High Erosion Potential Research Articles

AVALIAÇÃO DO POTENCIAL EROSIVO DE BEBIDAS À BASE DE SOJA

Aim: To evaluate the endogenous pH, titratable acidity (TA) and total soluble solid content (TSSC) of soy-based drinks. Methods: Twelve samples of soy-based drinks (9 juices and 3 milks) were analyzed. The endogenous pH was evaluated by potentiometry, titratable acidity was evaluated by the addition of 0.1N KOH increments to the mouthwashes, and TSSC readings were performed by Brix refractometry using the Abbe refractometer. The soy-based drinks were evaluated with 3 measurements for each sample, and the mean of the three values was recorded. Data were collected by a single examiner, recorded in study-specific charts and were analyzed statistically by Epi-Info software (mean and standard deviation). Results: All soy-based juices showed pH below the critical value of 5.5. Ades Abacaxi® presented the lowest pH (3.94), while Sollys Original® presented the highest pH (7.15). Regarding the titratable acidity, the lowest mean (0.04) to Ades Original® while Sollys Uva® showed the highest mean (0.33). The lowest TSSC (8.0) was to Ades Original®, while the highest TSSC (15.0) to Mais Vita Uva®. Conclusion: The industrialized soy-based juices evaluated in this study have a high erosive potential and may be potentially erosive to the dental tissues. DESCRIPTORS: Soybeans / adverse effects. Tooth erosion. pH

Cost effectiveness of conservation practices in controlling water erosion in Iowa

Iowa has severe water-induced soil erosion and associated water quality concerns because of intense agricultural activities. The objective of this study was to determine the effectiveness and economic benefits of selected conservation practices in sediment reduction by water erosion in major soil areas of Iowa. One farm was selected to represent the typical soil and slope gradient in each of the eight Major Land Resource Areas (MLRAs) in Iowa. Three tillage systems [no-tillage (NT), strip-tillage (ST), and chiselplow tillage (CP)] and three conservation structures [grassed waterways (GS), grass filter strips (FS), and terrace systems (TS)] were investigated under a corn–soybean rotation using the Water Erosion Prediction Project (WEPP) model. Corn yields of some areas were statistically lower under NT than under CP while soybeans showed little response to tillage operations. Estimated annual sediment yield with the chisel plow system ranged between 0.7 and 56.9 T ha 1 . The WEPP simulations showed that NT and ST systems were very effective in reducing soil erosion and sediment yield by approximately 90% in highly erodible lands compared to the CP system. The combination of conservation tillage with soil erosion control structures further mitigated soil loss and was more effective in areas with high water erosion potential than in the flat areas. The costs and benefits analysis indicated that the simulated conservation practices could increase the net benefit by up to $300 ha 1 compared to the CP system after the cost of eroded soil was taken into account. The findings suggest that NT and conservation structures have greater environmental and economic benefits in areas with high water erosion potential. The use of no-till in flat areas such as central Iowa may not be economically favorable because of the limited benefit in reducing soil water erosion. Overall, the study findings suggest that structural conservation practices coupled with tillage systems effectiveness were area-specific based on the soil and landscape in each area.

Modelagem espaço-temporal da erosão e potencial contaminação de Arsênio e Chumbo na bacia hidrográfica do rio Ribeira de Iguape (SP)

The simulation of a natural environment through computational techniques is a promising research theme that can append advantages for planning and decisions on environmental issues. Hydric erosion is triggered by the impact of rain drops on the soil surface. If rain-induced erosion is high, soil undergoes through hydraulic shearing and the yielded sediments are consequently transported. In the search for a better understanding of space-time dimensions of such natural phenomena, this work aimed to characterize the potential erosion of a selected area located in the Ribeira de Iguape River Hydrographic Basin. This was achieved using the Universal Soil Loss Equation (USLE) through Geotechnologies and computational routines. The period considered in the analysis spans between 1990 and 1999, within which areas with spatial coincidence of high erosive potential and high Pb and As content in soil (associated to a pre-existing, natural As anomaly) were compared. This multitemporal application showed the evolutionary trend of the erosive processes in the region, effectively those associated to the As and Pb anomalies. Areas with soil losses above 200 t/ha.year were identified, which ought to be considered in the process of land degradation and source of toxic elements under dispersion in the environment.

