System dynamics and environmental change: an exploratory study of Holocenelake sediments at Holzmaar, Germany

The idea that much environmental information may be gained by identifying u nderlying environmental system behaviours is examined. Six categories of sy stem behaviour for changes between and within steady-states are identified: disorder maximization: self-organization; linear process-response; stochas tic; self-organized criticality; and chaotic, In practical terms, predictab ility only exists for linear behaviour. Simple frequency distributions of t ime-series data are used to identify dominant behaviour in the proxy-record s from 10 000 years of annual laminations from Holzmaar, Germany. The resul ts suggest that before similar to 3000 yr cal. BP the catchment-lake system may have reached a state of self-organized criticality where fluctuations in system properties, for instance diatom productivity and sediment flux, w ere caused by internal reorganization as much as by external forces. Compar ison of the records for sediment flux with outputs from the GOLEM landscape model suggests that major shifts in the Holocene record were triggered by human actions rather than by climate. The approach offers a new perspective on the causes of minor and major changes in reconstructed environmental sy stems and the degree of interactions between subsystems.