Land abandonment and soil erosion following Late Antiquity in the northwestern Negev, Israel

During the 5^th and the 6^th centuries, the prosperous city of Gaza gained its reputation as a port of call for merchants and pilgrims to the Holy Land and as a port for shipment of products to the west. The economic hinterland of Christian Gaza included villages, monasteries and various agricultural estates that provided agricultural merchandise to the city residents (fruits, vegetables, field crops), along with the famous “Gaza Wine” exported across the Mediterranean. The houses in these settlements were built of unfired mud-bricks, while water was collected from roofs and courtyards into underground cisterns.  The cisterns were typically dug into the soil and made of a hardy mixture of cement, rubble, and gravel and coated with layers of hydraulic plaster. The cisterns were cylindrical, with a base diameter of 3-4.5 meters and a maximal depth of ca. 6-8 meters. About a meter below the rim, the cylinder structure tapered upwards into a cone shape, up to a diameter of 0.5 meters, where a stone slab with a square opening covered the cistern.

This study aims to examine to which extent the abandonment of agricultural fields in the late Byzantine - early Muslim period caused significant landscape and soil properties change.

We mapped ca. 150 water cisterns, typical of the period. Most cisterns are located north of the Nahal Gerar channel and along the lower catchment of the Nahal Besor. Mean annual precipitation in the area is 300-350 mm/year. Streams are ephemeral, characterized by flash floods during the winter.

While almost nothing remained of the flourishing above-ground settlements, soil erosion exposed the cisterns, which now serve as well preserved indicators of the presence and location of Late Antique houses and villages. The abandoned water cisterns protrude above the surface and may enable us to calculate the erosion rates since the settlement collapsed. Study results indicate that the abandonment of agriculture intensified soil erosion: rates of erosion along the steep (10-20%) river banks and gullies are up to 2.5 m (1.7 mm/yr), while along the interfluves and over the low-angle slopes (2-5%) rates of erosion reach 1.2 m (0.8 mm/yr).

Soil properties were also affected by human activity. In the Horvat Gerarit area, soil results from mud-brick degradation. Field identification is based on (1) relatively increase of fine fraction (clay and loam) within the villages sites, while median values changes from loam within the mud-bricks, to medium-sand over the agricultural fields; (2) mulch, that was added to the bricks to reduce cracking and increase tensile strength is incorporated into the soil; (3) direct observations of several degraded bricks into the soil.