Understanding the formation of long-term persistent soil organic matter (SOM) is key to optimizing soil management and predicting the response of the terrestrial organic carbon (OC) pool to climate change, yet our knowledge of the soil-type dependent weight of different stabilization pathways (e.g., recalcitrance and mineral binding) is fragmentary. Owing to their stratigraphy, the exceptionally SOM-rich (up to 2 m of mineral soil with >5% OC) colluvial slope deposits of Atlantic Europe (Haplic Umbrisol [colluvic/hyperhumic]) are archives of palaeo-environmental conditions including SOM formation pathways. The objective of this study was to determine how the different drivers of persistent SOM formation influenced the formation of these organic-rich soils. For this purpose, we use Holocene (similar to 9000 yrs) molecular composition records obtained from pyrolysis-GC-MS (Py-GC-MS) and thermally assisted hydrolysis and methylation (THM-GC-MS). The results emphasize three pathways to stability (i.e., persistence on millennial timescales): 1) palaeofires that generated recalcitrant pyrogenic SOM, 2) release of root-derived aliphatic macromolecules (suberin-like SOM), and 3) formation of microbial necromass. Pathways 1 and 2 are controlled by land use: Pathway 1 was relatively important under intense anthropogenic fire regimes and pyrophytic shrubland expansion; Pathway 2 was stimulated during early forest phases and under pasture conditions, when past societies focused vegetation management on grazing instead of fire; Pathway 3 was controlled by binding with aluminium-dominated mineral phases. However, we found indications that Pathway 2 (suberin input and preservation) relied partially on sorptive preservation as well. Aided by structured equation modeling (SEM), we show that the formation of persistent SOM pools was driven by balanced weights of i) microbial vs. plant-derived SOM and ii) intrinsic chemical properties of SOM (recalcitrance continuum) vs. mineral binding/occlusion, which varied in keeping with interactions between past land use, topography and vegetation. These findings are inconsistent with the prevalent paradigm of persistent SOM formation by sorptive/occlusive preservation of microbial necromass alone.

The present work aims at the archaeological characterisation and historical contextualisation of two large enclosures recently located through remote sensing in the Laboreiro Mountain on the border between Portugal and Galicia: Lomba do Mouro and Chaira da Maza. Ancient written sources, remote sensing, archaeological survey, and absolute dating will be combined in order to shed new light on these enclosures. Given the specificity of the archaeological structures and contexts under study, the need to use complementary absolute dating methods will be discussed, including luminescence and radiocarbon dating. The results in the case of the Lomba do Mouro enclosure point to it possibly being a Roman military camp of late-Republican chronology.

The Atacama Desert is among the driest places on Earth, yet ancient agricultural systems are present in the region. Here, we present a study of terraced agricultural soils in the high-altitude eastern margin of the Atacama Desert in northern Chile, mainly dating to the Late Intermediate Period (ca. 950-1400 AD) and Inka period (ca. 1400-1536 AD). Terraced fields were compartmentalized to distribute limited irrigation water originating mainly from springs. Natural soils used for agriculture are mostly Aridisols developed on Pleistocene alluvial fan terraces and hillslopes underlain by volcanic bedrock. One research objective is to evaluate long-term soil change from agriculture. In this hyperarid climate, agriculture is only possible with irrigation, so natural soils on the same geomorphic surface adjacent to irrigated soils provide baseline data for assessing anthropogenic soil change. Data from soil profiles and surface transects indicate intentional soil change through terracing, removal of soil rock fragments, and probable fertilization. Agricultural soils have anthropogenic horizons ranging from 16 to 54 cm thick. Most agricultural soils have higher phosphorus levels, suggesting enrichment from fertilization. Changes in soil organic carbon and nitrogen are also evident. Unintentional anthropogenic soil change resulted from CaCO3 input through irrigation with calcareous spring water. Initial studies suggest that agriculture here was sustainable in the sense of conserving soils, and maintaining and possibly improving soil productivity over centuries.

The identification and characterization of hearths is crucial for reconstructing the history of fire use and pyrotechnology. In addition to ashes and charcoals, an active fire will also produce alterations of the underlying substrate to varying degrees. To date, however, few studies have addressed how the characteristics of burned substrates relate to pyrotechnology. Here, we systematize the use of colour to identify burnt sediments by performing quantitative colour measurements in the CIELab system of experimentally heated soils and sediments. The experimental design included different temperatures, different heating durations and substrates with varied chemical and mineralogical compositions, including naturally red soils and sediments with different degrees of pedogenesis. The measured colours were analysed by multivariate statistics for diagnosing whether sediments have been heated or not, and to which temperature. We achieved an accurate identification of heated versus unheated samples independently of their composition. The determination of the temperature of heating required prior knowledge of basic mineralogy and chemical properties in the targeted sediments (silicate or carbonate material, total and secondary Fe, Ca contents and the amount and kind of organic matter). The algorithm developed can be applied to recognize burned layers and estimate burning temperatures in archaeological contexts.

