Spatial and Temporal Scales

Not only are there scales in organization, but scales over space and time exist. It is crucial to note that all of the functions described in previous sections act at a variety of spatial and temporal scales (Suter and Bamthouse 1993). Although in many instances these scales appear disconnected, they are in fact intimately intertwined. Effects at the molecular level have ecosystem level effects. Conversely, impacts on a broad scale affect the very sequence of the genetic material as evolution occurs in response to the changes in toxicant concentrations or interspecific interactions. 

The overlap of spatial and temporal scales in environmental toxicology. Not only are there scales in organization but scales exist over space and time. Many molecular activities exist over short periods and volumes. Populations can exist over relatively small areas, even a few square meters for microorganisms, but thousands of square kilometers are required for many bird and mammal populations. Although often diagrammed as discrete, each of these levels is intimately connected and they phase one into another along both the space and time scales. 

Perhaps the most important example of a new biochemical pathway generating a global impact was the development of photosynthesis. The atmosphere of Earth originally was reducing. Photosynthesis produces oxygen as a by-product. Oxygen, which is quite toxic, became a major constituent of the atmosphere. This change produced a mass extinction event, yet also provided for the evolution of much more efficient metabolisms. 

Effects at the community and ecosystem level conversely have effects upon lower levels of organization. The structure of the ecological system may allow some individuals of populations to migrate to areas where the species are below a sustainable level or are at extinction. If the pathways to the depleted areas are not too long, the source population may rescue the population that is below a sustainable level. Instead of extinction, a population may be 

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Turbulence is generally understood to refer to a state of spatiotemporal chaos that is to say, a state in which chaos exists on all spatial and temporal scales. If the reader is unsatisfied with this description, it is perhaps because one of the many important open questions is how to rigorously define such a state. Much of our current understanding actually comes from hints obtained through the study of simpler dynamical systems, such as ordinary differential equations and discrete mappings (see chapter 4), which exhibit only temporal chaosJ The assumption has been that, at least for scenarios in which the velocity field fluctuates chaotically in time but remains relatively smooth in space, the underlying mechanisms for the onset of chaos in the simpler systems and the onset of the temporal turbulence in fluids are fundamentally the same. 

Knapp, R. B., 1989, Spatial and temporal scales of local equilibrium in dynamic fluid-rock systems. Geochimica et Cosmochimica Acta 53, 1955-1964. 

To help address these issues, we define a new component for use in conceptual models the units of analysis. These are the lowest levels of biological, spatial, and temporal scale used in the quantitative part of the risk assessment (e.g., individual iterations in a simulation model). They also define the biological, spatial, and temporal units of the measures that will be needed as inputs to the assessment model. 

In principle avian exposnre conld be modeled at very hne levels of spatial and temporal scale e.g., estimating residnes of pesticides on individnal seeds and insects and then modeling individnal choices of a bird feeding on them — an analysis in nnits of centimeters and seconds. This level of analysis is very cnmbersome, and nsnally nnnecessary. If the resnlts wonld be the same, the analysis may be done at larger scales (e.g., in nnits of helds and days). 

A tabular approach to identifying appropriate biological, spatial, and temporal scales for different components of the assessment process, illustrated for a hypothetical assessment of risks to birds from a corn insecticide (see also Figure 2.2)... 

On a still-larger spatial and temporal scale, a "dispersion" cloud... 

Biodiversity can also be examined at ecosystem level. This is of special concern for ecology, because, although attention to ecological problems is increasing, the choice of the appropriate scale to look at the events is problematic (Levin 1999). The spatial and temporal scales needed are often of such large size to make any reliable observation difficult. This is especially true for the sea, due to the lack of barriers which, therefore, makes any subdivision into ecosystems difficult. This is why any quantitative evaluation of biodiversity at ecosystem level is far fi-om being an easy task. 

Balloon-Borne Measurements. To illustrate the versatility possible with balloon-borne platforms, the in situ techniques that have recently made important contributions to our understanding of stratospheric reactive trace gases are highlighted. Each technique is based on a fundamentally different physical principle, providing measurements with unique and characteristic spatial and temporal scales. But first the advantages and disadvantages offered (and suffered) in balloon-borne experimentation are reviewed. Some unique facets of balloon behavior that are relevant to a specific experiment are discussed with that experiment. 

