Terra Mulata Research Articles

Anthropogenic soil and settlement organisation in the Bolivian Amazon

AbstractAnthropogenic soils known as Amazonian Dark Earths (ADEs) have long been known as a key component of subsistence systems for various pre‐Columbian Amazonian populations. Often treated as a single category, ADE systems consist of two broad anthrosols (human‐modified soils): the darker ADE (traditionally known as terra preta) and a lighter brown Amazonian Brown Earth (ABE; traditionally known as terra mulata). Data on the characteristics and spatial distribution of these anthrosols are severely lacking. Transects of soil test pits at the Triunfo and Versalles archaeological sites in the Iténez Forest, in the Bolivian Amazon, show variability in the distribution of soil types, revealing aspects of settlement organisation and resource management. Geochemical, isotopic and archaeobotanical data from an ADE, ABE and control soil profile from the Triunfo site, established ca. 500 cal BCE, characterise the two anthrosols as distinct components of a polyculture agroforestry subsistence system that combines anthropogenic soil fertilisation, closed‐canopy forest enrichment, limited forest clearance for crop cultivation and low‐severity fire management.

Fulvic acids from Amazonian anthropogenic soils: Insight into the molecular composition and copper binding properties using fluorescence techniques

Fulvic acids (FA) are one of the components of humic substances and play an important role in the interaction with metallic species and, consequently, the bioavailability, distribution and toxicity of metals. However, only a few studies have investigated these FA properties in specific environment, such as anthropogenic soils. Therefore, knowledge about FA molecular composition as well as the FA-metal interaction is essential to predict their behavior in the soil. For this reason, the aim of this study was to investigate the molecular composition of FA extracted from two sites in an anthropogenic soil (Terra Mulata), from the Amazon region, as well as their interactions with Cu(II) ions as a model. Results from 13C NMR, infrared and elemental analysis showed that these FA are composed mostly by alkyl structures and oxygen-functional groups, e.g., hydroxyl, carbonyl and carboxyl. The interaction with Cu(II) ions was evaluated by fluorescence quenching, in which the FA showed both high quantity of complexing sites per gram of carbon and good affinity to interact with the metal when compared with other soil FA. The results showed that the complexation capacity was highly correlated by the content of functional groups, while the binding affinity was largely influenced by structural factors. In addition, through the lifetime decay given by time-resolved fluorescence, it was concluded that static quenching took place in FA and Cu(II) interaction with the formation of a non-fluorescent ground-state complex. Therefore, this fraction of soil organic matter will fully participate in complexation reactions, thereby influencing the mobility and bioavailability of metal in soils. Hence, the importance of the study, and the role of FA in the environment, can be seen especially in the Amazon, which is one of the most important biomes in the world.

Humic-like acids from hydrochars: Study of the metal complexation properties compared with humic acids from anthropogenic soils using PARAFAC and time-resolved fluorescence

Humic acids (HA) play an important role in the distribution, toxicity, and bioavailability of metals in the environment. Humic-like acids (HLA) that simulate geochemical processes can be prepared by NaOH aqueous extraction from hydrochars produced by hydrothermal carbonization (HTC). HLA can exhibit properties such as those found in HA from soils, which are known for their ability to interact with inorganic and organic compounds. The molecular characteristics of HLA and HA help to explain the relationship between their molecular features and their interaction with metallic species. The aim of this study is to assess the molecular features of HA extracted from Terra Mulata (TM) and HLA from hydrochars as well as their interaction with metals by using Cu(II) ions as a model. The results from 13C NMR, elemental analysis, FTIR, and UV–Vis showed that HA are composed mostly of aromatic structures and oxygenated functional groups, whereas HLA showed a mutual contribution of aromatic and aliphatic structures as main constituents. The interactions of HA and HLA with Cu(II) ions were evaluated through fluorescence quenching, in which the density of complexing sites per gram of carbon for interaction was higher for HLA than for HA. Furthermore, the HLA showed similar values for stability constants, and higher than those found for other types of HA in the literature. In addition, the average lifetime in both humic extracts appeared to be independent of the copper addition, indicating that the main mechanism of interaction was static quenching with a non-fluorescent ground-state complex formation. Therefore, the HLA showed the ability to interact with Cu(II) ions, which suggests that their application can provide a new approach for remediation of contaminated areas.

