FINAL DRAFT 12-13-04
Elkhorn Slough Tidal Wetland Plan
Historical Ecology Working Group (Science Panel) Meeting Summary
Meeting Date and Time: November 22, 2004, 1:00–4:00 p.m.
Meeting Location: Elkhorn Slough National Estuarine Research Reserve
Prepared by: Kerstin Wasson and Barb Peichel
Working Group Attendees: John Oliver, Dave Schwartz, Eric Van Dyke, Kerstin
Wasson, Andrea Woolfolk (Bob Curry was unable to attend)
Other Attendees: Becky Christensen, Bryan Largay, Sam Morgan, Barb Peichel, and
Peter Slattery
Purpose of Meeting: Come to a shared understanding of past historical changes
(interpretation of sediment cores and historical maps) in order to create a 1-5 page
summary.
A. Action Item
Review the historical ecology summary document (Andrea Woolfolk and Eric Van Dyke
will be sending this out for review in the next few weeks).
B. Next meeting date and agenda items
The next full Science Panel meeting is Thursday, January 6th at the Moss Landing
Marine Laboratories in Moss Landing.
C. Historic Changes
Andrea Woolfolk and Eric Van Dyke went over their talks on historical changes to tidal
habitats (http://www.elkhornslough.org/tidalwetland/meetings.htm) for the working
group in order to identify areas of uncertainty in the interpretation of the historical
information (sediment cores and historic maps).
1. Rapid sea level starts slowing already by 8000 ybp.
2. We are not sure that the Slough was becoming more shallow 6000 years ago and
prefers to phrase it as the “energy level was decreasing”.
3. Suggest that the Five Fingers, North Marsh area around 3000 ybp could have had
freshwater marsh.
FINAL DRAFT Historical Ecology WG Meeting Notes, Elkhorn Slough Tidal
Wetland Plan, November 22, 2004
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4. You should change the map so that it doesn’t show the mouth of Elkhorn Slough in
line with main channel.
5. On the 2000 ybp figure, a lot of “marine” on the map could be brackish.
6. “Brackish sting” refers to areas with enough salinity that freshwater plants can’t
grow.
7. There used to be a lot of positive pressure from freshwater (springs etc. in Moro Cojo
and elsewhere). You can have freshwater pushed up tidal creeks and this is what was
happening in Moro Cojo. You might get seasonal fluctuations, but that could have
happened in this system.
8. Change the map label so that blue in the channel indicates water in the channel, not
marine.
9. Mya arenaria fossils near the base of Moro Cojo and McClusky from 150 years ago
may tell you it was river meeting the ocean.
10. It seems like we have agreement that there was much stronger freshwater influence at
the top of the system than there is now and some tidal influence in the rest of system.
11. One area of uncertainty is the extent of tidal influence. One way to resolve this
uncertainty is to get an outside expert to assess how strong the marine influence has
to be to get these foram and diatom assemblages found in the cores. Roberta SmithEvernden (UCSC retired) might be good expert to consult on forams and diatoms
(Schartz can get her contact information).
12. For interpretation of the Hudson’s landing core - the freshwater pollen could just have
been deposited there or swept downstream from a freshwater source (this is the first
place where river sediments can settle down so evidence of redwoods could be from
the watershed).
13. You could check for improved carbon dates for pollen core data from the authors of
the paper or invite Scott Menzine to come and explain the data.
14. For the interpretation of the core data, it seems like a broad generalization that comes
out of this discussion is that the upper reaches of the estuarine system experienced
both fresh and saltwater influence to varying degrees at different times.
15. We found evidence of Assiminea 2000 ybp halfway up Moro Cojo, but need to check
how this differs from Tryonia and what sort of habitats it lives in.
16. It would be helpful to obtain additional pollen cores for other places in the watershed.
17. “Salting out” is when clay particles tie to ions in estuaries and settle out.
“Flocculation” occurs when clays can stick because their repulsion in decreased by
binding to sodium; so this can occur at velocities like would be needed for fine
sediments, but still need pretty quiet water, but it could be moving a bit faster than
you’d expect.
18. “High energy” as referred to in the profile book would be about 1-2 knots (open year
round) and “low energy” would be less than 1 knot (typically closed part of year).
FINAL DRAFT Historical Ecology WG Meeting Notes, Elkhorn Slough Tidal
Wetland Plan, November 22, 2004
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19. Schwartz found buried sand fans in the middle of marsh transects (may have predated intense agriculture and were natural activities in areas with springs).
20. Natural deposition of this sort was found at Bolinas Lagoon, but the rates increased
greatly due to logging.
21. There is agreement that for 2000-1000 ybp, there was some tidal influence still, but
the system was fairly quiet (this is consistent with clay deposits).
