Hydrologic Changes Attributed to a Century Old Railroad Grade in the Mojave Desert, CA, USA

Abstract:

Anthropogenic landscape modification, such as the emplacement of highways and railroads, has altered the natural hydrologic system by influencing surface-water flow paths, as well as the composition and distribution of biotic communities within the Mojave National Preserve, California, USA. Infiltration experiments were conducted at two alluvial fan sites, one impacted by railroad emplacement and one not impacted, to evaluate changes in hydrology as related to plant water availability and use. Previous studies have shown that plants on alluvial fans are more abundant near undisturbed ephemeral channels compared to channels where upslope catchments have been diverted by transportation corridor construction. During 30 single-ring infiltration experiments, water was applied along a transect in one active channel upslope and another abandoned channel down slope from a railroad built <100 years ago. The abandoned channel is still evident, but has been disconnected from major runoff derived from higher elevations. Excavation at both sites showed weak soil development with fewer plant roots present beneath the abandoned channel. Infiltration test results show that water infiltrates faster in the active channels above the railroad. Observations of weakly developed crusts within the abandoned channels suggest that early microbial succession is responsible for the changes in surface hydraulic properties. We also observed lower plant densities along the abandoned channel compared to the active channel. We infer that plants do not preferentially root toward abandoned stream channels to exploit the enhanced infiltration as extensively as they do above the railroad where flow in ephemeral channels is an additional water source.