Growth dilution in multilevel food chains

Microalgae can absorb contaminants from the aqueous environment, and harvesting microalgae has been proposed as a method to purify water. However, rapid growth of microalgae (stimulated by increased light, for example) results in lowered tissue concentration of contaminant. This reduction has been observed to propagate to herbivores. Here we investigate (with simulation and supporting analytical argument) the propagation of growth dilution in all trophic levels of a food chain. We are concerned with concentration as well as overall mass of contaminant in each level, for different functional relationships between levels. We find that transient (i.e., prompt) growth dilution occurs for all levels. However, the new steady state concentrations can increase or decrease, depending on functional relationships (e.g., ratio versus prey dependence). These results, which have implications for pollution control, call for experimental testing.