Late Holocene human activities and their impacts on the soils and sediments at La Playa, Sonora, Mexico

The activities carried out by preindustrial agricultural societies are not usually considered as important factors of soil degradation. Nonetheless, repetitive human daily activities for hundreds of years can substantially transform the natural properties of the soils. At the site of La Playa, Mexico, the activities of early farmers modified the landscape and had an important role in the physical transformations of the natural soil features. This paper depicts the characteristics of La Playa paleosols, which were the living surface of the Early Agriculture Period community (4000 – 1800 cal BP) and we discuss the influence of daily subsistence activities on the soil. The soil features (structuring, differentiation of horizons, texture–in field and laboratory, color, porosity, stoniness, magnetic properties, organic carbon content, carbonation, presence of cutans, nodules and/or concretions, among other pedological features) of three profiles with pedosediments (paleosols interbedded with sediments) formed during late Holocene are discussed. Our study suggests that La Playa Fluvisols are poorly developed and were formed with alluvial deposits (largely composed of reworked soils). The pedogenic properties indicate that overlapping developed during short time periods of stability, under arid conditions of the last 4000 years. The uniformity of the features in all the studied profiles indicate similar pedogenetic conditions across the site. The micromorphological and magnetic properties clearly show that the soil was deeply disturbed by human activities, mainly by roasting features to process food, crematories and grave digging to bury the dead, and removing soil for several agricultural activities. Las actividades realizadas por las sociedades agrícolas prehispánicas poco complejas, no son usualmente consideradas como factores importantes de degradación del suelo. Sin embargo, la repetición de actividades cotidianas durante cientos de años puede afectar sustancialmente sus características. En el sitio de La Playa, las modificaciones del paisaje producidas por las actividades cotidianas, tales como la construcción de hornos de tierra para cocer alimentos, campos de maíz con un complejo sistema de canales de riego, y la práctica de rituales mortuorios (crematorios, cremaciones e inhumaciones), juegan un papel importante en las transformaciones de los rasgos naturales del suelo. En este artículo se muestran las características de los paleosuelos de La Playa, que