What happens when you add salt: predicting impacts of secondary salinisation on shallow aquatic ecosystems using an alternative states model
Computing, Health and Science
Natural Sciences, Centre for Ecosystem Management
Alternative-state theory commonly applied, for aquatic systems, to shallow lakes that may be dominated alternately by macrophytes and phytoplanktons, under clear-water and enriched conditions, respectively, has been used in this study as a basis to define different states that may occur with changes in wetland salinity. Many wetlands of the south-west of Western Australia are threatened by rapidly increasing levels of salinity as well as greater water depths and permanency of water regime. We identified contrasting aquatic vegetation states that were closely associated with different salinities. Salinisation results in the loss of freshwater species of submerged macrophytes and the dominance of a small number of more salt-tolerant species. With increasing salinity, these systems may undergo further changes to microbial mat-dominated systems composed mostly of cyanobateria and halophilic bacteria. The effect of other environmental influences in mediating switches of vegetation was also examined. Colour and turbidity may play important roles at low to intermediate salinities [concentration of total dissolved solids (TDS) <10000 mg L-1]; however, coloured or turbid wetlands are rarely found at intermediate to high salinities (>1000 mg L-1 TDS). The role of nutrients remains largely unquantifies in saline systems. We propose that alternative-states theory provides the basis of a conceptual framework for predicting impacts on salinity adds a further tool to decision-making processes. A change in state represents a fundamental change in restoration strategies. Further work is required to better understand the influence of temporal variation in salinity on vegetation states and probable hysteresis effects.