Research Programme
With the introduction of a productive economy, mobility and even migrations did not become less important as compared to hunter-gatherer societies. In the matrix of possible migration influencing factors, cultural as well as environmental variables have to be considered. The project comprises two fields of research, one of which focuses on the diachronic comparison and description of the principal factors driving population dynamics. The other one focuses on soil fertility which became a new condition of paramount importance. The project D2 aims to identify how soils were selected or abandoned, when fertilisation became necessary in the Rhine region, and which additional climatic and cultural factors influenced the choice of settlement areas. New molecular geochemical analyses jointly with existing archaeological, archaeobotanical, dendrochronological and geoscientifical databases thereby promise a better understanding of past human-environmental-systems in the Rhineland.
At the beginning of the Neolithic (at about 5,500 BC), farmers started to use large parts of the landscape in Central Europe. Mobility and adaptation remained key factors of human survival during that time. Especially technical innovations, climatic variations, but also the dislocation of cultural centres led to a dramatic shift of settlements during a few centuries. In times of lower population densities, smaller groups, and migrations over distances, up to some hundreds of kilometres, were likely more common than trans-continental movements. The key factors for such migration and adaptation processes in sedentary communities are still unclear and are to be investigated in project D2. For this purpose, we will take advantage of better chronological resolution and higher spatial information density available, as compared to those during the period of forager communities. We expect that the detailed investigation of the driving factors of migration and adaptation in sedentary communities will provide an important basis for a better understanding of previous migration periods.
The cultural development included growth-cycles and processes of devolution. Also favoured and unfavoured areas changed over time and the population migrated between these areas. In the matrix of possible influencing environmental and cultural variables, next to climate, soils achieved a new and high significance. In specific epochs some soil types were preferred and some were abandoned. At the regional scale of the Rhineland, it is possible to observe that these internal migrations often connected to different agricultural practices and technologies. These changes are clearly visible in most terrestrial archives, e.g. colluvia and pollen. However, little is known about prehistoric soil conditions and their interaction with the intensity of farming. A molecular geochemical examination of recalcitrant constituents in buried soils could enable a reconstruction of former topsoil conditions, especially in terms of limitation of nutrients and fertilising methods. Thus, principal research questions deal with environmental factors, such as climate and soil, and their influence on internal migration and the spread of new agricultural technologies. Moreover, they deal with cultural factors, in particular the specific selection of soil types in particular time periods. This involves the methodological task to find new proxies for human impact in archaeological soil material indicated by molecular geochemical markers.
Thus, our project will comprise one comprehensive, multidisciplinary research field and a second, geochemical one, which is specifically devoted to human impact on soil.
- One field of research will combine archaeological and palaeoecological data derived from archaeobotany, climatology, geoarchaeology/palaeopedology and geochemistry. This integrative synopsis will allow us to extend the model of human impact and human reaction in pre-industrial societies. This is necessary to make the coherence between settlement-cycles, spatial mobility and preferred ecological units (soils or/and climate) visible. For this purpose we need to enhance and specify the existing geostatistical methods.
- Another field of research will be the reconstruction of ancient nutrient pools and their substitutes by means of geochemical proxies. Here we will apply novel biogeochemical techniques to trace ancient nutrient and fertiliser markers in archaeological soil material (e.g. buried A-horizons, colluvia and pit fillings). Stable organic P, which perhaps represents ancient fertilisation, is precisely characterised, complemented by a screening for essential trace elements that might have limited crop growth. Soil organic residues, indicative of fertilisation methods, are traced back using lipid fractionation and molecular analyses. Biomass burning, which likely served as fertilisation measures since the Neolithic, is indicated using benzenepolycarboxylic acids and selected polycyclic aromatic hydrocarbons as specific markers for charred remains. This information will contribute to the validation of spatio-temporal reconstruction of settlement areas within our first field of research.
Report
The matrix of factors influencing human mobility and migrations is composed out of cultural and environmental variables. Therefore cultural reasons for migrations are one point of interest (subproject a) and from environmental variables soils in general (subproject a) and deficiencies in soil nutrients (subproject b) could be another possible reason for human mobility in prehistory.
subproject a)
Specific patterns of land use, cultural growth-cycles and development of agricultural technology as well as pedology and climate are discussed as reasons for cultural mobility and even migrations. Therefore intercorrelations of these independent variables as well as dependent reactions of different archaeological cultures are a promising field of analysis. This was done by means of two MA-Theses.
