RESUMO Este estudo avaliou as mudanças históricas do uso do solo e da cobertura da terra na bacia hidrográfica de Arroio Marrecas (Caxias do Sul, RS) e simularam futuros cenários de uso do solo até 2034. As simulações espaciais e temporais foram conduzidas com o modelo CLUE-S (“Conversão de Uso da Terra e seus Efeitos-Pequena Extensão Regional”). Três cenários de uso da terra foram desenvolvidos para incluir políticas públicas e tendências agrícolas na região de estudo por 20 anos (2015-2034). A análise geoespacial mostrou que as áreas com pastagens e florestas diminuíram, o que pode ser atribuído à expansão de usos agrícolas intensivos, como fruticultura, silvicultura e urbanização. A dinâmica de realocação do uso da terra com o modelo CLUE-S foi afetada principalmente pelas classes de solos (especialmente Cambissolo Háplico e Húmico e Neossolo Litólico), com efeito reduzido da altitude e declividade. A análise dos mapas de uso da terra da bacia hidrográfica Arroio Marrecas até 2015 demonstrou mudanças induzidas pelo homem, impulsionadas pela expansão da produção agrícola, além da urbanização. A alocação de uso de terras derivada dos cenários futuros propostos com CLUE-S mostrou que neste contexto regional, Cambissolos e Nitossolos seriam os principais impulsionadores da alocação de expansão agrícola. Por outro lado, as políticas de conservação se mostraram com mais intensidade nos Cambissolos Háplicos. A principal limitação dessa abordagem é o reconhecimento de fatores determinantes que apresentam alta correlação com cada uso da terra como variáveis preditoras efetivas.

ABSTRACT This study evaluated historic land use and land cover changes in the Arroio Marrecas watershed (Caxias do Sul, Rio Grande do Sul state of Brazil) and simulated future land use scenarios until 2034. Spatial and temporal simulations were conducted with the Conversion of Land Use and its Effects - Small Regional Extent (CLUE-S) model. Three land use scenarios were developed to include public policies and agricultural trends in the study region for 20 years (2015-2034). Geospatial analysis of different land uses showed that areas that were originally covered grasslands and forests decreased, which can be attributed to the expansion of intensive agricultural uses, such as fruit farming/forestry and urbanization. The reallocation dynamics of land use with CLUE-S was primarily driven by the soil class (especially Typic and Humic Dystrudepts and Lithic Undorthents), with limited effects of altitude and slope. Analysis of the land use maps of the Arroio Marrecas watershed until 2015 identified major human-induced changes that were driven by expanding agricultural production and urbanization. The allocation of land use derived from the proposed future scenarios with CLUE-S showed that in this regional context, Humic Dystrudepts and Rhodic Kanhapludults were the key drivers of the allocation of agricultural expansion. Conversely, natural resource conservation was indicated to most likely occur in Typic Dystrudepts. The main limitation of this approach is the recognition of driving factors that have a high correlation with each land use as effective predictor variables.

The influence of silver nanoparticles (Ag-NPs) on the optical properties of Bi2O3-GeO2 glasses was investigated aiming the characterization of their potential for applications in photonic devices. The samples were prepared by the melt-quenching technique starting from high purity oxides (GeO2, Bi2O3 and AgNO3). Heat-treatment during different times was performed to nucleate Ag-NPs. A transmission electron microscope was used to confirm the presence of Ag-NPs and to determine their sizes and composition. The glass network was studied by spontaneous Raman scattering. The optical absorption spectra showed an absorption band at ca. 500 nm associated to the bismuth ions, and a 7-fold enhancement of absorption was observed in the samples with Ag-NPs. Photoluminescence (PL) spectra were obtained by exciting the samples with a 808 nm laser. Maximum enhancements of ca. 100% of the PL band centered at 1300 nm and ca. 70% of the Raman spectrum were observed due to the nucleation of the Ag-NPs. The enhanced optical response of the samples with Ag-NPs is attributed to the growth of the local field on the isolated bismuth ions and clusters that are located in the vicinity of the nanoparticles. The results illustrate the large potential of Bi2O3-GeO2 with Ag-NPs to be used in photonic devices.