Morphological analysis of soil particles at multiple length-scale reveals nutrient stocks of Amazonian Anthrosols

We have imaged the particles of Brazilian soils at multiple length scales, from a few microns to millimeters, and soil particle size distributions were calculated with unmatched precision. The analysis included the Amazonian soil “Terra Mulata de Índio” (TMI), an anthropogenic soil (Anthrosol) with sustained fertility and a large amount of stabilized organic matter. Firstly, the soils were imaged ex situ, without any chemical processing, with sequential electron scanning of the pelletized soil samples, covering a total area of 8×8mm. Secondly, it was performed a computational analysis of the large-field X-ray images assembled from hundreds of adjacent elemental maps, thus resulting in high-definition images (4800×4800pixels). This analytical approach provides a large sampling with the identification of >10,000 particles over the scanned area. The particles identified consisted of Al, C, Ca, Cr, F, Fe, Mg, Mn, Na, O, P, S, Si and Ti. A significantly larger concentration of C-, Ca- and P-based particles, of up to 100μm2 of cross-section area, was found in TMI samples in comparison with oxisol and ultisol soils. While the mean distance between neighboring C, Ca and P particles in TMI was of 40–70μm, the value was of hundreds of microns in oxisol and ultisol. Furthermore, mapping of micrometric carbon particles by Raman spectroscopy indicated that they have a graphitic structure with a large amount of defects, partially associated with particle oxidation, although a well-preserved sp2 graphitic structure is also present. From a technological perspective, improved soil amendments, such as biochar, can be rationally designed from the “fingerprint” described here for soil particles of Amazonian Anthrosols (i.e., morphological and structural characteristics), which can result in an increase in fertility and the optimization of carbon sequestration in the future.

Organic geochemical evaluation of organic acids to assess anthropogenic soil deposits of Central Amazon, Brazil

Terra Preta de Índio (TPI) and Terra Mulata (TM) are anthropogenic soils from the Amazon region and are rich in stable organic matter (OM). The formation and incorporation of OM in these soils has recently been under investigation. Organic geochemical analysis is an appropriated tool for the assessment of the sources of OM. Therefore, we have used the distribution of different acid classes preserved in the free and bound soil fractions of 12 samples from two contrasting anthropogenic soils (TPI, TM) and an adjacent soil, in order to infer the sources of OM and the magnitude of non-cultural influence on the formation of anthropogenic soils. The major acids in both fractions (i.e. free and bound) were n-saturated, branched and unsaturated alkanoic acids, hydroxyalkanoic acids, bile acids and lignin/suberin derived aromatic acids. In general, the acids in the free and bound fractions appeared to be complementary and together provided valuable information about OM incorporation into anthropogenic soils. Different incorporation of ω-hydroxyalkanoic acids (C22, C24 and C28) and 9(10),16-dihydroxyhexadecanoic acid, and presence/absence of bile acid showed a distinct genesis for the soils. The influence of modern vegetation was revealed by bound ω-hydroxyalkanoic acid (C22, C24 and C28) distributions only in the topsoil profiles of TPI and TM, indicating that organic geochemical analysis is a useful approach in the investigation of ancient human deposits in tropical archaeological soils.

Analysis of the spatial distribution of geochemical signatures for the identification of prehistoric settlement patterns in ADE and TMA sites in the lower Amazon Basin

The Archeological Dark Earth (ADE) and Terra Mulata (TMA) anthrosols found at Juruti, on the lower Amazon River, extend over a wide area located within the local ferralsol domain. The ADE soils are dark in color and contain large quantities of fragmented ceramics, while the TMA soils are also relatively dark, but lack ceramics. Multi-element chemical analyses of soil samples of ADE and TMA from the A2 horizon (depths of 10–20 cm) indicated that the ADE soils are characterized by higher concentrations of P2O5, CaO, K2O, MgO, Cu, Mn, and Zn, while the TMAs have median levels of these compounds, and the ferralsols have much lower concentrations. These chemical elements make up the geochemical signature of these anthrosols, whereas Al2O3, Fe2O3, TiO2, Cr, Sr, La, Li, Ni, Pb, V, Y, and Zr characterize the geochemical signature of the ferralsols, which was identified partially in the ADEs and TMAs. The isoline maps of these two geochemical associations permitted the delimitation of the different areas and the identification of the ADEs as sites of long-term human occupancy, and the TMA as an area of temporary occupation associated with agricultural activities. Seven villages were delimited within the study area, and were separated by corridors of ferralsols. These settlements were established on the riverbank, with the more temporary cultivated areas behind them, running almost parallel to the river. The identification of functional patterns based on geochemical associations, the abundance of ceramic material, and concentrations of organic matter, indicated that an area of more than 350 ha was occupied.

Do Anthropogenic Dark Earths Occur in the Interior of Borneo? Some Initial Observations from East Kalimantan

Anthropogenic soils of the Amazon Basin (Terra Preta, Terra Mulata) reveal that pre-Colombian peoples made lasting improvements in the agricultural potential of nutrient-poor soils. Some have argued that applying similar techniques could improve agriculture over much of the humid tropics, enhancing local livelihoods and food security, while also sequestering large quantities of carbon to mitigate climate change. Here, we present preliminary evidence for Anthropogenic Dark Earths (ADEs) in tropical Asia. Our surveys in East Kalimantan (Indonesian Borneo) identified several sites where soils possess an anthropogenic development and context similar in several respects to the Amazon’s ADEs. Similarities include riverside locations, presence of useful fruit trees, spatial extent as well as soil characteristics such as dark color, high carbon content (in some cases), high phosphorus levels, and improved apparent fertility in comparison to neighboring soils. Local people value these soils for cultivation but are unaware of their origins. We discuss these soils in the context of local history and land-use and identify numerous unknowns. Incomplete biomass burning appears key to these modified soils. More study is required to clarify soil transformations in Borneo and to determine under what circumstances such soil improvements might remain ongoing.

