Antônio José Teixeira Guerra

Spatial and temporal variation in two rainfall simulators: implications for spatially explicit rainfall simulation experiments

Rainfall simulators are widely used yet there is little evidence in the literature to show that their spatial and temporal variability has been adequately taken into account. For experiments that are concerned only with some aggregate or mean effect of simulated rain then such variations may be unimportant. However, where rainfall simulation is being used to study (and perhaps model) small-scale processes that are themselves spatially variable (such as rill initiation) then knowledge of the simulators inherent variability is vital. A first aim of this paper is therefore to examine this variability, and to appraise methodologies by which it may be quantified. A second aim is to evaluate the implications for spatially explicit rainfall simulation experiments. Two simulators were used, a portable drip-screen simulator and a laboratory-based full-cone nozzle simulator. Neither produced a spatially uniform distribution of rainfall depth: both produced distributional patterns that were fairly consistent despite varying intensities and run times. Small-scale, apparently random variations were superimposed on these more deterministic patterns. However, despite this marked spatial variability, calculation of uniformity coefficients (1−SD/mean) resulted in high values. Thus it appears that the uniformity coefficient gives little real indication of the spatial uniformity of simulated rainfall, despite its established usage in the literature. Additionally, spatial distributions of raindrop size –and hence kinetic energy –were calculated for the full-cone nozzle simulator. These show that zones of high rainfall amount do not necessarily relate to zones of high energy reaching the surface. The presence of such variability raises a number of issues for spatially explicit rainfall simulation experiments. While there has been little work on the spatial variability of natural rainfall at field scale and smaller, it appears that the spatial heterogeneity of simulated rainfall depths observed in this study does not differ greatly from that of natural rain. But since a major attraction of rainfall simulation experiments is additional control over rainfalls many variables, the spatial non-uniformity of depth observed in this study is unwelcome. The existence of an apparently deterministic component to this non-uniformity nonetheless suggests that it can, at least in principle, be corrected by calibration. Less easily handled is the discrepancy between spatial distributions of rainfall depth and energy, since this will certainly affect rainfall simulation experiments that are, for example, concerned with erosion processes due to raindrop impact. Copyright

Slope Processes, Mass Movement and Soil Erosion: A Review

Abstract Soil erosion and land degradation are global problems and pose major issues in many countries. Both soil erosion and mass movement are two forms of land degradation and humans play important roles in these geomorphological processes. This paper reviews slope processes associated with mass movement and soil erosion and contributory factors, including physical and human agents. Acting together, these cause diverse geomorphological features. Slope processes are illustrated by reference to case studies from Brazil and UK. The causes and impacts of erosion are discussed, along with appropriate remedial bioengineering methods and the potential of the measures to prevent these types of environmental degradation. Although there are several agents of erosion, water is the most important one. Cultivation can promote soil erosion, due to ploughing and harvesting, which moves soil down slopes. Soil erosion and mass movement data would inform the viability of soil conservation practices. Integrated management of drainage basins offers a promising way forward for effective soil conservation and soil remedial bioengineering in Brazil and UK.

Land rehabilitation with the use of biological geotextiles, in two different countries

This paper assesses the role of biological geotextiles on non-agricultural erosion environments, based on studies in the mine tailings Gauteng Province (South Africa) and urban area of Sao Luis City (Brazil). Gauteng Province (South Africa) has suffered immense problems related to sustainable rehabilitation of mine dumps. This is a huge challenge, as wastes are highly susceptible to both water and wind erosion. Establishing a grass cover to reduce erosion is the dominant reclamation method. Covering the slopes with biological geotextiles might constitute another option for mining companies to reduce erosion and aid natural re-vegetation. The objective of the waste part of this study was to determine the beneficial effect of palm mat cover on erosion control, using rainfall simulation. Results clearly illustrated that application of palm-mats more than halved the sediment load in runoff, thereby having the potential to effectively stabilize tailing dam slopes. Covering tailings with palm-mats did not reduce runoff or improve water infiltration, however. In Sao Luis City, biological geotextile mats were constructed from palm leaves which are an effective, sustainable and economically-viable soil conservation technique. At Sacavem Community biological geotextile mats were used in association with barriers of wooden stakes and the construction of terraces along contour lines. The aim is to minimize soil erosion, by intercepting rainfall, retarding runoff velocity and sediment loss.

