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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Article
Technical Completion Reports (2005)

While Elkhorn Slough wetlands are protected by a State ecological reserve and NOAA research reserve, intensified farming in the watershed has led to high soil erosion rates and sedimentation into the slough, where several sediment fans have formed at the base of slopes. The goal of this study was to determine how watershed land use change (i.e., increasing agriculture) and associated sedimentation over 30 years influenced changes in salt marsh soil physical properties, and in turn, plant composition through the use of remote sensing, GIS, and field methods. Objectives were to use current and historic aerial photographs to map historic wetland plant communities and quantify the extent and type of salt marsh vegetation change on sediment fans from 1971 to the present, and to explore the driving factors of this change through field sampling of marsh soil properties and topographic features. Analysis of historic aerial photos demonstrated that the formation of sediment fans in pickleweed salt marsh led to the expansion of arroyo willow into the marsh plain. A cattail and bulrush plant community also formed on the sediment fans, forming a band between the willow and pickleweed. This vegetation change occurred as sedimentation led to lower salinity levels, lower soil moisture, higher bulk density, higher elevation, and an increase in soil sand content. Resource managers are actively working with farmers to reduce soil erosion and off-farm sediment. Evidence of habitat change from sedimentation documented in this study supports the need for these continued erosion control efforts. As these efforts continue to reduce sedimentation into the slough, it would be valuable to continue to monitor the sediment fans to determine if any recovery in salt marsh vegetation occurs.

    Cover page: Use of remote sensing to link watershed land use change and wetland vegetation response in a California coastal watershed
    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2015)

    Background

    In previous research, neighborhood deprivation was positively associated with body mass index (BMI) among adults with diabetes. We assessed whether the association between neighborhood deprivation and BMI is attributable, in part, to geographic variation in the availability of healthful and unhealthful food vendors.

    Methods

    Subjects were 16,634 participants of the Diabetes Study of Northern California, a multiethnic cohort of adults living with diabetes. Neighborhood deprivation and healthful (supermarket and produce) and unhealthful (fast food outlets and convenience stores) food vendor kernel density were calculated at each participant's residential block centroid. We estimated the total effect, controlled direct effect, natural direct effect, and natural indirect effect of neighborhood deprivation on BMI. Mediation effects were estimated using G-computation, a maximum likelihood substitution estimator of the G-formula that allows for complex data relations such as multiple mediators and sequential causal pathways.

    Results

    We estimated that if neighborhood deprivation was reduced from the most deprived to the least deprived quartile, average BMI would change by -0.73 units (95% confidence interval: -1.05, -0.32); however, we did not detect evidence of mediation by food vendor density. In contrast to previous findings, a simulated reduction in neighborhood deprivation from the most deprived to the least deprived quartile was associated with dramatic declines in both healthful and unhealthful food vendor density.

    Conclusions

    Availability of food vendors, both healthful and unhealthful, did not appear to explain the association between neighborhood deprivation and BMI in this population of adults with diabetes.
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