Pig decomposition in lotic aquatic systems: the potential use of algal growth in establishing a postmortem submersion interval (PMSI).

While algal community composition has been examined as a qualitative indicator of postmortem submersion interval (PMSI), there have been no quantitative studies on using algal growth rates as PMSI estimators. The present study was undertaken to examine pig decomposition in streams and to develop a more quantitative approach to estimate a PMSI. Pigs and ceramic tiles were completely submerged and regularly sampled for periphyton growth. Five stages of decomposition were identified for the submerged pig carcasses according to physical characteristics. Algal growth rates, measured quantitatively as a function of chlorophyll-a concentration, were greater on pigs compared with tiles; however, microhabitat (pools versus riffles) did not significantly influence algal growth. Additionally, there was a strong correlation between algal growth rate and time on pigs and tile substrates. This strong correlation was observed after significant rain events. Our study documents for the first time a quantitative technique to determine the length of time a corpse has been submerged in water. We suggest that algal growth rates may be a useful quantitative indicator in criminal investigations involving corpses that are completely submerged in stream or riverine habitats.