Research Article: Assessment of biodegradation in ancient archaeological wood from the Middle Cemetery at Abydos, Egypt

Date Published: March 27, 2019

Publisher: Public Library of Science

Author(s): Ahmed M. Abdel-Azeem, Benjamin W. Held, Janet E. Richards, Suzanne L. Davis, Robert A. Blanchette, Andrea Zerboni.

http://doi.org/10.1371/journal.pone.0213753

Abstract

Abydos is a large, complex archaeological site located approximately 500 km south of Cairo in Upper Egypt. The site has served as a cemetery for thousands of years and is where most of the Early Dynastic royal tombs are located. North Abydos includes the Middle Cemetery and the North Cemetery, which are separated from each other by a wadi. The Middle Cemetery was the burial ground for important Sixth Dynasty (2407–2260 BC) officials and over time for thousands of elite and non-elite individuals as well. Excavations at the core area of the Old Kingdom mortuary landscape have revealed many culturally important wooden objects but these are often found with extensive deterioration that can compromise their preservation. The objectives of this study were to characterize the biodegradation that has taken place in excavated wooden objects, elucidate the type of wood degradation present, obtain information on soil properties at the site and identify fungi currently associated with the wood and soils. Light and scanning electron microscopy studies were used to observe the micromorphological characteristics of the wood, and culturing on different media was done to isolate fungi. Identification of the fungi was done by examining morphological characteristics and extracting rDNA from pure cultures and sequencing the ITS region. Wooden objects, made from Cedrus, Juniperus and Acacia as well as several unidentified hardwoods, were found with extensive degradation and were exceedingly fragile. Termite damage was evident and frass from the subterranean termites along with sand particles were present in most woods. Evidence of soft rot attack was found in sections of wood that remained. Fungi isolated from wood and soils were identified as species of Aspergillus, Chaetomium, Cladosporium, Fusarium, Penicillium, Stemphylium Talaromyces and Trichoderma. Results provide important information on the current condition of the wood and gives insights to the identity of the fungi in wood and soils at the site. These results provide needed information to help develop conservation plans to preserve these degraded and fragile wooden objects.

Partial Text

Abydos is a large archaeological site located approximately 500 km south of Cairo in Sohag Governorate, near El-Balyana City in southern Egypt. The cemetery is located on the low desert plateau of the Western Desert, adjacent to the village of Beni Mansour at the edge of the flood plain. Abydos is one of the most important archaeological sites in Egypt since it was the burial place of the first pharaohs of the united Egyptian state and the center of the cult for the god of the dead, Osiris [1]. The site is complex, consisting of cemeteries, settlements, and ritual spaces, divided into two main sections: South and North Abydos (Fig 1). The low desert landscape of North Abydos is, in turn, divided into the Middle Cemetery and the North Cemetery, separated from each other by a wadi which leads to the area known as Umm el-Qa’ab, where the Early Dynastic royal tombs are located [2]; and the area of Kom el Sutan, the location of the ancient town and Osiris temple. While mortuary activity throughout this landscape was initially restricted in the wake of its use for royal burials at Umm el-Qa’ab, the Middle Cemetery was subsequently primarily used for private funerary activity beginning in the later Old Kingdom including the burial sites for important officials of the regional and central government, e.g., the mastabas of Weni the Elder, Governor of Upper Egypt, his father the Vizier Iuu, and other individuals [3–7].

Wooden objects excavated at Abydos were found to have severe deterioration and decay resulting in an exceedingly fragile condition (Figs 2 and 3). Small fragments of wood from the objects, used for microscopic observations of anatomical characteristics, were identified as Cedrus, Juniperus, Acacia as well as several other unidentified hardwoods. A combination of termite damage and wood decay was present. In some woods such as Cedrus, termite damage was near wood surfaces and large zones of unaffected wood remained (Fig 3). However, in many of the hardwood objects, there was extensive attack by termites and most of the wood below the surface had been converted to frass and small wood particles. Sand was also present that had been brought in with the termites. The surfaces of wood remained but lacked structural integrity. Micrographs of sections from areas with advanced decay showed termite frass, sand particles and segments of deteriorated wood (Fig 4). Sections from the surface of many of the wood samples showed a thin layer of cells that were completely occluded. These occlusions were from resin, gesso, paint or other substances that had infiltrated the wood surfaces (Fig 4). Relatively sound cell walls were also found in some areas of Cedrus (Fig 4) but in other zones, soft rot attack by wood decay fungi was present (Fig 4). Light microscopy (Fig 5) of wood sections revealed cavities within the secondary wall of tracheids that was characteristic of Type I soft rot. Advanced stages of decay were present and many soft rot cavities were seen in a spiral pattern within the secondary walls. In transverse sections, small cavities were seen within tracheids (Fig 5). Wood from objects that had been made of various hardwoods also had evidence of soft rot. Some cavities within secondary walls were present but more commonly observed was a Type II soft rot where the secondary cell walls were eroded (Fig 5). In some cells with advanced decay, the entire secondary cell wall was removed leaving only the middle lamella. The altered cells were often collapsed and distorted. Sections from other wooden objects showed similar patterns of degradation with Type II soft rot in objects made from hardwood (Fig 6). The secondary walls were degraded leaving only a weak and fragile framework of the middle lamella and cell walls were often fractured and collapsed (Fig 6).

The rate and extent of wood decomposition by fungi is governed by environmental factors but even in the most extreme environments degradation can take place. Moisture is essential for decomposition processes and wood cell walls must have sufficient moisture to be above the fiber saturation level in order for extracellular microbial enzymes and non-enzymatic processes to cause degradation [43]. The cemetery at Abydos is a dry desert site with annual rainfall of about 1mm but greater amounts of rain can occur infrequently [44]. Average humidity is approximately 60% and this decreases in the winter months to less than 30%. Temperatures can range from 2° C in February to 45° C during June. Although these arid conditions would appear to restrict wood decay from occurring, flooding of the Nile and increases in the water table in soils beneath Abydos apparently contributes sufficient moisture intermittently for below ground microbial activity and degradation to take place [45].

 

Source:

http://doi.org/10.1371/journal.pone.0213753

 

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