Figure 2 illustrates major modeling methods, i.e., ab initio molecular dynamic (AIMD), molecular dynamic (MD), kinetic Monte Carlo (KMC), and continuum methods in terms of their spatial and temporal scales. Models for microscopic and macroscopic components of a PEFC are placed in the figure in terms of their characteristic dimensions for comparison. While continuum models are successful in rationalizing the macroscopic behaviors based on a few assumptions and the average properties of the materials, molecular or atomistic modeling can evaluate the nanostructures or molecular structures and microscopic properties. In computational... 

Balbuena et al. also conducted simulations at various water concentrations for various water contents (Fig. 8). At low water contents (A = 5), small water clusters are almost not connected with each other (Fig. 8a). At a very high water concentration (A. = 45), water forms a continuous phase (Fig. 8c). When A. is about 24, close to the amount in fully hydrated Nation membranes at room temperature, the interface is defined by a semi-continuum water film (Fig. 8b) where some water clusters with diameters of about 1 nm are interconnected by multiple water bridges. The average water density in this phase is estimated to be about 0.682 g cnr3, a much lower value than that of the bulk water phase at 353 K. These observations provide very valuable information for further investigating the OER and really highlight the power of atomistic simulations on the research topics for which currently existing experimental tools are lack of the resolutions in spatial and temporal scales. 

The construction of a mass balance model follows the general outline of this chapter. First, one defines the spatial and temporal scales to be considered and establishes the environmental compartments or control volumes. Second, the source emissions are identified and quantified. Third, the mathematical expressions for advective and diffusive transport processes are written. And last, chemical transformation processes are quantified. This model-building process is illustrated in Figure 27.4. In this example we simply equate the change in chemical inventory (total mass in the system) with the difference between chemical inputs and outputs to the system. The inputs could include numerous point and nonpoint sources or could be a single estimate of total chemical load to the system. The outputs include all of the loss mechanisms transport... 

Spatial and temporal scales also need to be considered in assessing the adversity of the effects. The spatial dimension encompasses both the extent and pattern of effect as well as the context of the effect within the landscape. Factors to consider include the absolute area affected, the extent of critical habitats affected compared with a larger area of interest, and the role or use of the affected area within the landscape. Adverse effects to assessment end points vary with the absolute area of the effect. A larger affected area may be (1) subject to a greater number of other stressors, increasing the complications from stressor interactions (2) more likely to contain sensitive species or... 

Simonson (1959) proposed a more general framework for soil formation based on four groups of processes additions, transfers, transformations, and removals. A dynamic approach to pedogenesis, building on the perspectives offered by Jenny (1941) and Simonson (1959), can be used to provide a framework for the assessment of soil properties at different spatial and temporal scales. 

Q. Yu, J. Multiscale asymptotic homogenization for multiphysics problems with multiple spatial and temporal scales a coupled thermo-viscoelastic example problem. Int. J. Solids Struct. 39, 6429-6452 (2002)... 

Figure 3-1. A diagram presenting spatial and temporal scales accessible by simulation methods...

In case of the dynamics, the simplification of the models and force fields allows to reach the spatial and temporal scales which are close to biological ones. However, one must be careful to choose an appropriate coarse-grained model in order to get rid of only those degrees of freedom that are not relevant to the problem under study. Future directions for the reduced biological models will include focusing on making the force field the most transferable with the least set of parameters involved. 

As sediments act as pollutant sinks in aquatic systems, they can be important sources of exposure, and so of the entry of chemicals into aquatic food chains. Sediments are the ultimate residence location for many pollutants released to water. The widespread presence of complex mixtures of contaminants in sediment is thus likely to occur in any location where multiple localized and diffuse contaminant sources contribute to the overall chemical load within natural waters. The role of sediment in the receipt and resupply of the chemical to the water phase means that there is interest in monitoring sediment chemical pollutant load over both different spatial and temporal scales. Because the process of sediment deposition and chemical adsorption on the one hand and solubilization and resuspension on the other link the pollutant loads of the sediment and water column, many of the species that can be used to sample the environment for waterborne pollutants (e.g., filter feeders such as mussels) can also describe the pollutant load present in sediments (Baumard et al. 1998). 

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