MODELING THE AZTEC AGRICULTURAL WATERSCAPE OF LAKE XOCHIMILCO: A GIS ANALYSIS OF LAKEBED CHINAMPAS AND SETTLEMENT
Open Access
- Author:
- Luna Golya, Gregory G
- Graduate Program:
- Anthropology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 01, 2014
- Committee Members:
- Kenneth Gale Hirth, Dissertation Advisor/Co-Advisor
Kenneth Gale Hirth, Committee Chair/Co-Chair
David Lee Webster, Committee Member
Matthew Bennett Restall, Committee Member
Erica A H Smithwick, Committee Member
Kirk Dow French, Committee Member - Keywords:
- chinampas
Lake Xochimilco
raised fields
GIS
landscape archaeology
Basin of Mexico - Abstract:
- This dissertation presents the first large, detailed spatial reconstruction of Aztec lakebed chinampas for a 1,010 hectare area of the former Lake Xochimilco lakebed. A general five stage model is proposed for the development and decline of the raised field socio-natural system in the southern Basin of Mexico. Widespread chinampas in the 18,000 ha Lake Chalco-Xochimilco were restricted to the relatively short-lived Aztec empire period especially between the mid-15th and early 16th centuries and were the result of top-down imperial planning, construction oversight, and hydraulic and facility management. Previous archaeological survey in 1969 and 1972 overwhelmingly dated lakebed occupation to the Late Aztec and Early Colonial periods (Aztec III-IV ceramics). The rapid inundation of Aztec drained fields after the Spanish conquest submerged most lakebed chinampas below the marshy southern lake surface. The relic fields were exposed for a short period in the 20th century after lake drainage completion and before post-WWII mechanized farming and urbanization obliterated the relic fields. By incorporating 1936-1941 air photos into a GIS, 23,094 relic beds and 400 mounds were manually digitized (traced) for the 1,010 ha study area. The built beds and mounds in the lake also defined complex canal networks and open pools within the system. The long, narrow beds averaged 3.75 meters wide and had an average length of 49.4 meters. The system land to water ratio was 1.07:1. Raised field experiments on the Andean high plain of Lake Titicaca and elsewhere demonstrate that narrow agricultural beds in 1:1 land to water systems benefit from both frost protection and intra-system nutrient replacement. Additionally, every plant on the narrow beds could have been irrigated by splash or scoop techniques from canoe bound farmers – an important benefit in the Basin of Mexico characterized by a long dry season, variable (temporal and spatial) summer monsoon rains, and summer droughts (canícula). In addition to many small lakebed habitation sites, larger lakebed wharves comprised of multiple mounds and platforms, open pools, and wider iv canals were identified in the air photos. These village-wharves probably formed the economic and social hub for the lakebed tenant farmers who were comprised of free peasants (macehualtin), serfs (mayeque), and slaves (tlacotin). Aztec chinampas built through land reclamation existed outside traditional corporate land holding capolli system and tenant farmers obtained rights of cultivation in return for approximately 50% of their agricultural production in rent payment to land grantees residing in Tenochtitlan (Calnek 1975). I estimate that approximately 2,525 farmers, administrators, dockworkers, merchants, and canoeists resided in the 1,010 ha study area (2.5 persons/ha) which included 2,000 full-time tenant farmers. Extrapolating these figures after adjusting for possible larger open pools within a 13,435 ha Chalco-Xochimilco Aztec drained field system, I calculate that after the consumption needs (dietary and non-dietary) of 30,000 lakebed residents were met, an annual 10,000,000 kg maize equivalent agricultural surplus, enough to feed 50,000 persons for a year, reached the storehouses and markets of Tlatelolco-Tenochtitlan. Also, this dissertation describes the temporal changes in agricultural bed width and land to water ratios resulting from a falling water table and canal in-filling accompanying Mexico City’s growth and constant water demand. The land to water ratios increased from 1.07:1 (Aztec) to 2.75:1 in 1941 to 10.11 in 2012. Average bed area in the desiccating system has risen from 221m2 (Aztec) to 2,054m2 in 1941 to 62,799m2 in 2012. Modern chinampas are no longer self-sustaining systems as plastic tarps (invernaderos) provide frost protection, gas-powered pumps deliver reclaimed urban water (transferred to the system) to the plants on the large fields, and external organic and chemical inputs introduce nutrients and contaminants to the soils. The Xochimilco lakebed chinampas, while still highly productive, have transformed from an Aztec period waterscape to a desiccating farmscape with a wetland agriculture ancestry.