Water management practices and climate in ancient agriculture: inferences from the stable isotope composition of archaeobotanical remains

An investigation into the archaeological application of carbon stable isotope analysis used to establish crop water availability: solutions and ways forward

“…The aim is to identify differences in Δ between these crops which could then be explained in terms of differences in irrigation and crop management techniques (Araus et al, 1997b;Ferrio et al, 2005;Riehl et al, 2008). In relation to this, Ferrio et al (2005) proposed comparing isotope data from major food crops with the remains of non-cultivated plants such as trees or with cultigens which are relatively well adapted to arid conditions and are therefore unlikely to have received any irrigation (see also Ferrio et al, 2005Ferrio et al, , 2006. Following this suggestion, Riehl et al (2008) used Δ values for barley as baseline data for non-irrigated crops.…”

“…They combined these data with the results of climate modelling to infer that irrigation was practised at some of the investigated sites. While the strategies employed to detect irrigation through carbon stable isotope signals of plants are therefore relatively sophisticated, all researchers concede that the trends observed in their datasets may well be explained by differences in the growing cycles or water use efficiency of individual species rather than by any water management strategies employed by humans (Ferrio et al, 2005;Riehl et al, 2008).…”

“…These can then be compared with archaeological samples from the same area. The majority of work establishing modern reference data has been undertaken by Araus and colleagues (Araus and Buxo, 1993;Araus et al, 1997b;Ferrio et al, 2005) and has centred on the Mediterranean, especially Spain. They employed the reference values from modern crops mainly in two ways: as baseline data for relative statements about past climate conditions ('wetter/drier than today') (Araus et al, 1997a;Ferrio et al, 2003Ferrio et al, , 2005, or for establishing relationships between the Δ of different types of crops grown under the same environmental conditions.…”

“…The majority of work establishing modern reference data has been undertaken by Araus and colleagues (Araus and Buxo, 1993;Araus et al, 1997b;Ferrio et al, 2005) and has centred on the Mediterranean, especially Spain. They employed the reference values from modern crops mainly in two ways: as baseline data for relative statements about past climate conditions ('wetter/drier than today') (Araus et al, 1997a;Ferrio et al, 2003Ferrio et al, , 2005, or for establishing relationships between the Δ of different types of crops grown under the same environmental conditions. As we have seen above, such data are essential for identifying irrigated crops by comparison with other, probably non-irrigated, plant species from the same site (Araus et al, 1997b(Araus et al, , 1999Ferrio et al, 2005).…”

“…Carbon stable isotope analysis of archaeological cereals is a relatively new approach for the investigation of ancient irrigation systems (Araus and Buxo, 1993;Araus et al, 1997b;Ferrio et al, 2005;Araus et al, 2007;Riehl et al, 2008). The approach relies on the basic principle that plants under water stress discriminate less against the 'heavier' carbon-13 ( 13 C) isotope than plants whose water requirements are fully met (Farquhar and Richards, 1984;Farquhar et al, 1989).…”