1. Tomales Bay: Reference Site for Question 2 in SF Bay?
Walker Creek
Watershed
Gambonini Mercury Mine
The Guadalupe River Watershed Mercury TMDL is coming soon.
We’ll be releasing our report for public review, then presenting it to our Board for adoption in the next several months.
The next mercury TMDL that I’m working on is in Tomales Bay. Like many other folks, I’d like to propose Tomales Bay as a reference site for Question 2 - on our agenda this afternoon – Which processes, sources, and pathways contribute disproportionately to food web accumulation?
Tomales is a long, skinny bay, with a mercury mine in the Walker Creek watershed close to its mouth. Relative to San Francisco Bay & Delta, the mining impacts are very localized to the Walker Creek delta. The largest tributary is at the head, Lagunitas Creek.
Lagunitas Creek
Watershed
Question 2:
Which processes, sources, and pathways contribute disproportionately to food web accumulation?

2. History and Inventory of Total Mercury at Walker Creek Delta
Dam Failure
El Nino
My slides today were prepared by Bryce Johnson, a recent PhD from Cal. You might remember him, he’s has attended a few RMP meetings.
On the left are Bryce’s measurements of mercury in sediments at Walker Creek delta – you can see that with a large, 100-year, storm event in 1982, the sediment mercury concentrations increased dramatically.
On the right is Bryce’s inventory of mercury accumulated in the Walker Creek delta – the red shows obvious high mercury accumulation right at the delta, with concentrations dropping off rapidly with distance.
(Johnson, 2007)

3. Sediment Total & Methylmercury
Here’s another way to illustrate that mercury concentrations drop off rapidly with distance from the Walker Creek delta.
On the left, sample names “WC Delta” have much higher total mercury concentrations than other locations in Tomales Bay.
On the right, samples were collected from many locations in the Walker Creek delta, and one – the bottom one - at McDonald. The higher methylmercury concentrations occur at intertidal locations in the Walker Creek delta, and they are higher than in the sample collected at McDonald.

4. Biota Total Mercury
Total mercury in biota shows a similar trend with distance from the Walker Creek delta.
Again, sample names “WC Delta” have much higher total mercury concentrations than other locations in Tomales Bay.
You can see that dramatically for the crab data, and there’s an obvious difference with the resident bivalves, depending on location (“WC Delta” or other locations.
Mussels transplanted to Tomales Bay had somewhat higher total mercury concentrations at “WC Delta” compared to other locations.
Lastly, farmed oysters at “WC Delta” had just slightly higher total mercury concentrations at “WC Delta” compared to other locations, and all are safe to eat (with respect to mercury).

5. Clam Total and Methylmercury
We also have total and methylmercury in one species, clams, and it shows a consistent trend in lower concentrations with distance from WC Delta, for both forms of mercury.
Health Advisory Tomales Bay (Data collected by department of Fish and Game 1999)

6. Your Ideas for Data Collection
If Tomales Bay is our reference site to help answer,
"Which processes, sources, and pathways contribute disproportionately to food web accumulation?"
what data should we collect in Tomales Bay?
5. If Tomales Bay is our reference site to help answer, "Which
processes, sources, and pathways contribute disproportionately to
food web accumulation?" what data should we collect in Tomales Bay?
my initial thoughts are sediments for TotHg & MeHg, and resident
benthic species (preferably not very mobile animals) for MeHg, from both
Walker & Lagunitas deltas
Please don’t hesitate to contact me with your ideas.