Reduction of erosion rate by particle size distribution ( PSD) modification of hematite as weighting agent for oil based drilling fluids

Natural hematite (Fe 2O 3) and barite (Ba 2SO 4) are usually employed as weighting agents for oil based drilling fluids in several venezuelan fields. Hematite has shown some physico-chemical advantages with respect to barite: a greater specific gravity and solubility in acid media and lower attrition rate. However, the most challenging issue related to hematite field applications has been to reduce its high erosive potential. Effects of particle size distribution ( PSD) have been evaluated with four different samples of hematite (48, 38, 30 and 18 μm based on the statistical parameter D ( v,0.9) ) respect to commercial barite. These samples were used to prepare fluids with a density of 1977 kg/m 3. An erosion test loop was used to expose different samples of AISI 1020 flat steel to the erosive action of jet fluid. Wear of metallic samples was measured by weight lost and wear mechanisms were identified by laser profilometry, SEM and EDS. The investigation showed that the erosion rate ( E) produced by hematite decreases potentially with size grain reduction ( D ( v,0.9) ) and depends on the morphology and angularity of the particle in comparison with barite. Laboratory results were validated on field tests with drilling fluids formulated with hematite of different PSD.

Control with anionic polyacrylamide of runoff and erosion induced by irrigation on Alentejo soils: surface and sprinkler irrigation (center pivot)

Most of the Mediterranean soils in Southern Portugal, now being converted to irrigation, were under rain-fed agriculture, in areas of sensitive soils, eroded or with high potential for erosion. The particular characteristic of these soils is its rapidly permeable A-horizon overlaying a B-horizon of very low permeability. Such fact leads to low infiltration of the applied irrigation water and, consequently high limitations to irrigation. Therefore for these soils to be under irrigation it is important to adopt soil and water conservation practices and correctly manage the irrigation systems, hoping that these practices will favour agriculture yields and preserve the environment by reducing runoff, preventing soil loss and enhancing the infiltration of applied water. One of the strategies that can be used to achieve such goals and also help to improve the soil physical properties is the use of soil conditioners, particularly the anionic polyacrylamide (PAM). Encouraging results have been obtained in the irrigated soils of Southern Portugal with their use being able to stabilize soil surface structure and curb irrigation-induced erosion in surface irrigation as well as in sprinkler irrigated fields. Since 1997, studies of anionic polyacrylamide (PAM) application have been conducted on field experiments, under surface irrigation and on contour and slopping furrows, and also with pressurized irrigation (center pivot and sprinkler simulators), as well as in more controlled laboratory studies, to test the PAM usefulness in controlling erosion and enhancing infiltration of irrigated soils. Several methodologies of applying PAM have been tested (direct application to the soil surface, in water suspension and later applied to furrows and pressurized systems through the irrigation water, and in multiple and/or single applications) as well as several application rates and timing. The results have been conclusive and in most of the studied soils PAM application has been positive in reducing runoff and sediment loss, enhancing also infiltration rates. The paper summarizes these studies, presents the state of the art, the methodologies used and the main results and conclusions.

Modelagem espaço-temporal da erosão e potencial contaminação de Arsênio

The simulation of a natural environment through computational techniques is a promising research theme that can append advantages for planning and decisions on environmental issues. Hydric erosion is triggered by the impact of rain drops on the soil surface. If rain-induced erosion is high, soil undergoes through hydraulic shearing and the yielded sediments are consequently transported. In the search for a better understanding of space-time dimensions of such natural phenomena, this work aimed to characterize the potential erosion of a selected area located in the Ribeira de Iguape River Hydrographic Basin. This was achieved using the Universal Soil Loss Equation (USLE) through Geotechnologies and computational routines. The period considered in the analysis spans between 1990 and 1999, within which areas with spatial coincidence of high erosive potential and high Pb and As content in soil (associated to a pre-existing, natural As anomaly) were compared. This multitemporal application showed the evolutionary trend of the erosive processes in the region, effectively those associated to the As and Pb anomalies. Areas with soil losses above 200 t/ha.year were identified, which ought to be considered in the process of land degradation and source of toxic elements under dispersion in the environment.

