Tabitha Kabora’s research while affiliated with The Graduate Center, CUNY and other places

Reconstructing historical land-use and land-cover change (LULCC) inevitably involves interpolation across regions for which there is limited data to support reconstructions. Here, we evaluate the extent to which the global land-use model HYDE v3.2.1 reflects historical land use in sub-Saharan Africa (including Madagascar) when compared to archaeological and historical reconstructions. Both the HYDE models and Widgren’s archaeological and historical reconstructions estimate that agriculture was widely scattered across sub-Saharan Africa in 1800 CE. However, in steep terrain, at slopes greater than 10°, the HYDE model estimated 0% cropland allocation while archaeological and historical observations suggest intensive, mixed and extensive farming was common in these areas. In addition, while HYDE allocates farmland primarily into high-quality soils, archaeological reconstructions suggest that intensive farming occurred across a wide range of soil qualities. Gaps in our knowledge of cropland distribution have significant impacts on models of biodiversity change since understanding biodiversity in the Anthropocene is reliant on our understanding of past land-use changes. While HYDE’s mismatches are known, the research presented here provides an important resource in identifying where these allocation rules fail. These mismatches in global land-use models such as HYDE might also be replicated for other regions of the world, such as South America. These mismatches also need to be accounted for when generating model projections that use historical land-use models to impute present and future trends in land-use, climate and biodiversity change. Localised archaeological and historical data can therefore be used to support historical global land-use reconstructions for Africa and other regions across the world.

Chapter 14 of the Europe's Lost Frontiers Volume 1 : "This volume is the first in a series of monographs dedicated to the analysis and interpretation of data generated by the project. As a precursor to the publication of the detailed results, it provides the context of the study and method statements. Later volumes will present the mapping, palaeoenvironment, geomorphology and modelling programmes of Europe’s Lost Frontiers. The results of the project confirm that these landscapes, long held to be inaccessible to archaeology, can be studied directly and provide an archaeological narrative. This data will become increasingly important at a time when contemporary climate change and geo-political crises are pushing development within the North Sea at an unprecedented rate, and when the opportunities to explore this unique, heritage landscape may be significantly limited in the future." https://www.archaeopress.com/Archaeopress/Products/9781803272689

Unmanned aerial vehicle (UAV) surveys provide a viable methodology for conducting archaeological surveys, and Structure-from-Motion (SfM) techniques allow for the development of high-resolution maps, digital elevation models (DEMs) and 3-dimensional models of heritage sites. The archaeological site of Engaruka in Tanzania, covering c. 20 km2, was utilised in a series of projects to assess the potential of UAV surveys and SfM techniques to develop high-resolution imagery, combined with DEMs generated from archival aerial photographs. Data were processed using SfM software to create a DEM with a resolution of up to 3 m, providing a considerable improvement on the current 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global DEM (GDEM). Rigorous analysis using GIS indicated issues to consider when applying this technique to analogue photos. Further aerial surveys were then undertaken to establish the feasibility of using the innovative UAV survey techniques on the ground to generate aerial photographs and the use of SfM to develop high-resolution maps and DEMs at 0.25 m resolution, compared with the 0.7 m resolution Quickbird satellite image. These facilitate the remote analysis of smaller archaeological features that would otherwise not be identifiable, supporting further research and monitoring of these heritage sites.

Previous research using the content of rare earth elements (REE) in bulk soil samples has suggested that REE geochemistry can be used for recognizing sediment provenance in archaeological sites. Here we seek to test this hypothesis by studying the REE geochemistry of three soils with different degrees of pedogenetic development at a sedimentary basin in the 13th-18th centuries agricultural site of Engaruka (N Tanzania). The study location comprises a small, half-moon shaped catchment, in which all the sedimentary materials that accumulate in the thalweg come necessarily from the small hills to its N and E. The sediment accumulation was enhanced by anthropogenic structures built for capturing detritus derived from up slope weathering and erosion which was then used for cultivation. The materials accumulated behind these traps thus provide a record of the erosion-sedimentation processes of this small area. ICP-MS and XRF analyses have been carried out for major, minor and trace elements (including REE) in bulk samples of all the sedimentary layers, as identified in the field, from three sampling spots that form a topographic catena. We calculated REE ratios and Ce and Eu anomalies, and checked their correlation with major and minor elements. We also used multivariate statistics for discerning the compositional differences between samples. The results show differences in the REE signature of the three sampling locations that, together with correlations between REE and other elements, suggest that the REE abundance in bulk samples reflects the degree of weathering and pedogenesis, and not the source of the sediments. Additional physical and chemical treatments are needed for isolating the signal of the source rocks, and thus for assessing the sediments’ provenance. Keywords: Rare earth elements, geochemistry, sediment, weathering, Tanzania

