zone due to episodic events such as upwelling or hurricanes. Quantifying this phenomenon would be very difficult and most likely would not result in any increase in the accuracy of tracing the fate and effects of oil in the ocean.

The Biota Module

The biota module is the most difficult of the modules to describe quantitatively. It includes both fates and effects. To better illustrate the processes that must be quantified in this complex module, the biota module shown in Figure 4-1 is illustrated in more detail in Figure 4-7.

Basically the fate of petroleum hydrocarbons in the biota module results from (1) ingestion (uptake) of one suite of petroleum hydrocarbons by an organism and subsequent excretion to the sediment or the water column of a different suite after digestion and metabolism; (2) transfer of petroleum hydrocarbons up the food chain through the predatorprey relationship; and (3) sorption or ingestion of petroleum hydrocarbons by a marine organism followed by death of the organism and return of the petroleum hydrocarbon to the water column or sediment column through biochemical decay of the organism. In addition, certain petroleum hydrocarbons will be carried away from the sea by birds, and land-based animals, when oil adsorbs on their bodies and they carry the oil away from the sea or ingest seafood and then excrete products or die onshore.

Perhaps the best way to quantitatively describe the biota module would be through the application of a trophic-level food web model that describes the movement up the food chain of petroleum hydrocarbons ingested at any given level. Writing an ingestion-growth-excretion relationship for each trophic level and coupling trophic levels with a predator-prey relationship would enable one to track the migration of petroleum hydrocarbons through the food chain and to determine the concentration of the petroleum hydrocarbons per gram of biomass at each trophic level. Ingestion into the food chain would be a sink for petroleum hydrocarbons in the water-column or bottom-sediment modules, and petroleum hydrocarbons excreted in the biota module would become sources for the water-column or bottom-sediment modules.

Computer Models

The advent of fast personal computers has enabled the development and wide distribution of a number of fairly comprehensive composite fates models that include many of the elements in the ideal conceptual model described in the pre

FIGURE 4-7 Detailed interactions among components of the biota module of conceptual model for the fate of petroleum in the marine environment shown in Figure 4-1.

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