The Swan Coastal Plain (SCP) in southwest Western Australia (SWA) is known for its highly biodiverse, groundwater-fed wetlands. Since 1975, climatic drying has caused groundwater tables, runoff and freshwater biodiversity to decline in streams and wetlands across SWA because once permanent waterbodies are now dry for long periods. Although SCP wetlands have high conservation and community value, the impacts of wetland drying on biodiversity are unknown.
In freshwaters, invertebrates are responsible for many ecosystem functions and provide the largest component of animal diversity in these systems. Seasonal wetting and drying patterns (i.e. hydroperiod) are a strong filter on invertebrate communities, although many invertebrates can survive drying using life stages (e.g. desiccation resistant eggs) in sediment or in the damp bottom of sediment fissures, but survival is proportional to sediment moisture content. Refuges such as fissures may be imperative to maintaining biodiversity in wetlands, but little is known about how they function. Once hydrological thresholds are crossed, and wetlands fail to fill in successive years, the ability of invertebrate communities to recover may be diminished due to both moisture loss and drying duration.
My project will use a comprehensive dataset of historical invertebrate and water quality data from 1989-1990 when 16 of the 21 wetlands were permanent, and 7 were seasonal. The water regime commenced drying in 7 wetlands in the early 2000s. I will compare these data to newly collected data from all 21 wetlands (autumn, spring 2025) to determine impacts of drying vs controls (wetlands where water-regime is unchanged). I will also sample sediment refuges in a subset of those wetlands still experiencing seasonal, and drier hydroregimes. Addressing two questions; 1) Have drying water-regimes altered biodiversity and water quality in 21 SCP wetlands? 2) Are seasonal wetlands still suitable for animals to survive drying given prolonged dry periods?