An indicator of the disturbance of natural systems, the landscape development intensity (LDI) index, was used to assess the potential for land-use within watersheds to influence the production/ accumulation of methyl-mercury (MeHg) in river sediments. Sediment samples were collected from locations impacted by well-identified land-use types within the Mobile-Alabama River Basin in Southeastern USA. The samples were analyzed for total-Hg (THg) and MeHg concentrations and the obtained values correlated to the calculated LDI indexes of the sampled watersheds to assess the impact of prevalent land use/land cover on MeHg accumulation in sediments. The results show that unlike THg, levels of MeHg found in sediments are impacted by the LDI indexes. Overall, certain combinations of land-use types within a given watershed appear to be more conducive to MeHg accumulation than others, therefore, pointing to the possibility of targeting land-use practices as potential means for reducing MeHg accumulation in sediments, and ultimately, fish contamination.

This study reports on levels and speciation of mercury (Hg) in different environmental compartments of selected park units in the Gulf Islands National Seashore (USA), and on potential rates of methyl-Hg (MMHg) formation and degradation in sediments. In the aqueous phase, total (THg) and MMHg concentrations ranged from 0.19 to 14.26 ng/L (n=32) and <0.5 to 1.58 ng/L (n=32), respectively. In sediments, THg concentrations varied from 6.4 to 838 ng/g wet weight (n=32), while MMHg levels ranged from 1 to 17 ng/g (n=21). Potential rates of MMHg formation (M) and degradation (D) in sediments resulted in M/D ratios that were mostly <1, suggesting a low tendency for accumulation of produced MMHg in these sediments. Finally, the detection of THg concentrations averaging 168.18 ± 48 ng/g in tissues of Ulva prolifera points to the tendency of Hg bioaccumulation, and therefore, the need for investigation of Hg levels in fish and shellfish. Overall, our findings show that coastal waters and sediments with very low Hg concentrations could support Hg-contaminated biota, which should justify the need for stringent regulations on Hg introduction to natural systems at both local and regional levels. @JASEM