Measuring the Isotopic Landscape
Principal Investigator: Professor Robert Hedges
Co-Investigator: Professor Mark Robinson
Research Assistant: Julie Hamilton
Carbon and nitrogen stable isotopes
have been used to investigate human diets for many years. To interpret
the human values we need to know the isotopic composition of foods, so
faunal data have also been collected. There is frequently more
variation within herbivorous domestic animals than within humans from
the same sites. Part of this variation depends on ecological factors
which are relevant in reconstructing past environments and agricultural
systems. Using isotope data from domestic animals from a careful
selection of sites with good environmental information, we aim to
investigate ecological interactions at scales from site to landscape.
We are particularly interested in how human farming and animal
management both responded to and caused environmental change. The Upper
and Middle Thames Valley is particularly suited for this study, with
well characterised contrasts and changes in settlement, agriculture and
environment, good environmental information, and large well-documented
collections of animal bone. Just as stable isotopes have allowed us to
integrate plant and animal food sources in palaeodiet studies, they
also provide a way of integrating zoological, botanical and
environmental information to shed new light on archaeological questions.
Research Questions
- The accurate characterization of variation in animal isotope values. This is to provide a better basis for reconstructing human palaeodiets and address the specific issues below.
- Some changes in animal isotope values apparently reflect diet/management change, e.g. pig δ15N and δ13C values. When and where does this occur?
- Use of woodland resources as reflected in δ13C values. Environmental evidence of woodland clearance/regeneration can be related to use of woodland or open environments to graze animals. This is of particular interest in the Neolithic where the agricultural system is still controversial (e.g. Rowley-Conwy 2004).
- From the Bronze Age there is increasing evidence of settlement, land division and field systems and also, by inference, manuring. Is this reflected in higher δ15N values?
- From the Iron Age onwards there is evidence of rising water tables followed by alluviation, changes which are not synchronous throughout the area. Do C and N isotope ratios reflect changes in site use and farming pattern that have been attributed in part to these hydrological factors, e.g. seasonal wetland grazing?
- Over the Iron Age and Romano-British periods, increased cereal production may have been achieved by conversion of pasture to arable accompanied by extensified grazing, leading to a new balance between arable and pastoral agriculture. Do C and N isotope ratios reflect the accompanying changes in animal management at site or landscape scales?
- From environmental evidence, the use of hay (which includes a higher proportion of nitrogen-fixing leguminous species than pasture grassland) seems to have been introduced during the Romano-British period. Is this reflected in lower δ15N?
- More generally, a large, coherent body of data will allow us to compare sites, environments and areas, and to investigate the statistical properties of assemblages, e.g. whether there is more variability at some types of site.