Browsing by Subject "Bioturbation"

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Effects of bioturbation on the bacterial community in contaminated sediment
(2006-08) Smith, Anthony Michael; Reible, Danny D.
Bioturbation has been shown to expedite the degradation of refractory compounds in contaminated sediments. In an effort to determine whether bioturbation influences sediment bacterial community diversity, a river simulation was operated in microcosm cells with sediment samples from the Anacostia River (Washington D.C.). Sample cells contained the freshwater oligochaete Ilyodrilus templetoni at a density of 20,000 / m² while control cells were operated without benthic organisms. Vertical profiles of redox potential, sulfide, and dissolved oxygen concentrations were determined during river simulations. As compared to the condition without macrobenthos, Ilyodrilus expedited oxygen consumption and lowered the redox potential in the top four centimeters of sediment. Sulfide concentrations were below the limit of detection. After five months the cells were extruded and analyzed by layer for select microbial parameters. Bacteria were quantified by direct count and communities were profiled at different depths using denaturing gradient gel electrophoresis (DGGE).
The interaction of benthic oligochaetes, T. tubifex with mercury impacted sediments: an assessment of bioaccumulation and biogeochemistry
(2014-05) Offutt, Alyssa Jane; Reible, Danny D.
Mercury is a pervasive environmental contaminant which is globally distributed in freshwater ecosystems. In order to assess the risk that mercury and methylmercury pose to public health through consumption and trophic level transfer, it is first necessary to understand the interactions and uptake that occurs between benthic organisms and mercury impacted sediments. Delineation of these interactions currently rely on correlating measurements of bulk sediment concentrations with bioaccumulation of either total mercury or methylmercury. However, it has been proposed that porewater concentrations, rather than sediment concentrations, should be used to predict uptake and bioavailability. Diffusive gradient in thin films (DGTs) have been proposed as a viable technique for porewater measurements to assess the bioavailable fractions of mercury. DGTs were compared to traditional bulk solid sampling to assess their capabilities for the prediction of total and methylmercury bioaccumulation in benthic oligochaetes, T. tubifex. DGTs performed similarly to the bulk solids sampling approach in respect to their correlation with mercury bioaccumulation in the sediment matrix studied. Bioturbation was shown to impact redox profiles in the sediment which led to a decrease in porewater methylmercury concentrations in the uppermost surficial sediment depths. These results indicate that monitoring tools such as DGTs are necessary to better understand the fate of mercury at field scale contaminated sites.