ElkhornSlough National Estuarine Research Reserve: Tidal Wetland Project

JOINT Strategic Planning Team and Science Panel meeting

Emphasis: Water Quality- Eutrophication

Monday, September 22, 2008, 9am-4pm

Attendees:

Ivano Aiello, Josh Collins, Mike Foster, Ken Johnson, Jessie Lacy, Bryan Largay, Todd Martz, Erin McCarthy, Erika McPhee-Shaw, Jim Oakden, Mark Silberstein, Becky Suarez, Eric Van Dyke, Peter von Langen, Kerstin Wasson, Andrea Woolfolk

Facilitator: Bryan Largay; Notes prepared: by Erin McCarthy

Presenter: Bryan Largay

Tidal Wetland Project process and timelines

Biophysical status; process for planning and implementation; current stage is design and development; goals; planning principles; contributing research and projected timeline; Parsons Slough update; today’s focus is on eutrophication; Dec. meeting focus is on sedimentation; relationships between management and eutrophication.

Meeting goals:

1- Receive reports on water quality related to large scale actions

2- Consider implications of reports in light of the Tidal Wetland Project

3- Draft consensus statements

4- Identify information gaps

Proposed meeting dates:

Scientific agreement 3/09

Prioritization 4/09

Restoration targets: objectives 4/09

Action plans 5/09

Strategic plan update 6/09

Discussion

Key Points

  • Collective statements of agreement are an important step in establishing specific objectives.
  • Establishing what is feasible, both from a scientific and political perspective, is a prerequisite to further actions.
  • The process strives to make progress while accommodating new information, and needs to continually return to the adaptive management approach.

Josh- How are you going to set objectives about acreage of habitat? Other processes have done a group think- for example at Bolinas Lagoon. If you can get to those collective statements of agreement then you are at the threshold of drawing lines on a map. These statements should include acknowledgement of potential error.

Jessie- We also need to establish what is feasible.

Erika- Is there coverage of what political constraints the process may be facing?

Group: Judy Kildow is covering that topic.

Joanna- How do you galvanize action while being accommodating to new and evolving research?

Josh-The more specific you can be the more efficiently that you can solve the problem.

Erika- according to recent information from Larry Breaker, sea level rise may not be occurring on the PacificCoast- a result of complex processes.

Presenter: Ken Johnson

Nitrate dynamics in Elkhorn Slough

What is happening in the Slough and how might it change under different engineering scenarios?

LOBO is an MBARI initiative to monitor water quality in real time. The data is available on internet, with 5 years of data for Elkhorn Slough this November.

Key findings:

  • The OldSalinasRiver delivers .75 cubic meters per second at 2000 micromole nitrogen year round.
  • Elkhorn Slough is sink for 500kg nitrate/day
  • 50-65% of the load from OldSalinasRiver channel goes into Elkhorn Slough and 80% of that does not come back out
  • nitrate uptake creates hypertrophic conditions (past eutrophic) resulting in major changes in oxygen balance
  • ReroutingOldSalinasRiver channel would prevent this, but there would be secondary effects on MontereyBay or the Salinas River Lagoon.

Discussion

Key Points

  • Nitrate loading to Elkhorn Slough is substantial.
  • It appears to be going into primary production and denitrification.
  • A substantial flux of ammonia coming out of the sediment occurs as well.
  • It would be valuable to collect data from OldSalinasRiver channel water.
  • The Tidal Wetland Project should place additional effort into identifying the primary sources of nitrogen to the slough.
  • The implications of the high level of nitrate input for Elkhorn Slough could help catalyze the effort to ramp up agricultural regulations.

Jim: There are sources of high nitrogen within the system.

Jim- Can we sample OldSalinasRiver water when it breaches during a storm event?

Erika- That is a complicated procedure.

Bryan- How much effort should I put into the relative prioritization of sanctuary water quality?

Josh- the Elkhorn Sloughshould know what that nitrogen source is and why. It’s a priority (other members of group agree).

Jessie- Can you put 500kg of nitrate per day into perspective?

Ken- Elkhorn Sloughis equivalent to 5km of upwelling coastline.

Peter- Main issue is agriculture. Right now they’re ramping up regulatory efforts.

Mike- This work being done at Elkhorn Slough could be a stimulus for nitrate source control on the end of the Regional Water Quality Control Board.

Break

Presenter: Ken Johnson(cont)

Dissolved oxygen under current conditions and large scale actions

Key presentation points

● Elkhorn Slough is hypertrophic (beyond eutrophic). It exhibits extreme rates of oxygen production and consumption when compared to any site in the literature.

● Biologic is the main driving force in determining oxygen concentrations, not flow or circulation.

● Depth is a key parameter, directly related to the amount of oxygen present: the shallower the water, the more vulnerable it is to becoming anoxic.

Oxygen production and consumption is driven by biology and physics. The physics include: Gas exchange, driven by water and wind speed, introduces oxygen from the atmosphere. Circulation of water from the bay brings in oxygenated water.

The biology includes: Production on the mudflats. In summer, with low tides in day the oxygen produced is lost to atmosphere, but overnight oxygen demand by the mudflats draws oxygen out of the water. In the winter the oxygen is produced in the water. Production and consumption in the water column (phytoplankton): these rates are also high. Benthic oxygen demand is among the highest in the literature.

The observed removal of nitrate is sufficient to support just 33 to 50% of observed carbon production (250 g C/sq. m/y) (as evidenced by rates of photosynthesis). There must be additional internal nitrogen source such as ammonia in soils.