The 15th–18th century CE site of Engaruka in Tanzania is often described as primarily comprising drystone agricultural terraces, but it is now known that many of these former farming plots are not terraces per se, but are instead sediment traps. Stratigraphic excavations of these traps show that they were built by constructing low drystone walls adjacent to either natural or artificial water courses in order to capture fine alluvial sediments entrained within water flows. In the northern area of the site sediments were accumulated to a depth of up to 700 mm, while in one area in the south of the site over 2 m of deposits were accumulated over at least a 300 year period. The presence of sediment traps on archaeological sites allows investigations of the efficacy and sustainability of these structures over decadal to centennial timescales, since stratigraphic excavations can define the process of construction, and geoarchaeological analyses can explore changes within accumulated sediments over time. Although a combination of stratigraphy and absolute dating can discern the broad sequence and timing of sediment capture they cannot determine sediment-accumulation rates, and these techniques are too time consuming to be used to map the development of over 9 km² of sediment traps. The ESTTraP agent-based model provides these data by simulating sediment accumulation under different hydrological conditions. Four scenarios were simulated for a period of 100 years: constant water availability (SIM-01), seasonal variability (SIM-02), long-term climate variability (SIM- 03), and vegetation-cover impact (SIM-04). The model results suggest that the fields can be constructed over a short period of time, approximately 1–3 months per 6 × 6 m field, and that to construct a block of 90 fields covering 3,000 m² it would take between 8 and 13 years in periods of high water availability, and up to 27 years during prolonged dry periods. The results define the amount of time needed to construct individual fields, and suggest that farmers constructed blocks of fields concurrently rather than sequentially expanding across the landscape, and that the c. 10 km² area of sediment traps at Engaruka could have been constructed by a number of households working independently. The ESTTraP model presents an important resource in the assessment of sediment dynamics and patterns of field development, is relevant to a range of archaeological sites worldwide that include intentional or unintentional alluvial deposition, and has applications for modern landscape management.

In this study rare earth elements (REE) signatures (REE ratios, cerium and europium anomalies) are applied to a complex soil stratigraphic sequence from the site of Konso, Ethiopia, with the aim of determining whether REE can distinguish the strata observed in the field. Forty soil samples were taken from a depositional sequence that includes overlapping human induced and ‘natural’ erosional and depositional processes. The samples were analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to determine trace elements and REE, with concentrations of major elements determined using X-ray fluorescence (XRF). Cluster Analyses (CA) were used to observe differences between strata. The mechanisms that influenced REE values and fractionations were related to OM accumulation, pyrogenic SOM, redox and secondary CaCO3 precipitation, suggesting the addition of proxies to the REE, Sc and Y data processing. This produced a clustering of samples that more accurately reflected the stratigraphic field observations. It is expected that this approach, combining the analysis of REE concentrations with an understanding of the mechanisms driving them in a given site or profile, will be replicable for other stratigraphic sequences. The results demonstrate that REE signatures are not just able to detect stratigraphic differences defined through field observations but also highlight variations within the same deposits. REE analysis could therefore become a powerful geoarchaeological tool, even for studies of complex stratigraphies.

Over the last twenty years Rare Earth Elements (REE) have started to be part of archaeometric studies. Due to their particular characteristics there have been several attempts to apply REE analysis to different archaeological scenarios including stratigraphically-controlled agricultural soils, demonstrating that this is an effective tool to understand how human activity is reflected in soil development. Our study proposes a new methodological approach for the identification of anthropogenic deposits through REE soil analysis, pushing current limitations of traditional chemical and sedimentology techniques. Our study represents the first application of REE concentrations in soils from tropical Africa within an archaeological context. The agricultural soils were captured in an artificial sediment trap that forms part of the terraced landscape in Konso, Ethiopia; a system thought to have developed over the last 500 years, and which was awarded World Heritage status in 2011. Forty samples were taken from successive alluvial layers down a c. 2m thick soil sequence that had accumulated behind a series of drystone walls. The samples were analyzed for trace elements and REE via ICP-MS. To understand the causes of enrichment or depletion of REE, the data were compared with soil organic matter, organic carbon and fire markers. To aid interpretation we crossreferenced our results with archaeobotanical and soil micromorphology data. Data were analysed using multivariate statistics. Taken together these results present a very different picture of landscape development to previous presented accounts; the REE analyses provide significant details regarding the source and transportation of sediments.