APPENDIX C
Investigation of Soil pH at Cox's Woods Site, 12 Or 1
Timothy M. Wright
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[acknowledgement]
[background]
[method]
[result]
[conclusion]
[references]
Acknowledgements
I would like to begin by saying thank you to the Honors Division at Indiana University
for funding this research. I would also like to express my gratitude to the staff
and to all the graduate students and fellows at the Glenn A. Black Laboratory
of Archaeology for graciously sharing their expertise and for giving me valuable
advice and constant encouragement. I would also like to give recognition to the
students of the field school in archaeology, Emily Brouwer, Chad Harvey, Jake
Miller and Teresa Naomia, all of whom assisted me in the actual data collection.
Lastly I would especially like to thank Dr. Brian G. Redmond and Mr. Bret Ruby.
Background
For the past four years, the IU Field School in Archaeology has focused on the
Upper Mississippian Oliver Phase occupation on the East Fork of the White River,
primarily in Lawrence, Martin and Orange Counties. From the excavations during
this period all the bone that has been recovered has been in a uniformly poor
state of preservation. When anyone asked why this was so, the standard answer
was--"The soil is too acidic."
For the past year, this author has been working on a faunal collection from another
Oliver Phase site located in Marion County. Although the Marion County site is
about 100 years older than the East Fork sites in the study area, the bone from
the Marion County site is better preserved.
Assuming that the cooking and disposal behaviors remained constant within the
culture, the only explanation for this noticeable difference in bone preservation
would seem to lie with the soil itself.
Soil acidity is commonly measured and expressed as pH. A pH reading of less than
7.0 is considered acidic while a pH reading greater than 7.0 is alkaline. If soil
acidity, as measured on the pH scale, is the main determinant in bone deterioration,
bone preservation should be at its best where pH is highest and acidity is lowest.
Thus, my initial research plan was to search for a relationship between soil pH
and bone preservation and to see if pH readings have any value in detecting archaeological
deposits.
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Method
With the help of field school students, two separate transects were laid out across
the site (See Fig.7). The first transect ran
due east-west on the East 500 line of the site grid. There has been a great deal
of excavation along this axis so pH readings along this transect could be associated
with known deposits. This means the east-west transect serves as a control. The
second transect ran diagonally across the site from the southeast to the northwest.
Both transects began and ended outside the perimeter of the circular village.
This perimeter had been established by earlier excavation. The village being circular,
it was expected that these two transects would yield similar pH profiles.
Along these two transects, at 5-meter intervals, holes were drilled with a bucket
auger. These test holes were divided into four 10-cm levels, and a pH reading
was taken from each level using a Soil pH and Humidity Tester.{1} This instrument
is not particularly sophisticated, but it was considered adequate for giving relative
readings across the site.
On the east-west transect, 27 holes were drilled for a total of 108 pH readings.
Along the southeast-northwest transect, 29 test holes were drilled and a total
of 116 readings taken. During analysis, the data (8 readings) from the last two
test holes on the extreme northwestern end of this transect was omitted. This
seemed justified because this end of the transect was in the Haymond silt/loam
soil group which is a recent fluvial deposit (Wingate 1984). Thus, this soil is
an anomaly when compared to the main soil types at 12 Or 1. In addition if there
were cultural deposits in this area, they would likely be buried far below the
40cm. level which is the maximum depth tested. This also gives both transects
an equal number of readings which makes statistical and graphic comparisons easier.
The total sample from each 10 cm interval was screened through 1/4-inch mesh to
insure good contact with the device. A reading was taken and recorded. All samples
except level 1 (0-10 cm) were bagged and are now curated at the Glenn Black Laboratory.
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Results
The results of the pH readings are shown in graphic form{2} (Figures 1,
2,
3,
4,
5 &
6) and in Table 5.
On the east-west transect (Figures 1-3), levels 1 and 2 form a distinct grouping
with a mean pH of 6.3, while levels 3 and 4 have a mean of 6.6 (Table 1).
Table 1.