The Influence of Global Greenhouse-Gas Emissions on Future Rates of Soil Erosion: a Case Study from Brazil Using WEPP-CO2

Since the mid-198os, increases in the global concentrations of greenhouse gases have been paralleled by rising international concern over their potential to affect climate. Concentrations of these gases (most importantly, carbon dioxide, methane, nitrous oxide, tropospheric ozone, chlorofluorocarbons and water vapour) have been observed to increase dramatically during the last 1oo years or so. This rise results from anthropogenic activity. Emissions of the naturally-occurring gases have increased due to modifications of natural cycles by growing human populations, while some new gases (e.g. chlorofluorocarbons) have been added. Atmospheric concentrations of carbon dioxide, for example, have risen by about 26% since the Industrial Revolution (Fig. 1.1): this results both from increased burning of fossil fuels, and from deforestation (Houghton et al. 1990).

Artificial neural networks applied for soil class prediction in mountainous landscape of the Serra do Mar

Soil information is needed for managing the agricultural environment. The aim of this study was to apply artificial neural networks (ANNs) for the prediction of soil classes using orbital remote sensing products, terrain attributes derived from a digital elevation model and local geology information as data sources. This approach to digital soil mapping was evaluated in an area with a high degree of lithologic diversity in the Serra do Mar. The neural network simulator used in this study was JavaNNS and the backpropagation learning algorithm. For soil class prediction, different combinations of the selected discriminant variables were tested: elevation, declivity, aspect, curvature, curvature plan, curvature profile, topographic index, solar radiation, LS topographic factor, local geology information, and clay mineral indices, iron oxides and the normalized difference vegetation index (NDVI) derived from an image of a Landsat-7 Enhanced Thematic Mapper Plus (ETM+) sensor. With the tested sets, best results were obtained when all discriminant variables were associated with geological information (overall accuracy 93.2 - 95.6 %, Kappa index 0.924 - 0.951, for set 13). Excluding the variable profile curvature (set 12), overall accuracy ranged from 93.9 to 95.4 % and the Kappa index from 0.932 to 0.948. The maps based on the neural network classifier were consistent and similar to conventional soil maps drawn for the study area, although with more spatial details. The results show the potential of ANNs for soil class prediction in mountainous areas with lithological diversity.

RELAÇOES ENTRE POTENCIAL MATRICIAL NO SOLO E COBERTURA VEGETAL EM UMA ESTAÇÃO EXPERIMENTAL, UBERLÂNDIA - MG

Faz-se neste artigo uma analise sobre a relacao entre o potencial matricial e a cobertura vegetal em uma estacao experimental na Fazenda do Gloria, Uberlândia- MG, com base nos dados obtidos nos tensiometros e na fotocomparacao. Foram adotados os seguintes procedimentos: a. Construcao de duas parcelas de 10 m2 cada, uma com Solo Exposto (SE) e outra com Geotexteis e Gramineas (SG); b. A analise granulometrica dos sedimentos foi baseada na proposta da EMBRAPA; c. Monitoramento de duas baterias de tensiometros nas parcelas com solo exposto e com geotexteis em diferentes profundidades (15, 30, 80 e 120 cm), com o auxilio de um tensimetro digital INFIELD 5; e d. Fotocomparacao com classificacao supervisionada usando software de sensoriamento remoto. Os resultados foram divididos em tres fases: 1. na fase 1, a ocupacao da cobertura vegetal variou entre 0 a 6,4%, destacando-se o tensiometro de 120 cm cm na parcela com geotexteis, que atingiu -20 kPa; 2. na fase 2, com uma taxa de ocupacao variando entre 15,2% a 59,4 % na parcela com geotexteis e gramineas, o potencial matricial chegou a -32,4 kPa na profundidade de 15 cm; e 3. na fase 3, com uma taxa de ocupacao da graminea entre 63,9% a 100% , cita-se o tensiometro de 30 cm, que chegou a -67 kPa.