An assessment of the economic and environmental potential of biomass production in an agricultural region

The establishment of deep-rooted perennial species and their processing for biomass-based products such as renewable energy can have benefits for both local and global scale environmental objectives. In this study, we assess the potential economic viability of biomass production in the South Australian River Murray Corridor and quantify the resultant benefits for local and global scale environmental objectives. We model the spatial distribution of economically viable biomass production in a Geographic Information System and quantify the model sensitivity and uncertainty using Monte Carlo analysis. The total potentially viable area for biomass production under the Most Likely Scenario is 360,728 ha (57.7% of the dryland agricultural area), producing over 3 million tonnes of green biomass per annum, with a total Net Present Value over 100 years of A$ 88 million. The salinity in the River Murray could be reduced by 2.65 EC (μS/cm) over a 100-year timeframe, and over 96,000 ha of land with high wind erosion potential could be stabilised over a much shorter period. With sufficient generating capacity, our Most Likely Scenario suggests that economically viable biomass production could reduce carbon emissions by over 1.7 million tonnes per annum through the production of renewable energy and a reduced reliance on coal-based electricity generation. Our analyses suggest that biomass production is a potentially viable alternative agricultural system that can have substantial local scale environmental benefits with complimentary global scale benefits for climate change mitigation.

Bodengesellschaften von geomorphen Einheiten unter Berücksichtigung des Gefügestils im Stormarner Jungmoränengebiet (Brandenburger Stadium) in Nordwestdeutschland

AbstractAls Ergebnis einer intensiven Boden‐ und Substratinventur wurde von einem Ausschnitt einer älteren Jungmoränenlandschaft Schleswig‐Holsteins (Stormarner Jungmoränengebiet, Brandenburger Stadium) die Bodenvergesellschaftung verschiedener geomorpher Einheiten unter Berücksichtigung ihrer Gefügestile (Hang‐, Platten‐, Senkengefüge) analysiert und die Konsequenzen für die Boden‐ und Bodengesellschaftsklassifikation diskutiert. Mittels morphometrischer Analyse des Reliefs wurden fünf geomorphe Einheiten ausgegrenzt: Grundmoränenplatte mit Söllen (I), Glazilimnisches Becken mit Moränenrand (II), Stauchendmoräne (III), Moränen‐Steilhänge an einem Tunneltalrand (IV) und Stauchendmoränen‐Tal mit Steilhängen (V).Im Untersuchungsgebiet mit intensiver ackerbaulicher Nutzung ist die regelhafte Abfolge von Erosions‐ und Akkumulationsböden aufgrund einseitig gerichteter Kopplungsprozesse (Hanggefüge) typisch. In Abhängigkeit vom Erosionsgrad dominiert die erodierte Parabraunerde bzw. die Rumpf‐Parabraunerde/Kolluvisol‐Bodengesellschaft. Wir empfehlen, die als flächenhaftes Phänomen auftretende Parabraunerde mit anstehendem Bt‐Horizont als Rumpf‐Parabraunerde bereits auf Niveau des Bodensubtyps in der deutschen Bodenklassifikation zu berücksichtigen. Als zusätzliche Endglieder der (Hang‐)Bodengesellschaften treten in Tiefenbereichen Kalkgleye, (sedimentdurchsetzte) Niedermoore und subhydrische Böden auf. Innerhalb der Grundmoränenplatte hat durch (historische) Bodenerosion, belegt durch den hohen Flächenanteil der Kolluvisole von 20 %, ein Reliefausgleich stattgefunden, so dass ein Plattengefüge ohne wesentliche laterale Stofftransporte vorliegt. Die Steilhänge des Tunnel‐ und Stauchendmoränen‐Tals weisen neben Rumpf‐Parabraunerden stellenweise bereits Pararendzinen auf, was auf ein hohes Erosionspotential (Erosionsrate geomorphe Einheit IV: 13 t ha–1 a–1) hinweist. In den von Bächen durchflossenen Tiefenbereichen ist es seit dem Mittelalter zu einer zusätzlichen Vermoorung durch Mühlenstaue gekommen.

