Towards lumped integrated models of complex heterogeneous environmental systems

Two examples of the problems of integrating heterogeneous chemical data within the framework of a lumped model are described. For the case of cation exchange controls in acidic soils, the lumping of data may lead to equations for averaged data that mirror reactions in localized regions of the soil. However, subsequent testing of the underlying equations at a representative scale in the field indicate that the equations themselves may well be inappropriate. The second example describes the hydrogen ion and bicarbonate concentration relationships for averaged rainfall data; such a system is representative of a Mediterranean area subjected to both acidic and alkaline inputs. A negative but linear correlation between hydrogen ion and bicarbonate concentrations results for the averaged data, but an inverse relationship applies to individual rainfall events. This means that in this case the lumping procedure is invalid. It is concluded that before the environmental system can be described adequately so that reliable environmental impact models can be developed, much greater attention must be paid to assessing the nature of heterogeneous behaviour and the appropriateness of lumped models.