Landscape multifunctionality is increasingly recognized as an important aspect in sustainability and developmental debates. Yet, how and why a multifunctional landscape configuration develops over time has not been sufficiently studied. Here we present the geoarchaeological investigation of the Santa Mariña de Augas Santas site, in northwestern Spain. We focus on the role of religious practice, and of its interplay with productive strategies, in landscape transformation. A geochemical, mineralogical, and geochronological characterization of the pedo-sedimentary record (including XRF, EA-IRMS, XRD, OSL and 14C measurements) allowed to characterize catchment scale sedimentation processes in relation to agricultural activities. The geographical and chronological coincidence of production functions with documented religious activities demonstrate that both aspects shared geographical spaces during the last millennium. Current landscape multifunctionality at Santa Mariña is thus not the final outcome of a specific evolution, but an essential aspect of traditional land use strategies through history and a driver of change. This work highlights the need of a long-term study of the processes of landscape configuration when assessing the sustainability of traditional productive systems.

Silicate weathering and within soil redistribution of released metals are a near universal process believed to drive the formation of Podzols in various bioclimatic zones, ranging from tropical forest to Arctic environments. Yet the importance of climate and the fractionation of Al, Fe and Si in Podzols remains largely unknown. The aim of this study was to increase our understanding of climate-related variability in the podzolization mechanisms by conducing high-resolution chemical probing of seven soils in different bioclimatic zones and under different hydrological regimes: one well drained and one seasonally hydromorphic from the boreal zone (Sweden), two well-drained Podzols from a mild and humid area (NW Spain) and three, two poorly drained and one well drained soils, from the tropics (Brazil). The analytical strategy included seven selective dissolution techniques, in order to understand the distribution of Fe, Al and Si in organic (high, medium and low stability metal-OM complexes) and inorganic secondary compounds (short-range order and crystalline forms) in relation to their bioclimatic setting. Results indicate that the translocation of metals is coupled to the soil organic matter (SOM) mobilization in all three bioclimatic zones. The accumulation of metals and organic matter in the spodic horizons, in contrast, is contingent upon temperature, as well as on the local hydrological conditions and pH. Multivariate statistics allowed to identify the effect of climate, of soil hydrological conditions and of parent material in the soil vertical development. The high vertical resolution sampling and the extended fractionation employed were key for detecting the differences in Al, Fe and SOM dynamics in the studied soils, and revealed that different podzolization mechanisms are active in each bioclimatic zone.

A high-resolution soil sampling has been applied to two forest podzols (ACB-I and ACB-II) from SW Europe in order to investigate the soil components and processes influencing the content, accumulation and vertical distribution of Hg. Total Hg contents (THg) were 28.0 and 23.6 mu g kg(-1) in A horizons of ACB-I and ACB-II, then they strongly decreased in the E horizons and peaked in the Bhs horizons of both soils (55.3 and 63.0 mu g kg(-1)). THg decreased again in BwC horizons to 17.0 and 39.8 mu g kg(-1). The Bhs horizons accounted for 46 and 38% of the total Hg stored (ACB-I and ACB-II, respectively). Principal component analysis (PCA) and principal components regression (PCR), i.e. using the extracted components as predictors, allowed to distinguish the soil components that accounted for Hg accumulation in each horizon. The obtained model accurately predicted accumulated Hg (R-2 = 0.845) through four principal components (PCs). In A horizons, Hg distribution was controlled by fresh soil organic matter (PC4), whereas in E horizons the negative values of all PCs were consistent with the absence of components able to retain Hg and the corresponding very low THg concentrations. Maximum THg contents in Bhs horizons coincided with the highest peaks of reactive Fe and Al compounds (PC1 and PC2) and secondary crystalline minerals (PC3) in both soils. The THg distribution in the deepest horizons (Bw and BwC) seemed to be influenced by other pedogenetic processes than those operating in the upper part of the profile (A, E and Bhs horizons). Our findings confirm the importance of soils in the global Hg cycling, as they exhibit significant Hg pools in horizons below the uppermost O and A horizons, preventing its mobilization to other environmental compartments. (C) 2020 Elsevier Ltd. All rights reserved.

