Identification of Ancient Irrigation Practices based on the Carbon Isotope Discrimination of Plant Seeds: a Case Study from the South-East Iberian Peninsula

This study presents the analysis of carbon isotope discrimination (Δ) in cereal and faba bean seeds from archaeological sites as a rapid method of evaluating the occurrence or otherwise of ancient irrigation in the Mediterranean basin. Further, application to the south-eastern Iberian Peninsula, one of the regions of the western Mediterranean basin in which advanced social structures first appeared, is reported. Currently there is a strong debate about when irrigation practices started in this region. It has been argued, on the basis of scattered, indirect evidence, that irrigation was already practiced during the Bronze Age (from 4400bp). However, this remains to be confirmed. Kernels of durum wheat, hulled and naked barley and faba bean grains from a set of archaeological sites in the south-eastern Iberian Peninsula were analysed. Samples ranged from late Neolithic (about 6500bp) to the Iron Age (2400bp). None of the results, apart from those of the faba bean, support the existence of irrigation practices during this period. Grains of faba bean showed consistently high values of Δ at all the archaeological sites studied. This could reflect not only growth habit, faba beans being less determined plants than cereals, but also selective irrigation of faba bean crops.