Higher Levels of the Food Web

In the biogeochemical model components, the model zooplankton is typically considered as 

Such models describe the life history of animals as propagation through the different size or mass classes and need a sophisticated formulations of predator-prey interaction. There are several approaches to describe life histories of copepods by models (Carlotti et al., 2000). A new theoretical formulation to allow the consistent embedding of dynamical copepod models into three-dimensional circulation models was given in Fennel (2001). Examples of simulations for the Baltic were given in Fennel and Neumann (2003). The basic idea is that both biomass and abundance of different stages or mass classes are used as state variables, while the process control is related to mean average individuals in each mass class, that is the ratio of biomass over abundance. 

Apart from theoretical problems and the variety of timescales involved, a three-dimensional version of such a type of model also challenges the capacity of current supercomputers. Since the life span of fish can be of the order of one or two decades, it is evident that such model must be susceptible for longer simulations, say 20-40 years. A first consistent approach toward a food web model reaching from nutrients to fish was presented by Fennel (2007) in terms of a box model. 

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Humans, fish, and wildlife are exposed to PCBs from a number of different exposure routes, including respiration, water consumption, food consumption, and dermal contact with contaminated water, soil, etc. However, the dominant exposure route is food consumption, and especially the consumption of fish. This is because PCBs bioaccumulate effectively in fats and lipids [35]. As a result, most PCB congeners (including the most toxic ones) biomagnify in the food web, which means that the higher levels of the food web will have greater concentrations than lower ones (see full discussion in the section on food web dynamics). As a result, adverse effects have been observed in fish-eating animals and birds, and in humans that have consumed fish (occupationally exposed workers are not considered in this discussion). 

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