Groundwater-derived U and Ba exports from a coastal acid sulfate soil (CASS) catchment following rain events

Abstract

Coastal acid sulfate soil (CASS) catchments are regions of enhanced weathering due to sulfur mineral oxidation following drainage of anoxic wetland soils. Heavy rainfall flushes CASS soils, releasing dissolved metals to nearby estuaries and the coastal ocean. The importance of CASS environments on the release of uranium (U) and barium (Ba) to the coastal ocean is not well understood. Here, we discuss daily observations of dissolved Ba and U in an extensively drained CASS system in Australia under contrasting hydrological conditions. Radon-traced groundwater discharge following rain events released trace metals to surface waters. Groundwater fluxes of Ba and U were on average 10% and 30% of the total surface fluxes in the Tuckean Swamp, respectively. The average local surface water fluxes from the Tuckean Swamp were 1692 and 1.6 μmol/m2/yr from the catchment. On a global scale, dissolved Ba and U derived from CASS systems may be equivalent to 1.0% and 2.5% of rivers, respectively, even though CASS cover only ∼0.1% of the global continental area. While CASS may not be a major contributor of dissolved Ba and U to the global ocean, fluxes on a square meter basis indicate that CASS may be highly important to regional U and Ba budgets.