Chapter 13 - Multiple Stressors in Australia and New Zealand: Key Stressors and Interactions

Abstract

Australia and New Zealand contain four freshwater biomes. In temperate coastal rivers, the main stressors outside the urban areas originate from agriculture: nutrient enrichment, fine sediment, pesticides, and changes to flow regimes (e.g., water abstraction and flow regulation). Invasive exotic species also affect many streams and rivers, and urban waterways are ecologically degraded by the Urban Stream Syndrome. Temperate floodplain rivers, the biome comprising Australia's most important agricultural region, are impacted by the same agriculture-related stressors plus salinization, with changes to flow regimes and salinization being the most well-researched stressors. In tropical and subtropical coastal rivers, flow regime changes, sediment, and nutrient inputs from agriculture remain the major stressors of concern (including their impacts on coastal waters and coral reefs), along with mining activities. For xeric freshwaters and endorheic (closed) river basins, research is scarce, but the likely key stressors are contaminants from mining, flow regime changes, and salinization. Most agriculture-related stressors are predicted to increase in intensity during the coming decades. Climate change will probably intensify stresses related to water scarcity due to hotter temperatures and lower, more variable rainfall. Stressor interactions are unusually well researched in this part of the world, especially in New Zealand. The combined findings from this body of research, which comprises regional-scale surveys, reach-scale experiments in multiple streams and outdoor stream mesocosm experiments, indicate the need to manage for complex stressor interactions. This will require developing predictive tools for interactive stressor effects.