R. Peters analyzed cultural cycles of the early Neolithic Bandkeramik in the lower Rhine basin and the younger Neolithic Pfyn at the western shore of Lake Constance. The result was that in fact clear patterns of cycles exist with four phases. The beginning is cultural reorganization (α-phase) and growth (r-phase). Then typically for some generations a high level of population density can be maintained (K-phase) before the cycle finds his end by a crisis (Ω-phase). The results are published in the paper Widlok et al. 2012. Based on these results a generalized model of cultural cycles for the epoch of pre-state agrarian societies of Central Europe was developed (Zimmermann 2012). It is to be summarized that cultural cycles develop a dynamic which could be a reason for mobility and migrations even during periods of good environmental conditions.
subproject b)
The geochemical part of the project D2 (subproject b) aimed to reconstruct the ancient fertility of agricultural soils. The application of molecular geochemical analyses jointly with existing archaeological, archaeobotanical, dendrochronological and geoscientifical databases thereby promise a better understanding of past human-environmental-systems. This part of the project was supported by one PhD student with soil analytical focus, (University of Bonn: PhD: Franziska Lauer). Decreasing soil fertility, plant nutrient deficiency and a related decrease of yields are discussed as possible factors inducing human mobility and/or adaptation during the Neolithic. In our analytical subproject we aimed at reconstructing the prehistoric soil nutrient status. For this purpose we selected buried archaeological topsoil relicts (e.g. slot pit fillings and pit alignments) outside prehistoric settlements, which comprised the ancient agricultural soil. Pit alignments and pit fillings are both enigmatic features with typical characteristics: slot pits are deep and very narrow (Struck 1984; Döhle & Hüser, 2010), whereas pit alignments consist of a series of pits arranged in long lines (Stäuble 2002). Both features are mainly filled with humic topsoil material, without artefacts such as ceramics, and both features occurred in the vicinity of settlements but outside the residential area. They can therefore be seen as archaeological offsite features and as a part of the prehistoric arable land. Samples were taken from in- and outside the pits with recent arable topsoil as reference and characterized for different nutrient contents and binding forms as well as for proxies of ancient fertilization strategies. In particular we focused on the following research questions:
- What nutrient status exhibited agricultural soils in the Neolithic, and do we find any evidence for nutrient deficiencies?
- Do we find proxies to trace potential strategies for fertilization?
In enlargement of the existing proposal we sampled not only features in the Lower Rhine Basin (LRB; n=96) but also features in the Central German dry region (CDR; n=110), thus comprising pit alignments of the Bronze Age as well as Neolithic slot pits. Both regions are located in the loess landscapes in Germany, and both regions are ancient settlement areas.
The soil analyses were performed as outlined in our main proposal. Main focus to answer question 1 was lain on the status of soil phosphorus and trace elements. The former usually limits crop yields in the absence of P fertilizers; deficiencies of trace elements may induce additional health risks for the consumers. As proxies for possible ancient fertilization (question 2), we analyzed benzene polycarboxylic acids (BPCA) as marker for charred burning residues (cf. project F03) and therewith also an evidence for slash-and-burn-induced increase of labile P fractions, amino acid enantiomers and δ15N ratios as markers for ancient legume inputs (current MSc thesis of Sarah Urmersbach), and we adapted soil lipid analyses to the characterization of ancient topsoil samples as tracers of ancient manure inputs. However, since the second PhD position for this requested work was not funded in the frame of this CRC, we concentrated on method development with the help of additional funding from the "Braunkohlestiftung für Archäologie" concerning the lipid analyses. The BPCA analyses of the pit fillings will run in the final half year of our CRC project.
Report - Goals and Methods
subproject a)
As proxy for the development of cultural cycles demographic indicators (frequency of households or settlements) are used. Cultural variables such as homogeneity vs. diversity of material culture and openness concerning influences from the outside vs. active influence of neighborhood are analyzed in their dependency of the specific stadium of cultural cycles.
As environmental parameter land use concerning soil is analyzed using GIS-methods (Zimmermann et al. 2009).
subproject b)
Soil phosphorus is characterized by sequential extraction acc. to Hedley (modified by Tiessen & Moir 1993) which includes numerous laboratory steps and results in six different fractions. These fractions differ in binding form and strength: labile P, moderately labile P, Ca-bound P and stable P. Due to separate measurements these fractions can be differentiated into inorganic P (spectrophotometer) and total P (ICP-OES). Organic P is calculated as the difference between the two components (organic P= total P - inorganic P).
