Effects of riparian land use changes on soil attributes and concentrations of potentially toxic elements

Influence of land use on spatial distribution of mobile phosphorus forms in the sediment of a tropical semi-arid reservoir

Changes in land use and land cover influence the transport of nutrients, mainly phosphorus (P), to aquatic ecosystems. P can be available in the water column to primary producers' assimilation or be stored in different forms in limnic sediment. Therefore, this study aims to analyze the impact of land use and land cover on the spatial distribution of phosphorus forms in the sediment of a tropical semi-arid reservoir. We hypothesize that agriculture, exposed soil and the presence of floodable vegetation increase the amount of mobile phosphorus in the sediment and the sediment closer to the dam show a greater amount of mobile phosphorus due to the confluence of the flows. The classification of land use and land cover was carried out through supervised analysis at the level of the reservoir's drainage basin and area of influence. Sediment samples from the reservoir were collected at four different sampling points within the influence of two sub-basins. P forms were obtained through chemical fractionation of these sediment samples along the reservoir. Sparse Caatinga was the predominant land cover in the drainage basin and in the influence area, accounting for >50 % of these areas. This land cover represents a risk for nutrient transport to aquatic environments. The sediment samples from Boqueirão reservoir exhibited a high amount of phosphorus, mainly in the mobile forms. These forms were heterogeneously distributed throughout the reservoir. Agriculture activities, exposed soil, and floodable vegetation, influence the distribution and increase of mobile forms of phosphorus in the reservoir sediment. This suggests the need for specific strategies for manage these activities properly. Additionally, the sediment closest to the dam showed a lower amount of mobile phosphorus compared to samples further upstream.

Soil degradation and Cu, Cr, Ni, Pb and Zn contamination in dumpsites of humid and semiarid tropical regions in northeastern Brazil

We investigated soil characteristics and heavy metal content changes in 12 inactive dumpsites in humid and semiarid tropical climates in Northeast Brazil. The metals Cu, Cr, Ni, Pb and Zn in soil samples were determined by atomic absorption spectrophotometry. Other parameters measured include pH, electric conductivity, soil texture, soil organic carbon, total porosity and available P. The soil contents of sand, clay, soil organic carbon, available P and heavy metals, and soil bulk density, total porosity and pH were efficient indicators of soil degradation. We found no influence of current use, soil class or climate on the soil response. The mean concentrations of heavy metals in the dumpsite soils followed the order Zn (49.96 mg kg^-1) > Cu (38.48 mg kg^-1) > Pb (24.64 mg kg^-1) > Cr (21.94 mg kg^-1) > Ni (7.77 mg kg^-1). They were 6- to 36-fold higher than the background values for the region and were above the Brazilian guideline values for metals. The four dumpsite soils that showed simultaneous contamination with two or more heavy metals were located in the semiarid region. This challenges the assumption that soil impacts in the semiarid region are minimal due to lower leaching and high evaporation. Soil changes increase with time under activity, size and decommission time of the dumpsite. These data are important for local authorities to establish more effective targeting policies for closure of dumps and control of the spread of contaminants in areas impacted by the disposal of municipal waste.