Descriptive Statistics for East-West Transect, 12 Or 1
Level 1 Level 2 Level 3 Level 4 Transect
Maximum pH 6.5 6.5 6.9 7.0 7.0
Minimum pH 6.0 6.0 5.8 5.8 5.8
Range 0.5 0.5 1.1 1.2 1.2
Mean 6.3 6.3 6.6 6.6 6.5
Std. Dev. 0.144 0.169 0.241 0.252 0.253
Variance 0.021 0.029 0.058 0.063 0.064
This pattern of separation between the upper two levels and the lower two is persistent
on the east-west transect. There are two possible explanations for this:
1)The 500 line was used as the main trail across the site by the field school
over the last two seasons. This traffic may have compacted the surface which effected
the soil pH, or
2)Levels 3 and 4 were tested several days after levels 1 and 2. There were several
rain days in this interval which may have changed the moisture content and pH
of the lower levels.
Regardless of the cause, the readings from levels 1 and 2 were viewed by this
author as anomalous and excluded from any statistical tests.
The important thing to notice in the graphs is the increased variability or "static"
that appears at both ends of this transect.
Readings at E525 and E520 coincide with visible earthworks at the perimeter of
the village. Readings at E425 and E420 are at the west perimeter of the stockade,
the exact position of which was only established through excavation. This same
pattern of "static" shows up again on the Southeast-Northwest transect
(Figures 4-6). In these areas (tests 3 and 4 and 23 and 25) there is no surface
indication of the earthwork, and there have been no excavations to verify its
exact location. If this "static" does coincide with the earthwork, one
would be inclined to show the stockade line as a closed circle rather than the
horse-shoe shape depicted in Figure 7.
I have no explanation for the erratic readings in the middle of the graphs, but
it appears on both transects. Perhaps wild fluctuations in soil pH, whether to
the high or low end of the scale, would indicate some kind of soil mixing which
may or may not be associated with prehistoric human activities. It may be suggested
that this central part of the village should be assigned high priority for future
excavation to determine the exact agent responsible for this soil mixing.
Nowhere is the difference between the two transects more obvious than in the graphs
of the linear fit (Figures 3 and 6). The east-west fit shows the split that separates
levels 1 and 2 from levels 3 and 4. It should also be noted that levels 3 and
4 intersect at E470. This is interesting in that it mimics the actual stratigraphy
of the site. On the east end of the site, cultural deposits are first encountered
at about 20 cm below surface and exhausted by 30 cm, so the bulk of known cultural
material is in level 3. The west end of the site is more deeply buried with intact
features first encountered at about 30 cm below the surface. So, on this transect
the best fit line constructed from pH readings gives an accurate indication of
the actual slope of the subsurface deposits. In 1994, there were no excavations
on the southeast-northwest transect to verify the value of this observation.
Descriptive statistics also serve to illustrate the dissimilarities in the two
transects.
Table 2.
Descriptive Statistics for Southeast-Northwest Transect, 12 Or 1
Level 1 Level 2 Level 3 Level 4 Transect
Maximum pH 6.9 6.9 7.0 7.0 7.0
Minimum pH 6.2 6.4 6.4 6.5 6.2
Range 0.7 0.5 0.6 0.5 0.8
Mean 6.7 6.7 6.7 6.7 6.7
Std. Dev. 0.156 0.155 0.137 0.131 0.146
Variance 0.024 0.024 0.019 0.017 0.021
Figure 6 shows all four levels clustered around the mean of 6.7. The separation
into upper and lower cluster is not nearly as extreme in the southeast-northwest
transect, but it does still exist. In addition levels 3 and 4 intersect again.
In order to determine if the east-west readings have any predictive value, a correlation
was run on level 4. Readings along the east-west (control) transect were the independent
variable. Readings along the southeast-northwest transect were the dependent variable.{3}
Results showed an extremely weak (-0.069) negative relationship with a very high
probability (p< .05) that any relationship is a matter of chance.
