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When limnologists focus on the lake as a dynamic system, the drainage basin (the paralim nion, also and inappropriately called" watershed") is treated as a black box. In eutrophication theory (204), as long as the basin's most interesting output (" nutrients") is seen as the lake's most essential input, it is unnecessary to disaggregate the box, or to consider non-nutrient outputs. Where outflow of water balances inflow and residence times are short... retention of certain inputs by the sedimentary sink... is often estimated by subtraction (27). The dynamic structure of the ecosystem can then be seen, in terms borrowed from macroeconom ic theory (173), as a set of measurable fluxes of materials between" compartments"(58).