ABSTRACT
Three-Dimensional Flow ........................................................ 73 2.5 Summary and Conclusions ................................................................. 75 Acknowledgments ....................................................................................... 79 Appendix 1: Breakthrough Curve Data Analysis ....................................... 79
Moment Analysis ............................................................................... 79 Temporal Analysis.............................................................................. 80
References ................................................................................................... 80
The soil is a three-dimensional continuum, a temporally dynamic and spatially heterogeneous anisotropic medium comprising the outer layer of the solid earth in which liquids, gases, and solids interact over an extreme range of space and time scales. This life-sustaining open system evolves through weathering processes driven by soil formation factors: parent material, climate, organisms, and topography acting over time. The variation in these factors across different locations provides the soil with its inherent heterogeneity from one site to another (even for close locations). As a result, characterizing soil processes requires a capacity to consider both the mechanisms and the magnitudes of spatial and temporal variability in soil features. The magnitude of these scales may range from ion exchange and sorption reactions on the surface of kaolinite and iron oxide clay minerals, occurring at nanosecond time and microscopic scales, to the development of well-structured soil illuvial horizons and the formation of toposequences over thousands of years at the watershed scale.