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.

This paper evaluates the complexities of radiocarbon ( C-14) dates from soil organic matter (SOM) in archaeological scenarios. The aqueous NaOH-insoluble residual SOM from Neolithic to medieval sites in NW Spain produced consistently older calibrated C-14 ages than NaOH-extractable SOM. Using pyrolysis-gas chromatographymass spectrometry (Py-GC-MS) and thermally assisted hydrolysis and methylation (THM-GC-MS). we analyzed the molecular composition of these SOM fractions, aiming to understand the differences in C-14 ages and to gain insight on SOM dynamics in relation to age fractionation. The molecular composition of the NaOH-extractable SOM, which accounts for roughly two-thirds of total SOM, has a larger proportion of microbial detritus than the NaOH-insoluble SOM. This might suggest that the discrepancies between the two fractions is due to microbial rejuvenation in the extractable fraction, leading to C-14 results that are younger than the activity that is to be dated. However, archaeological evidence presented here unambiguously shows that the C-14 age of the extractable SOM provides the more accurate age for the targeted activity, and that the insoluble fraction contains inherited old carbon. After statistical data evaluation using Partial Least Squares-Regression (PLS-R), it is concluded that this inherited SOM is a mixture of Black Carbon from wild and/or domestic fires and recalcitrant aliphatic SOM.

We applied selective dissolution extractions (Na‐pyrophosphate, acid oxalate, cold NaOH and citrate‐dithionite) to study Al, Fe and Si fractionation in 38 volcanic pedons located on the windward slopes of Santa Cruz (Galápagos Islands) that form a climosequence. The aim was to evaluate the distribution of secondary Fe, Al and Si phases in relation to environmental variables. Two main trends were observed: a geographical pattern in relation to altitude and a vertical differentiation within soil profiles. Soils from the drier coastal area had the smallest amounts of secondary Al, Fe and Si, whereas values were larger in soils at higher altitude, under a more humid climate. Organo–metallic complexes dominate the organic‐rich topsoils in these wetter areas as a result of larger availability of free Al, more humified organic matter with a greater capacity for metal adsorption and larger organic matter contributions from vegetation. This has led to increased accumulation of organic carbon in soils at higher altitudes. At lower elevations, inorganic secondary materials are more frequent, with short‐range‐order minerals prevailing in topsoils, whereas crystalline minerals dominate subsoils. Crystalline minerals are also frequent in some soils at higher altitudes in relation to acid pH. Vertical differentiation within the soil profile is also responsive to altitude: differences between topsoils and subsoils are generally more marked in soils at higher locations, thus wetter areas. A greater degree of weathering seems to be the main factor controlling both altitudinal trends and horizonation through its effect on pH, organic matter content and humification, ultimately controlled by climatic variation.Highlights We analysed soils developed on volcanic material along the windward slope of Santa Cruz Island. Organo–metallic complexes are abundant in acidic, organic‐rich epipedons at higher elevation. Short‐range‐order minerals are more abundant in non‐acidic subsoils and tend to increase with altitude Crystalline minerals predominate at lower elevation and in acidic subsoils at higher altitude.

