A Validation Test of a Field-Based Phosphate Analysis Technique

Environmental Geochemistry and Health, 1988

High soil phosphate concentrations are commonly related to intense past human activity although full understanding of this relationship requires further research. At present, practical constraints in the field, the need for extensive sampling and for rapid results, leads to the archaeologist frequently using crude but portable techniques of chemical analysis. The problems associated with the collection and interpretation of archaeological soil phosphate data are discussed. The use of Bayesian change-point analysis is proposed as a suitable statistical aid to the interpretation of such data.

Phosphorus (P) is unique among the elements in being a sensitive and persistent indicator of human activity. It has long been of interest to archaeologists because of its potential to inform them about the presence of past human occupation and to offer clues regarding the type and intensity of human activity. A wide variety of methods have been developed in both soil science and in archaeology to extract and measure soil P, resulting in a tremendous amount of data and a wide array of interpretations, but also considerable confusion over appropriateness of methods and terminology. The primary purpose of this paper is to address these issues by clarifying soil P analyses. Anthropogenic additions of phosphorus to the soil come from human refuse and waste, burials, the products of animal husbandry in barns, pens, and on livestock paths, or intentional enrichment from soil fertilizer. Once added to the soil, phosphorus in its common form as phosphate is stable and generally immobile in soils. Soil P comes in many forms, organized for the purposes of this paper on the basis of extraction and measurement procedures as (1) extraction for available P (Pav); (2) portable field techniques (the spot test or ring test); (3) chemical digestion of a soil sample for total P (Ptot); (4) extractions of inorganic P (Pin) for fractionation studies and extractions to look at individual compounds of P; (5) measurements of organic P (Porg); and (6) extractions for total elemental analysis. To compare the suitability of various extractants as the ''best'' indicator of human input and activity we subjected samples from three very different archaeological sites (Lubbock Lake, TX; Hulburt Creek, IA; British Camp, WA) to four methods of soil P extraction: perchloric acid digestion (Ptot), sulfuricenitric acid extraction Ptot), hydrochloric acid extraction after ignition (Pin), and citric acid extraction (Pav). Further, methods of measurement were compared via colorimetry vs. Inductively Coupled Plasma (ICP) spectrometry, and the two methods of supposed ''total P'' were both measured via ICP. In general, the stronger extractants yielded more soil P, but the result are not clear-cut. Likely variables include the intensity of occupation, nature of the parent material, and postdepositional weathering (e.g., the addition of dust).

Journal of Sistan and Baluchistan Studies, 2022

Phosphate is unique among the elements in being a sensitive and persistent indicator of human occupation. It has long been of interest to archaeologists because of its potential to inform them about the presence of past human activity and to offer clues regarding the type and intensity of human occupation. In fact, the soil of settlements is part of the phosphorus reservoir. The reconstruction of the human activities areas of archaeological sites using soil phosphate analysis is a well-known technique. This study aims to identify and compare the activity area at ancient mounds of Rivi through the measurement of the quantity of phosphates in the soil. In this study, 29 soil samples were collected from the study area, and phosphorus quantity was measured using Spectrophotometry. Multivariate statistical methods were used to classify the obtained results. The results showed that the phosphorus concentrations in the ancient areas were higher than in the control area, and among the ancient areas, the phosphorus quantity related to Rivi B was higher than in other mounds. Previous studies have shown that the Rivi area has been inhabited from around 2900 years ago to the last Sassanian years (1,500 years ago), and in the middle of the Islamic age (1000 years ago), it was a great village. In total, the archaeological site of Rivi was inhabited during the Iron Age, Achaemenid, Parthian, Sassanid, and Islamic periods, and that is why there was a high concentration of phosphorus in the Rivi area compared to the control area.

Journal of Archaeological Science, 2000

Human occupation enriches soils with phosphorus, which may provide a useful chemical tracer for site delineation in archaeological studies. In the present study, fine scale soil profiles of inorganic, particulate organic and total phosphorus through a prehistoric Indian site and nearby control site in Cape Cod, MA, indicated a greater predictive value of particulate organic P over inorganic P and total P in determining the vertical boundaries of an anthrosol. The value of inorganic P and total P as occupation tracers was confounded by vertical migration of inorganic P species. Inorganic P mobility was found to result from diagenesis and other post-depositional alterations, including the effects of recent sea water flooding on soil concentrations of dominant exchangeable cations. Parallel measurements of organic carbon and total nitrogen confirmed organic enrichment within the anthrosol. Evaluations of elemental ratios distinguished the anthrosol from the unimpacted soil locations by a 50% higher average C:P ratio and a two-fold higher average C:N ratio of its residual organic fraction which declined exponentially with depth. Combining C, N and organic P data yielded a robust tracer for distinguishing anthropogenic organic matter enrichment from naturally occurring deposition through all soil levels examined at this prehistoric site. Profiles of organic matter C:OP and C:N ratios indicated that C enrichment occurred well below the stratigraphically defined anthrosol boundary indicating site habitation prior to the anthrosol deposition. This contention of earlier site usage was supported by comparison of depth profiles of C:OP ratios with lithic debitage density profiles. Significant correlations between C:OP ratios and lithic debitage density suggested that C enrichment relative to OP may be a useful indicator of habitation and may yield insight into intra-site variation in the intensity of land use.

