Studies of Soils from an Aleutian Island Site

Chapter 11

Studies of Soils from an Aleutian Island Site Henry J. Chaya

Downloaded by CHINESE UNIV OF HONG KONG on November 3, 2016 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0625.ch011

Department of Chemistry, Vassar College, Poughkeepsie, NY 12601

The study of properties of archaeological soils may give valuable information as to the location of middens and previously settled areas. A study is described of a site on Chernabura Island in the Aleutian Islands which was occupied by marine hunter-gatherers for at least 1500 years. Relatively simple analytical procedures for phosphorus and organic content were used to locate possible middens and places and manner of occupation. Phosphorus determination utilizing the molybdovanado-phosphate colorimetric method rather than the molybdenum blue method is described. Methods used for successfully dealing with interference for the determination of total phosphorus, organic phosphorus, and inorganic phosphorus are discussed. Most of the analytical steps for phosphorus and organic carbon determinations were performed by students using simple laboratory equipment. The methods used were simple and rapid.

High soil phosphorus content may indicate past human settlement activity (7). Phosphorus content in soils may indicate past human settlement even after 2500 years. Therefore, there is a need among archaeologists for a simple, rapid, economical, and reasonably accurate means of analyzing phosphorus in soils. Several authors have published modifications of procedures for the analysis of soil phosphorus (2 - 6), and portable field tests for phosphorus (2, 6, 7). Another consideration is the fractional separation of different forms of phosphorus that relate to aspects of previous human occupation (4). This paper will deal with fractional separations of soil phosphorus in terms of total phosphorus, inorganic phosphorus, and organic phosphorus as recommended by Bethel, et al. (8) as a useful breakdown of soil phosphorus. The determination of total phosphorus by wet chemical extraction is considered one of the most accurate measures of archaeological soil phosphorus. Wet chemical extraction of total phosphorus from soils and sediments is time consuming and in some cases requires the use of dangerous reagents such as perchloric acid. There is however, a more practical, if slightly less accurate means of preparing the

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soil sample for the determination of total phosphorus. This preparation involves heating the sample to 550 °C followed by acid extraction of the total phosphorus. Ordinarily, inorganic phosphorus determination involves acid extraction without the ignition step. For soil sample preparation, the ignition method is easier and safer than a chemical digestion. It permits the determination of total, organic and inorganic phosphorus and as a bonus, total organic matter (9 - 77). Organic phosphorus is cal culated as the difference between total and inorganic phosphorus (72). In the situation described here, extracted phosphorus is determined colorimetrically using the molybdovanado-phosphate (MVP) color procedure. In our experience, this color complex is more stable and measurements more reproducible than the molybdenum-blue colorimetric procedure commonly reported in the archaeological literature. The MVP colorimetric determination is recommended (75, 14) for its stability, freedom from temperature and time factors and ease of color development. Phosphorus in the Soil Calcium, aluminum, and iron are present in most soils. At high pH, inorganic phosphate is formed by bonding to calcium in an ionic manner and as the pH decreases, phosphate bonds to aluminum and iron. Organic phosphate on the other hand is bonded as an ester. Organic phosphate is found in all living things and it is known that some mineralization to the inorganic form has taken place over time. Mineralization takes place relatively slowly in temperate regions and somewhat more rapidly in tropical regions. Bone which contains phosphorus will be preserved for long periods of time in soils with basic pH, but decomposes fairly quickly in acidic soils (5, 75). Phosphorus found in organic refuse accumulates in the soil and even after several thousand years may still be detected. The soil samples analyzed for phosphorus in this report were from Archaeological Site XSI-040 located on Chernabura Island in the Shumagin Islands which are a part of the Aleutian Islands of Alaska. It is a place that was occupied by marine hunter-gatherers at various times probably over a period of at least 1500 years as indicated by radiocarbon dating. The area, a strip of land on a cliff overlooking a northern part of the beach, is approximately 130 m long and extends inland for approximately 50 m. Soil samples were taken in a systematic manner utilizing a grid to locate middens or areas where refuse was deposited. Soil samples were also taken at surface points of interest, such as signs indicating probable former underground dwellings (76}. Methodology Our previous use of the analytical procedure briefly described above involved taking two portions of the same soil sample. The first portion was ignited to 550 °C, extracted with 2 M HC1 and then subjected to "total phosphorus" determination using the molybdovanado-phosphate colorimetric procedure. The second portion was directly extracted with 2 M HC1 for the determination of "inorganic phosphorus" using the same colorimetric procedure. Any interference due to brown soil coloration was satisfactorily accounted for by running a blank with each sample consisting of just the acid solution without the color reagent. The net colorimetric instrument reading between the two was taken as that due to the phosphorus content. The procedure of using a sample blank to account for brown coloration was checked by removing the brown coloration with activated carbon for several samples. No interference was ever encountered in the acid extract of the ignited portion. The difference between the total and inorganic phosphorus was regarded as that due to organic phosphorus.