East African landscapes today are the result of the cumulative effects of climate and land-use change over millennial timescales. In this review, we compile archaeological and palaeoenvironmental data from East Africa to document land-cover change, and environmental, subsistence and land-use transitions, over the past 6000 years. Throughout East Africa there have been a series of relatively rapid and high-magnitude environmental shifts characterised by changing hydrological budgets during the mid- to late Holocene. For example, pronounced environmental shifts that manifested as a marked change in the rainfall amount or seasonality and subsequent hydrological budget throughout East Africa occurred around 4000, 800 and 300 radiocarbon years before present (yr BP). The past 6000 years have also seen numerous shifts in human interactions with East African ecologies. From the mid-Holocene, land use has both diversified and increased exponentially, this has been associated with the arrival of new subsistence systems, crops, migrants and technologies, all giving rise to a sequence of significant phases of land-cover change. The first large-scale human influences began to occur around 4000 yr BP, associated with the introduction of domesticated livestock and the expansion of pastoral communities. The first widespread and intensive forest clearances were associated with the arrival of iron-using early farming communities around 2500 yr BP, particularly in productive and easily-cleared mid-altitudinal areas. Extensive and pervasive land-cover change has been associated with population growth, immigration and movement of people. The expansion of trading routes between the interior and the coast, starting around 1300 years ago and intensifying in the eighteenth and nineteenth centuries CE, was one such process. These caravan routes possibly acted as conduits for spreading New World crops such as maize (Zea mays), tobacco (Nicotiana spp.) and tomatoes (Solanum lycopersicum), although the processes and timings of their introductions remains poorly documented. The introduction of southeast Asian domesticates, especially banana (Musa spp.), rice (Oryza spp.), taro (Colocasia esculenta), and chicken (Gallus gallus), via transoceanic biological transfers around and across the Indian Ocean, from at least around 1300 yr BP, and potentially significantly earlier, also had profound social and ecological consequences across parts of the region. Through an interdisciplinary synthesis of information and metadatasets, we explore the different drivers and directions of changes in land-cover, and the associated environmental histories and interactions with various cultures, technologies, and subsistence strategies through time and across space in East Africa. This review suggests topics for targeted future research that focus on areas and/or time periods where our understanding of the interactions between people, the environment and land-cover change are most contentious and/or poorly resolved. The review also offers a perspective on how knowledge of regional land-use change can be used to inform and provide perspectives on contemporary issues such as climate and ecosystem change models, conservation strategies, and the achievement of nature-based solutions for development purposes.

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 – in one important river valley at least – 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.

We combine high-resolution soil sampling with lead (Pb) analyses (concentrations and stable isotopes) in two temperate podzols, together with previous data obtained with selective Al and Fe dissolution techniques. We aim to assess how atmospheric Pb is incorporated into the soils during pedogenesis. Partial least squares modelling for Pb concentrations shows that the podzolization process has the largest effect on Pb concentration (803% of the variance). The proportion of inorganic secondary compounds, the input of fresh organic matter from the soil surface and the relative abundance of Fe versus Al are responsible for a small part of the Pb concentration variance. Lead isotopic composition (Pb-206/Pb-207 ratios) depends on soil organic matter content either fresh/poorly humified (573% of the variance) or humified (247% of the variance). The Pb linked to inorganic compounds and the overall podzolization process play a minor role in isotopic signature (53 and 37% of the variance respectively). Soil pH appears to be the controlling variable of the different transport and retention mechanisms. The relatively low isotopic ratios observed in spodic horizons result from geogenic Pb released through the preferential dissolution of the isotopically distinct most weatherable minerals of the parent material in the eluvial horizons, which undergoes downward mobilization. An accurate knowledge of soil reactive components and formation mechanisms is essential to a correct diagnose of the scope of Pb pollution and a more effective design of remediation strategies. Copyright (c) 2017 John Wiley & Sons, Ltd.

Recent investigations showed that bromine is incorporated to soil organic matter (SOM), its content increasing with humification. But few research was done on its long-term accumulation and the role played by pedogenetic processes, as those involved in organic matter stabilization. We investigated bromine content and distribution in four deep, acidic, organic-rich, Holocene soils from an oceanic area of Western Europe. Bromine concentrations (93–778μgg−1) in the silt+clay (<50μm) fraction were on average 3-times higher than those (17–250μgg−1) in the fine earth (<2mm), the former containing almost all bromine (90±5%). Inventories were between 148 and 314gm−2, indicating a rather large variability in a small area, and total estimated retention was low (6–16%). The degree of SOM bromination, expressed as the Br/C molar ratio, varied between 0.03 and 1.20mmol Br/mol C. The ratio was highly correlated (n=23, r2 0.88, p<0.01) with the age of the SOM for the last ∼12ka. Partial least squares modeling indicates that bromine concentration depends on the amount of organic matter stabilized as aluminium-OM associations, and to a lesser extent on soil acidity (pH) and iron-OM associations. Thus, at scales of thousands of years, bromine accumulation in acidic soils is linked to the pool of metal–clay-stabilized organic matter.

We analyzed the isotopic (13C and 15N) composition of a polycyclic terraced soil located in Santiago de Compostela (NW Spain) and compared it with previous results on total aluminum, iron and silicon and their fractionation by selective dissolution techniques. The aim was to recognize the imprints of land management changes, with particular attention to fertilization techniques applied during the use history of the terrace (~1600 y). The buried paleosol, found below the terraced layers, is considered to preserve the soil properties prior to the terrace construction. The isotopic composition (13C, 15N) provided evidence of extensive land use previous to the construction of the terrace, with the utilization of fire as liming and clearance tool. In the Late Antiquity and Early Medieval Ages the soil use was more intense and amendments with vegetal remains from nitrogen fixing shrubs were likely applied. Since the Early Middle Ages, animal wastes were used as a way to maintain or increase soil fertility because of an intensification of the agrarian use.

