Estimating the Impact of Laminar Flow on the Pattern and Rate of Decomposition in Aquatic Environments—Is There a Better Way of Modeling Decomposition?

Determining the Postmortem Submersion Interval (PMSI) is challenging for forensic anthropologists due to the variability of decomposition in aquatic environments. One possible cause of this variability that has received little attention in the literature is the impact of laminar flow. In order to determine whether flow affects the pattern or rate of decomposition, this study analyzed six rabbit carcasses submerged in two different sites: one with slow, laminar flow (“River Site”) and one without flow (“Canal Site”). A pulley system was designed in order to periodically bring the carcasses out of the water for sampling, with the pattern of decomposition monitored using visual descriptions of the decomposition process and the rate monitored using the Heaton et al. 2010 method of scoring aquatic decomposition in conjunction with accumulated degree days (ADD). The rate of decomposition was found to be significantly different between the two sites ( F (1, 126) = 89.569, p  < 0.01). In addition, decomposition was observed to occur in four distinct stages, which were modeled as a series of curves, and a Staged Decomposition Model was created as the possible basis for an improved predictor of PMSI versus the current loglinear approach. While the traditional loglinear approach appears to give a good approximation to the Staged Decomposition Models in environments with laminar flow, this research suggests that it may be less accurate for nonflowing sites.