Effects of erosion on soil quality and productivity of a field near Saskatoon

Non-Peer ReviewedSoil erosion has been identified as a major contributor to soil degradation on the Prairies. An 84 ha cultivated watershed near Saskatoon was selected to study the variability in erosion and deposition. 137Cs deposited mainly in the early 1960's was used as a tracer for soil movement. Soil erosion ranged from 35 t/ha/yr in small tributaries to the main channel, to 4 t/ha/yr or less on upper slope areas which occupied 60 % of the area. High rates of soil deposition were found in. upland depressions and in the main channel. The net soil loss from the basin was 2340 t or about 1 t/ha/yr. Seventy to 80% of the lost soil was retained ahead of a dam in the coulee leaving the field. It is estimated that the eroding areas of the field (approximately 77 ha) suffered an organic C loss of 275 t from the early 1960's to mid 1980's. Preliminary estimates indicate that about 215 t of organic C were deposited in the upland depressions and the main channel inside the field boundaries. Estimates of the organic C trapped in the coulee are in the order of 50 to 90 t. Further sampling will be needed to resolve the discrepancy between estimates of organic C lost from the field, and organic C trapped, in the coulee. Based on approximate relationships between soil depth and yield potential, it is expected that the production of about one quarter of the eroding area is adversely affected by erosion when other growing conditions are good

Trends in the Statistical Assessment of Reliability

Changes in technology have had and will continue to have a strong effect on changes in the area of statistical assessment of reliability data. These changes include higher levels of integration in electronics, improvements in measurement technology and the deployment of sensors and smart chips into more products, dramatically improved computing power and storage technology, and the development of new, powerful statistical methods for graphics, inference, and experimental design and reliability test planning. This paper traces some of the history of the development of statistical methods for reliability assessment and makes some predictions about the future

Flooding countries and destroying dams

In many applications of terrain analysis, pits or local minima are considered artifacts that must be removed before the terrain can be used. Most of the existing methods for local minima removal work only for raster terrains. In this paper we consider algorithms to remove local minima from polyhedral terrains, by modifying the heights of the vertices. To limit the changes introduced to the terrain, we try to minimize the total displacement of the vertices. Two approaches to remove local minima are analyzed: lifting vertices and lowering vertices. For the former we show that all local minima in a terrain with n vertices can be removedintheoptimalwayinO(n log n) time. For the latter we prove that the problem is NP-hard, and present an approximation algorithm with factor 2 ln k, wherek is the number of local minima in the terrain