Himmelheber et al. 2009

Himmelheber DW, Thomas SH, Löffler FE, Taillefert M, Hughes JB. 2009. Microbial colonization of an in situ sediment cap and correlation to stratified redox zones. Environmental Science & Technology 43: 66-74.

These authors previously studied the changes in geochemistry associated with the common practice of adding a sediment cap to cover contaminated sediments at the sediment-water interface. Such caps are commonly clean sand, with the underlying idea being the layer of sand provides a transport barrier to various contaminants moving through the system by diffusion. Sediment geochemistry, like soils, includes layers of redox conditions generated by both biotic and abiotic factors. These zones of chemical conditions migrate upwards when a sediment cap is added; not surprising considering the effect the cap has on diffusion of oxygen and other chemicals important for redox considerations.

This study shows that the microbial populations also migrate upwards when a cap is added. The primary concern here seems to be the effect this population shift may have on the transport and decontamination of such pollutants as are often found in the river-bottom sediments of the eastern USA. The primary effect is likely positive: populations of bacteria and archaea in sediments will metabolize, mineralize, and generally detoxify most compounds moving up from the sediments to the cap. A few classes of contaminants, however, may not be decontaminated and it is possible their transport and release into the water column may be accelerated by these microbes.

There are two key parts of the methods of this paper that interest me. First, the microbial populations were analyzed by a range of techniques including real-time quantitative PCR (qPCR). The procedure of primer design, evaluation, and data interpretation looks very similar to what I will be attempting with my own samples. Second, diversity estimates for the various strata within the sediments, derived from qPCR data, includes the use of the statistical technique Canonical Correspondence Analysis. This allows direct testing of hypotheses regarding the relationship between environmental parameters, in this case depth below surface, and estimates of biodiversity such as the Shannon-Weiner index.