The effects of soil composition on the decomposition rates of buried mice.

Aslin Fanning

Senior

Southern Illinois University Edwardsville

Taphonomy

• Taphonomy is the study of the processes of decay (Forbes cited in Tibbett M and Carter DO (editors) 2008, p 205-216). Physical anthropologists can use information on the rate of decay for many applications.

• Little research has been conducted on how burial in soil effects these processes.

• This experiment aimed to determine how soil composition effects taphonomy in burial settings.

Soil Composition• Soils are classified in taxonomic levels just like organisms.

There are twelve main soil orders and each of these orders have suborders ([NRCS, USDA] 2003).

• Two of the three soil orders that can be found in Illinois are located near Southern Illinois University Edwardsville. The experimental conditions for this experiment were obtained from Eldon Hazlet State Park in Carlyle, IL.

• The experimental conditions belong to the Alfisol and Entisol family and are commonly called Bluford Silt Loam and Wakeland Silt Loam.

• The soil composition is the only variable that will influence the carcasses. To ensure this, the soils were sterilized to remove all microorganisms.

Alfisol EntisolBluford Silt Loam Wakeland Silt Loam

Mice As Animal Models• Hairless rodents, like mice, can be used in these studies when

pigs and other larger hairless animals are not suitable (Petersen 2003).

• Mice are the best-suited models for this particular study. The mice were received already euthanized and frozen. The were purchased from RodentPro.com and did not require IRB approval for use.

• Mice are more cost efficient, require less space and decompose faster than larger organisms. It is ethically responsible to use the smallest possible organisms when an experiment requires the death of that organism, especially in preliminary studies like this one.

• The time constraints of this experiment were limited to one academic semester.

Setup and Preparation• Carcasses were housed in specially

designed wooden viewing containers with

plexiglass bottoms for viewing.

• The top and bottom compartments

separate to allow for photographs and

observations.

• Container 1 housed specimen A. The

carcass was covered by the Alfisol sample,

Bluford Silt Loam.

• Container 2 housed specimen B. The

carcass was covered by the Entisol sample,

Wakeland Silt Loam.

• Container 3 served as the control and

remained uncovered with soil.

• There was also a container 4 (not pictured)

that contained only the subsoil and no top

portion or carcass. All containers were held

in a temperature controlled environment

that remained at approximately 68°F with

no insect activity possible.

Soil Chemistry and Decomposition

• As an organism decays the cells break down and liquefy (Byers 2008). As these bodily fluids leach into the subsoil, they change the chemistry of the underlying soil. A good way to measure changes in soil chemistry is by measuring the pH levels.

• The measurement of changes in acidity can signal different stages of decay (Stokes and others cited in Ritz and others (editors) 2009, p 360-374).

• Experiments conducted on the effects of decomposing carcasses on the underlying subsoil suggested that nitrogen and phosphorus levels could also be good indicators of the level of decomposition of the carcass lying above.

• They measured nitrogen and phosphorus in addition to measuring the pH levels (Stokes and others cited in Ritz and others (editors) 2009, p 360-374).

Observations• In addition to the measurement of chemical changes in

the sub-soil, the experiment also utilizes visual observations.

• The containers were designed to allow the researcher to view and photograph the buried carcasses throughout the entire experiment.

• Since burial research in taphonomic studies needs further exploration, the ability to watch the entire decomposition process as it occurs beneath soil is a unique component to the experiment.

• These descriptions were used to place the carcasses into five stages of decomposition: fresh, early decay, active decay, skeletonization and advanced skeletonization (Galloway et al 1989). I further split the early decay category into two separate categories based on the presence of bloating.

MethodsVisual Data pH

• Initial appearance of each

mouse was documented prior to burial and carcass

photographed.

• Each carcass was viewed

and photographed daily

and any changes to the carcasses were noted.

• Carcasses were classified

into stages (Galloway et al

1989) and then scored to

track differences between specimen.

• The pH levels of the subsoil

in this experiment was

measured using pH test

strips.

• The testing solution was

acquired from a 50/50 mixture of soil and distilled

water that mixed for 1 week

was shaken for 30 seconds

and filtered for testing.

• The pH levels were recorded

initially, and then every Monday, Wednesday, and

Friday for the remainder of

the experiment.

MethodsNitrogen Phosphorous

• Levels of both NO2 and

NO3 were recorded in

ppm using the same

solution as the pH.

• The nitrogen levels were

recorded at the start of

the experiment, then on

every Monday,

Wednesday, any Friday

for the remainder of the

experiment.

• Phosphorus was also

measured using the same

solution as the pH and

nitrogen.

• The phosphorus levels

were recorded initially,

then every Monday,

Wednesday, any Friday

for the remainder of the

experiment.

*The testing of these variables was ceased after the fourth week.

Initial Burial 1/25/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Week 1 2/1/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Week 2 2/8/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Week 3 2/15/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Week 4 2/22/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Week 5 3/1/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Week 6 3/8/13

Specimen AAlfisol

Specimen CControl

Specimen BEntisol

Results• The results of the experiment are inconclusive as to determine

the precise effects of the soil on decomposition rates.

