Sedimentation Rates in Fairfield Osborn Preserve Marsh

osborn marshstudents drive corer into marshstudent examining core in fieldmuddy core sample

Project Description: A marsh at the Fairfield Osborn Preserve has been gradually filling with sediment. We quantified rates of sedimentation and successional infilling by dating cores taken from the marsh. In 3 additional locations, we characterized soils in the upper watershed. These techiques are helpful for understanding erosion processes in the headwaters of Copeland Creek.

Duration: Fall 2012

Type of Educational Activities: service-learning

Project Faculty: Michelle Goman

Partners: Sonoma County Water Agency, SSU Preserves

Participating Courses: Lab Methods in Physical Geography (GEOG 317) - 11 students

aerial image of osborn marsh

Sampling Locations:

  • Marsh: In image on right, polygon shows location at the Osborn Preserve. Lichau Road is at top right. Osborn Preserve faclities at at top, just right of center.
  • Soil Characterization: 8 sites near the Osborn Preserve facilities (4 in grassland and 4 in mixed woodland)

Field Methods:

  • Marsh: Two cores were collected approximately 5 m interior to the southern edge on the marsh. A shovel was used to get through the surface soil and we used Livingstone and Russian Peat corers. We were unable to core all the way to the bottom but core depth provides a starting point for measuring sedimentation rates. Future sampling efforts will focus on obtaining deeper and multiple cores.
  • Soil Characterization: bucket augers were used to sample grassland and mixed woodland sites

Lab Methods:

Soils were analyzed for color (Munsell Color System), texture, loss on ignition (LOI), grain size, pH, magnetics, charcoal and macrofossils. Marsh soils were additionally analyzed for, 210Pb and 137Cs. Lead 210 analyses were conducted to date the periods of erosion. Pb 210 is suitable for looking at aging sediments from the last 125+ years. Multiple samples establish a decay curve for the Pb. Erosive pulses were compared to weather data to identify rain events that linked to high rates of sedimentation.

Field surveys were conducted under the guidance of Michelle Goman. Students conducted all analyses except for the PB10 analysis which was submitted to a certified laboratory at Rensselaer Polytechnic Institute (RPI).

Summary of Results: Testing for 210Pb dating results were complicated as the lead was too diffuse within the sediment to produce a well-developed curve. This is likely because of very high rates of sedimentation (Figure 27). Testing for 137Cs, however, proved more successful, and the lab at Rensselaer was able to identify a spike for the 1963 mark of peak nuclear activity, and thus calibrate depths for age. This resulted in their estimating a sedimentation rate of 0.3 cm per year for this site from 1950 to present.

Data: (see data disclaimer)


  • Soil and Sediment Analysis at Fairfield Osborn Preserve. Gavin Beach, Lareina Earls, Stephen Garibaldi, Adrienne Gause, Joshua Goudy, Robert Gleaton, Sarah Hebern, Alexander Pugliese, Camilla Rockefeller, Kirstie Watkins, Brain Woodward, Caitlyn Yates, Collin Yballa, Tom Ziegler (Michelle Goman Advisor Geography 317). Beach et al. 2012 (pdf, 3.2 Mb)


Potter, C. and S. Hiatt. 2009. Modeling river flows and sediment dynamics for the Laguna de Santa Rosa watershed in Northern California. Journal of Soil and Water Conservation. 64 (6): 383-393.