Assessing change in floodplain wetland condition in the Murray Darling Basin, Australia

Abstract

Lowland Australian rivers and floodplains have been affected by agriculture and flow regulation for more than a century. Our capacity to understand the complex causes of ecosystem change is limited by the lack of historical records of ecosystem condition. Records of change over this critical period are available through analysis of sedimentary records. These provide benchmarks of the range of natural conditions and, by providing a long time series of conditions, trends and trajectories of change. Over recent decades, 51 sediment records from billabongs and lagoons throughout the southern Murray Darling Basin have been subject to palaeoecological analysis. The picture that emerges from this synthesis is that ecosystems have undergone substantial ecological change in response to human activities. Diatom assemblages preserved in wetland sediments attest to salinisation in 34% of sites and increased nutrient concentrations in 48%. More extensive is the impact of increased sediment flux with evidence for increased sedimentation rate, turbidity or macrophyte loss in 80% of sites. Intriguing differences exist in the timing and nature of change experienced by aquatic ecosystems in different parts of the Basin. These patterns of ecosystem response suggest underlying differences in the resilience of these ecosystems to different anthropogenic stressors, which may result from contrasting hydrologic, geomorphologic and climatic contexts. This systematic compilation of the palaeoecological evidence of change in the aquatic ecosystems of the Basin sheds light on what are the principal drivers of change across the region and provides guidance as to how these systems can be best restored.