Kansas Geological Survey, Open-file Report 1994-12
M. Sophocleous and M. Bagheri
KGS Open File Report 1994-12
Nitrate is the most common contaminant of the subsurface, and nitrate contamination of ground water plagues many rural areas of the United States. The transition between the unsaturated and saturated soil zones may be a biologically active zone through which natural and anthropogenic chemicals must pass before entering the ground water. Factors that control nitrogen and carbon dynamics in such transitional systems are poorly understood. The objectives of this three-year project are to: (1) describe temporal and spatial variation in the physical, chemical, and biological aspects of pristine and agriculturally impacted subsurface ecosystems with special emphasis on the transitional zone between groundwater and soil; (2) observe the functional responses of microbes in this transitional zone to nitrogen and carbon availability and the relative flux rates of different forms of nitrogen; (3) delineate the biotic and abiotic controls of the microbial community in the transition zone.
The study will involved (1) characterization of the physical, chemical, and biological properties of the profile to the water table at two sites (one pristine, the other agricultural) on the Konza Prairie of Kansas; (2) microcosms to evaluate flux rates and microbial activity due to perturbations; (3) field manipulations to determine transport of N, C, and microorganisms from the surface; and (4) modeling of transport and transformations. The proposed research will foster development of a multi-disciplinary team to tackle a complex but extremely important problem to Kansas and the U.S. The basic understanding will generate expertise and resources for future research.
One of the objectives of this study is to compare and evaluate a number of well-known soil-water and solute transport models of varying complexity using the field and laboratory data collected from this study. Also, a sensitivity analysis of the various parameters involved in these models will be performed and their relative effect in NO3- breakthrough curves will be assessed. Other objectives of the modeling aspect are to better understand the transport mechanisms involved, to test the adequacy of existing theories, to establish a framework for the collection of data, and to provide a means for predicting, and thus controlling, the fate of agrichemicals in soils and aquifers.
Although we examined a number of available models, we evaluated and tested the following models, which we considered as most suitable for our project: SWMS_2D, UNSAT2, LEACHM, and HYDRUS. We also employed the RETC code for quantifying the hydraulic functions of unsaturated soils. A general overview of each one of these models follows.
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Kansas Geological Survey, Geohydrology
Placed online Dec. 4, 2013
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