Anthropogenic soils in the Central Amazon: from categories to a continuum

Amazonian Dark Earths (ADE), one of the best-known examples of anthropogenic (man-made) soils, are the result of Amerindian settlements in the pre-Columbian period. ADE are highly variable in terms of their size, shape, depth and physical and chemical make-up. Scholars tend to divide ADE into two categories: terra preta and terra mulata. The former are dark and highly fertile soils replete with ceramic shards, indicating former areas of habitation, while the latter are lighter in colour, less fertile, lacking pottery and thought to be old agricultural fields. While a scientific consensus on the origins of terra preta has existed for several decades, the origins of terra mulata remain enigmatic and contested. We argue that owing to the overlapping and constantly changing boundaries of agricultural and habitational areas, it is unlikely that there exist two clear soil fertility classes. This article examines the hypothesis that rather than two distinct anthrosol categories, ADE sites should exhibit a highly fertile ‘core area’, which grades into more subtly modified soils, with a continuum of fertility between them. Using principal components analysis (PCA) and interpolations based on the geographic distribution of the soil samples, we show that ADE along the Middle Madeira, Brazilian Amazon are extremely diverse, but data support more of a gradient between areas of greater and lesser fertility rather than two distinct categories. We also assess local people's perceptions and classifications of anthropogenic and surrounding soils using ethnographic data. Rather than discarding the terra preta–terra mulata opposition however, we suggest abandoning only the idea that they are separate categories, and instead emphasise a continuum, the darker, bluff edge ‘central’ regions with abundant ceramics are consonant with published descriptions of terra preta, which grade into surrounding areas with lighter, less fertile soils that better fit terra mulata descriptions.

Anthropogenic Soils and Tree Distributions in a Lowland Forest in Bolivia

ABSTRACTThe distributions of 17 tree species with seeds or fruits that are commonly eaten or otherwise used by humans were studied in reference to anthropogenic soils in a seasonally dry lowland tropical forest in Bolivia. Two types of anthropogenic dark earths (ADEs) were identified: terra preta (TP: darkened with charcoal fragments and with abundant pottery shards) and terra mulata (TM: somewhat darkened but with little or no pottery). In 216 ha, we compared the densities of trees >10 cm dbh of useful species in nine TP patches, three TM patches, and six areas with nonanthropogenic soils (N‐ADE). The TP, which covers approximately 20 percent of the sample area, has higher contents of organic matter, extractable P, and extractable Ca than N‐ADE soils, as well as higher pH and extractable P than TM. TM has organic matter and Ca contents similar to N‐ADE soils but significantly less extractable K. In general, TP has higher nutrient content than surrounding soils, both at the surface (0–10 cm) and deeper in the profile (40–50 cm). Despite these differences in soil fertility and contrary to our expectations, none of the 17 tree species were concentrated on TP perhaps because interactions between local dispersal agents and natural disturbances have masked historical patterns. Alternatively, past inhabitants of the study area may have enriched forests with useful tree species in areas where they were not practicing the intensive soil husbandry that results in ADEs.

Dark Earths and manioc cultivation in Central Amazonia: a window on pre-Columbian agricultural systems?

Many commentators highlight the fertility of Anthropogenic Dark Earths (ADE), emphasizing their potential for sustainable agriculture. Some scholars believe that terra mulata (the less fertile, more extensive form of ADE) was created by means of agricultural practices used by large settled populations of pre-Columbian farmers. But what was it that these Amerindian farmers were growing? Until recently, scholarly consensus held that manioc does not perform well on ADE. New research on the middle Madeira River is showing, however, that this consensus was premature. In this region, the most common crop in ADE fields is bitter manioc. Farmers there have various landraces of manioc that they believe yield particularly well on ADE, and logically plant more of these varieties on ADE. Aspects of the behaviour and perception of manioc cultivation among 52 farmers at the community of Barro Alto were measured quantitatively on four terra firme soil types (Terra Preta, Terra Mulata, Oxisols and Ultisols). These farmers plant different configurations of landraces in different soils, according to their perception of the suitability of particular landraces and their characteristics to certain soil types and successional processes. This, in turn, shapes selective pressures on these varieties, as new genetic material incorporated from volunteer seedlings is more likely to contain traits present in the most prevalent landrace(s) in each soil type. Owing to localized population pressure at Barro Alto, manioc is under more intensive cultivation systems, with shorter cropping periods (5-10 months) and shorter fallow periods (1-2 years). The outcome of these processes is different co-evolutionary dynamics on ADE as opposed to non-anthropogenic soils. Further anthropological study of manioc swiddening in one of the richest agricultural environments in Amazonia can fill a gap in the literature, thus opening an additional window on the pre-Columbian period.