Blue carbon systems are important estuarine environments that provide a variety of ecological services, including carbon burial and the sequestration of pollutants. However, urban development and anthropogenic activities can impact the ability of these estuarine systems to retain and store pollutants, with unknown consequences for marine communities. Here, we present dated sediment cores from within the Solitarily Island Marine Park, a marine sanctuary in Australia subject to runoff from highly developed catchments. We reveal historical accumulation rates of trace metals and pesticides associated with agricultural activities. Propiconazole and tebuconazole, fungicides highly reactive in marine habitats, were recorded throughout the site nearest the freshwater source. Furthermore, mercury content revealed elevated levels in the most recent sediments, while methylmercury (MeHg) was found to range from 0.1 mg kg^-1 in 2017 to 0.2 mg kg^-1 in 2019. Additionally, arsenic accumulation rates are shown to have significantly increased from 19.1 mg m^-2 year^-1 in 1930 to 259.6 mg m^-2 year^-1 in 2020. These substances were determined to be mostly of terrestrially derived sources, likely related to historical catchment deforestation, as indicated through δ¹³C and C:N molar ratios. This study highlights the importance in evaluating agriculture-derived pollutant discharge to protected coastal regions, providing a robust dataset that may be used to mitigate pollutant runoff in catchments impacted by expanding activities throughout Australia, and around the globe.

Primary Presenter: Melanie TAYLOR, Southern Cross University (meltinicreations@gmail.com)

Authors:

Melanie Taylor, Southern Cross University  ()

Shane White,   ()

Tiago Passos,   ()

Christian Sanders,   ()