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Table I represents total phosphorus content of a group of sediments and soils that were analyzed by electron microprobe (77) and then by the analytical procedure described above. Table I. Total Phosphorus of Sediment and Soils Analysis


Samples

A Β C D Ε F G H

%P %P MVP Electron Microprobe Colorimetric 0.022 0.052 0.054 0.073 0.022 0.057 0.057 0.086

0.023 0.051 0.052 0.075 0.023 0.057 0.058 0.086

When the above analytical procedure was applied to the archaeological soils from Site XSI-040, no interference was experienced for the determination of total phosphorus. Serious interference was encountered in the determination of inorganic phosphorus in the form of dark brown colors in the (unignited) acid solutions that masked the developed color. Use of activated charcoal (Norite™) effectively removed the brown soil coloration, but a disadvantage was that it gave a high blank for phosphorus. For some samples, even after the brown color had been removed, a greenish color developed instead of a yellow one. According to the literature (72), the greenish color indicated the presence of Fe(II), an interference factor. The greenish color was removed by adding a small amount of hydrogen peroxide to each sample, which did not interfere with the MVP determination. In order to overcome the interference problem described above, it was necessary to analyze for total phosphorus and inorganic phosphorus in different portions of the same archaeological sample. This was done in the following manner: a sample of soil was taken and its total phosphorus was determined as previously described. Another portion of the same sample was taken and extracted with 2 M HC1. The acid extract was separated from the solid portion by either centrifuging or Biichner funnel filtration with ashless filter paper. The solid contained organic phosphorus, while the acid extraction contained inorganic phosphorus. Each separated portion was analyzed following the procedure for total phosphorus content. In the solid portion, the total phosphorus represented the organic phosphorus of the original soil sample, while the total phosphorus from the acid extraction represented the inorganic phosphorus of the original sample. The two forms of phosphorus from this second portion should add up to the value for total phosphorus determined directly on the first portion of the sample. Table II represents a number of soil samples analyzed from Archaeological Site XSI-040. A comparison is shown between total phosphorus expressed as the sum of individually determined organic and inorganic phosphorus, and total phosphorus determined directly. The sums for total phosphorus compare well with the directly determined total phosphorus values. In practice, therefore, total phosphorus may be determined directly and in another portion only the organic phosphorus as described above. The inorganic phosphorus may be calculated by difference.


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Table II. Total Phosphorus as a Sum and as a Direct Determination


Sample Number % Inorganic Ρ 1 2 3 4 5 6 7 8 9 10

0.86 1.40 0.08 0.05 0.10 0.16 0.11 0.27 0.11 0.52

% Organic Ρ 0.20 0.22 0.01 0.06 0.07 0.10 0.13 0.14 0.15 0.17

% Total Ρ Direct % Total Ρ (Sum) Determination 1.06 1.62 0.09 0.11 0.17 0.26 0.24 0.41 0.26 0.69

