Relationship between forest clearing and biophysical factors in tropical environments: Implications for the design of a forest change monitoring approach

The relationship between forest clearing, biophysical factors (e.g, ecological zones, slope gradient, soils), and transportation network in Costa Rica was analyzed. The location of forested areas at four reference datas (1940, 1950, 1961, and 1977) as derived from aerial photography and LANDSAT MSS data was digitilized and entered into a geographically-referenced data base. Ecological zones as protrayed by the Holdridge Life Zone Ecology System, and the location of roads and railways were also digitized from maps of the entire country as input to the data base. Information on slope gradient and soils was digitized from maps of a 21,000 square kilometer area. The total area of forest cleared over four decades are related to biophysical factors was analyzed within the data base and deforestation rates and trends were tabulated. The relatiohship between forest clearing and ecological zone and the influence of topography, sils, and transportation network are presented and discussed

Effect of hydraulic parameters on sediment transport capacity in overland flow over erodible beds

Sediment transport is an important component of the soil erosion process, which depends on several hydraulic parameters like unit discharge, mean flow velocity, and slope gradient. In most of the previous studies, the impact of these hydraulic parameters on transport capacity was studied for non-erodible bed conditions. Hence, this study aimed to examine the influence of unit discharge, mean flow velocity and slope gradient on sediment transport capacity for erodible beds and also to investigate the relationship between transport capacity and composite force predictors, i.e. shear stress, stream power, unit stream power and effective stream power. In order to accomplish the objectives, experiments were carried out in a 3.0 m long and 0.5 m wide flume using four well sorted sands (0.230, 0.536, 0.719, 1.022 mm). Unit discharges ranging from 0.07 to 2.07 × 10<sup>−3</sup> m<sup>2</sup> s<sup>−1</sup> were simulated inside the flume at four slopes (5.2, 8.7, 13.2 and 17.6%) to analyze their impact on sediment transport rate. The sediment transport rate measured at the bottom end of the flume by taking water and sediment samples was considered equal to sediment transport capacity, because the selected flume length of 3.0 m was found sufficient to reach the transport capacity. The experimental result reveals that the slope gradient has a stronger impact on transport capacity than unit discharge and mean flow velocity due to the fact that the tangential component of gravity force increases with slope gradient. Our results show that unit stream power is an optimal composite force predictor for estimating transport capacity. Stream power and effective stream power can also be successfully related to the transport capacity, however the relations are strongly dependent on grain size. Shear stress showed poor performance, because part of shear stress is dissipated by bed irregularities, bed form evolution and sediment detachment. An empirical transport capacity equation was derived, which illustrates that transport capacity can be predicted from median grain size, total discharge and slope gradient

Weathering Characteristics of Sloping Fields in the Three Gorges Reservoir Area, China

For the purpose of understanding the weathering characteristics of surface layers in purple mudstone sloping fields of the Three Gorges Reservoir area of China, oxide content of major elements, composition of clay minerals, magnetic susceptibility, and difference in weathering characteristics of surface layers under different slope gradients were determined. The results showed that the oxide content of Si, Al, and Fe ranged from 60% to 75% and the weathering coefficient with depth showed no trend along the slope gradient. Also, for gentle (10° and 15°) and intermediate (25° and 40°) slopes the clay relative diffraction peak for kaolinite at the surface between 0–10 cm and 10–20 cm declined with an increase in slope gradient, while the relative diffraction peak for kaolinite in weathered layers on steep slopes (50° and 60°) disappeared altogether. Magnetic susceptibility decreased with increasing depth and, for a given depth layer, decreased with an increase in slope gradient. Analysis of the oxide content, weathering coefficients, clay minerals, and magnetic susceptibility showed that in the Three Gorges Reservoir area, the pedogenesis of the weathering layer in purple mudstone sloping fields was weak with weaker soil formation going from gentle slope to steep slope

Mass movement susceptibility mapping using satellite optical imagery compared with InSAR monitoring: Zigui County, Three Gorges region, China

Mass movements on steep slopes are a major hazard to communities and infrastructure in the Three Gorges region, China. Developing susceptibility maps of mass movements is therefore very important in both current and future land use planning. This study employed satellite optical imagery and an ASTER GDEM (15 m) to derive various parameters (namely geology; slope gradient; proximity to drainage networks and proximity to lineaments) in order to create a GIS-based map of mass movement susceptibility. This map was then evaluated using highly accurate deformation signals processed using the Persistent Scatterer (PS) InSAR technique. Areas of high susceptibility correspond well to points of high subsidence, which provides a strong support of our susceptibility map

