Land use, spatial heterogeneity of organic matter, granulometric fractions and metal complexation in reservoir sediments

Uso e ocupação do solo, heterogeneidade espacial de matéria orgânica, frações granulométricas e complexação de metais em sedimentos de reservatório

Abstract 

Aim  This study aimed to evaluate land use, distribution of particle size fractions, organic matter (OM) and perform a metal quantification liable to complexation in the Itupararanga Reservoir (São Paulo, Brazil). This aquatic ecosystem is used for water supply and energy generation and is constantly subjected to anthropogenic impacts that alter its physical and chemical characteristics.

Methods  In a single campaign, samples of surface sediment (10 cm) were collected from nine sampling stations, in triplicate, along the reservoir. The collection was carried out with a “Lenz” type bottom sampler. The physicochemical variables, including the quantification of the metals copper, chromium, manganese, nickel, lead and zinc, were evaluated by basic descriptive statistics techniques combined with geostatistics and the use of remote sensing.

Results  All along the reservoir the sediment is predominantly organic and water depth interfered directly in the OM concentration and particle size distribution. Therefore, heterogeneity was observed regarding OM contents, particle size fractions and metals, with the exception of chromium, and the three zones of the reservoir proved to be distinct from each other. The land use classification showed the real situation of the Environmental Protection Area (EPA) and the results indicate that the central portion is more subject to anthropic impacts, while the dam region has high levels of metals, probably originated from the activities in the reservoir’s surroundings.

Conclusions  The soil erosion in the reservoir’s region shows the lack of efficiency in the Itupararanga EPA’s management, being needed a strategic coordination among the municipalities to enhance its conservation.

Keywords:  decomposition; complexing of metals; freshwater reservoir; sedimentation; water depth