• From the variables analyzed, it is not possible to determine if the two experimental conditions used caused significant changes in the rate of decomposition.

• The testing of nitrogen and phosphorus levels was ceased after week 4. The data that was being recorded indicated problems with the testing methods and not the effects of the experimental conditions.

• Prior to the beginning of the experiment it was presumed that water testing kits would be sufficient to test these variables but the results indicate that the testing kits used, were insufficient for these purposes.

• The carcasses decomposed in a similar manner to carcasses in arid environments and the stages are recorded based on those observations.

• Visual observations were also complicated by the unexpected effects of the containers on the carcasses.

• The Alfisol sample had semi-obstructed views from day 28 on, potentially complicating the score assessments.

Post-Experiment AnalysisVisual Data

Specimen AAlfisol

Specimen CControl

• Fresh decay

lasted days 1-4.

• Early Decay (a)

lasted days 5-11.

• Early Decay (b)

lasted days 12-

43.

• Decomposition

score of 99.

• Fresh Decay lasted days 1-2.

• Early Decay (a) lasted days 3-7.

• Early Decay (b) lasted days 8-18.

• Advanced Decay lasted days 19-43.

• Decomposition score of 125.

Specimen BEntisol

• Fresh Decay lasted days 1-2.

• Early Decay (a)

lasted days 3-11.

• Early Decay (b)

lasted days 12-

38.

• Advanced

Decay lasted

days 39-43.• Decomposition

score of 101.

pH Results

Nitrogen Results

Phosphorous Results

Decomposition Score

Decomposition Score

Stage Description Score

Fresh Fresh, no discoloration 1

Early Decay (a) lighter discoloration and presence of bloating 2

Early Decay (b) darker discoloration and absence of bloating 3

Advanced Decaybeginning of desiccation and appearance of bone on less that 50% of body 4

SkeletonizationBone visible on more than half of body and desiccated tissue on less than 50% of body 5

Advanced Skeletonization Skeletonization with bleaching to bone 6

(Galloway et al 1989)

Discussion 1/2• The results of this experiment proved to be inconclusive

due to all of the unforeseen factors that were

encountered.

• The results of this experiment proved that further

exploration into the effects of soil composition on

decomposition still need to be explored using different

methods and testing methods that directly test the soil.

• There was a slight difference in the decomposition score

of the Alfisol and Entisol specimens but it is possible that

due to the burial conditions of specimen A, the stage

indicators went unseen in the Alfisol covered specimen.

• The initial goal of the experiment may not have been

satisfied but the experiment yielded several options for

potential research opportunities.

Discussion 2/2• The containers in which the carcasses were housed were

unique to this project. Further research with enclosures

like these, is required to understand the effects they

have on burial decomposition.

• All of the carcasses in the experiment, including the

control, behaved in unexpected manners for the

environment of the St. Louis area.

• The carcass reacted as if they were housed in an arid

environment. This may be due to the season of testing.

• The results of this experiment open up research ideas for

further exploration on the effects of containers and soil

sterilization on buried carcasses.

• It is also possible that the size of the animal was the

cause of the observed behaviors and further research

on the size of carcass on decomposition rates would be

another useful area of exploration in burial settings.

Acknowledgements • Special recognition goes to Everett Clark for the funding

of this experiment. And to my family for all their love and support.

• Thanks are also given to Bryan Fitch from the Marion, IL USDA-NRCS office for his help and advisement in locating the soil samples.

• Credits additionally go to the very dedicated professors of the SIUE Anthropology Department, especially Dr. Rehg who was the primary advisor for this research and my mentor during my time at Southern Illinois University Edwardsville.

• I would also like to thank Southern Illinois University Edwardsville for giving me the opportunity to conduct this research.

References Cited• Byers S. 2008. Introduction to Forensic Anthropology. Boston, MA. Pearson

Publishing. p. 110-119.

• Carter DO, Tibbett M. 2008. Cadaver Decomposition and Soil: Processes.

Tibbett M, Carter DO (editors). In Soil Analysis in Forensic Taphonomy:

Chemical and Biological Effects of Buried Human Remains. CRC: Press. p. 31-

44.

• Forbes SL. 2008. Decomposition Chemistry in a Burial Environment. Tibbett M,

Carter DO (editors). In Soil Analysis in Forensic Taphonomy: Chemical and

Biological Effects of Buried Human Remains. CRC: Press. p. 205-216.

• Galloway A, Birkby WA, Jones AM, Henry TE, Parks, BO. 1989. Decay Rates of

human remains in an arid environment. Journal of Forensic Sciences 34:607-

616.

• [NRCS, USDA] Soil Survey Staff. 2003. Keys to Soil Taxonomy. 9th ed.

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• Stokes KL, Forbes SL, Benninger LA, Tibbett M and Carter DO. 2009.

Decomposition Studies Using Animal Models in Contrasting Environments:

Evidence From Temporal Changes in Soil Chemistry and Microbial Activity. Ritz

K, Dawson L, and Miller D (editors). Cited in Criminal and Environmental Soil

Forensics. Springer Publishing. p. 360-374.