~(197)Hg(II) radio tracer determination of methylmercury production potential rates in sediments of Lake Escondido, Argentine Patagonia

摘要

The variation in seasonal Hg(II)-methylation rates in Lake Escondido sediments was assessed using ~(197)Hg as a radiotracer. Sediment was collected from the near shore (littoral) rooted macrophyte zone (4 m water depth), and from the non-vegetated profundal lake center (8 m water depth). Experiments consisted of amending triplicate samples with ~(197)Hg(II) and incubating for 4 to 48 hours. In addition, samples in which microbial activity was inhibited by flash freezing immediately after inoculation were assayed as controls. The Hg-methylation potential rates for the two sites exhibited contrasting seasonal trends, with peak rates for the littoral site occurred during spring-summer, whereas the highest rates for lake-center were during autumn-winter. The recovery of ~(l97)Hg in non-incubated control samples from both sites was up to 15X higher in autumn-winter (May to September) compared to spring-summer (December to February). It is unclear if these seasonal differences in the controls reflect abiotic Me~(197)Hg production or the carry-over of organic-bound non-methylated ~(197)Hg(II) in the extraction. The results suggest that the seasonal and spatial differences in how mercury is cycled may be strongly influenced by carbon dynamics within this small mountain lake.