The influence of riparian vegetation on near‐bank turbulence: a flume experiment

AbstractMeasurements from a fixed‐bed, Froude‐scaled hydraulic model of a stream in northeastern Vermont demonstrate the importance of forested riparian vegetation effects on near‐bank turbulence during overbank flows. Sections of the prototype stream, a tributary to Sleepers River, have increased in channel width within the last 40 years in response to passive reforestation of its riparian zone. Previous research found that reaches of small streams with forested riparian zones are commonly wider than adjacent reaches with non‐forested, or grassy, vegetation; however, driving mechanisms for this morphologic difference are not fully explained. Flume experiments were performed with a 1:5 scale, simplified model of half a channel and its floodplain, mimicking the typical non‐forested channel size. Two types of riparian vegetation were placed on the constructed floodplain: non‐forested, with synthetic grass carpeting; and forested, where rigid, randomly distributed, wooden dowels were added. Three‐dimensional velocities were measured with an acoustic Doppler velocimeter at 41 locations within the channel and floodplain at near‐bed and 0·6‐depth elevations. Observations of velocity components and calculations of turbulent kinetic energy (TKE), Reynolds shear stress and boundary shear stress showed significant differences between forested and non‐forested runs. Generally, forested runs exhibited a narrow band of high turbulence between the floodplain and main channel, where TKE was roughly two times greater than TKE in non‐forested runs. Compared to non‐forested runs, the hydraulic characteristics of forested runs appear to create an environment with higher erosion potential. Given that sediment entrainment and transport can be amplified in flows with high turbulence intensity and given that mature forested stream reaches are wider than comparable non‐forested reaches, our results demonstrated a possible driving mechanism for channel widening during overbank flow events in stream reaches with recently reforested riparian zones. Copyright © 2007 John Wiley & Sons, Ltd.

Indicator of risk of water contamination by phosphorus: Temporal trends for the Province of Quebec from 1981 to 2001

An indicator of risk of water contamination by phosphorus (IROWC-P) was developed to estimate the risk of phosphorus (P) contamination in water by agriculture, and to evaluate how this risk changes over time based on the census data obtained every 5 yr. For the province of Quebec, IROWC-P is calculated with census data from 1981, 1986, 1991, 1996 and 2001. In 2001, 85% of the Soil Landscapes of Canada (SLC) agricultural polygons of Quebec were in the low and moderate risk classes and the remaining 15% in the high risk class. Although agricultural production statistics show marked changes from 1981 to 2001 in livestock herd composition, area under cultivation, agricultural land use and use of inorganic phosphorus fertilizer and animal manure, no trend was observed in the estimated risk over the same period. Increased risk of P transport from agricultural fields to water is expected when agricultural soils are rich in P or have excess P relative to crop needs and have a high potential for soil erosion and surface runoff. Key words: Risk indicator, water contamination, phosphorus, soil landscapes of Canada, agriculture

