Disturbance (geology)

About: Disturbance (geology) is a research topic. Over the lifetime, 11368 publications have been published within this topic receiving 175735 citations.

A note on the relation between temporally-increasing and spatially-increasing disturbances in hydrodynamic stability

Abstract: The frequency and amplification rates for a disturbance growing with respect to time are compared with those of a spatially-growing wave having the same wave-number. For small rates of amplification it is shown that the frequencies are equal to a high order of approximation, and that the spatial growth is related to the time growth by the group velocity.

Anthropogenic Disturbance of the Terrestrial Water Cycle

Abstract: climate, ecology, and biogeochemistry of the planet. Mounting historical evidence for the influence of greenhouse warming on recent climate, and modeling projections into the future, highlight changes to the landbased water cycle as a major global change issue (Houghton et al. 1995, Watson et al. 1996, SGCR 1999). Disturbance of the hydrologic cycle has received significant attention with respect to land–atmosphere exchanges, plant physiology, net primary production, and the cycling of major nutrients (Foley et al. 1996, Sellers et al. 1996, McGuire et al. 1997). Changes in land use are also recognized as critical factors governing the future availability of fresh water (Chase et al. 2000). Another important but seldom articulated global change issue is direct alteration of the continental water cycle for irrigation, hydroelectricity, and other human needs. Although the scope and magnitude of water engineering today are colossal in comparison with preindustrial times, most of the very same activities—irrigation, navigation enhancement, reservoir creation—can be traced back several thousand years in the Middle East and China. Stabilization of water supply has remained a fundamental preoccupation of human society and is a key security concern for most nations. Reducing flood hazard, enhancing food security, and redirecting runoff from water-rich to water-poor areas continue to provide a major challenge to our engineering infrastructure. In this article we address three issues. First, we document the nature and magnitude of direct human alteration of the terrestrial water cycle, specifically through construction of engineering works for water resource management. We focus on the redistribution of freshwater among major storage pools and the corresponding changes to continental runoff. Second, we explore some of the impacts of this disturbance on drainage basins, river systems, and land-to-ocean linkages. Finally, we review key uncertainties regarding our current understanding of human–water interactions at the global scale and make suggestions on potentially useful avenues for future research. Evidence for global-scale human impacts on the terrestrial water cycle Although an exact inventory of global water withdrawal has been difficult to assemble, the general features of anthropogenic water use are more or less known. Reviews of the recent literature (Shiklomanov 1996, Gleick 2000) show a range in estimated global water withdrawals for the year 2000 between approximately 4000 and 5000 km3/yr. Despite reductions in the annual rate of increase in withdrawals from 1970 (Shiklomanov 1996, 2000, Gleick 1998a), global water use has grown more or less exponentially with human population and economic development over the industrial era. By one account (L’vovich and White 1990), there was a 15-fold increase in aggregate

Plant life-history attributes: their relationship to disturbance response in herbaceous vegetation.

Abstract: I Species composition and disturbance state (level of soil disturbance, grazing and water addition) were recorded for 120 (30-m2) plots in temperate grassland of the New England Tablelands (Australia). Three different classificatory schemes were used, based on (a) life-form (sensu Raunkiaer); (b) dispersal unit morphology and (c) vegetative reproduction. We analysed the effects of the different disturbance types and intensities on number and proportion of species belonging to these groups. The results were used to describe the spectrum of life-histories likely to be present at sites in different states of exogenous disturbance. 2 Soil disturbed sites had proportionately more therophytes, versatile/flat rosettes and wind dispersed species. Two features are likely to lead to success in soil disturbed sites: ability to colonize open space (e.g. therophytes, wind dispersal) and capacity to capture resources effectively (e.g. flat architecture of rosettes). Non-disturbed sites had more geophytes, chamaephytes, phanerophytes, proto-hemicryptophytes and erect rosettes, with greater numbers of vegetatively reproducing species. 3 Heavily grazed sites had higher proportions of therophytes and versatile/flat rosettes and species with mobile seeds than sites with light grazing. Moderately grazed sites had increased proportions of versatile and erect rosettes and more species with adhesive seeds (mainly grasses). Lightly grazed sites had a greater diversity in terms of evenness of all life-forms, dispersal morphologies and reproductive modes. 4 Water enriched sites had fewer geophytes and phanerophytes and some chamaephytes, erect rosettes and proto-hemicryptophytes. This loss was only partially compensated by a gain in versatile and partial rosettes but richness decreased overall. Water enrichment was unrelated to dispersal unit morphology or the potential for vegetative reproduction. 5 Of the three attributes examined, life-form was most useful in characterizing community response to different disturbance types. Traits related to regeneration (seed morphology and capacity of vegetative reproduction) were relevant to soil disturbance only. Our results support the use of such classifications for monitoring the effects of disturbance.

The ecological concept of disturbance and its expression at various hierarchical levels

Abstract: Current definitions of disturbance are intuitive, narrow, and only implicitly based on system structure. This is because the concepts are based on experience at particular levels of organization or on systems whose structure is well known. The definitions are thus inadequate for the development of a general theory of ecological disturbance. A universally applicable definition would 1) identify the object disturbed; 2) distinguish between change in the object that is disturbance versus change that is not; and 3) distinguish between direct and indirect consequences of disturbance. To meet these requirements, we formally link the hierarchical organization of ecological objects and the concept of disturbance. Any persistent ecological object will have a minimal structure, or system of lower level entities that permit its persistence. Disturbance is a change in the minimal structure of an object caused by a factor external to the level of interest. Using these definitions, disturbance can be unequivocally identified and associated with various specific ecological levels of organization. Because of the dependence of the concept of disturbance on recognizing the minimal structure of ecological systems, application of the concept will advance as refined models of the hierarchical structure of ecological systems are elaborated.