas reflorestadas e preservadas apresentaram recuperação da MO.

The state government of Ceará has initiated a program of releasing water from dams in order to sustain a continual flow of water in the state's naturally intermittent rivers. However, river/ ground water connections in alluvial areas impose heavy losses on regulated discharges. Our study area, the “Ilha de Limoeiro” (Isle of Limoeiro), is located in the Lower Jaguaribe Basin and comprises an area of approximately 120 km2. We used environmental oxygen‐18 and deuterium, together with hydrochemistry, in order to identify the origin of ground water which is heavily exploited for intensive small‐scale irrigation in that part of the flood‐plain of the Jaguaribe River. This paper discusses the mechanisms of recharge for the different hydrogeologic systems: crystalline basement, thick alluvium, and alluvium/Agu.

The Cariri region is the largest sedimentary basin in the state of Ceará, Brazil. Located in the southern portion of the state, it comprises the Araripe Plateau and the Cariri Valley on its northern foot. The region's groundwaters are being heavily exploited. Using electric conductivity (EC) and 18O, 14C and 3H data, we differentiate groundwaters from various origins. We identified three horizons of springs on the slope of the Plateau through their geologic environment and the EC of their waters. Groundwaters from wells in the Cariri Valley are classified according to the aquifers exploited as indicated by the drilling profiles. However, strong tectonic features and intense fracturing in the Valley produce a great many horizontal discontinuities, which result in a mixing of groundwaters from different aquifers. Mixing systems are described in terms of δ18O–14C and EC–14C linear trends.