Paleolimological investigation of the use of stable isotopes of carbon and nitrogen in bulk sediment and cladoceran zooplankton to reveal ecosystem changes in Kings Billaong Northwest Victoria, Australia

Northwest Victoria hosts a large number of shallow floodplain wetlands along the Murray River system. One of these, Kings Billabong, is known for its high conservation values. However, the naturally occurring flood pulses, which maintain ecological connectivity between river and wetlands, have been altered impacting the ecology of Kings Billabong. The human-induced river regulation in the Murray River following the arrival of Europeans, and increased farming activities around Mildura for irrigation, has switched Kings Billabong to a permanent water regime resulting in accelerated sedimentation rates and changed sources of carbon and, subsequently, altered ecological character. This study focuses on a 90 cm long sediment core taken from Kings Billabong in 2011, where the 210Pb dating detected sediments at c. 60 cm depth to be c. 65 years old. Around this time (c. 1940-1945 AD), a systemic change occurred in the billabong. The enrichment of carbon substantially declined, while, in the meantime, nitrogen enrichment increased. Coincidently, the subfossil cladoceran zooplankton assemblages revealed changes in the limnological conditions of the wetland ecosystem. Among the littoral species, the Chydorus sphaericus group, which prefers eutrophic water, became dominant. Since the early 2000s, the abundance of Biapertura affinis, a pioneer plant dwelling species, has declined. Before the assemblage of B. affinis began to decline, a large number of cladoceran ephippia were recorded in sediment samples indicating the elevated stress in the wetland. This study suggests that paleolimnological investigations, together with the use of stable isotopes of carbon and nitrogen in sediment samples, provides an opportunity to reveal the impacts of anthropogenic disturbances on the floodplain wetlands of the Murray River system across northwest Victoria, and potentially more widely across Australia. © The Authors