Complex Polygenesis and Soil Stratigraphy of Soils of the Eastern Sevilleta National Wildlife Refuge, Belen, NM

The eastern Sevilleta Long Term Ecological Research Site (Belen, NM) presents a unique opportunity to study soils occurring under the same climate regime and at the intersection of three desert bio-zones. Thirteen study sites were located at similar elevation on active Holocene fans of the Los Pinos Mountains, old fans (at least Mid-Pliestocene), and in fill of the Belen Basin of the Rio Grande Rift Zone. The stratigraphy of trenches on young surfaces revealed that the buried soils reflect the patterns of alluvial fan development along the Los Pinos Mountains: 1) younger fans have buried older fans at the mountain front, and 2) young surfaces have not yet been affected by large base level drops associated with the Palo Duro Wash incision. Polygenesis in older soils is linked to climate change and related plant community changes, eolian fluxes, and surface evolution influenced by the Palo Duro Wash incision. The relationships between plant distributions, pH, conductivity, grain size, carbonate content and horizon depth were compared with statistical methods. The results indicate that soil development is unique to each profile and that soil profiles located within a few meters can differ significantly. In younger soils, many properties, such as pH, conductivity, grain size, carbonate content and horizon depth, are correlated with grain size and their distributions change systematically with depth. In contrast, carbonate content, pH and conductivity do not appear to be influenced either by depth or grain size in older soils. Plant distributions are correlated to grain size and to depth to Stage III calcic horizons. Stable isotopes of carbon and oxygen in pedogenic carbonate were also analyzed. The results do not exhibit the depth function observed in other soil profiles. The most negative ä13C values (0/00 vs. PDB) were obtained from the near surface horizons in all five trench sites.