Soils in ancient irrigated agricultural terraces in the Atacama Desert, Chile

The Atacama Desert is among the driest places on Earth, yet ancient agricultural systems are present in the region. Here, we present a study of terraced agricultural soils in the high-altitude eastern margin of the Atacama Desert in northern Chile, mainly dating to the Late Intermediate Period (ca. 950-1400 AD) and Inka period (ca. 1400-1536 AD). Terraced fields were compartmentalized to distribute limited irrigation water originating mainly from springs. Natural soils used for agriculture are mostly Aridisols developed on Pleistocene alluvial fan terraces and hillslopes underlain by volcanic bedrock. One research objective is to evaluate long-term soil change from agriculture. In this hyperarid climate, agriculture is only possible with irrigation, so natural soils on the same geomorphic surface adjacent to irrigated soils provide baseline data for assessing anthropogenic soil change. Data from soil profiles and surface transects indicate intentional soil change through terracing, removal of soil rock fragments, and probable fertilization. Agricultural soils have anthropogenic horizons ranging from 16 to 54 cm thick. Most agricultural soils have higher phosphorus levels, suggesting enrichment from fertilization. Changes in soil organic carbon and nitrogen are also evident. Unintentional anthropogenic soil change resulted from CaCO3 input through irrigation with calcareous spring water. Initial studies suggest that agriculture here was sustainable in the sense of conserving soils, and maintaining and possibly improving soil productivity over centuries.info:eu-repo/semantics/publishedVersio

Floodwater farming, discontinuous ephemeral streams, and Puebloan abandonment in southwestern Colorado

Geoarchaeological study on the southern piedmont of Sleeping Ute Mountain in southwestern Colorado indicates the presence of discontinuous ephemeral streams that were the foci of episodic Puebloan occupation between A.D. 600s and 1280. Characterized by arroyos, discontinuous ephemeral streams contain alternating aggrading and degrading reaches and are well suited for ak chin floodwater agriculture. Episodic Puebloan abandonment of the southern piedmont correlates with periods of drought but does not appear to be linked to stream entrenchment. We question a priori assumptions of droughts correlated to stream entrenchment and urge caution in the use of drought-arroyo models for settlement shifts in alluvial flood plains without supporting stratigraphic or geomorphic evidence

Late-Holocene stream dynamics on the middle Gila River, Pinal County, Arizona

An archival-stratigraphic investigation of the middle Gila River provides insights into late-Holocene channel behavior and flood-plain formation. Historical records detail changes in channel patterns that correlate with changing frequency of large floods, but channel sensitivity is also affected by factors such as flood seasonality, changes in sediment load, human disturbances, and internal thresholds. Because the frequency of large floods is the dominant factor in channel changes, radiocarbon-dated flood deposits in late-Holocene alluvial terraces allow for a reconstruction of prehistoric channel behavior. A period of reduced large flood frequency and channel stability 4,000-1,000 years BP separates periods of increased large flood frequency and channel instability 5,000-4,000 and 1,000-0 years BP. Transformations between braided and single channel morphologies affect the conveyance of floods and change the spatial characteristics of flood hazards. These channel dynamics are also important in analyzing changes in Hohokam-Pima irrigation technology and settlement patterns.hydrology collectio

Geoarchaeology virtual issue: Ancient water management

12 month embargo; first published: 13 June 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Combining Radiocarbon and Single-Grain Optically Stimulated Luminescence Methods to Accurately Date Preceramic Canals, Tucson, Arizona

We present 12 accelerator mass spectrometry (AMS) 14C and five quartz single-grain optically stimulated luminescence (OSL) ages from three Early Agricultural period irrigation canals recently discovered in the floodplains of the Santa Cruz River and Rillito Creek in Tucson, Arizona. Significant discrepancies in the AMS 14C ages are associated with fluvial redeposition of charcoal, producing at times, age overestimates of ∼1000 years. Single-grain OSL ages on canal sediments and application of a minimum age model accurately date the final operation of the canals but have relatively large standard errors of several hundred years. Based on single-grain OSL, one canal dates 730–310 B.C. and the other two date 560–100 B.C. This corresponds with a period of predominant floodplain aggradation (∼500 B.C.–A.D. 1) conducive to water control and irrigation agriculture. Stratigraphic evidence of uncontrolled flooding and rapid sedimentation is present in all three canals and marks the abandonment of two canals. Determining the age of the earliest canals is important for understanding the origins of water management and the transition from foraging to intensive agriculture in the North American Southwest. Due to potential problems with reworked organic material for 14C dating and partial bleaching (resetting) of luminescence signals in fluvial settings, we recommend a combined AMS 14C and single-grain OSL approach for dating early canals

Dating the Ascope Canal System: Competition for Water during the Late Intermediate Period in the Chicama Valley, North Coast of Peru

Here we present the first C-14 ages for the Ascope Canal System (ACS), a large prehispanic hydraulic network in the Chicama Valley on the north coast of Peru. Composed of multiple alignments that irrigated areas north of the river, our results indicate that the ACS was constructed and operated in the Late Intermediate Period, ca. a.d. 1000-1400. This overlaps in time with the Chicama-Moche Intervalley Canal that diverted water on the south side of the Chicama River and extended to the city of Chan Chan. Conservative estimates of discharge capacity indicate that the combined flow through the canals would have exceeded stream flow in the Chicama River during half of the year. The ACS appears to have functioned for several centuries and would have been in direct competition with the Intervalley Canal. There was, apparently, insufficient water for both systems and other Chicama Valley canals during most of the year. This study underscores the complexities of understanding the operations and histories of irrigation systems in complex societies.National Science Foundation Polar Programs as part of the Long-Term Human Ecodynamics in Coastal Peru: A Case Study of Polar-Tropical Teleconnections [1152156]18 month embargo; published online: 31 October 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Flood-damaged canals and human response, A.D. 1000–1400, Phoenix, Arizona, USA

The scale of prehistoric canal construction in the North American Southwest peaked in A.D. 450–1450, during what has been named the Hohokam Millennium. Explanations for the eventual Hohokam “collapse” remain elusive. Environmental disturbances, such as floods, that were once manageable may have become unmanageable. Recent archaeological excavations of Hohokam canals in Phoenix identified stratigraphic evidence for three destructive floods that date to A.D. 1000–1400 within two large main canals in System 2, Hagenstad and Woodbury’s North. Woodbury’s North Canal was flood-damaged and abandoned sometime after A.D. 1300. Thereafter, no main canals of similar size were constructed to supply villages within System 2 and the area was depopulated. Our investigation provides the first stratigraphic evidence for a destructive flood during the late Classic period in the lower Salt River Valley and is compatible with the hypothesis of diminished resilience to environmental disturbance at the end of the Hohokam Millennium.Desert Archaeology, Inc.; City of Phoenix18 month embargo; published online: 13 Nov 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]