Response behavior of antibiotic resistance genes and human pathogens to slope gradient and position: an environmental risk analysis in sloping cultivated land

Soils, especially in farmlands, are key media for the transmission of antibiotic resistance genes (ARGs) and their hosts from the environment to humans. Sloping farmland is an important agricultural resource, but there lack of studies on the fate and risk of ARGs in sloping land. Also, the behavior and drivers of ARGs in response to slope gradient and position are unclear. Here, metagenomics was used to investigate the profiles of ARGs, mobile genetic elements, and microbial communities in soils from lands of five slope gradients (5°, 10°, 15°, 20°, and 25°) with two slope positions (uphill and downhill). Results showed that while the abundance (except 15°) and diversity (except 20°) of ARGs increased as the slope gradient increased, the diversity of ARGs with health risk, especially the high-risk ones, decreased. For slope positions, abundant and diverse ARGs were more likely to accumulate at downhill. Furthermore, 52 bacterial genera and 12 human pathogenic bacteria (HPB) species were identified as the potential hosts for ARGs with high risk, and abundant HPB species were also detected in the soils with low gradients at downhill. Moreover, the structural equation model analysis revealed that the slope gradient and the slope position have both direct and indirect effects on the abundance of ARGs. Further correlation analysis revealed that the slope gradient has a positive effect (p < 0.05) on nitrite nitrogen in the soils. Also, the slope position has a negative effect (p < 0.05) on total phosphorus and microbial nitrogen, while positively affected (p < 0.05) on particulate nitrogen and microbial carbon, which were the key factors driving the behavior of ARGs. Overall, this study provided comprehensive information on ARGs with health risks and their potential pathogenic hosts in sloping farmland. It can be important for controlling antibiotic resistance transmission and be consistent with the One Health framework

The effects of degree of erosion and slope characteristics on soybean yields on Memphis, Grenada, Lexington, and Loring soils

Soil erosion is a very serious problem in upland soybean fields in West Tennessee. This study was undertaken for the purpose of determining the effects of degree of erosion and slope characteristics on soybean yields on four West Tennessee soil series - Memphis, Grenada, Lexington, and Loring. In 1976 and 1977, yield samples were taken from areas of various soil mapping units of each soil series in soybean fields on West Tennessee farms and experiment stations. Soil mapping units sampled varied in slope from 1% to 12%, and in degree of erosion from slight to severe. The yield data collected were analyzed by use of a least squares analysis of variance. Least squares mean yields were obtained for each soil mapping unit sampled within each soil series. Erosion and slope effects on yields were determined by comparisons of pairs of least squares mean soil mapping unit yields. Results in 1976 showed no effect of degree of erosion on yield on any soil series. A trend toward reduced yields as slope gradient increased was evident on all soils. Results in 1977 showed significant yield reduc-tions on all soils due to the combined effects of degree of erosion and slope gradient. On Grenada soils, the reduction in yields was due largely to degree of erosion, while on the other soils it was equally due to slope gradient and erosion. A combined analysis of both years\u27 data showed no differences in yield due to degree of erosion and slope gradient on Memphis soils. On the other three soils, yields were reduced significantly by a combination of severe erosion and increased slope gradient. Neither increased slope gradient alone, nor severe erosion alone caused a significant yield re-duction. Yields on Lexington and Memphis soils did not differ significantly from year to year, but yields on Grenada and Loring soils declined signifi-cantly from 1976 to 1977. The differences in the effects of degree of erosion and slope gra-dient between 1976 and 1977 were probably a result of lower 1977 growing season rainfall. The drier conditions in 1977 resulted in lower yields on steeper, more eroded sites due to their lower moisture supplying capac-ity. The greater variability in yields on the Grenada and Loring soils was due to the fragipans in their subsoils, which restricted rooting and led to more moisture stress in a drier year. The overall lack of reduction in yield on Memphis soils was due to their deep, silty subsoils, which were able to supply more water to the soybeans than the less favorable subsoils of the other three soils. Shape of slope, either convex, concave, or smooth, had no signifi-cant effect on yields on any soil in either year when included in a model with field and soil mapping unit. The inclusion of linear and quadratic effects of pH and available potassium in the model had a significant effect on yields on Memphis soils in 1977. Adjustment of soil mapping unit yields for pH and available potassium eliminated significant dif-ferences between yields. The inclusion of linear and quadratic effects of pH in the model had a significant effect on yields on Grenada soils in 1977. Adjustment of soil mapping unit yields for pH increased the differences caused by slope gradient and degree of erosion

