Keywords
goulburn catchment, salinity, bifurcation, multiple states, resilience
Start Date
1-7-2006 12:00 AM
Abstract
Over the last decade, many ecosystems have begun to be understood as having multiple coexistent stable states. Often such states are characterized as socially desirable and undesirable, with for instance high/low fish stocks or oligotrophic / eutrophic lake states. Within catchment planning modeling, a frequent assumption is that the equilibrium state would not change with state variable initial conditions. That is, different initial conditions will not cause a shift to a different equilibrium point, thus implicitly assuming only one stable state. Until recently no investigation of regional agricultural catchments as having multiple stable states has been published.Simple analytical models have been developed to numerically predict the existence of such multiple stable states. Termed resilience models, they are exclusively based upon coupled differential equations, thus allowing identification of stable states and their thresholds. They do not provide improved predictive accuracy but rather the contemplation and identification of dimly perceived possible system wide changes.The only existing catchment-resilience model is a salt and water groundwater-unsaturated zone, two region lumped model of the Goulburn catchment in Victoria, Australia [Anderies 2005]. Its minimal numerical validation and most invalidating assumption of a within-region homogenous depth to water table is discussed. Both are addressed with an expansion to it to a semi-distributed model. This was implemented for a sub-catchment of the original model in order to facilitate a more robust validation. Calibration to 29 year yield and stream salt load records is to be undertaken with consideration of equifinality. The significant prediction of saline catchments as having multiple states is thus to be validated for the first time with any rigor. Its utility to catchment planning is in encouraging a departure from assuming catchments have a single equilibrium state and thus dramatically expanding the decision space.
Validation of Multiple Stable States and Thresholds within a Saline Catchment
Over the last decade, many ecosystems have begun to be understood as having multiple coexistent stable states. Often such states are characterized as socially desirable and undesirable, with for instance high/low fish stocks or oligotrophic / eutrophic lake states. Within catchment planning modeling, a frequent assumption is that the equilibrium state would not change with state variable initial conditions. That is, different initial conditions will not cause a shift to a different equilibrium point, thus implicitly assuming only one stable state. Until recently no investigation of regional agricultural catchments as having multiple stable states has been published.Simple analytical models have been developed to numerically predict the existence of such multiple stable states. Termed resilience models, they are exclusively based upon coupled differential equations, thus allowing identification of stable states and their thresholds. They do not provide improved predictive accuracy but rather the contemplation and identification of dimly perceived possible system wide changes.The only existing catchment-resilience model is a salt and water groundwater-unsaturated zone, two region lumped model of the Goulburn catchment in Victoria, Australia [Anderies 2005]. Its minimal numerical validation and most invalidating assumption of a within-region homogenous depth to water table is discussed. Both are addressed with an expansion to it to a semi-distributed model. This was implemented for a sub-catchment of the original model in order to facilitate a more robust validation. Calibration to 29 year yield and stream salt load records is to be undertaken with consideration of equifinality. The significant prediction of saline catchments as having multiple states is thus to be validated for the first time with any rigor. Its utility to catchment planning is in encouraging a departure from assuming catchments have a single equilibrium state and thus dramatically expanding the decision space.
