Soil genesis and mineralogy in arid-hyperarid climatic gradient in Atacama Desert, Northern Chile

O Deserto do Atacama pode ser considerado o extremo de aridez no planeta, por conjugar as menores precipitações anuais registradas, e a mais longa história de aridez conhecida. Os solos de regiões áridas são relativamente pouco conhecidos, e em geral quanto maior a aridez, menor o nível de informações disponíveis. O Atacama é bem estudado do ponto de vista geológico e geoquímico, mas estudos pedológicos são raros. Este estudo se concentra em diferentes aspectos relacionados aos solos em um amplo gradiente climático seco no norte do Chile, incluindo a área core do deserto e áreas adjacentes (climas hiperárido, árido e semi-árido). Os solos dos diferentes conjuntos foram caracterizados morfológica, química, física e mineralogicamente, o que permitiu a discussão acerca dos principais fatores e processos envolvidos na sua gênese. O fator climático é importante no condicionamento dos processos de formação ao longo da climossequência. Teores de sais e matéria orgânica são correlacionados com a precipitação média anual, embora fatores geomorfológicos possam ter maior importância local. Sob clima semiárido os solos não são salinos, e ocorre colonização vegetal significativa e acúmulo de matéria orgânica. Sob os climas árido e semiárido a acumulação de minerais solúveis é o principal processo de formação dos solos. Bacias fechadas condicionam solos salinos em qualquer setor climático. O estudo dos regimes térmico e hídrico de um gradiente climático, pedológico e vegetacional de solos semiáridos de elevada altitude (>4500 m) apontam para um regime típico de ambientes periglaciais em todas as altitudes estudadas. Contudo, permafrost não foi detectado na profundidade dos solos. Fatores relacionados à altitude (temperatura média do ar e precipitação) são importantes na definição dos regimes pedoclimáticos, mas fatores locais, como textura dos solos e duração da radiação solar, também agem sobre o comportamento térmico e hídrico dos solos mais elevados. O estudo de distribuição e organização dos minerais solúveis nos solos submetidos aos climas árido e hiperárido evidenciou que a acumulação destes minerais é o principal processo de formação dos solos. No sistema hiperárido o processo de acumulação é muito avançado, e algum processo de redistribuição ocorre apenas dentro do perfil, com perdas negligenciáveis por lixiviação. No sistema árido, a intensidade do processo de acumulação varia em função da posição na paisagem. Nos solos bem drenados a acumulação coexiste com perdas por lixiviação, enquanto os solos mal drenados recebem sais provenientes de outros setores da paisagem. O processo de calcificação é generalizado na paisagem, embora pouco avançado. O processo de gipsificação é generalizado, e todas as fases do processo foram observadas – incluindo horizontes com gipsificação completa. O processo de salinização está vinculado à proximidade das fontes destes minerais, à posição na paisagem ou a taxas muito baixas de precipitação.Atacama Desert is the arid endmember on Earth, due to very low rainfaw and longest aridity history. Arid region’s soils are poorly known and in greather aridity lower level of information is available. Atacama is well known to geochemical and geological point of view, but pedological studies are scarce. The present study focusing in different soil aspects in a dry climate gradient (hyperarid, arid and semiarid climates) in northern Chile. Soils from climatic zones were characterized, wich allow discuss main factors and processes involved in soil genesis. Climate is the main factor conditioning soil forming processes in the climossequence. Organic Matter and Salt accumulation are correlated with rainfall levels, but local factors can also act. Under semiarid climate we observed non-saline soils, with plant colonization and Organic Matter accumulation. Under arid and hyperarid climates salt accumulation is the main soil forming process. Closed basins conditioning saline solils in any climatic zone. Soil thermic and hydric regime study in a semiarid high-mountain climatic-pedological gradient point to a periglacial regime, without permafrost in soil-depth zone. Altitude-related factors (mean air temperature and precipitation) are important to regimes, but local factors (soil texture and solar radiation duration) also act over thermic and hydric behaviour of soils. The investigation on the distribution and organization of soluble minerals in arid and hyperarid zones show that salt accumulation is the main soil-forming process in that zone. In hyperarid system the accumulation is advanced, and salt redistribution is closed to the soils profile, with negligible losses. In the arid system, accumulation intensity vary with landscape position. In well-drained soils salt accumulation coexists with leaching losses, and in poorly- drained soils receive salts from other landscape positions. Cabonatation is generalized but weak in the study areas. Gipsification is generalized, and all stages of the process is observed, including horizons subject to complete gipsification. Salinization in linked with salt sources proximity, landscape position, and very low rainfall levels

Soils and Geoenvironments of the northern part of Seymour (Marambio) island, Antarctica

