Are the faecal pellets of kangaroos (Macropus spp.) a source of nutrients and carbon in an inland floodplain wetland during flooding? A preliminary experimental inundation study in the Macquarie Marshes, New South Wales

Kangaroos (Macropus spp.) are one of the most abundant native macrofauna on Australian floodplains with a positive relationship between their density and the deposition of faecal pellets that contain nutrients and carbon. We tested whether kangaroo faecal pellets are a source of nutrients and carbon during flooding in the Macquarie Marshes, an inland floodplain wetland, in south-eastern Australia. The faecal pellets of kangaroos, most likely of Red Kangaroo (M. rufus), were found on the dry floodplain adjacent to Bora Channel (∼30.6433 °S/∼147.5351°E) at a density of 142±54 m ^-2 (mean±SE, n=3). Following artificial inundation, we monitored the release of total nitrogen (TN), total phosphorus (TP) and dissolved organic carbon (DOC) five times over a six-day period from mesocosms deployed in situ. Three mesocosms contained faecal pellets and three mesocosms contained marsh floodplain sediments (top 5 cm of sediment consisting of soils and plant material) with faecal pellets removed. The concentrations (mean±SE, n=3) of TN, TP and DOC in the mesocosms containing the pellets were 0.037±0.017, 0.22±0.060 and 0.69±0.14 g m ^-2at day 6, while the mesocosms containing only the marsh floodplain sediments were 1.03±0.23, 0.49±0.083 and 7.27±1.02 g m ^-2. On average, the kangaroo faecal pellets contributed ∼6% of TN, ∼31% of TP and ∼ 8% of DOC of the total amounts respectively released from the inundated floodplain over the six-day experiment Nutrient and carbon depositions to floodplains in the form of faecal pellets from large terrestrial animals such as kangaroos are an important process of cycling these elements in inland floodplain wetlands, especially where large populations of these animals occur.