(52) Evaluation of California Native Grasses for Revegetation Sod

The California Department of Transportation (Caltrans) has used hydroseeding, imprinting, and drill seeding methods to revegetate highway construction sites, with varying degrees of success. Ecological concerns, particularly in areas with high erosion potential, have led Caltrans to search for more-reliable plant establishment methods. One possibility is native sod, which should reduce erosion potential, and, the species would also be better suited to local environments, require less maintenance, and pose no invasive threat to adjacent ecosystems. In addition, the use of native sod may also reduce or prevent weed establishment. Our project aims to evaluate different native grass species mixes to determine the best species combinations for sod. We selected 21 species of native grasses in order to determine their suitability for sod production in six Californian ecoregions. Grasses were grown in six growth chambers that mimic the climate of the six ecoregions. Mixtures of varying species included either one rhizomatous species with three bunch grasses, one rhizomatous species and five bunch grasses, two rhizomatous species with three bunch grasses, or two rhizomatous species with five bunch grasses for each ecoregion. The mixtures were grown and tested for yield, species composition, and percentage of cover over time. At the end of the 6-month production time, a final harvest evaluated root depth and biomass as well as sod strength. Rhizomatous grasses, if planted with Bromus sp., were quickly overwhelmed. At the first harvest ground coverage was between 10% and 15% for all species mixes. Ground coverage increased over the production cycle, but maximum ground coverage remained less than 80% overall.

Biogeochemistry of an afrotropical montane rain forest on Mt. Kilimanjaro, Tanzania

In contrast to their well-studied counterparts in the Neotropics and in Asia, East African montane rain forests are surrounded by semi-arid savanna plains. These plains have a high erosion potential for salt crusts accumulated at the soil surface. Hence it may be hypothesized that East African montane forest ecosystems experience strongly enhanced nutrient inputs via dry deposition, which alters their overall biogeochemistry. The aim of our study was to test this hypothesis by investigating K, Mg, Ca, Na and N-forms in rainfall, throughfall, fine litter, litter percolate and soil solution of a montane rain forest at Mt. Kilimanjaro. Four forest plots situated at elevations between 2250 and 2350 m asl on the south-western slopes of Mt. Kilimanjaro were studied for 2 y. In contradiction to our hypothesis, inputs of K, Mg, Ca and Na via rainfall (7.5, 0.9, 2.3 and 6.2kg ha−1y−1) and throughfall (35, 2.0, 3.5 and 11kg ha−1−1) were low on Mt. Kilimanjaro. Fluxes of NH4-N and NO3-N were within the range observed at other montane rain forests, with NO3-N being the only nutrient partly absorbed in the forest canopies (2.9kg ha−1y−1 in rainfall, 0.9kg ha−1y−1 in throughfall). The highest overall nutrient concentrations in water samples occurred in litter percolate (1.4mg l−1 K, 0.3mg l−1 Mg, 0.8mg l−1 Ca, 0.3mg l−1 NH4-N, 0.9mg l−1 NO3-N), with values still being low compared to other sites. Nutrient concentrations in seepage water strongly declined with increasing soil depth. Thus, both inputs and losses of base cations from the forest by water pathways are assumed to be low. N or P limitation of growth is not expected since high fluxes of N and P in fine litter (119 and 5.9kg ha−1y−1 for N and P respectively) indicate low within-stand efficiency.

Establishment of a Vegetation Cover on Tundra Kimberlite Mine Tailings: 2. A Field Study

Abstract High erosion potential of dewatered kimberlite mine tailings after diamond extraction has prompted research at the Ekati Diamond Mine in the Canadian subarctic heath tundra ecosystem. Greenhouse and field studies aimed at establishing a permanent vegetation cover on these dewatered tailings began in spring 2000. Coarse texture, no organic component, lack of available macronutrients, and a serpentine chemistry are the principal limitations of kimberlite tailings to plant colonization. Structure‐improving (peat moss, lake sediment, and sewage sludge) and nutrient‐providing (fertilizer, rock phosphate, calcium carbonate, and gypsum) amendments were tested to ameliorate these conditions, facilitating the establishment of a permanent vegetation cover, which stabilizes surface materials and promotes natural colonization by the surrounding tundra vegetation. Seven native grass species (Arctagrostis latifolia, Calamagrostis canadensis, Poa glauca, Poa alpina, Deschampsia beringensis, Deschampsia caespitosa, and Festuca rubra) were used to measure amendment success. With the addition of structure‐improving and nutrient‐providing amendments, plant growth on these kimberlite tailings under field conditions was significantly improved over unamended tailings material. Tailings properties, including cation exchange capacity, organic carbon, and macronutrient availability, were also improved with amendment addition.