A Ilha Seymour/Marambio (ISM) se localiza no norte do Mar de Weddell, na região da Península Antártica, em uma transição climática entre os domínios da Antártica Marítima e da Antártica Continental, apresentando um clima pseudo-continental ou subpolar semiárido. A ISM é predominantemente composta por rochas sedimentares originadas entre o Cretáceo e o Terciário. Os objetivos deste trabalho foram identificar, mapear e caracterizar as unidades geoambientais que compõem a paisagem da porção norte da Ilha Seymour/Marambio, Antártica Peninsular; e estudar os atributos morfológicos, físicos, químicos e mineralógicos dos solos ao longo de uma topossequência, e discutir os processos e fatores envolvidos na sua pedogênese. A estratificação geoambiental foi feita com base nos atributos pedo-lito-geomorfológicos da paisagem tratados de forma integrada, onde foram agrupados sob uma mesma denominação setores com características similares em relação aos atributos de interesse. Para o estudo dos solos foram descritos e coletados nove perfis ao longo de uma topossequência abrangendo diferentes materiais de origem e geoformas. As amostras foram submetidas a fracionamento textural, análises químicas de rotina, extrações químicas com Oxalato de Amônio e Ditionito-Citrato-Bicarbonato, e difração de Raios-X. A aplicação da metodologia de estratificação permitiu a identificação de 13 unidades geoambientais, representativas de ambientes periglaciais situados na zona de transição climática. Nota-se forte controle da geologia sobre a distribuição dos ambientes, influenciando o estabelecimento do relevo e os atributos dos solos. Constatou-se presença generalizada de permafrost ao longo da área de estudo, em geral nos primeiros 100 cm de profundidade, determinando uma predominância de solos das ordens Gelisols (Soil Taxonomy) e Cryosols (WRB). Outras feições comuns em solos afetados por congelamento, relacionadas com a crioturbação e acumulação de matéria orgânica, não foram observadas. A análise dos atributos dos solos permitiu identificar dois grupos de solos: os Sulfatados Ácidos e os Não Sulfatados Alcalinos. Os solos sulfatados ácidos são os mais desenvolvidos da área de estudo, evidenciando significativa alteração morfológica, física e mineralógica. As características destes solos apontam para baixo pH, alta saturação por alumínio, alta acidez potencial. A acidez favorece o intemperismo de silicatos primários, que não são observados na fração argila. Os principais minerais secundários são relacionados com a oxidação dos sulfetos, podendo ser listados sulfatos solúveis, sulfatos insolúveis, hidróxidos de ferro mal cristalizados e óxidos de ferro cristalinos. O peculiar desenvolvimento de cor amarelada nos solos sulfatados ácidos é creditado à presença de óxidos e sulfatos de ferro. A presença de minerais silicatados do tipo 2:1 (esmectita e ilita) na fração argila destes solos é atribuída ao pedoambiente ácido (favorável ao intemperismo dos silicatos primários) e com baixa lixiviação. Os solos Não Sulfatados Alcalinos não apresentam sinais de transformações expressivas. Os dados químicos apontam para altos valores de pH, alumínio trocável nulo e baixa acidez potencial. A transformação mais importante na gênese destes solos é o intemperismo físico na forma de crioclastia e haloclastia. Nota-se a presença de minerais primários facilmente intemperizáveis na fração argila, confirmando o baixo grau de transformações químicas. A geoforma é determinante para a disponibilidade de bases nestes solos, na medida em que favorece ou dificulta a lixiviação. Conclui-se que os principais processos atuantes na gênese dos solos da área de estudo são a sulfurização e o halomorfismo.The Seymour/Marambio island (ISM) is located in the northern sector of the Weddell Sea, at the Antarctic Peninsular area, representing a transitional zone between Maritime and Continental Antarctica, with a subpolar, semiarid climate. The ISM is predominantly composed by marine sedimentary rocks of Cretaceus to Eocene age. The aims of this work were: identifying, mapping and characterization of the geoenvironmental units at the northern part of ISM landscape, as well as studying chemical, physical, mineralogical and morphological attributes, across a selected, representative toposequence. Also, pedogenetic processes and factors were discussed. The geoenvronmental stratification was based on pedo-litogeomorphological attributes, in an integrated landscape approach, in which sectors with similar attributes were grouped together. For the soil study, nine profiles were described, collected and analysed, following a toposequence according to different parent materials and landforms. Samples were subjected to textural analysis, routine chemical analysis, chemical extractions by ammonium oxalate and CBD, as well as X ray diffraction. Thirteen geoenvironments were identified, representing periglacial environments at this transitional climatic zone. The geology exerts a control on the geoenvironments, with great influence on landforms and soils. Permafrost is continuous and widespread, generally at depths of less than 100 cm, so the Gelisols order (Soil Taxonomy), or Cryosols (WRB), are the dominant soils. Cryoturbation and organic matter accumulation were not observed. Soils were separated into two groups: acid-sulphate soils and alkaline soils, unaffected by sulphates. The first are the best developed in the study area, meaning a significant physico-chemical and mineralogical alteration. Low pH and high Al saturation and potential acidity are typical. This accounts for primary mineral dissolution, and its absence in the clay fraction. Secondary minerals are those related to sulphide oxidation: soluble and insoluble sulphates, low crystalline Fe-hydroxides and little crystalline Fe phases. The peculiar yellowish colour of these soils are attributed to the presence of Fe-oxides and Jarosite. The presence of 2:1 clays (smectite and illite) in the Clay fraction despite the acidity is due to low leaching. The alkaline soils, non affected by sulphates do not showed any marked weathering or transformation, with high pH, low potencial acidity and zero Al saturation. The main process is cryoclastic and haloclastic weathering. Primary minerals are present even in the clay fraction, corroborating its low weathering degree and chemical alteration. The landform is determinant for the chemical status of theses soils, by favoring or reducing leaching. Sulphurization and halomorphism are the dominant soil-forming processes in Seymour-Marambio island