Soil structural indicators of hillslope destabilization in the Serra do Mar mountain range (Rio de Janeiro State, Brazil)

Mass movements are amongst the main problems related to natural disasters in Rio de Janeiro State. The cities which suffer most due to these events remain on alert during each rainy season. Many surveys have been conducted to map hazard risk areas. Many authors associate these phenomena with geological characteristics, and some recognize the role of soil properties. This paper outlines the soil indicators which contribute to hillslope destabilization in the Serra do Mar mountain range. A hillslope was selected and soil samples collected from six trenches, along the slope. Soil micromorphological and physico-chemical analyses were conducted to assess mass movement hazard. The presence of gibbsite on the upper third of the slope is one of the factors that can decrease horizon permeability and therefore destabilize slopes. On the lower third of the slope, structures demonstrate that part of this soil is formed by material originating from the upper slope.

Mapping of heavy metal contamination in alluvial soils of the Middle Nile Delta of Egypt

Areas contaminated by heavy metals were identified in the El-Gharbia Governorate (District) of Egypt. Identification used remote sensing and Geographical Information Systems (GIS) as the main research tools. Digital Elevation Models (DEM), Landsat 8 and contour maps were used to map physiographic units. Nine soil profiles were sampled in different physiographic units in the study area. Geochemical analysis of the 33 soil samples was conducted using X-ray fluorescence spectrometry (XRF). Vanadium (V), nickel (Ni), chromium (Cr), copper (Cu) and zinc (Zn) concentrations were measured. V, Ni and Cr concentrations exceeded recommended safety values in all horizons of the soil profiles, while Cu had a variable distribution. Zn concentrations slightly exceeded recommended concentration limits. Concentrations were mapped in each physiographic unit using the inverse distance weighted (IDW) function of Arc-GIS 10.1 software. Pollution levels were closely associated with industry and urban areas.

The climatic risk of drought to the Brazilian semi-arid region

Droughts and the floods of the rainy period are risk factors of meteorological and climatic phenomena, which characterize semi-arid environments, like north eastern Brazil. This article addresses the climatic risk of drought, associating climatic seasonality, human actions and environmental vulnerability to erosion and silting of the Teixeira Mountain Range springs, with the example of the historic case of Acude (weir) de Pocos, in Teixeira Municipality, Paraiba State. This research work is based on assumptions related to semi-arid morphodynamics, observing factors peculiar to the Teixeira Mountain Range, such as irregular precipitation, climatic regime, steep relief, areas with degraded vegetation, soils prone to erosion and the effect of runoff on the slopes. From the analysis it is verified that both the climatic and the human factors are causes of environmental risk for the region, considering the alternation of dry and torrential rains, the expanse of rural areas and the mismanagement of natural resources.

Gully Erosion and Land Degradation in Brazil: A Case Study from São Luís Municipality, Maranhão State

Soil erosion and land degradation are global problems and pose major problems in Brazil, which is characterized by a great diversity of soil types. This chapter discusses gully erosion and land degradation in Brazil, outlining a case study from Sao Luis City, Maranhao State. This diversity is related to a wide variety of landforms, climates, parent materials, vegetation cover and biota and is influenced by land use and management. Therefore, a brief description of different types of land degradation, mainly gully erosion and mass movements, is presented, and illustrative photographs are presented. These hazards affect both urban and rural areas within the extensive national territory (8,547,403 km2). Consequently, these problems have serious environmental impacts and pose socio-economic challenges.