Soil carbon dynamics and aquatic metabolism of a wet-dry tropics wetland system

Freshwater wetlands are a key component of global carbon dynamics. Globally, wet-dry tropics wetlands function as wet-season carbon sinks or dry-season carbon sources with low aquatic metabolism controlled by predictably seasonal, yet magnitude-variable flow regimes and inundation patterns. However, these dynamics have not been adequately quantified in Australia’s relatively unmodified wet-dry tropics freshwater wetlands. A baseline understanding is required before analysis of land-use or climate change impacts on these systems can occur. This study characterises geomorphology and sedimentology across a seasonally connected ephemeral and permanent wet-dry tropics freshwater wetland system at Kings Plains, Queensland, and quantifies soil carbon stocks and wet- and dry-season aquatic metabolism. Sediment from 33 cores was assessed for carbon content using loss-on-ignition. Soil carbon stocks to 1 m depth are 51.5 ± 7.8 kg C m-2, with potential for long-term retention at greater depths. This is higher than other wet-dry tropics wetlands found globally. Aquatic metabolism was measured using biological oxygen demand method on sediment collected during both seasons and inundated under laboratory conditions. Results show overall low productivity, with respiration dominant in both seasons. Quantification of sediment and aquatic metabolism carbon in this nutrient-limited wetland system serves as a baseline for future research and environmental management.