Ethnopedology of a Quilombola Community in Minas Gerais: Soils, Landscape, and Land Evaluation

ABSTRACT Quilombolas are Afro-brazilian rural peasants who descended from escaped slaves who tried to carve out territories of autonomy (called Quilombos) by collective organization and resistance. Despite many anthropological and ethnopedological studies, little research has been carried out to identify the agricultural practices and the knowledge of people who live in the Quilombos (Quilombolas). Peasant communities who live from land resources have wide empirical knowledge related to local soils and landscapes. In this respect, ethnopedology focuses on their relationship with local practices, needs, and values. We carried out an ethnopedological evaluation of the soils, landscape and land suitability of the Malhada Grande Quilombola Territory, aiming to examine the local criteria involved in land-use decision making, and evaluate the legitimacy of local knowledge. For this purpose, participatory workshops allowed environmental stratification of the Quilombolas into landscape units, recognition of soil types, and evaluation of land-use criteria. This approach was combined with conventional soil sampling, description, and analysis. The Brazilian System of Soil Classification and its approximations to the WRB/FAO system and the SAAT land evaluation system were compared with the local classificatory systems, showing several convergences. The Quilombolas stratified the local environment into eight landscape units (based on soil, topography, and vegetation) and identified eight soil types with distinct morphological, chemical, and physical attributes. The conventional soil survey identified thirteen soil classes, in the same eight landscape units, organized as soil associations. The apparent contradictions between local knowledge and Pedology were relative since the classification systems were established based on different criteria, goals, and sampling references. Most soils are only suitable for pasture, with restricted agricultural use, due to water or oxygen deficiencies. The current land use was only inconsistent with the technical recommendations when socioecological constraints such as the semiarid climate, land availability, and economic conditions for land management led to overuse of the land. Local knowledge demonstrated its legitimacy and allowed a useful and fruitful exchange of information with the academic view of soil-landscape interplays. Although mostly unknown by the scientific community, local knowledge proved capable of achieving social welfare and food security. In addition, a participatory survey proved to be a core factor for more grounded and detailed data collection on how Quilombolas decide land use on a local scale

Ethnopedology of a quilombola community in Minas Gerais: Soils, landscape, and land evaluation

Quilombolas are Afro-brazilian rural peasants who descended from escaped slaves who tried to carve out territories of autonomy (called Quilombos) by collective organization and resistance. Despite many anthropological and ethnopedological studies, little research has been carried out to identify the agricultural practices and the knowledge of people who live in the Quilombos (Quilombolas). Peasant communities who live from land resources have wide empirical knowledge related to local soils and landscapes. In this respect, ethnopedology focuses on their relationship with local practices, needs, and values. We carried out an ethnopedological evaluation of the soils, landscape and land suitability of the Malhada Grande Quilombola Territory, aiming to examine the local criteria involved in land-use decision making, and evaluate the legitimacy of local knowledge. For this purpose, participatory workshops allowed environmental stratification of the Quilombolas into landscape units, recognition of soil types, and evaluation of land-use criteria. This approach was combined with conventional soil sampling, description, and analysis. The Brazilian System of Soil Classification and its approximations to the WRB/FAO system and the SAAT land evaluation system were compared with the local classificatory systems, showing several convergences. The Quilombolas stratified the local environment into eight landscape units (based on soil, topography, and vegetation) and identified eight soil types with distinct morphological, chemical, and physical attributes. The conventional soil survey identified thirteen soil classes, in the same eight landscape units, organized as soil associations. The apparent contradictions between local knowledge and Pedology were relative since the classification systems were established based on different criteria, goals, and sampling references. Most soils are only suitable for pasture, with restricted agricultural use, due to water or oxygen deficiencies. The current land use was only inconsistent with the technical recommendations when socioecological constraints such as the semiarid climate, land availability, and economic conditions for land management led to overuse of the land. Local knowledge demonstrated its legitimacy and allowed a useful and fruitful exchange of information with the academic view of soil-landscape interplays. Although mostly unknown by the scientific community, local knowledge proved capable of achieving social welfare and food security. In addition, a participatory survey proved to be a core factor for more grounded and detailed data collection on how Quilombolas decide land use on a local scale