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Brazilian sediment quality criteria were established based on pseudo-total metal contents, which is not suitable to determine their bioavailability and the ecological risk for aquatic biota. Therefore, the geochemical speciation of five metals (Cu, Fe, Ni, Pb and Zn) was determined to assess the distribution and ecological risk of sediments in a tropical shallow reservoir from Brazil. The paper aims to discuss these issues.

A survey of metals in ten representative stations of surface sediments (0-20 cm) from Carlos Botelho (Lobo-Broa) Reservoir was conducted during the dry season in April 2014. Sediment parameters were measured in situ. The geochemical speciation of metals was carried out using the modified three-stage BCR-701 procedure (Davutluoglu et al., 2011) and compared with pseudo-total metal contents.

Contamination at S-1 and S-8 was more severe than other sampling sites, especially for Cu, Ni, Pb and Zn. Metals such as Cu, Ni and Zn occasionally may be associated with adverse biological effects based on the comparison with sediment quality guidelines. The risk assessment code suggests no risk for Fe and low risk for Cu and Ni.

Geochemical speciation of metals could be useful in developing effective management strategies to control metal pollution in the Lobo-Broa Reservoir. Substantial amounts of Pb (classified as medium risk) were bound to humic substances and/or insoluble metal sulfides, and could pose serious risk to the benthic community through the food chain. Zinc at S-1, S-3 and S-8 showed high risk, indicating that an appreciable portion of Zn could be available to aquatic biota.

Erosion is the main cause of soil and water degradation, which demands investments for the recovery of such natural resources. The purpose of this paper is to quantify and spatialize soil losses in a municipality with large areas of monoculture of sugarcane.

The Universal Soil Loss Equation was applied for the identification of areas susceptible to erosion in the municipality of Jahu, SP, Brazil. Soil maps, statistical census data from Brazilian Institute of Geography and Statistics, radar images from SRTM, rainfall data from Fatec-Jahu hydrometeorological station and digital satellite images from Landsat 5 TM were used for the analyses. Four basic parameters were evaluated: topography of the terrain, rainfall erosivity, soil erodibility, and soil use and management factors. The analyses were conducted in the Geographic Information System (ArcView software).

The results show most of the municipality (91 percent) consists of areas of erosion potential. However, the remaining 9 percent can potentially produce 40 percent of the sediment load, which indicates the need for conservation practices and environmental recovery for a reduction in the erosion process acceleration.

In view of the expansion of sugarcane culture in the cities of São Paulo, the results show the importance of a master plan for new areas of sugarcane planting and the need for restoration of riparian vegetation in the surrounding streams and springs for the reduction of erosion.

Finer sediment particles (silt and clay) transported by rivers carry the major part of nutrient loads by absorption; thus, sediment settling can remove nutrients from the water column. The purpose of this paper is to analyze the relation between reservoir sedimentation and water quality by assessing the reservoir sedimentation process and the sediments’ characteristics.

Bathymetric surveys from 2004 to 2014 were analyzed to assess the sedimentation process. Core samples provided information on a layer-by-layer basis of the sediment deposits, and water samples near the surface and near the bottom provided information on sediment concentration, and adsorbed and dissolved nutrients.

The upstream region of a reservoir is already silted. From 2004 to 2014, the delta evoluted approximately 500 m downstream and the deposits were mainly composed of clay. An area of approximately 1,000 m between the delta and the dam should still be able to continue allowing sediment deposition in the coming years. Most of the nutrients were absorbed into the sediment particles, except for the nitrogen measured in the dry season.

Although analyses of the full cycle of the nutrients were not carried out, the constant sediment trapping of finer sediments and the high rate of absorbed nutrients in the suspended sediment support the hypothesis that the reservoir has removed nutrients from aqueous media by adsorption into sediments.

In the studied case, reservoir sedimentation has led to better water quality downstream.

It is shown in this study that reservoir sedimentation may have positive effects on river water quality.