22. Crespi’s statements about the rise and fall of tides of Salinas could be in part
freshwater being pushed by tides.
23. Brackish salinity could be the result of water trapped from the mouth of Salinas
broken through the dunes (e.g. in current Salinas river lagoon area) from past winter.
24. 1830s map may suggest why the clay was settling out because of the indirect
meandering connection to the ocean.
25. Tidal lines on 1854 map don’t tell you whether it was fresh or tidal water because it
could be like the Sacramento delta with freshwater rising and falling. It could be
alkali ponds that accumulate salt in areas far from the ocean. There might be further
evidence of freshwater from the geomorphology.
26. The depth of channel influences the velocity you’re going to see so the friction is
higher over shallow water and as the energy is expended more quickly, you would
find slower moving water and lower tidal amplitude (i.e. Hudson’s landing).
27. One way to formulate the question is to ask what amount of water was tidally
exchanged daily. Having a sense of how deep and wide the opening could be a very
good indicator of this.
28. A barrier beach model might be appropriate for this system, alternating between
backwater lagoon and a system open to ocean sometimes with lots of variation on
different scales (season, annual, decadal, etc.) in the size of the mouth and thus in the
amount of tidal exchange, ranging from a wide mouth with a lot of tidal exchange to a
small or even absent mouth with little or no tidal exchange.
29. From Andrea’s conclusion slide, take out “at least seasonally” in reference to
freshwater. Take out “of” from second bullet point. Take out the final bullet from
conclusion slide.
30. Massive alluvial fans can be worsened by agriculture, but these are also natural
occurrences (contributing to sedimentation pattern in Porter Marsh area); loamy-sand
formations around here are 1/4 silt clay and the rest is sand, so it is not just the topsoil
but the whole formation that has a fair amount of fines which is easily mobilized if
vegetation is lost.
31. Interested in cores up Carneros creek to see what was way up there; sheep grazed on
steep Carneros land after 1860s drought, probably contributed to erosion and
neighbors that were in Aromas anecdotally talk of a foot of fine sediments that eroded
away.
32. Agrees that Spanish grazing and earlier American agriculture and clearing oaks led to
erosion of fine sediments and topsoil, which then filled in the wetlands.
FINAL DRAFT Historical Ecology WG Meeting Notes, Elkhorn Slough Tidal
Wetland Plan, November 22, 2004
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33. Overall, the area under tidal influence was decreasing consistently over time until
1947.
34. Want to make the point that there was a large tidal prism when Hermann surveyed the
area and that presumably would have submerged the marsh plain.
35. General agreement that during the rainy season, presumably the Salinas River
punched the mouth of Elkhorn Slough open by freshwater force, but during the rest of
year, tidal exchange kept it open – in contrast to river mouths that are closed during
dry season.
36. If the former exit channel was too shallow for 4 ft draft when those steamships
stopped, and now there is 20 ft entrance channel, you have a huge increase in tidal
currents just from this size, and also from the lack of a meander to dampen that
energy (if you double the size of opening, you more than double the tidal current
speeds).
37. Be sure to correct bullets on the web presentation posted on web site too.
38. Some of the fines that had filled in the Slough pre-1946 have been removed by
erosion; in cores, there was a dramatic change from silt/clay to hard gravelly
sediment.
D. Areas of uncertainty from presentations & strategies to resolve the uncertainties
(flip charts)
1. How much of the Elkhorn Slough watershed was marine 2000 ybp?
There was agreement that for the time period of 2000-1000 ybp, the estuarine system was
fairly low energy with some tidal influence and at least seasonal influences of freshwater.
One strategy to determine the historic tidal influence in different areas of the Elkhorn
Slough watershed would be to contact an outside expert to assess the foram and diatom
assemblages found in the cores. Another strategy would be to analyze the historic clams
found by Hornberger to assess how saline of waters they could tolerate.
2. Is the interpretation of the pollen cores near Hudson’s landing accurate?
There was discussion that some of the pollen could have been wind blown or influenced
by river actions so that we need to be careful about extrapolating from this data.
One strategy to understand the pollen core data better would be to contact Scott Menzine
to explain the results in more detail. Another strategy would be to take additional cores
in the areas of interest and have those interpreted professionally.
3. The interpretation of tides from the 1879 report of the Salinas River was questioned.
Basically, the influence of tides in the historic report could also be attributed to either the
influence of tides or from influence of freshwater on the system.
One strategy to better understand these statements would be to analyze the
geomorphology of historic river channels.
FINAL DRAFT Historical Ecology WG Meeting Notes, Elkhorn Slough Tidal
Wetland Plan, November 22, 2004
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