Geoarchaeological evidence for the construction, irrigation, cultivation and resilience of the 15th-18th-century AD terraced landscape at Engaruka, Tanzania.

Agricultural landscapes are necessarily human manipulated landscapes, most obviously in areas modified by terracing, irrigation, or both. Examples exist in temperate, arid and desert environments worldwide, and have attracted the attention of many disciplines, from archaeologists, palaeoecologists and geomorphologists interested in landscape histories, to modern economists, agronomists, ecologists and development planners studying sustainable resource management. This paper combines these interdisciplinary interests by exploring the role archaeology can play in assessing landscape sustainability; focussing on Engaruka, Tanzania. Archaeologically famous as the largest abandoned irrigated and terraced landscape in east Africa, the site has been seen as an example of economic and/or ecological collapse, and has long been assumed to have been irrigated out of necessity; the assumption being that agriculture would be near impossible without irrigation in what is now a semi-arid environment. Geoarchaeological research refutes this assumption, demonstrating that the site flooded with sufficient regularity to allow the construction of over 1000ha of alluvial sediment traps, in places over 2m deep. Soil micromorphology and geochemistry also record changes in irrigation, with some fields inundated to creating paddy-like soils. These techniques can be applied to both extant and abandoned systems, thereby contributing to an understanding of their history, function and sustainability

When is a terrace not a terrace? The importance of understanding landscape evolution in studies of terraced agriculture

Before the invention of modern, large-scale engineering projects, terrace systems were rarely built in single phases of construction, but instead developed gradually, and could even be said to have evolved. Understanding this process of landscape change is therefore important in order to fully appreciate how terrace systems were built and functioned, and is also pivotal to understanding how the communities that farmed these systems responded to changes; whether these are changes to the landscape brought about by the farming practices themselves, or changes to social, economic or climatic conditions. Combining archaeological stratigraphy, soil micromorphology and geochemistry, this paper presents a case-study from the historic and extensive terraced landscape at Konso, southwest Ethiopia, and demonstrates e in one important river valley at least e that the original topsoil and much of the subsoil was lost prior to the construction of hillside terraces. Moreover, the study shows that alluvial sediment traps that were built adjacent to rivers relied on widespread hillside soil erosion for their construction, and strongly suggests that these irrigated riverside fields were formerly a higher economic priority than the hillside terraces themselves; a possibility that was not recognised by numerous observational studies of farming in this landscape. Research that takes into account how terrace systems change through time can thus provide important details of whether the function of the system has changed, and can help assess how the legacies of former practices impact current or future cultivation

Testing the capability of Rare Earth Elements to identify archaeological strata in an African site: The case of the terraced landscape at Konso, Ethiopia

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

Rare Earth Elements analysis to identify anthropogenic signatures at Valle del Serpis (Spain) Neolithic settlements

Due to their particular geochemical properties and stability Rare Earth Elements (REE) can act as a ‘fingerprint’ for soils, and as a consequence have been employed in a variety of different archaeological scenarios in order to identify past human activities.In this study, for the first time, we apply REE signatures in different Spanish Neolithic settlements, all located in the Valle del Serpis region. More than 100 Neolithic settlements have been identified in this area, and most of these open sites are characterised by dark brown strata that are in contrast with the light brown soils of the valley. These dark brown deposits are usually covered by paleosols and have been interpreted as markers of anthropogenic activities. However, in order to demonstrate whether these strata are anthropogenic or natural features requires a better understand-ing of soil development processes. A total of fifty samples were taken across six different sites, and from each site the sam-pling was carried out at different depths through 3m deep sections. Four sites are clearly associated with archaeological findings (sites BF, LP, PB and AC); another one is from a natural section near the Neolithic site of Mas d’Is (MD) and has been radiocarbon dated to the beginning of the Holocene (7751-7611 cal BC); and the last corresponds to a place of uncertain attribution (BK). Major, minor and trace elements including REE were determined using XRF and ICP- MS, with Principal Components Analysis (PCA) used to statistically analyze these data. Results were then compared with the strata soil properties analysed by XRD and particle size analysis, and cross-referenced with archaeological data to aid interpretation. The results demonstrate that REE analyses provide significant details regarding anthropogenic activities and strata development history, and in this instance confirm and elaborate on the archaeological interpretation that these dark brown deposits are evidence of a region-wide agricultural system in the Neolithic Valle del Serpis

"Ancient and Backward or Long-Lived and Sustainable?" The Role of the Past in Debates Concerning Rural Livelihoods and Resource Conservation in Eastern Africa

Summary Attempts by external agencies to intervene in the operation of local resource exploitation strategies frequently include reference to historical arguments. These vary in accuracy and sophistication but are nevertheless rhetorically useful since discussions of economic or environmental sustainability or degradation are substantially strengthened by historical comparisons and precedents. Focussing on examples of indigenous intensive agriculture in eastern Africa, this paper agues that relevant evidence of this sort is often unavailable or far from unambiguous. It is therefore necessary to be critical of the ways in which perceptions of the past are invoked within these discourses, and to be aware of the strengths and weaknesses of historical arguments in this regard.historical ecology archeology intensive agriculture indigenous knowledge east Africa

Towards an applied archaeology of East African intensive agricultural systems

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Developing REE parameters for soil and sediment profile analysis to identify Neolithic anthropogenic signatures at Serpis Valley (Spain)

In this study, patterns of rare earth elements (REE) have been developed and applied for the first time to sediments and soils to identify anthropogenic or natural layers in profiles sampled at several Neolithic settlements in the Serpis Valley area (Alicante, Spain). Most of these sites are characterized by dark brown paleosols that are easily distinguishable from the light brown paleosols of the valley. To demonstrate whether these strata are anthropogenic or natural requires a better geochemical understanding of sediment. Soil samples were taken across six different sites; four sites are associated with archaeological findings (sites BF, LP, PB and AC8); another one is from a natural section from Mas D'Is (MD) located close to the archaeological site in which evidence of human occupation from the Neolithic period has been found; and the last corresponds to a place of uncertain attribution (BK5), where no archaeological remains have been found, but where layers of a recent agricultural activity are present. REE results comprising REE ratios, cerium and europium anomalies, and La/Yb-Sm/Eu correlations were compared with major and minor chemical components, mineralogical properties of the soil layers and, when it was possible, cross-referenced with archaeological data to aid interpretation. The results demonstrate the potential of REE data to distinguish strata associated with Neolithic occupation from those that have not been subjected to anthropogenic modification

The capability of Rare Earth Elements geochemistry to interpret complex archaeological stratigraphy

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 analyzed 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, 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