Establishment of a Vegetation Cover on Tundra Kimberlite Mine Tailings: 1. A Greenhouse Study

Abstract High erosion potential of dewatered kimberlite mine tailings after diamond extraction has prompted research at the Ekati Diamond Mine in the Canadian subarctic heath tundra ecosystem. Coarse texture, no organic component, lack of available macronutrients, and a serpentine chemistry are the principal limitations of these kimberlite tailings to plant colonization. Structure‐improving (peat moss, lake sediment, sewage sludge, Agri‐Boost, and composted papermill sludge) and nutrient‐providing (fertilizer, calcium carbonate, gypsum, and rock phosphate) amendments were tested in the greenhouse to ameliorate these limitations, thereby facilitating the field establishment of a permanent vegetation cover, which would stabilize the surface materials and promote natural colonization by the surrounding tundra vegetation. Seven native grass species (Arctagrostis latifolia, Calamagrostis canadensis, Poa glauca, Poa alpina, Deschampsia beringensis, Deschampsia caespitosa, and Festuca rubra) were used to measure amendment success. With the addition of structure‐improving and nutrient‐providing amendments, plant growth on kimberlite tailings was significantly enhanced. Tailings properties, including cation exchange capacity, percentage of organic carbon, and macronutrient availability, were also improved by amendment addition.

Comparison of EPM and PSIAC models in GIS for erosion and sediment yield assessment in a semi-arid environment: Afzar Catchment, Fars Province, Iran

This research was conducted in the Afzar sub-catchment area of Ghara-Aghaj River, a semi-arid region in SW Iran, using a Geographic Information System (GIS) to compare the Erosion Potential Method (EPM) and Pacific Southwest Interagency Committee (PSIAC) models in erosion-potential mapping and sediment-yield assessment. Data layers used in this study were generated from topographic maps, Landsat ETM + imagery, aerial photographs, field surveys and barometric and pluviometric data; factor-class evaluation was used to determine EPM and PSIAC parameters. A raster-based Geographic Information System (GIS) was applied to generate the erosion-severity and sediment-yield maps. Output data was verified by field observation and by comparison with a Global Assessment of Soil Degradation (GLASOD) map. Comparison of the EPM and PSIAC results with field observations and the GLASOD map showed that although the results of the two erosion potential maps correspond in most areas, the results of EPM model were not as reliable as the PSIAC in identifying areas with very high erosion potential. It is suggested the EPM model should be used for rapid mapping of erosion-potential in regions with limited data layers, but field verifications indicated that PSIAC results were the more reliable.

Sources of sediment to the Great Barrier Reef World Heritage Area

To reduce sediment exports discharging to the Great Barrier Reef (GBR), it is essential to identify the sources of exported sediment. We used modelling of spatial sediment budgets (the SedNet model) to identify sources and deposition of sediment as it is transported through river networks. Catchments with high levels of land clearing, cattle grazing and cropping show the largest increases in sediment export compared with natural conditions. Hillslope erosion supplies 63% of sediment to the rivers. Gully erosion and riverbank erosion are lower sources of sediment at the GBR catchment scale, but they are important in some catchments. Overall, 70% of sediment exported from rivers comes from just 20% of the total catchment area, showing that much of the problem can be addressed in a relatively small area. This is a much more manageable problem than trying to reduce erosion across the entire GBR catchment. Areas of high contribution are all relatively close to the coast because of the high erosion and high sediment delivery potential.

Is moral hazard good for the environment? Revenue insurance and chemical input use

Using farm level data we evaluate the input use and environmental effects of revenue insurance. A priori, the moral hazard effect on input use is indeterminate. This paper empirically assesses the input use impact of the increasingly popular, and federally subsidized, risk management instrument of revenue insurance and the extent to which its effects on input use may differ from those of the older yield based instruments. We conclude that among winter wheat farmers, those who purchase revenue insurance tend to spend less on fertilizers but do not appreciably alter pesticide expenditures. Thus, any improved environmental outcomes due to crop insurance are likely due to reduced fertilizer not pesticide use. When the environmental indicators included indicated a potential environmental fragility (i.e. high erosion, pesticide leaching or pesticide runoff potential), the input use equation suggested that fertilizer expenditures decreased. Revenue insurance undoubtedly further reduces fertilizer applications on these fields as well, but the marginal environmental benefit of revenue insurance is lessened because the reduction, where it matters most, accrues on land on which fertilizer use has already been curtailed to some degree.