In this paper we characterise the mineralogical and elemental composition and the colour (CIELab space) of Bronze Age pottery sherds from NW Spain, using X-Ray diffraction, X-Ray fluorescence and reflectance spectroscopy, respectively. For half of the samples we also determined the content in secondary iron oxi-hydroxides (sFe, iron extracted with dithionite-citrate), using atomic absorption. The aim of the investigation was to study the relationship between the colour and the elemental and mineralogical composition, and to explore the intentionality of the resulting colour. Samples had a low luminosity and were located in the quadrant of the CIELab space ranging from red to yellow (hab: 0-90 degrees), showing low hue variability but a wider range of variation in chromaticity. In terms of composition they showed a large mineralogical (12 different minerals were identified) and chemical (from acidic/felsic to basic-ultrabasic/mafic compositions) variation.A principal components analysis using elemental composition and colour parameters demonstrated that luminosity (L*) depends on organic matter (OM) content and to a lesser extent on sFe content. Chromaticity (C*(ab)) depends on sFe content, but also on the felsic/mafic relative composition and OM content, while hue (h(ab)) is only related to iron mineral phases. We also verified that these general trends differ to a certain extent depending on whether the pottery contains amphibole or not: the effect of sFe on L* and of OM on b* (yellowing) and C*(ab) was only detected for pottery sherds without amphibole, while an increase in felsic in relation to mafic minerals has a more decisive effect on the chromaticity (C*(ab)) of the amphibolic clays. Thus, colour seems to result from the interplay between i) the original colour of the raw material/clays, ii) compositional factors (overall composition -felsic vs mafic-, and sFe and OM content), and iii) interactions between composition and processing (sFe and firing conditions controlling yellowing). We interpret that there was an intentional selection of raw materials (felsic or mafic) and their processing (addition of iron oxides and organic matter) and a control over the firing conditions in order to give the vessels a specific colour. (C) 2014 Elsevier Ltd. All rights reserved.

We analyzed the isotopic (13C and 15N) composition of a polycyclic terraced soil located in Santiago de Compostela (NW Spain) and compared it with previous results on total aluminum, iron and silicon and their fractionation by selective dissolution techniques. The aim was to recognize the imprints of land management changes, with particular attention to fertilization techniques applied during the use history of the terrace (~1600 y). The buried paleosol, found below the terraced layers, is considered to preserve the soil properties prior to the terrace construction. The isotopic composition (13C, 15N) provided evidence of extensive land use previous to the construction of the terrace, with the utilization of fire as liming and clearance tool. In the Late Antiquity and Early Medieval Ages the soil use was more intense and amendments with vegetal remains from nitrogen fixing shrubs were likely applied. Since the Early Middle Ages, animal wastes were used as a way to maintain or increase soil fertility because of an intensification of the agrarian use. Descifrando la evolución de las tecnologías agrarias durante los últimos ~1.600 años utilizando la huella isotópica (δ13C, δ15N) en un suelo aterrazado policíclico - Hemos analizado la composición isotópica (13C y 15N) de un suelo policíclico aterrazado situado en Santiago de Compostela (NO de España) y la hemos comparado con resultados geoquímicos previamente obtenidos de aluminio, hierro y silicio totales, así como las fracciones en las que se distribuyen estos elementos, mediante técnicas de disolución selectiva. El objetivo era reconocer las señales de los cambios de manejo del suelo agrícola, con especial atención a la aplicación de técnicas de fertilización, durante la historia de uso de la terraza (~1600 años). Se asume que el paleosuelo enterrado, que se conserva bajo los niveles de aterrazamiento, preserva las propiedades del suelo previas a la construcción de la terraza. La composición isotópica (13C y 15N) proporcionó evidencias de un uso extensivo del suelo con anterioridad a la construcción de la terraza, con la utilización del fuego como principal herramienta para el encalado y el clareo del terreno. Durante la Antigüedad tardía y la Alta Edad Media el uso del suelo se intensificó y se introdujeron técnicas de fertilización basadas en la adición de restos de vegetales de arbustos fijadores de nitrógeno. A partir de la Alta Edad Media se detecta el uso de abonos de origen animal, como medio para mantener o aumentar la fertilidad del suelo, ante una creciente intensificación del uso.