The isotopic footprint of irrigation in the western Mediterranean basin during the Bronze Age: the settlement of Terlinques, southeast Iberian Peninsula

The isotopic composition of the remains of cereals and pine has been studied, from three different chronological phases from 2140 to 1500 cal BC at the Terlinques site, southeast Iberian Peninsula. The δ¹³C values range between −24.91 and −21.19 ‰ (V-PDB), with an average of −23.05 ‰ (STD = 0.69). The archaeological cereals show an average isotopic discrimination (Δ¹³C) with the past atmospheric CO₂ of 16.96 ‰, which is much greater than the average Δ¹³C of 13.89 ‰ of the rainfed Triticeae (wheat and barley) in modern times. However, considering the effect of the atmospheric CO₂ concentration, which is included in the WUEi (intrinsic water-use efficiency), this difference is even greater, 77 for archaeological samples versus 144 for present-day rainfed cereals. This could represent some of the earliest evidence of the use of irrigation techniques in Europe. Modern cereals which have been irrigated show a general Δ¹³C average of 17.17 ‰, very similar to those of the middle Holocene. However, when the WUEi is calculated, the value of 108 indicates that present-day irrigated cereals are more stressed than the archaeological samples. For comparison, we have included pine trees, since these have an extensive root development which is capable of reaching the water table. In the past, both cereals and pine present similar WUEi values (77 vs. 72), however at present only irrigated cereals show similar WUEi values to pine (108 vs. 107). This again suggests irrigation of cereals in the past. The processes of climatic degradation towards drier conditions which started in the middle Holocene could be responsible for the use of land near water sources, on riverbanks and near shallow lakes. According to the isotopic and plant macrofossil data, irrigation or water management techniques were used at the Terlinques site, located close to the Laguna de Villena, a lake which has now dried out.