Soil Analysis for Restoration on the Santa Clara River
Margot Mason1*, Adam Lambert2
1University of California, Santa Barbara, California, USA; 
2University of California, Santa Barbara, California, USA; 
Understanding abiotic site conditions, including soil properties, is important in the creation of informed restoration plans. The Santa Clara River is one of the most hydrologically intact biodiverse riparian corridors in Southern California, but suffers from agricultural impacts and rapid urbanization. The Sespe Cienega is a site of particular interest owing to its persistently rising groundwater and the potential for restoring a significant groundwater-dependent ecosystem in river. The Cienega is heavily infested by giant reed (Arundo donax), saltceder (Tamarisx spp.), and many herbaceous invasive species. Restoration efforts based on invasive species removal have been underway on the site, which was historically a watercress farm, and is co-located with an operational fish hatchery, since 2017. Understanding soil conditions is especially important at the Cienega as agricultural land use changes, and flood scour and deposition history have created diverse soil conditions which vary in appropriateness for different native species. An array of 60 soil samples was collected on the 278 acre site in July 2020 and analysed for pH, conductivity, texture, and bulk density to prepare soil maps and identify locations that may need remediation before active planting. Preliminary findings linear modelling findings show that pH can be modelled using distance to the river and percent clay (p<0.006), whereas conductivity is only significantly predicted by soil texture. Areas with current or previous Arundo stands were found to have significantly lower compaction than areas with other vegetation cover types (ANOVA, p<0.01). The inverse distance weighted interpolation tool in ArcGIS was used to create maps of the variation in soil characteristics across the site to aid in management decisions, and Theissen polygons with appropriate soil properties were selected to guide planting of various desired native species. This process of sample collection and subsequent spatial analysis may provide a suitable model for other projects wishing to make informed restoration decisions at a low budget.