José Antônio Louzada

Adaptação metodológica no cálculo de cargas contaminantes de fósforo em bacias hidrográficas gaúchas

The excess of phosphorus in the environment can cause several negative impacts, especially with regard to water quality. Hence adequate methodologies are needed for assessing this risk at the watershed scale, emphasizing that the non-point agricultural sources impose greater estimate difficulties. The objective of this work was to propose an adapted methodology to quantify the dissolved and total reactive phosphorus movement in agricultural areas, based on the influence of agricultural crops (arboreous and herbaceous size), native pasture and its management in the State of Rio Grande do Sul (Southern Brazil). The methodology used was the study of reactive phosphorus release in plots covered by different crops and its relation to the methodology of calculation of maximum daily loads, currently accepted by the state environmental agencies for the environmental licensing of potentially polluting activities. The results show that the calculation of load of phosphorus contaminant currently in use, may be underestimating the Brazilian conditions, especially in Rio Grande do Sul, and that the new methodology allows one to include temporal variation as an element in the process of analysis, turning the licensing analysis into a dynamic and punctual process.

Fósforo reativo: Arraste superficial sob chuvas simuladas para diferentes coberturas vegetais

O fosforo e um elemento quimico chave para a qualidade da agua, agindo principalmente como gatilho desencadeador das floracoes algais. A principal fonte de fosforo nas pequenas bacias rurais advem da agricultura feita nas encostas das bacias, podendo chegar de varias formas ao corpo d’agua, porem as formas mais impactantes sao o fosforo reativo total e o dissolvido. A forma dissolvida e a que apresenta maiores riscos pois pode percorrer distâncias comparativamente maiores do que o fosforo reativo nos sedimentos em suspensao que podem acabar depositados ao longo do caminho. Portanto, este trabalho visa avaliar se diferentes coberturas do solo por culturas anuais podem interferir no arraste destas formas de fosforo, afetando o risco da degradacao dos recursos hidricos das pequenas bacias rurais. Apesar de nao ter havido diferenca significativa entre os tratamentos, verificou-se sazonalidade ao longo do experimento representando uma estacao de cultivo. Isto significa que houve variacao do nivel de risco, uma vez que, no terco inicial das primeiras chuvas, o risco de arraste de fosforo na enxurrada foi mais elevado em relacao a periodos chuvosos mais distantes da epoca de plantio/fertilizacao, tornando-se possivel avaliar o risco a bacia de forma sazonal e nao anual.

Impacts of Climate Change on Soybean Irrigation Water Requirements inNorthwest Region of Rio Grande do Sul, Brazil

Higher temperatures and a larger variability in precipitation will cause, in general, higher irrigation water requirements. The most important non-irrigated crops for the economy of the state of Rio Grande do Sul, Brazil, are corn and soybeans and the mesoregion which most contributes to the annual harvests of these crops is the Northwest region. This article aims to assess whether the impacts of climate change on agriculture in this region will be positive or negative and in what intensity they may occur. Hence, data from future climate projections generated by different climate models, as well as soil sampling for characterizing physical and hydraulic soil properties were considered. The one-dimensional SWAP model was used to estimate the irrigation water requirements. The results of the hypothesis tests performed for all simulations supports the premise that the irrigation water requirements in the near future (2025s) are not statistically different from the baseline period (1960-1990). On the other hand, water irrigation requirements in 2055s and 2085s reject this hypothesis.

Transferência superficial de fósforo reativo potencialmente contaminante por chuvas simuladas intensas

Phosphorus is naturally present or added to the soil and, depending on the mix of factors, may trigger a high environmental risk to water resources in river basins. The aim of this study was to quantify the transfer for soil surface of some forms of reactive phosphorus originating from phosphorus fertilization on bare soil, carried by the runoff. The experiment was carried out in Lages, SC, Brazil, with two replications in the field under intense simulated rainfall (64 mm h−1 for 50 minutes). The results indicate that phosphorus may represent a serious environmental risk to water resources of basins at different scales in time and space, through the reactive forms of phosphorus and their different ways of transportation.

Applying and assessing SWAP and HYDRUS 1D models in different agricultural scenarios.

O entendimento dos processos de fluxo e armazenamento de agua no solo e extremamente importante, pois permite planejar e gerenciar o uso dos recursos hidricos no sistema solo-planta-atmosfera. Diversos modelos denominados agro-hidrologicos sao empregados com essa finalidade, sejam eles de dominio publico ou comerciais, simples ou complexos. No presente trabalho, dois modelos publicos, SWAP e HYDRUS 1D, amplamente utilizados em simulacoes unidimensionais do fluxo de agua foram aplicados para quantificar o balanco hidrico em dois cenarios agricolas significativamente distintos. A partir dos seus resultados, os modelos foram avaliados tendo como referencia dados observados de profundidades do lencol freatico e drenagem pela base do perfil do solo. As avaliacoes indicaram um bom desempenho de ambos os modelos, expresso por meio dos coeficientes estatisticos adotados. Adicionalmente, os resultados dos dois modelos relativos a outras variaveis nao observadas em campo foram comparados entre si. A aderencia foi muito boa tanto para os perfis de umidade como para os valores de evaporacao calculados.