Runoff and sediments from hillslope soils within a native American agroecosystem

Farmers of the Zuni Indian Reservation in New Mexico rely on materials transported from upper watersheds to maintain productivity of some of the oldest agricultural fields in North America. This study determined runoff and sediment production from hillslopes as functions of slope position, soil cover, and rainfall characteristics. Runoff was collected from plots in summit or shoulder [SU], backslope [BS], and footslope [FS] positions and in bare soil, microbiotic crust, oak, juniper, pinyon, and grass cover. In rainfall events that generated runoff, sediment C and N concentrations decreased with total sediment yield, but C/N ratios increased. Carbon/nitrogen ratios were generally lower in sediments from early season events. Backslope plots yielded the most sediment (125 g m(-2)) and the most organic C (2.2 g m(-2)), total N (116 mg m(-2)), and total P (34.2 mg m(-2)), but those from SU plots had the highest concentrations (e.g., 31 g C kg(-1) compared with 23 g C kg(-1) at BS and FS). Bare soil and microbiotic crust plots yielded the most sediments (441 g m(-2)) and grass the least (107 g m(-2)). Though variable, oak plots yielded more C (32.6 g m(-2)) and N (1.5 g m(-2)) than others, but bare soil and microbiotic crust plots yielded the most P (62.7 and 54.4 mg m(-2), respectively). Slope position, cover type, and rainfall characteristics interact to influence movement and processing of materials responsible for agriculturally, ecologically, and hydrologically important alluvium-derived soils in this semiarid agroecosystem.