Short-term impact of Coppice management on soil in a Quercus ilex l. stand of Sardinia

The short-term impact of coppice-with-standards management on soil in a Mediterranean holm oak forest was assessed to contribute to address appropriate recommendations to minimize possible negative effects of the silvicultural practices. For this purpose, soil surface features and topsoil properties were investigated in two representative areas located in a public forest in southwest Sardinia (Italy) and coppiced in the periods November 2012-March 2013 and November 2011-March 2012, respectively. Regardless of differences in soils and slope gradient, the same management, in terms of final density of trees standing after the clear-cut and accumulation of brushwood in strips along the maximum slope gradient, was applied in both areas. Field observations and laboratory data highlighted the disturbances caused to the soil by the silvicultural practices in the stands when compared with the undisturbed stands. These disturbances involved the almost complete removal of organic horizons, with consequent negative impact on organic carbon content, and the activation of erosion processes, mostly related to rainsplash erosion. Although soil mobilization locally largely exceeded the tolerable erosion rates, no extreme rainfall events occurred after the coppicing to produce critical situations at the catchment level. The adjustment of the final density of trees standing after the clear-cut in relation to soil properties, slope gradient and the possibility of extreme rainfall events, a different brushwood management and the restriction to the passage of wild animals would have strongly reduced the negative impacts on soils

Rainfall and earthquake-induced landslide susceptibility assessment using GIS and Artificial Neural Network

A GIS-based method for the assessment of landslide susceptibility in a selected area of Qingchuan County in China is proposed by using the back-propagation Artificial Neural Network model (ANN). Landslide inventory was derived from field investigation and aerial photo interpretation. 473 landslides occurred before the Wenchuan earthquake (which were thought as rainfall-induced landslides (RIL) in this study), and 885 earthquake-induced landslides (EIL) were recorded into the landslide inventory map. To understand the different impacts of rainfall and earthquake on landslide occurrence, we first compared the variations between landslide spatial distribution and conditioning factors. Then, we compared the weight variation of each conditioning factor derived by adjusting ANN structure and factors combination respectively. Last, the weight of each factor derived from the best prediction model was applied to the entire study area to produce landslide susceptibility maps. <br><br> Results show that slope gradient has the highest weight for landslide susceptibility mapping for both RIL and EIL. The RIL model built with four different factors (slope gradient, elevation, slope height and distance to the stream) shows the best success rate of 93%; the EIL model built with five different factors (slope gradient, elevation, slope height, distance to the stream and distance to the fault) has the best success rate of 98%. Furthermore, the EIL data was used to verify the RIL model and the success rate is 92%; the RIL data was used to verify the EIL model and the success rate is 53%

Investigation of the appropriate slope gradient for humps on railway platforms

Gaps between the train and the platform are a major safety concern for railway users, especially those who are disabled, and London Underground will introduce platform humps to solve this problem. In order to realise properly designed platform humps, it is necessary to investigate the effects of the design factors of the hump. As an initial attempt to understand the complexity of the design factors of humps, this study focused on the slope and backfall gradients. A series of experiments was conducted in the Pedestrian Accessibility Movement and Environment Laboratory (PAMELA) at University College London. In total, 45 participants with various types of disabilities were asked to walk on simulated slopes and to board or alight from the simulated train from or onto the slope. The tested slope gradients were 3.0% (1:33), 5.2% (1:19) and 6.9% (1:14) with the backfall gradients 1.5% (1:67), 2.0% (1:50) and 2.5% (1:40). It was found that the slope gradient did not largely affect performance and subjective evaluation of the participants’ longitudinal walking on slopes, but would add additional difficulty for them to board/alight from the train from/onto a slope. This suggests that train doors should not stop next to the slope. There was little evidence as to the effects of the backfall gradient. The results will be used in the development of the design guidelines of platform humps