The results show that the pit fillings in both regions on average amounted to 86% of the P content of the modern, fertilized topsoil. The difference to the recent topsoils was partly even insignificant. Nevertheless, the total P contents and also in the proportions of organic P are enriched in the soil relicts in comparison to the surrounding subsoil. Thus, there is no evidence of severe P limitations in prehistoric agriculture (Neolithic and Bronze Age). In both study regions, especially the moderately labile inorganic P fractions are even enriched, whereas stable P pools showed less enrichment. Obviously, high amounts of plant available P was sustained over millennia (see also Wilke 1979), thus also not limiting crop yields in prehistoric agriculture. Furthermore, these high amounts of labile P fractions are consistent with the slash-and-burn-induced increase in available P forms. The practice of slash-and-burn was proved by Gerlach et al. (2012) for the Lower Rhine Basin. In the Central German dry region, Kleber et al. (2003) also supposed anthropogenic burnings in prehistoric agriculture due to
high black carbon contents in ancient soils. Hence, we have to refute the hypothesis that P deficiency of Neolithic and Bronze Age agricultural soils was a reason for the abandonment of arable fields and human mobility at that time.
The total element contents were analyzed by X-ray fluorescence spectroscopy (XRF) in cooperation with AG Lehmkuhl/Protze (RWTH Aachen) to screen trace element contents for potential soil deficiency situations. Additionally, all archaeological soil samples were analyzed by aqua regia extraction to gain information on the extractable element contents. Low Ca:Ti ratios also confirmed a higher weathering degree of the pit fillings in comparison to the respective subsoil in both regions, as required for fillings from former surface soil. The recent topsoils revealed the highest weathering degrees in the respective regions. Trace element analyses concentrated on Cu, Zn and Mn. Again, and in accordance with the findings from soil P analyses, these trace element contents were also not depleted in the pit fillings comparable with recent topsoil (data not presented), indicating also no dramatic trace element deficiency in Neolithic and Bronze Age agriculture.
Since legume cultivation is proved by archaeobotanical investigations for the Neolithic (Lüning 2000, Zimmermann et al. 2005), we want to elucidate ancient legume cultivation for fertilizing purposes by geochemical markers. Therefore, we apply δ15N investigations and amino acid analyses in bulk soil samples which were carried out by Sarah Urmersbach as part of her diploma thesis. The data evaluation is still running and will be finished by September 2012. First results indicate that the isotopic composition of bulk total N differs between the two regions: the CDR soils exhibit on average a significantly higher δ15N value of 6.5 ± 0.2‰ than the LRB soils (5.3 ± 0.2‰). This indicates better N management efficiency in the LRB soils than in the CDR soils which could be due to the local climate. Furthermore, all pit fillings show δ15N values close to these of the recent topsoils (mean values not significantly different) and higher than in the adjacent subsoils.
First results of amino acid analyses suggested that the pit fillings in both regions revealed similar amino acid contents (expressed in g amino acids over kg soil N) as the adjacent subsoil. However, we found some differences in the amino acid pattern. Leguminous plants are characterized by a lysine/threonine ratio of 0.6, while cereals reveal a lysine/ threonine ratio of 1 or higher (Bellhoff et al. 2004). Accordingly, we found that recent topsoil cultivated three years with legumes (Trifolium pratense) shows a threonine/lysine ratio of 0.6. The recent topsoils under cashcrop production showed lysine/threonine ratios of > 1, thus reflecting the dominance of cereal production in modern crop rotations. In contrast, the pit fillings of both regions exhibited threonine/lysine ratios of also 0.6 to 0.7. Such low threonine/lysine ratios are consistent with leguminous plant cultivation in prehistoric agriculture (data not shown). Current research is still running to prove, if these markers are also produced during humification processes in soils. To validate the presence of legumes by geochemical markers, we
have to analyze the δ15N ratio of both amino acids in the ancient topsoils. Presence of legumes would be supported if the compound-specific δ15N values shift towards zero.
In summary, we conclude;
the character of Neolithic and Bronze Age soil relicts (pit fillings) as prehistoric topsoil was confirmed. The investigations indicate
- no significant P depletion,
- no severe trace element depletion, and
- they are consistent with slash-and-burn practices and legume cultivation.
Soil nutrient depletion as reason for human mobility is thus unlikely; in contrast, fertilization indices like slash-and-burn practices and legume cultivation indicate a human adaptation, but more research is still needed to substantiate the latter hypothesis. We are optimistic that we can provide this last evidence in the final year of our CRC funding, and do thus not apply for a continuation of the current project phase.
