Contemporary fluvial charcoal supply to floodplain wetlands of the Macquarie Marshes, NSW, Australia

Fire plays a pivotal role in modifying and shaping the Australian landscape, including floodplain wetlands, which respond dynamically to flooding, fire and geomorphological changes. Buckiinguy Swamp, a key ecological asset in the Macquarie Marshes, has experienced numerous fires in the past. For example, a total of 32 fires occurred in the period 2004-2014 within a ~10 km2 zone in and around the wetland, as shown on contemporary satellite imagery (Geoscience Australia Sentinel Hotspot data). However, the volumes of charcoal produced in situ by local fires and that supplied to the wetland from the upstream catchment (i.e. not representative of local fires) are unknown. This study assesses the fluvial input of macroscopic charcoal (>125 μm) associated with sediment from upstream to disentangle these two major sources of charcoal. Sediment was collected from synthetic grass mats that were deployed in the wetland for 7 months to establish the contemporary charcoal flux to Buckiinguy Swamp. Preliminary results show that charcoal counts were highest at site B4 and consistently lower at the three other sites. Sites B1, B2 and B3 appear to yield a consistent fluvial charcoal signal. Charcoal found at B4, near the outlet of the reed bed and with the lowest volume of deposited sediment, may have been remobilised and redeposited from nearby in the wetland, rather than being supplied from upstream. The results showed that B2 and B3 near the terminus of Buckiinguy Creek had the highest volume of deposited sediment (0.74 to 0.98 kg m-2). The amount of charcoal and sediment deposited near the channel and on the adjacent floodplain was highly variable, probably due to flow attenuation by vegetation (e.g. Phragmites australis and Paspalum distichum) and differential patterns of sedimentation. The findings from this study will help to provide a baseline charcoal flux (i.e. a background fluvial deposition rate) for Buckiinguy Swamp, which will be used to separate the in situ and fluvial charcoal signal from sediment cores and to determine the historical charcoal signal related to local fires preserved in the wetlands.