ABSTRACT The cities of Petra and Udhruh were administrative and cultural centers in southern Jordan from Nabataean through Roman and Byzantine times into the early Islamic periods (first century BCE to eighth century CE ). These communities built water harvesting systems to be able to survive in this arid environment. Water harvesting was either based on the use of runoff, so‐called “green water”, or on subterranean collection of streamflow and groundwater and subsequent distribution, so‐called “blue water”. Archeological research in the Udhruh region and the nearby Wādī al‐Fiqai revealed an elaborate qanat system, including subsurface water‐harvesting, subsurface and covered surface distribution channels, large reservoirs, and irrigated fields. Some fields were very likely irrigated because of a direct connection to a water reservoir, but for many others, it is less obvious. In order to assess the extent of the agricultural production area, it was necessary to gain insight into the historic land use of the Wādī al‐Fiqai area. An earlier study revealed soils of enwalled fields associated with a water reservoir to have relatively low soil electrical conductivity (EC) values as compared to non‐irrigated soils in comparable landscape positions. Here, we propose that pedogenic carbonates (CO 3 2 − ) may also serve as a proxy to identify prolonged irrigation, that is, carbonate‐rich water may enrich soils in secondary carbonate, whereas low‐carbonate water may deplete them. Landforms and soils were described and sampled along seven transects at Wādī al‐Fiqai downstream from the remnants of two water reservoirs of, respectively, the northern and southern irrigation systems. Based on landform and surface processes, four classes were distinguished: (1) eroded, (2) recently covered with alluvium, (3) hilly or undulating, and (4) nearly level surfaces. Soils were sampled either “full‐depth” or at 0–10 and 10–20 cm depth. For full‐depth soil profiles, variability in Bk horizon depth in soils on nearly level surfaces suggests differential depletion of pedogenic carbonate, with irrigated fields displaying greater depths. Moreover, for all soils, EC was observed to be the best proxy for past irrigation. Based on transect analysis, fields of the northern and southern irrigation systems had significantly lower EC values than non‐irrigated, nearly level, undulating, and hilly landforms. Based on these soil analyses, we estimate that the northern and southern irrigation systems supported up to 28 and 26 ha, respectively.
Hoosbeek et al. (Thu,) studied this question.