Quantifying the erosion processes and land-uses which dominate fine sediment supply to Moreton Bay, Southeast Queensland, Australia

In this paper, the contributions from the three major erosion sources in the catchments of Moreton Bay are quantified, specifically for the <10 μm sediment size class. The erosion sources are classified as (i) sheet erosion from cultivated land, (ii) sheet erosion from uncultivated land, and (iii) subsoil erosion from gullies and channels. The catchments were the Brisbane and Logan rivers as well as the coastal catchments. A GIS based analysis of erosion risk was used to define areas of high erosion potential in each of the erosion source types. Radionuclide concentrations of 137Cs and 226Ra were measured on the <10 μm fraction of eroding soils from these areas and then compared to concentrations on the same size fraction on deposited sediments within the rivers. A mixing model was then used to calculate the contributions from the different sources to the sediments. The contributions in the Brisbane and Logan catchments were found to be subsoil erosion (∼66±10%); sheet erosion from cultivated lands 33±10% and sheet erosion of uncultivated land 1±10%. Surface and subsoil erosion contributions from the coastal catchments were found to be variable.

Application of remote sensing and GIS to locate priority intervention areas after wildland fires in Mediterranean systems: a case study from south-eastern Spain

Wildland fires are one of the major causes of ecosystem degradation, especially in semiarid climates, where the erosion hazard is high. The identification of potential erosion zones is typically difficult as it requires expensive field and laboratory work. This paper proposes a methodology based on remote sensing and GIS techniques, which permits speedy identification of erosional areas in a semi-automatic way, tested in a large burn scar in south-eastern Spain. Inputs were slope, aspect, and fire severity. In order to obtain the latter a new method has been proposed, based on the difference in NDVI between two images (acquired before and after the fire event). Combining these maps in a GIS, a Forest Intervention Priority map (FIP) is produced, which identifies areas of high erosion potential. Field work was conducted to assess the method. Results indicate that the applied methodology reliably predicted the extent of very severe fire and, further, was generally useful for identifying sites of significant erosion. Additional work is required to refine: (1) remotely sensed fire severity thresholds, particularly for other Mediterranean forest systems and substrate conditions; and (2) associated mapping tools for informing post-fire management applications.

Simulação de cenários alternativos de uso da terra em uma microbacia utilizando técnicas de modelagem e geoprocessamento

O modelo SWAT (Soil and Water Assessment Tool) foi aplicado na simulação de cenários alternativos de uso da terra na microbacia hidrográfica do Ribeirão dos Marins, em Piracicaba (SP), no biênio 1999/2000. Dois cenários foram simulados. No primeiro, o uso atual foi mantido numa faixa de mata ciliar de 30 m em toda a extensão dos cursos d'água e de 50 m ao redor das nascentes, de acordo com o Código Florestal. No segundo cenário, como as pastagens ocupavam 30,9 % da área da microbacia, nas encostas mais íngremes, com alto potencial erosivo, as áreas de pastagem foram substituídas por vegetação florestal. As simulações dos dois cenários foram comparadas com as condições do cenário atual em termos de produção de sedimentos. Os cenários geraram diferentes padrões espaciais da produção de sedimentos. Uma redução de 94,0 % na produção de sedimentos foi obtida com a substituição da pastagem por vegetação nativa (cenário 2). No cenário 1, a redução foi de 10,8 %. Esses resultados evidenciam a necessidade de tratar a paisagem em bacias hidrográficas de forma global, identificando as "áreas sensíveis ambientalmente", onde são necessárias práticas de controle dos processos erosivos e não somente práticas de proteção dispensada aos cursos d'água por meio da mata ciliar.