Pedogenesis in an Archaeological Dark Earth – Mulatto Earth Catena over Volcanic Rocks in Western Amazonia, Brazil

ABSTRACT Archaeological Dark Earth (ADE) pedogenesis and pre-Columbian history are fundamental for understanding the biodiversity and pedodiversity of the Neotropical rainforest in the Amazon region. This study aimed to evaluate the morphological, physical, chemical, and mineralogical properties as well as NaOH-extractable organic matter [OM(NaOH)] in ADE and Mulatto Earth (ME) overlying volcanic rocks along a toposequence (four soil profiles) in western Amazonia, Brazil. The soil profiles show anthropic A horizons over an argic horizon (Bt) in the ADE (Humic, Pretic Luvisols) and Bi in the ME (Clayic, Dystric Cambisols). The soil-forming processes in all of the profiles are associated with organic matter accumulation, such as humification and melanization, besides the formation of organometallic complexes. Calcium, Mg, P, and organic carbon contents were higher in ADE compared to ME. High-activity clays are derived from parent volcanic material, distinguishing the soils studied from Amazonian soils (Tertiary Plateau, Terra Firme) and most Amazonian anthropic soils. The anthropic horizons generally have a large contribution from OM(NaOH), predominantly humin and humic acids associated with Ca, Mg, and poorly crystalline Al hydroxides. The results suggest that the anthropic driving-forces caused greater differences in pedogenesis than the soil location in the landscape.

摘要 考古黑土（Archaeological Dark Earth, ADE）的土壤发生学与前哥伦布时期历史，是理解亚马逊地区新热带雨林生物多样性与土壤多样性的核心基础。本研究旨在评估巴西西部亚马逊区域某地形序列（含4个土壤剖面）中，赋存于火山岩之上的ADE与穆拉托土（Mulatto Earth, ME）的形态学、物理学、化学及矿物学特性，同时测定其NaOH提取态有机质[OM(NaOH)]。供试土壤剖面中，ADE（腐殖质型黏磐淋溶土）的人为影响A层覆于黏化层（Bt）之上，而ME（黏化不饱和雏形土）的人为影响层则为Bi层。所有剖面的土壤发生过程均伴随有机质积累（如腐殖化与暗化作用）及有机金属络合物的形成。相较于ME，ADE中的钙、镁、磷及有机碳含量更高。高活性黏土源自母质火山物质，这一特征将本研究供试土壤与亚马逊地区典型土壤（第三纪高原Terra Firme）及多数亚马逊人为土壤区分开来。人为影响土层通常富含OM(NaOH)，其主要组分为与钙、镁及低结晶度氢氧化铝结合的腐黑物与腐殖酸。研究结果表明，人为驱动因子对土壤发生的影响程度，远大于景观内土壤位置带来的差异。