Monitoring soil productive potential

Desertification involves the loss of soil productive potential, but a means of assessing and monitoring the progress of desertification on the soil has been elusive. Soil is so varied and complex that methods of assessing condition are too slow, tedious, and expensive for routine use. Moreover, differences in soil type can be confused with soil condition. This paper presents a structured method of assessing soil condition. This method is based on recognizing and classifying soil surface features and examining soil properties that reflect the status of the processes of erosion, infiltration, and nutrient cycling. Published in the form of a user manual, the method has the following three stages: (1) defining the geomorphic setting of the site, (2) recognizing patch/interpatch associations and the mode of erosion at the landscape scale, and (3) assessing soil surface condition ratings in quadrats sited within the landscape pattern patches. Stage 3 is achieved by observing each of 11 features in the field and classifying their status according to detailed fieldnotes and photographs. The method applies to a wide range of soil types and biogeographical regimes and has proven to be repeatable among observers and quickly transferred to new observers.     

Simulation of wind-driven dispersion of fire pollutants in a street canyon using FDS

Air quality in urban areas attracts great attention due to increasing pollutant emissions and their negative effects on human health and environment. Numerous studies, such as those by Mouilleau and Champassith (J Loss Prevent Proc 22(3): 316–323, 2009), Xie et al. (J Hydrodyn 21(1): 108–117, 2009), and Yassin (Environ Sci Pollut Res 20(6): 3975–3988, 2013) focus on the air pollutant dispersion with no buoyancy effect or weak buoyancy effect. A few studies, such as those by Hu et al. (J Hazard Mater 166(1): 394–406, 2009; J Hazard Mater 192(3): 940–948, 2011; J Civ Eng Manag (2013)) focus on the fire-induced dispersion of pollutants with heat buoyancy release rate in the range from 0.5 to 20 MW. However, the air pollution source might very often be concentrated and intensive, as a consequence of the hazardous materials fire. Namely, transportation of fuel through urban areas occurs regularly, because it is often impossible to find alternative supply routes. It is accompanied with the risk of fire accident occurrences. Accident prevention strategies require analysis of the worst scenarios in which fire products jeopardize the exposed population and environment. The aim of this article is to analyze the impact of wind flow on air pollution and human vulnerability to fire products in a street canyon. For simulation of the gasoline tanker truck fire as a result of a multivehicle accident, computational fluid dynamics large eddy simulation method has been used. Numerical results show that the fire products flow vertically upward, without touching the walls of the buildings in the absence of wind. However, when the wind velocity reaches the critical value, the products touch the walls of the buildings on both sides of the street canyon. The concentrations of carbon monoxide and soot decrease, whereas carbon dioxide concentration increases with the rise of height above the street canyon ground level. The longitudinal concentration of the pollutants inside the street increases with the rise of the wind velocity at the roof level of the street canyon.     

Desertification in Australia: An eye to grass roots and landscapes

Desertification in some form is estimated to have occurred over about 42% of the 5 million km² of arid and semiarid lands in Australia. The most common form of desertification is loss of perennial grasses from grasslands, savannas, and open woodlands, often with a replacement by inedible shrubs. Desertification continues to be a problem, especially during droughts when grazing pressures reduce ground cover, laying bare landscapes to wind and water erosion. But two national programs, Drought Alert and Landcare, are giving new hope in controlling land degradation. Both use a grassroots approach by promoting action through local pastoralist and farmer groups and by encouraging the use of effective techniques for rehabilitating landscapes. A strategic application of ponding banks and contour traps with an eye to the landscape has proven successful in stopping and reversing desertification processes.     

Assessing landscape structure and pattern fragmentation in semiarid ecosystems using patch-size distributions

Spatial vegetation patterns are recognized as sources of valuable information that can be used to infer the state and functionality of semiarid ecosystems, particularly in the context of both climate and land use change. Recent studies have suggested that the patch-size distribution of vegetation in drylands can be described using power-law metrics, and that these scale-free distributions deviate from power-law linearity with characteristic scale lengths under the effects of increasing aridity or human disturbance, providing an early sign of desertification. These findings have been questioned by several modeling approaches, which have identified the presence of characteristic scale lengths on the patch-size distribution of semiarid periodic landscapes. We analyze the relationship between fragmentation of vegetation patterns and their patch-size distributions in semiarid landscapes showing different degree of periodicity (i.e., banding). Our assessment is based on the study of vegetation patterns derived from remote sensing in a series of semiarid Australian Mulga shrublands subjected to different disturbance levels. We use the patch-size probability density and cumulative probability distribution functions from both nondirectional and downslope analyses of the vegetation patterns. Our results indicate that the shape of the patch-size distribution of vegetation changes with the methodology of analysis applied and specific landscape traits, breaking the universal applicability of the power-law metrics. Characteristic scale lengths are detected in (quasi) periodic banded ecosystems when the methodology of analysis accounts for critical landscape anisotropies, using downslope transects in the direction of flow paths. In addition, a common signal of fragmentation is observed: the largest vegetation patches become increasingly less abundant under the effects of disturbance. This effect also explains deviations from power-law behavior in disturbed vegetation which originally showed scale-free patterns. Overall, our results emphasize the complexity of structure assessment in dryland ecosystems, while recognizing the usefulness of the patch-size distribution of vegetation for monitoring semiarid ecosystems, especially through the cumulative probability distributions, which showed high sensitivity to fragmentation of the vegetation patterns. We suggest that preserving large vegetation patches is a critical task for the maintenance of the ecosystem structure and functionality.