Soil loss risk and habitat quality in streams of a meso-scale river basin Risco de perda de solo e qualidade do habitat numa bacia hidrográfica de meso-escala

Soil loss expectation and possible relationships among soil erosion, riparian vegetation and water quality were studied in the São José dos Dourados River basin, State of São Paulo, Brazil. Through Geographic Information System (GIS) resources and technology, Soil Loss Expectation (SLE) data obtained using the Universal Soil Loss Equation (USLE) model were analyzed. For the whole catchment area and for the 30 m buffer strips of the streams of 22 randomly selected catchments, the predominant land use and habitat quality were studied. Owing mainly to the high soil erodibility, the river basin is highly susceptible to erosive processes. Habitat quality analyses revealed that the superficial water from the catchments is not chemically impacted but suffers physical damage. A high chemical purity is observed since there are no urban areas along the catchments. The water is physically poor because of high rates of sediment delivery and the almost nonexistence of riparian vegetation.<br>Expectativa de perda de solo e possíveis relações entre erosão, vegetação ripária e qualidade da água foram estudados na bacia do rio São José dos Dourados (SP). Através de recursos de geoprocessamento e da Equação Universal de Perda de Solos, os dados sobre expectativa de perda de solo foram levantados. Para a área de drenagem total e a faixa tampão dos corpos d'água de 22 sub-bacias aleatoriamente selecionadas, analisou-se a cobertura do solo predominante e qualidade do habitat. Devido principalmente à alta erodibilidade do solo, a área estudada é altamente suscetível ao processo erosivo. As análises de qualidade da água revelaram que as águas superficiais das sub-bacias estão quimicamente não impactadas, mas fisicamente degradadas. A alta pureza química deve-se, possivelmente, à ausência de áreas urbanizadas ao longo das sub-bacias e as alterações nas características físicas são, possivelmente, decorrentes das altas taxas de transferência de sedimento aos corpos d'água e à quase ausência de mata ciliar

Sources of reactive nitrogen affecting ecosystems in Latin America and the Caribbean: current trends and future perspectives

While the amount of reactive nitrogen circulating at the global level has increased markedly in the last century, the effects of this increase are largely seen at the regional level due to interacting ecological and socio-economic factors. In contrast with most other regions of the world, Latin America and the Caribbean (LA-Ca) stand out due to the fact that the major input of reactive nitrogen (Nr) still occurs naturally via biological nitrogen fixation (BNF) in natural ecosystems as opposed to anthropogenic inputs of synthetic fertilizer, fossil fuel combustion and cropping with leguminous species. Largely due to economic reasons, the consumption of fertilizer N in the LA-Ca region is still low in comparison with the average consumption of the world. However, the fertilizer N consumption is increasing at a much faster rate than that in developed regions of the world, like USA and Canada. The Nr production through BNF in cultivated plants that fix nitrogen (C-BNF) is 5 times lower than that occurring naturally in Latin America, but is still equivalent to 16% of the world C-BNF. The cultivation of nitrogen-fixing crop species in the LA-Ca region is also increasing, almost entirely due to the expansion of soybean fields in the central and northern regions of Brazil and the Pampa region of Argentina. Other anthropogenic activities in the region that contribute to an increase in the circulation of reactive nitrogen include the impact of biomass burning and urbanization. In the last decade, an average of 47,000 km 2 per year of forests was burned in the LA-Ca region. The environmental impact of urban centers in the LA-Ca region has become very important, since an intense urbanization process is occurring in this region, at an intensity that far exceeds urban development in the northern hemisphere. The consequences of increased urbanization include increased emissions of NO x to the atmosphere due to the fossil fuel combustion, and the lack of sewage treatment facilities in most cities of the LA-Ca result in a large volume of untreated sewage discharged into surface waters, creating serious environmental problems. The combination of rapid urbanization and agricultural intensification in this region suggest that concern is warranted for the potential for increase in the circulation of reactive nitrogen in the very near future. At the same time, the opportunity still exists to mitigate some of the consequences of human impact on the nitrogen cycle in a region that still maintains a large fraction of its natural ecosystems intact.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46029/1/10533_2006_Article_9000.pd

Can land use changes alter carbon, nitrogen and major ion transport in subtropical brazilian streams? Modificações no uso da terra podem alterar o transporte fluvial de carbono, nitrogênio e íons maiores?

Several studies in tropical watersheds have evaluated the impact of urbanization and agricultural practices on water quality. In Brazil, savannas (known regionally as Cerrados) represent 23% of the country's surface, representing an important share to the national primary growth product, especially due to intense agriculture. The purpose of this study is to present a comprehensive evaluation, on a yearly basis, of carbon, nitrogen and major ion fluxes in streams crossing areas under different land use (natural vegetation, sugar cane and eucalyptus) in a savanna region of SE Brazil. Eucalyptus and sugar cane alter the transport of the investigated elements in small watersheds. The highest concentration of all parameters (abiotic parameters, ions, dissolved organic carbon DOC - and dissolved inorganic carbon - DIC) were found in Sugar Cane Watersheds (SCW). The observed concentrations of major cations in Eucalyptus Watersheds (EW) (Mg, Ca, K, Na), as well as DIN and DOC, were found frequently to be intermediate values between those of Savanna Watersheds (SW) and SCW, suggesting a moderate impact of eucalyptus plantations on the streamwater. Same trends were found in relation to ion and nutrient fluxes, where the higher values corresponded to SCW. It is suggested that sugar cane plantations might be playing an important role in altering the chemistry of water bodies.<br>Diversos estudos têm sido desenvolvidos em bacias de drenagem tropicais no intuito de avaliar o impacto da urbanização e das práticas agrícolas na qualidade dos corpos d'água. No Brasil, as savanas (conhecidas regionalmente como Cerrado) representam 23% do território brasileiro, sendo uma região importante no crescimento nacional, especialmente devido às intensas atividades agrícolas. A finalidade deste trabalho é apresentar uma avaliação dos fluxos de carbono, nitrogênio e principais íons em córregos com diferentes usos do solo (vegetação, cana de açúcar e eucalipto) em uma região de Cerrado, SE Brasil. A cana de açúcar e o eucalipto alteram o transporte dos elementos investigados nessas pequenas bacias de drenagem. As concentrações mais elevadas de todos os parâmetros analisados (parâmetros abióticos, íons, carbono orgânico dissolvido e carbono inorgânico dissolvido) foram encontradas na bacia de cana de açúcar (SCW). As concentrações observadas para os cátions na bacia do eucalipto (EW) (Mg, Ca, K, Na), assim como Carbono Inorgânico Dissolvido (CID) e Carbono Orgânico Dissolvido (COD), apresentaram valores intermediários entre as bacias do Cerrado e da cana de açúcar, sugerindo um impacto moderado dessa plantação aos corpos d'água. Mesma tendência foi observada para os fluxos de íons e nutrientes, sendo, novamente, os maiores valores encontrados na bacia de cana-de-açúcar. Os autores sugerem que o cultivo da cana de açúcar representa um importante fator na modificação da química de pequenas bacias de drenagem