The Sonoma Ecology Center and Sediment

The Sonoma Ecology Center, based in the City of Sonoma, Sonoma County, is a nonprofit group working toward a condition of sustainable ecological health in the Sonoma Valley through community-supported research, education, restoration, and preservation. An example of our research is stream sediment monitoring, which began in 2001 with funding from the S.F. Foundation (www.sff.org/initiatives/bayfund.html) and a Clean Water Act 319(h) grant administered through the State Water Resources Control Board (SWRCB) and Regional Water Quality Control Board (RWQCB).

Monitoring Turbidity in Sonoma Creek
The Sonoma Ecology Center is monitoring sediment in Sonoma Creek by measuring turbidity (water clarity) and suspended sediment (sediment carried in water) exposures for aquatic organisms in mainstem Sonoma Creek and selected tributaries. We're studying whether our creek is turbid enough to harm fish, freshwater shrimp, benthic macroinvertebrates (creek bugs), and other stream life.

Why Monitor Creek Sediment?
California's Clean Water Act lists Sonoma Creek as impaired by sediment. The concern about sediment in stream water stems from its potentially adverse effects to habitat for threatened native species such as steelhead and salmon. During storms, heavy runoff carries sediment to tributaries and creeks. Increased stream sediment (suspended sediment) can elevate turbidity levels (i.e., cloudiness of the water), which negatively impacts fish. Highly turbid waters have been observed to promote physiological stress, reduce growth rates, and impair the ability of species to feed. Damage by sediment to gills can cause outright fatalities. Given the right conditions, stream sediment also clogs spawning gravels, limiting reproductive success.

Even in a pristine watershed, suspended sediment and turbidity increase due to the natural forces of erosion during storm runoff. But land-use trends such as paving and clearing bring more upland and bank erosion, with intensified sediment delivery to streams. Because even small increases in suspended sediment can bring large changes in turbidity, water-quality experts regard turbidity as a sensitive measure of the impact of land uses on streams.

Available Data
Until recently, information about suspended sediment and turbidity in Sonoma Creek has been limited. An important source of water-quality data, the U.S. Environmental Protection Agency (EPA) Storage and Retrieval System (STORET) database, contains little information related to suspended sediment and turbidity for Sonoma Creek, and none collected after 1988. More turbidity data has long been needed for Sonoma Valley waterways.

Monitoring Program Features
For the first year of monitoring (wet season 2001-2002), the Sonoma Ecology Center conducted intensive sampling at a site near the Sonoma Valley Watershed Station on Sonoma Creek. The following key features were integral to the program:

• Volunteers collected grab samples of creek water during and after storms. Samplers used Mr. Longarm, an extension-pole device, to dip two sample bottles simultaneously from the shore. Turbidity readings (expressed in Nephelometric turbidity units, or NTU) were taken in the field using a portable Hach turbidimeter, and the suspended sediment samples were delivered to the M.U.D. Laboratory (see below) for processing. (SSC values are expressed in milligrams per liter, mg/L). The stage (height of creek) and water velocity were recorded manually each time a sample was collected. This information allows us to calculate stream discharge for correlation with SSC/turbidity levels.
• A continuous monitoring station (Station A) was installed in July 2001 and has been electronically logging readings for turbidity, creek depth, and water temperature at ten-minute intervals. The logged information is retrieved using a handheld computer. Later the continuous turbidity readings are "cross calibrated" with grab sampling turbidity results collected by Sonoma Ecology Center staff and Stream Stewards.
• A laboratory (the M.U.D. Laboratory) was established for filtering, oven drying, desiccation, and weighing water samples for suspended sediment concentration (SSC). The lab was set up at the Sonoma Valley Watershed Station near Sonoma following protocols documented in our SWRCB-approved Quality Assurance Project Plan (available on our website, http://www.vom.com/sec/research/suspendedsed/qapp.htm [inactive 10/28/04]).
• A depth-integrated (DI) device was also used to sample the entire column of water. DI samples of SSC and turbidity will be correlated with those obtained by grab sampling, resulting in a more reliable stream signature than can be ascertained from grab sampling alone.

Program Status
For the second year of monitoring (wet season 2002-2003), the Sonoma Ecology Center added to its program by sampling at ten tributaries. As of early 2003, we are analyzing the second-year data and preparing for a third year of monitoring.

For more information on our project, please read final report:
http://www.vom.com/sec/research/suspendedsed/index.htm" [inactive 10/28/04] Volunteer Monitoring of Suspended Sediment Concentration and Turbidity and Watershed Monitoring of Road Remediation in Annadel State Park