Nutrient fluxes modeling

Vorosmarty, C.J., and Peterson, B.J. (2000) Macro-scale models of water and nutrient flux to the coastal zone. In Estuarine Science, a Synthetic Approach to Research and Practice (Hobbie, J.E., ed.), pp. 43-79, Island Press, Washington, DC. 

Weber, G. E. 1997b. Modelling nutrient fluxes. In The Central Amazon Floodplain, ed. W. J. Junk (Ecological Studies, Springer-Verlag, Berlin), pp. 109-118. 

Smith, L. K., and T. R. Fisher. 1985. "Nutrient fluxes and sediment oxygen demand associated with the sediment-water interface of two aquatic environments." In Sediment Oxygen Demand Processes, Modeling, and Measurement,... 

Figure 1 Conceptual model for the origin of mixed detrital-biogenic facies relating the three major inputs to the processes that control them. The major inputs are shown in boxes with bold-type labels. ControlUng factors are shown in italics. Large and medium scale arrows represent fluxes of key components involved in sedimentation and the biogeochemical cycles of carbon, sulfur, and oxygen. Thin arrows illustrate relationships between major controlling factors and depositional processes and/or feedback. Dashed thin arrows apply to major nutrient fluxes only. Dotted thin arrows apply to major authigenic fluxes only. See text for further explanation.

There already exist two solid and validated frameworks for models of nutrient flux that can provide a basis for a transcriptional control model in cattle and swine. The first is the 40 years of modeling work of Baldwin and colleagues (Baldwin et al., 1987a,b,c Baldwin, 1995), which has lead to tremendous improvement in understanding of the mechanistic connections between diet and animal performance. The model in question is titled Molly and the full history and detail can be found in... 

PROFILE is a biogeochemical model developed specially to calculate the influence of acid depositions on soil as a part of an ecosystem. The sets of chemical and biogeochemical reactions implemented in this model are (1) soil solution equilibrium, (2) mineral weathering, (3) nitrification and (4) nutrient uptake. Other biogeochemical processes affect soil chemistry via boundary conditions. However, there are many important physical soil processes and site conditions such as convective transport of solutes through the soil profile, the almost total absence of radial water flux (down through the soil profile) in mountain soils, the absence of radial runoff from the profile in soils with permafrost, etc., which are not implemented in the model and have to be taken into account in other ways. 

Nutrients are carried back to the sea surface by the return flow of deep-water circulation. The degree of horizontal segregation exhibited by a biolimiting element is thus determined by the rates of water motion to and from the deep sea, the flux of biogenic particles, and the element s recycling efficiency (/and from the Broecker Box model). If a steady state exists, the deep-water concentration gradient must be the result of a balance between the rates of nutrient supply and removal via the physical return of water to the sea surface. 

Ion transport is also often coupled with cellular energy production and with nutrient and product membrane transport. Aside from Papoutsakis work on the influence of methanol transport on growth of methanol-consuming bacteria, the importance of membrane control of nutrient and product fluxes into the cell has been largely ignored by biochemical engineers [25]. Better methods for measuring the pH and electrical potential differences across cell membranes are needed, as is more careful consideration of membrane-mediated processes in cell kinetics models. 

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