Botanical Signatures of Water Storage Duration in a Hohokam Reservoir

Abstract

Although large-scale canal irrigation technology is commonly associated with the prehistoric Hohokam (A.D. 200–1450) of south-central Arizona, earthen reservoirs were essential for domestic water storage in areas of the Sonoran Desert away from perennial streams. Interpretations of seasonal water storage in prehistoric Hohokam reservoirs are often based on direct analogy with the historic Tohono O'odham (formerly called the Papago). This assumption of seasonal water storage is a hypothesis that should be tested rather than uncritically accepted by archaeologists. Sediments recovered with a hand-driven bucket auger from an earthen reservoir at a large Classic-period (ca. A.D. 1200–1450) Hohokam site (AZ AA:3:32 [ASM]) yielded uncarbonized seeds of an aquatic plant belonging to the genus Lemna (duckweed). The high number of Lemna seeds indicates that water may have been stored on a long-term, perhaps perennial, basis. Analyses of sediments from other reservoirs should generate further discoveries of uncarbonized seeds or other biological remains (e.g., pollen, phytoliths, diatoms, snails) and refine our understanding of prehistoric water storage facilities throughout the world.