Also, an analysis of variance was run on all four levels to determine if there
was any pattern in the dissimilarity of the two transects. Since the correlation
analysis showed the poor predictive value of any individual pH reading, test number
was used as an independent "dummy" variable for an analysis of variance.
This procedure also showed that no statistically significant relationship exists
between the two transects. So, despite the apparent similarity in the graphic
displays, pH readings have almost no predictive value as concerns location of
subsurface archaeological deposits. Whether we look at individual readings or
patterns in the entire transect, there are too many confounding factors that effect
soil pH to make it an effective tool for archaeology.
So far none of this has addressed the other question of, "How does soil pH
relate to bone preservation?" Throughout the entire survey process, no bone
was recovered, and only three readings of pH 7.0 were recorded. Fortunately, in
the course of excavation bone was recovered by Stephen Ball and his crew in Unit
BBB in a matrix that read 7.0. Also in Unit QQ bone was recovered by Rex Garniewicz
and his team in a matrix that tested 6.5 pH. A fluctuation in pH reading reflects
an exponential change in ion exchange capacity of the soil that could have a marked
effect on chemical leaching, i.e., bone deterioration. A small fluctuation in
pH reading can make a big difference in the preservation potential, but it is
not a direct relationship. A pH 7.0 (neutral) does not guarantee good bone preservation.
There was no discernable difference in the state of preservation of bone from
the two above-mentioned contexts. In both cases, the bone was in the same poor
condition we have come to expect in the East Fork study area. It is apparent that
pH alone is not the sole determining factor in bone preservation. In fact, it
seems likely that as soil pH increases the potential for leeching also would increase,
leading to a more rapid deterioration.
Bone is made up primarily of potassium and calcium. If the surrounding soil is
lacking in these minerals, they will be quickly removed from the bone when H2O
is available in sufficient quantities to act as the catalyst. The water retention
properties of southern Indiana soils are well known. In regard to bone preservation,
or the lack thereof, the mineral content of the soil matrix and water retention
properties of the soil are much more important than soil acidity as measured on
the pH scale (Brady,1984, Foth 1984).
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Conclusion
Based on pH readings, the soils at the Cox's Woods site cannot be characterized
as acidic. Therefore, soil acidity as measured on a pH scale does not directly
determine quality of bone preservation in archaeological contexts. In addition
pH is a very localized and fickle property of the soil and can be effected by
numerous agents other than subsurface archaeological deposits.
The parent material establishes the baseline pH and chemical characteristics of
a soil group. These are then locally altered by such diverse factors as climate,
vegetation, compaction, mixing, and/or the inclusion of organic matter in the
form of archaeological deposits. As a result a particular pH reading can be the
product of many factors. This makes the value of a pH survey questionable as a
means of pinpointing subsurface archaeological deposits. This is why no statistically
significant relationship could be shown between the two transects, even though
we were dealing with a circular village in which archaeological deposits are in
a predictable concentric ring. Excavation is still required to establish cause
for any recorded variation in soil pH and to locate archaeological deposits.
Though a pH survey of this kind has obvious limitation as a predictive or interpretive
tool for archaeologists, this author does not feel it was a waste of time. Soil
pH is a property of all archaeological sites. As a universal feature, it should
be routinely recorded in all excavations. It is not that time- consuming or expensive
to do so. Because one does not see the value of a data set now does not mean someone
else won't come along at a later date and reinterpret it to the benefit of the
entire discipline.
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References cited
Brady, Nile C.
1984The Nature and Properties of Soil. 9th ed. Macmillan Publishing Company: New
York.
Courty, Marie Agness, Paul Goldberg, and Richard Macphail
1989Soils and Micromorphology in Archaeology. Cambridge Manuals in Archaeology:
Cambridge University Press.
Foth, Henry D.
1984Fundamentals of Soil Science. 7th ed. John Wiley and Sons, Inc.: New York.
Redmond, Brian G
ndbThe summer 1993 excavations of the Cox's Woods site (12 Or 1), a late prehistoric
Oliver phase village in the Pioneer Mothers Memorial Forest Recreation Area, Hoosier
National Forest. Glenn A. Black Laboratory of Archaeology, Indiana University.
