FINAL DRAFT 12-13-04

ElkhornSlough 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: ElkhornSlough 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 ( 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.
  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 Smith-Evernden (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 ofAssiminea 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 obtainadditional 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).
  19. Schwartz found buried sand fans in the middle of marsh transects(may have pre-datedintense 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.
  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 andat 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.

  1. 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.

  1. The interpretation of tides from the 1879 report of the SalinasRiver 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.

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FINAL DRAFT Historical Ecology WG Meeting Notes, ElkhornSlough Tidal Wetland Plan, November 22, 2004