In situ measurement of soil pH

Soil pH is one of the most important factors affecting the in situ preservation of archaeological artefacts of e.g. bone, shells and iron. It is therefore important to have good, reliable methods for determining the pH. However, in all methods that involve sampling of soil or water, loss of gaseous species such as carbon dioxide from the samples as well as oxidation of reduced species may lead to results that do not reflect the in situ pH value. In this paper a method for taking pH measurements directly in the soil that avoids problems with degassing and oxidation is described. The method involves the use of a solid state pH electrode (ISFET) and a specially designed steel probe for introducing the electrode into the soil. The method has been developed and used at a waterlogged site, Nydam, Denmark. The same electrode has also been used to obtain detailed pH profiles during an archaeological excavation at Amosen, Denmark. Here the major advantage is a high spatial resolution and instant results during the excavation. The method is compared to standard methods for measuring pH in soil, and it is demonstrated that such standard methods in extreme cases can give differences of up to 2 pH units compared to the in situ pH. The implications of the measured pH values for the archaeological remains at the two sites are discussed briefly.

[1]  D. Gregory,et al.  Siderite as a Corrosion Product on Archaeological Iron from a Waterlogged Environment , 2003 .

[2]  R. Janaway,et al.  Death, Decay and Reconstruction: Approaches to Archaeology and Forensic Science , 1987 .

[3]  J. Stewart,et al.  Reburial of the Red Bay Wreck as a form of preservation and protection of the historic resource , 1995 .

[4]  M. Nilsson,et al.  Methane and Carbon Dioxide Concentrations in Bogs and Fens--with Special Reference to the Effects of the Botanical Composition of the Peat , 1993 .

[5]  Werner Stumm,et al.  Fresh Water and Ocean. (Book Reviews: Aquatic Chemistry. An Introduction Emphasizing Chemical Equilibria in Natural Waters) , 1982 .

[6]  D. Skoog.  Fundamentals of analytical chemistry , 1963 .

[7]  J. Crowther.  The Experimental Earthwork at Wareham, Dorset after 33 Years: Retention and Leaching of Phosphate Released in the Decomposition of Buried Bone , 2002 .

[8]  C. Caple.  Defining a reburial environment: research problems characterising waterlogged anoxic environments , 1994 .

[9]  P. Jensen,et al.  Environmental Monitoring at Nydam, a Waterlogged Site with Weapon Sacrifices from the Danish Iron Age. I: A Comparison of Methods Used and Results from Undisturbed Conditions , 2004 .

[10]  Mark Robinson,et al.  Saving the Sweet Track: The in situ preservation of a Neolithic wooden trackway, Somerset, UK , 2000 .

[11]  S. Limbrey,et al.  The Experimental Earthwork on Morden Bog, Wareham, Dorset, England: 1963 to 1972: Report of the Experimental Earthworks Committee of the British Association for the Advancement of Science , 1974, Proceedings of the Prehistoric Society.

[12]  A. M. Pollard,et al.  The surface alteration features of flint artefacts as a record of environmental processes , 2002 .

[13]  D. Gregory.  Re-burial of timbers in the marine environment as a means of their long-term storage : experimental studies in Lynæs Sands, Denmark , 1998 .

[14]  P. Sheppard,et al.  Weathering of archaeological cherts: A case study from the Solomon Islands , 1992 .

[15]  O. Borggaard.  Soil chemistry in a pedological context , 1996 .

[16]  Christina M. Nielsen-Marsh,et al.  Patterns of Diagenesis in Bone I: The Effects of Site Environments , 2000 .

[17]  B. Elberling,et al.  Soil solution pH measurements using in-line chambers with tension lysimeters. , 2000 .