Reports of Investigations 94-17.
Wingard, Robert C., Jr.
1984Soil Survey of Orange County, Indiana. United States Department of Agriculture,
Soil Conservation Service.
Table 3.
Raw Data for East-West Transect, 12 Or 1
Test# North East pH1 pH2 pH3 pH4
1 500 535 6.3 6.1 6.5 6.5
2 500 530 6.2 6.5 6.8 6.8
3 500 525 6.4 6.4 6.7 6.9
4 500 520 6.4 6.0 6.7 6.3
5 500 515 6.2 6.4 6.7 6.3
6 500 510 6.5 6.0 6.7 6.7
7 500 505 6.4 6.2 6.9 6.7
8 500 500 6.4 6.4 6.8 6.8
9 500 495 6.4 6.4 6.9 6.8
10 500 490 6.4 6.4 6.6 6.6
11 500 485 6.4 6.4 6.7 6.6
12 500 480 6.1 6.1 6.3 6.3
13 500 475 6.0 6.0 6.8 6.7
14 500 470 6.2 6.2 6.3 6.4
15 500 465 6.4 6.4 6.8 6.8
16 500 460 6.4 6.4 6.8 6.7
17 500 455 6.5 6.5 6.8 6.8
18 500 450 6.5 6.5 6.5 6.8
19 500 445 6.3 6.3 6.4 6.4
20 500 440 6.4 6.4 6.6 6.6
21 500 435 6.2 6.2 6.4 6.6
22 500 430 6.1 6.1 6.3 6.3
23 500 425 6.4 6.4 6.6 6.6
24 500 420 6.0 6.0 5.8 5.8
25 500 415 6.4 6.4 6.4 6.6
26 500 410 6.4 6.4 6.6 6.8
Table 4.
Raw Data for Southeast-Northwest Transect, 12 Or 1
Test# North East pH1 pH2 pH3 pH4
1 440.00 520.00 6.8 6.5 6.5 6.6
2 443.54 516.46 6.4 6.6 6.7 6.7
3 447.07 512.93 6.4 6.5 6.4 6.5
4 450.61 509.39 6.7 6.7 6.9 6.7
5 454.14 505.86 6.7 6.7 6.7 6.7
6 457.68 502.32 6.8 6.5 6.7 6.8
7 461.22 498.87 6.7 6.8 6.7 6.6
8 464.75 495.25 6.7 6.8 6.7 6.7
9 468.29 491.71 6.7 6.8 6.7 6.7
10 471.82 488.18 6.8 6.8 6.6 6.7
11 475.36 484.64 6.5 6.7 6.7 6.8
12 478.90 481.10 6.7 6.8 6.9 6.8
13 482.43 477.57 6.8 6.9 6.9 6.9
14 485.97 474.03 6.8 6.8 6.8 6.8
15 489.50 470.50 6.5 6.4 6.7 6.8
16 493.04 466.96 6.8 6.5 6.5 6.5
17 496.58 463.42 6.5 6.5 6.7 6.7
18 500.11 459.89 6.2 6.4 6.8 6.7
19 503.65 456.35 6.8 6.9 6.8 6.9
20 507.18 452.82 6.9 6.9 7.0 7.0
21 510.72 449.28 6.8 6.9 6.9 6.8
22 514.26 445.74 6.8 6.8 6.8 6.8
23 517.79 442.21 6.8 6.8 6.9 6.8
*
25 524.86 435.14 6.7 6.7 6.6 6.5
26 528.40 431.60 6.7 6.5 6.7 6.7
27 531.94 428.06 6.7 6.7 6.6 6.5
**28 535.47 424.53 6.7 6.7 6.7 6.5
*29 539.01 420.99 6.7 6.6 6.6 6.6
* Test #24 omitted because it fell within an excavated unit.
** Test #s 28,29 dropped from graphs and regression.
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