LITTORAL ZONE OF SOUTH-BRAZILIAN COASTAL LAKES: ELEMENTAL COMPOSITION OF THE SEDIMENTS

Abstract

The interrelationships of the nutrient elements phosphorus, nitrogen, calcium, magnesium, sodium and potassium along the sediment cores and in the uppermost strata differentiated the littoral zones of nine coastal lakes in Rio Grande do Sul. Nutrients in the superficial layer are likely to be related to the dynamics of the processes occurring in the water column, and to the detrital decomposition. Phosphorus, nitrogen, and calcium showed similar chemical relationships in the uppermost strata. The correlation among the nutrient elements and the heavy metals lead, cadmium, cooper and zinc suggested a common trend of increasing and decreasing along the sediment gradient. Only 29.6% of the observed variance is explained by other mechanisms related to anomalous strata in the sediment cores. The pattern of heavy metal accumulation differed greatly among the littoral zones. Its distribution along the sediment profiles ref1ects naturally occurring processes and, in some cases, weak atmospheric inputs. The levels of heavy metals commonly observed in lacustrine sediments in other brazilian aquatic systems are by far higher than the values found in the presente study.