1.02 1.67 0.10 0.13 0.17 0.24 0.26 0.35 0.26 0.68

Experimental Procedure The soil samples were broken into small particles by percussion without grinding and allowed to dry at room temperature for at least four days. The determinations were based on the weight of sample at equilibrium with room temperature and ambient humidity. The soil samples were then ground with a mortar and pestle and sieved using 1 mm mesh screen. For the determination of total phosphorus, 1 g of each of the prepared samples was weighed into a 20 mL glass scintillation vial with a Teflon™lined cap which was included in the tare. The vial should be capable of withstanding a temperature of at least 550 °C. A reagent blank was included with each set of samples. The uncapped samples were placed in a drying oven at 105 oC for one hour, then capped, cooled and weighed to 0.1 mg. The uncapped samples were then placed in a muffle furnace that was slowly brought up to 550 °C over 1.5 h and maintained at that temperature for an additional 0.5 h. The samples were capped, cooled, and weighed again. The measured weight difference, the "loss on ignition" or LOI, has been shown to have a linear relationship to organic carbon content and will be discussed in the next section. After addition of 10 mL 2 M HC1, each sample was weighed to 0.01 g and heated in a 90 °C water bath for 1 h with occasional swirling of each vial. The samples were weighed again, and additional distilled water was added to make up for any lost through evaporation. The samples were then removed from the water bath and any insoluble materials were allowed to settle over a period of several hours. After the insoluble materials in the sample vials had settled, each sample was treated in the following manner: an aliquot not exceeding two mL of the supernatant liquid was quantitatively transferred to a 25 mL volumetric flask. Five mL of MVP color reagent (13, 18) were added and the solution was diluted to the mark with distilled water. The color was allowed to develop for at least ten minutes. The absorbance of the solution was measured using distilled water as a reference at a wavelength of 470 nm in a colorimeter. A cell with a pathlength of 2 cm is recom mended. The amount of phosphorus the absorbance represents was read from a calibration curve prepared from standard phosphorus solutions treated in the same manner as the samples.


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Results and Discussion Total phosphorus content in soil is a well-accepted form for indicating places of human occupation for an archaeological site. Locations of high phosphorus content help an archaeologist decide where to excavate. Figure 1 is a map of Site XSI-040 showing the distribution of total phosphorus content in terms of three value ranges. The distribution of phosphorus content indicates the location of probable middens and underground houses called barabaras which are of primary interest here. The various circles represent soil samples from test pits of surface points of interest in terms of definite and probable barabara locations. The distribution clearly indicates several areas of high soil phosphorus concentration. Since middens usually have high soil phosphorus content, it appears that the previous settlers threw much of their refuse over the cliff to the beach below. Other areas of high phosphorus concentration are in the middle and southeastern parts of the site. About 150 soil samples were analyzed for total phosphorus and corresponding loss on ignition. The samples were run usually in groups of 20. Each group included a reagent blank, and three control soil samples to monitor reproducibility, which was within five percent. Some samples were collected off the site to determine the total phosphorus in "unlived" areas away from the site. At six different sampling points, two soil samples were taken at depths of 20 to 40 cm. and 40 to 60 cm. The range in concentrations of total phosphorus was 0.09 to 0.13 %. A soil sample is dried at 105 c and weighed and then ignited at 550 «C and reweighed. The weight difference or loss on ignition represents the organic carbon ignited. A linear relationship between organic carbon content and percent loss on ignition (LOI) has been demonstrated in the literature (19). In this work the LOI was determined as a routine step for each total soil phosphorus determination. Just as Figure 1 shows a distribution of total phosphorus content in three ranges of concentration, Figure 2 shows the LOI for the same samples in three ranges of values. There are similarities in the distribution of both soil properties. Conclusions We have described herein a method for analyzing phosphorus in archaeological soils in the laboratory. This method is rapid, simple, and agrees well with results from other methods in terms of total, organic, and inorganic phosphorus. The use of the stable molybdovanado-phosphate (MVP) colorimetric procedure for phosphorus determination was evaluated. Interference in the soil samples prevented the direct determination of inorganic phosphorus. In turn, the organic phosphorus could not be determined by difference. The problem was solved, using modifications that were relatively simple and straightforward. A major objective in this work was to provide the archaeologist with a rapid and reliable method for obtaining archaeological soil phosphorus data. Using the ignition method, total phosphorus content and organic carbon content were determined in soil samples from an Aleutian Island archaeological site. The results have provided useful information on dwelling construction and on house and midden locations. This type of information is particularly advantageous in soil-survey archaeology, and since the color development and reagents used are stable over long periods of time, this method has the potential, with modification, to become useful as a field test.




