An 1800-year water-quality and vegetation record from Junction Park Billabong, Murray River, Australia: an assessment of European impacts and sensitivity to climate

The Murray River is Australia’s economically most important river system. As a result of its economic importance, land use change and river regulation have resulted in ecological degradation of the river and associated river wetlands (known throughout Australia as “billabongs”). Palaeolimnology can provide otherwise unobtainable information about the relative impacts of stressors and identify “refuges” from such impacts. We examine an approximately 1800 year history of water quality and vegetation at Junction Park Billabong, on the Murray River approximately 25 km upstream of the Murrumbidgee River confluence. Throughout this period the billabong has maintained a strong connection to the Murray River. Planktonic Aulacoseira granulata has been the dominant diatom in the Murray River, while surrounding vegetation has been dominated by open eucalpyt woodland. Around 500 years before present (BP), there was an increase in effective rainfall as indicated by a decline in Chenopodioideae (Amaranthaceae: saltbush) and an increase in Callitris (native pine) pollen. At the same time, there was an expansion in wetland submerged aquatic macrophytes, as evidenced through increases in the relative abundance of the epiphytic diatom, Cocconeis placentula and sediment organic matter. European settlement resulted in declines in aquatic macrophytes and nutrient enrichment but minimal increases in diatom-inferred salinity. There was relatively little post-settlement change in both the diatom stratigraphy and inferred water quality from Junction Park Billabong which contrasts somewhat with that observed in floodplain water bodies both upstream and downstream of Junction Park. The record from Junction Park Billabong highlights the sensitivity of floodplain wetlands to climate change and suggests that examination of these records can provide insights into late Holocene climate from a region where few high-resolution records from other sources exist.