Quantifying blue carbon and nitrogen stocks in surface soils of temperate coastal wetlands

Coastal wetlands are carbon and nutrient sinks that capture large amounts of atmospheric CO2 and runoff of nutrients. 'Blue carbon' refers to carbon stored within resident vegetation (e.g. mangroves, tidal marshes and seagrasses) and soil of coastal wetlands. This study aimed to quantify the impact of vegetation type on soil carbon stocks (organic and inorganic) and nitrogen in the surface soils (0-10 cm) of mangroves and tidal marsh habitats within nine temperate coastal blue carbon wetlands in South Australia. Results showed differences in surface soil organic carbon stocks (18.4 Mg OC ha for mangroves; 17.6 Mg OC ha for tidal marshes), inorganic carbon (31.9 Mg IC ha for mangroves; 35.1 Mg IC ha for tidal marshes), and total nitrogen (1.8 Mg TN ha for both) were not consistently driven by vegetation type. However, mangrove soils at two sites (Clinton and Port Augusta) and tidal marsh soils at one site (Torrens Island) had larger soil organic carbon (SOC) stocks. These results highlighted site-specific differences in blue carbon stocks between the vegetation types and spatial variability within sites. Further, differences in spatial distribution of SOC within sites corresponded with variations in soil bulk density (BD). Results highlighted a link between SOC and BD in blue carbon soils. Understanding the drivers of carbon and nitrogen storage across different blue carbon environments and capturing its spatial variability will help improve predictions of the contribution these ecosystems to climate change mitigation.