Agroecology, hydrology, and conservation of ephemeral streams and alluvial fans, Zuni Pueblo, New Mexico

Zuni farmers grow corn (Zea mays) on alluvial soils farmed for as long as 2000 years. These studies focus on traditional knowledge and agroecology of alluvial soils that have key cultural, ecological, and hydrological functions but are vulnerable to erosion in the dynamic semiarid environment. Collaboration with local Zunis during this research changed fundamental scientific assumptions about alluvial fan agroecology in unanticipated ways that contribute to the relevancy of this work. Zuni rain fed farming has been portrayed as irrigation where ephemeral storm flows must supplement rainfall. Collaborative fieldwork and non-structured interviews show that Zuni farmers prioritize flood deposits and conserving depositional regimes more than diverting runoff, and that crops can be grown with rainfall alone. Hydrological data suggests that stormwater irrigation is infeasible; ephemeral streams flow an average of once in 1.5 to two years. Historical evidence shows decline in rain fed farming coincides with accelerated arroyo cutting and suggests that Zuni farming is effective conservation. Analyses of watershed plant-soil-landform interactions show that upland slopes provide runoff, sediment, and organic debris responsible for alluvial soil productivity. Forest litter from woodlands decomposes as it moves downslope. SOM peaks on steep slopes under pinyon-juniper (Pinus edulis-Juniperus spp.) cover, but plant-available N and P from decomposing OM increase down hillslopes and ephemeral streams, peaking in alluvial fan soils. Rainfall intensity and runoff-erosion data suggest that frequent minor showers drive decomposition and selectively transport decomposed OM. Less frequent floods flush slopes and channels, depositing mixed sediment and OM on alluvial fans. An in-situ decomposition study in fresh flood-deposited soils and adjacent incised terraces suggests that frequent freeze-thaw and drying-rewetting cycles cause rapid decomposition that may deplete soil fertility without fresh OM from floods. Soil texture analysis suggests that exclusion of flushing flows also deteriorates soil hydrological properties. Traditional conservation methods, evaluated with pre- and post-treatment surveys, proved to be rapid, low-cost, and effective for preventing down cutting and restoring depositional regimes. Brush dams act as permeable energy dissipaters during moderate flows and contribute to channel-modifying debris jams during floods. This research supports alternative perspectives and approaches to conservation, restoration and management in dynamic semiarid environments where many conventional approaches have failed.