PARENT SESSION
Oral Session #70: Riparian Ecology. Presiding: R. Cosgriff.
Thursday, August 9, 2001. 1:00 PM to 4:45 PM. Hall of Ideas I.

Soil variability along the middle Rio Grande floodplain related to vegetation type and flood frequency.

Bailey, Nicole¹, McFadden, L.¹, Dahm, Cliff¹, ¹

ABSTRACT- The riparian forest along the Rio Grande of New Mexico, which until recently, was a Cottonwood (Populus deltoides ssp. wislizenii) dominated ecosystem, is slowly being replaced by exotic phreatophytic plants like Saltcedar (Tamarix ramosissima). This trend can be partly attributed to the effects of Cochiti Dam, which altered the normal flood frequency, resulting in an artificially stabilized floodplain. The purpose of this study is to determine if the dramatic changes in flooding behavior and vegetation have had any discernable effect on soil development. Eight sites, associated with an ongoing interdisciplinary Bosque Evapotranspiration study, were selected (four are cottonwood -dominated, four are saltcedar-dominated). For each vegetation type, two sites are undergoing experimental flooding. Initially, we expected to find that soils in saltcedar-dominated areas would be more saline. Field and lab analyses reveal a more complex story. First, the results of damming can be clearly observed in the soil stratigraphy, as all sites exhibit a fine-grained package of sediments over a coarse-grained package. This fine-grained package, composed of silt and clay layers, is controlling surface water infiltration and concentrates salts and carbonates, both of which are used as indicators of soil development. Second, the highest soluble salt and carbonate concentrations are coincident with the clay-rich horizons. These results indicate that parent material is controlling salt and carbonate distributions. Finally, flooding at the saltcedar sites appears to have flushed out much of the soluble salts.

KEY WORDS: soils, riparian forest, Tamarix, floodplain