A Novel in Situ Sulfate Sampler for Aquatic Systems

High-resolution records of porewater sulfate concentrations are critical to understanding the modern biogeochemical sulfur cycle, particularly the connection between microbial metabolic activity, ambient geochemistry, and feedbacks on global carbon cycling and climate. To date, the nature of sulfate measurements requires extraction of fluids or sediments from the field, often leading to significant disturbances in the systems studied. Further, the resulting data may have limited spatial resolution (due to volume restrictions of porewater sampling), hindering the ability to reconstruct key biological and geochemical processes. Here a novel passive sampler that is seeded with barium oxalate is optimized for the in situ sampling of sulfate to improve both the fidelity and the spatial resolution of sulfate profiles that may be obtained. Simulated sediment studies showed that consistent profiles could be resolved in both 2 and 6 h deployments that were in good agreement with traditional porewater reconstructions from adjacent core samples. Although the sampler has been calibrated for water concentrations between 2 to 28 mM of sulfate, the detection limits may be improved with modified sampler geometry or longer deployment times