Journal of Archaeological Science, 2014

Elevated soil phosphorus levels are often used as indicators for prehistoric manuring. However, in this article it is argued that though P is indeed a good anthropogenic marker, multi-element analyses can provide more insight into former fertilisation practices and land use. Here, we compare the ability of both traditional total P analysis and multi-element analysis by ICP-MS to identify prehistoric manuring on soil samples from a well-preserved prehistoric Celtic field system in Denmark. The ICP-MS data set of 58 soil samples was furthermore analysed by multivariate analysis (PCA). Results show that the stronger extraction for the multi-element analysis releases significantly more P than the traditional analysis but similar archaeological interpretations based on relative P enrichments can be made. Among the 42 analysed elements, 11 were significantly (P < 0.01) enhanced in the fields relative to a reference soil, namely Na, P, K, Ca, Mn and Sr and the rare earth elements (REE's), Nd, Sm, Eu, Gd and Dy. Cobalt was the only element which was depleted within the field system. Enhanced P levels show that manuring was practiced, while elevated concentrations of Sr indicate that not only animal manure but also bones/domestic waste was added. Furthermore, the enhancement pattern of some major and minor elements indicate that unweathered subsoil was incorporated into the topsoil – probably through tillage erosion until approximately 2000 years ago. The study also indicates that the banks demarcating the individual fields were made of the same material as the field plough-layers, which makes within-field soil relocation the most likely cause of the banks.

Settlement structure plays an important role in explanations of social and political change in Late Prehistoric eastern North America but ethical and logistical challenges posed by extensive horizontal excavations mean that archaeologists must develop low cost, minimally-invasive methods for inferring key properties of village structure. There are two important components of most villages in the region: 1) the peripheral distribution of middens; and 2) the size and location of formal communal spaces or plazas, each of which leaves traces in soil chemistry. In shallowly buried, plowed village sites where artifacts have been physically displaced, the chemical signature of middens may be more resistant to disturbance and provide an enduring signature of ancient settlement structure. We conducted a systematic soil phosphorus survey at the Late Prehistoric Period (AD 1000-1600) Reinhardt Site (33PI880) in central Ohio to test for the presence and approximate size of a central plaza and the shape and distribution of peripheral midden deposits. Soil samples from the modern plowzone (N=131) were analyzed for Mehlich-2 extractable phosphorus using molybdate colorimetry. The interpolated phosphorus distributions indicate a clear ring midden approximately 160m across with an internal plaza that is roughly 30m x 40m. Artifact distributions from a shovel-test pit survey and interpolations of plowzone magnetic susceptibility measurements identify the location of the village but are ambiguous with regards to village size and do not clearly distinguish the central plaza. Our results suggest that systematic surveys of soil phosphorus are a rapid, minimally-invasive, and inexpensive method for generating data on the size and shape of villages and their plazas.

…, 2000

Currently there is a wide interest in the use of chemical analyses for the evaluation of anthropogenically altered soils and other archaeological deposits. Because soil phosphorus levels increase in areas of human habitation, and leave a permanent signature that can only be removed by erosion of the soil itself, phosphorus mapping has become a popular field procedure to indicate areas of habitation where overt evidence of ancient occupance is absent. We have developed a methodology to obtain accurate acid-extractable phosphorus concentrations (mg/kg) in calcareous soils under the primitive field conditions of Piedras Negras, Guatemala. Predicated on Mehlich-II acid extractant and colorimetric methods, this procedure processed 36 samples per hour at very low cost per sample. Based on eight replicate measurements of a group of samples, the coefficient of variation of the procedure was 8.3%. Subsequent analysis of 35 soil samples in a controlled laboratory revealed a moderate correlation of 0.44 between the Mehlich-extractable phosphorus and total phosphorus. The correlation was 0.91 between the Mehlich procedure and Olsen bicarbonate extractable phosphorus, indicating that Mehlich-based results are similar to those obtainable using a traditional extractable phosphorus method on soils of neutral to alkaline pH. There was a moderate correlation between Mehlich P and ring-test rating (r ϭ 0.42). The wider dynamic range of the Mehlich extraction, coupled with the use of a battery-operated colorimeter, facilitated the finding of a refuse midden within an area of phosphate enriched soils. Further tests indicated that phosphorus concentrations measured in the field deviated by only 7% from those made under controlled laboratory conditions. ᭧

Journal of Archaeological Science, 2009

Soil multi-element analysis is now a routine technique employed to help answer questions about space use and function in and around archaeological sites. The pattern of enhancement of certain elements, including P, Pb, Ca, Zn, and Cu, has been shown by numerous studies to correlate closely with the archaeological and historical record.