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Acknowledgments


The author thanks Professor Lucille Lewis Johnson, Department of Anthropology, Vassar College, and her students, Mindy Perilla, Rachel Goddard, and Jonathan Howard who participated in the excavations and also helped in the analysis of the soil samples, and Adrienne Fowler who prepared the SITE XSI-040 maps. Thanks are also extended to the members of the Chemistry Department of Vassar College for their advice and for the use of laboratory facilities. This research was supported by National Science Foundation Grant OPP-9223473 and by Vassar College. Literature Cited 1. Cook, S. F.; Heizer, R. F. Studies on the Chemical Analysis of Archaeological Sites; University of California Publications in Anthropology 2: Berkeley, CA, 1965. 2. Eidt, R. C. American Antiquity 1972, 38, 206-210. 3. Eidt, R. C. Science 1977, 197, 1327-1333. 4. Eidt, R. C. Advances in Abandoned Settlement Analysis: Application in Prehistoric Anthrosols in Colombia, SouthAmerica;University of Wisconsin/Milwaukee, Center for Latin America: Milwaukee, 1984. 5. Cavanagh, W. G.; Hirst, S; Litton, C. D. Journal of Field Archaeology; 1988, 15, 67-83. 6. Craddock, P. T.; Gurney, D.; Pryor, F.; Hughes, M. J. Journal of Archaeology; 1985, 142, 361-376. 7. Overstreet, D. F. The Wisconsin Archaeologist 1974, 55, 262-270. 8. Bethel, P.; Maté, I. Scientific Analysis in Archaeology and Its Interpretation; Henderson, J., Ed.; Oxford University Committee for Archaeology, Institute of Archaeology: Oxford, 1989; pp 1-29. 9. Andersen, J. M . Water Research 1976, 10, 329-31. 10. Hamond, F. W. Landscape Archaeology in Ireland; Reeves-Smyth, T.; Hamond, F., Eds.; Bureau of Archaeological Research: Oxford, 1983; pp 47-80. 11. Gurney, D. A. A Guide for the Field Archaeologist. Technical Paper No. 3; Institute of Field Archaeologists: Birmingham, (UK), 1985. 12. Water and Environmental Technology, "Total Recoverable Phosphorus and Organic Phosphorus In Sediments"; American Society for Testing of Materials: Philadelphia, 1983; 11.02, pp 716-720. 13. Gee, Α.; Deetz, V. R. Anal. Chem. 1953, 25, 1320-1324. 14. Kitson, R. E.; Mellon, M. G. Ind. Eng. Chem. 1944, 16, 379-383. 15. Provan, D. M. J. Norwegian Archaeology Review 1970, 4, 37-50. 16. Johnson, L. L.; Perilla, M. J.; Chaya, H. J. Journal of Archaeological Science, in press. 17. McKinley, T. D.; Heinrick, K. F. J.; Wittry, D. B. The Electronmicroprobe; John Wiley & Sons: New York, NY, 1966. 18. Standard Methods for the Examination of Water and Wastewater, 13th Ed.; American Public Health Association, Washington DC, 1971, 527-530. 19. Dean, W. E. Jr. Journal of Sedimentary Petrology 1974, 44, 242-248. RECEIVED

October 9, 1995


Studies of Soils from an Aleutian Island Site

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