The work included development of a box model to simulate oxygen fluctuations. Water level vs. flow – PWA model vs. box model show consistency. Examining water level vs. velocity for each alternative compared to PWA model was also generally consistent for Parsons, Low Sill, the combination of those two and the New Inlet.

Discussion

Mike: How important is …

Bryan: It’s extremely important.

Ken: If you eliminate flow from the model there is almost no change. Because productivity rates are so high, oxygen changes are not the driver.

Jessie: If you eliminate flow from the model is there no change at L01, as well?

Ken: L01 does respond to changes in flow, but does not reach a critical value.

Suppose you make Parsons Slough shallower- assume half as deep at average tide; it is clearly going below satisfactory oxygen levels now… if you make it more shallow- for example like Azevedo Pond, it will get worse.

The driver is depth- if I make the water column shallower, the stock of oxygen to be consumed is less, at Azevedo Pond it gets driven down to zero quickly because it is so shallow. The water depth in this modeltells you how much oxygen there is to consume; at Parsons, if I make it shallower, it’s below 75 uM much of time.

As far as physics: wind dominates in Parsons Slough. 17% of observations are less than 75 uM; oxygen sensitivity to low light is exacerbated at low flow [See the presentation for a table of oxygen values – Editor]

If you end up with the right combination of parameters, Parsons could go anoxic, and it is feasible that it will happen. Oxygen can get low in Parsons depending on how you reduce depth; a more eroded and deeper slough would create a better scenario for oxygen in the slough- it would result in more oxygen.

Predictions

  • A shallower slough will be more sub-oxic.
  • Lower currents will not directly lead to oxygen changes- low currents will lead to greater extremes.Extensive mudflats will result in lower oxygen in summer as the flats are submerged at night and drawing oxygen out of the water column.
  • Reducing the tidal prism in Parsons has no effect on main channel oxygen, but may result in extensive periods of hypoxia in Parsons Slough if the site is made uniformly shallower. Very shallow areas (such as salt marsh) and deep areas such as channels are greatly preferable to uniformly shallow mudflats.

Discussion (see below)

Key Points

  • The model does not account for stratification, which has implications for hydrogen sulfide production and anoxia.
  • There is a data gap regarding the uptake of nitrogen by macroalgae tissue and export of nitrogen via algalmats exiting the slough.
  • Rerouting the OldSalinasRiver channel could lead to decreased productivity and respiration, and once a transition period is reached; high levels of ammonia would gradually run down. This might be an optimal time to begin a Parsons project.

Mike: With reduced flow, primary production is accumulating- have you tried to model that?

Ken: I treat each box of water separately. There is a limitation to the approach. Nitrate goes up when I remove Parsons Slough because Parsons is a nitrate sink (25% of it); ammonia gets smaller.

Bryan- There is no stratification accounted for here?

Ken- You could get the Stanford folks to do that. Stratification has implications for hydrogen sulfide production.

Jim- There would be less productivity and less oxygen consumption at low tide if the OldSalinasRiver channel was blocked.

Ken- If you slow the flow and have shallower depths, you will see ammonia increase, until the transition period happens when it burns off. If you reroute the OldSalinasRiver, in time the ammonia signal will burn away, and then take actions in Parsons. I recommend doing pilot experiments.

Mike- You’d be modifying two things: nutrient input and flow.

Jim- We’ll need to think about the implications for oxygenlevels in Parsons.

Ken- It’d be nice to have Ulva mat data. Hypertrophic data- benthic primary productivity data- seems to be underestimated by at least a factor of 2.

Mark-It would be good to understand the implications of Ulva leaving the slough… (consistent with Mike’s point).

Jim- A lot of the pelagic respiration will be gone.

Jessie- How much are these alternatives going to move that line between the fully flushed and not flushed regions? Your model is spatially uniform, and that’s what changes under the different scenarios. The question is “How is the line changing between region a and b – between the upper should and lower slough?” not “How is region a or b changing?”

Lunch

Presenter: Bryan Largay

Elkhorn Slough residence times – hydrodynamic model output

Conceptual models of eutrophication advanced by Jim Cloern (2001) indicate that nutrient loading leads to eutrophication and dissolved oxygen problems in some estuaries but not the others. What makes a difference are filters that prevent the problem from getting established. In Elkhorn Slough, it looks like a few filters are operating: a large tidal range with high current velocities tends to mix the water column, preventing stratification, and a short residence time in the lower slough may prevent primary production from producing too much biomass. The large scale actions would affect both of these filters in the direction that might increase the likelihood of problems.

It would be helpful to get information from the group about the possible changes to tidal velocity, tidal range and residence times and for the Tidal Wetland Project.

[See presentation for more information - Editor]

Discussion

Key Points

  • Information gaps need to be identified, followed by a second phase of technical analysis.
  • More data collection may be preferable to additional modeling projects, which are uncertain.
  • The group may be able to form consensus statements about the range of conditions that are or aren’t acceptable- threshold conditions. The threshold conditions should reflect Tidal Wetland Project priorities.
  • Measurable indicators need to be identified.
  • Experiments with a specific focus should be designed to inform threshold boundaries.

Mike- If Elkhorn Sloughis so shallow, how does it stratify? It seems like wind would mix it.

Ken- solar energy

Jim- We ought to take opportunities to get data; there are so many variables. I don’t think we should pour huge amounts of money into more modeling, since it’s uncertain.

Ken- Design experiments that would test specific ideas.

Bryan- We need to identify information gaps and then undertake a second phase of technical analysis.

Josh- At some point there needs to be a general idea of what level of change is good and what is bad.

Kerstin- Maybe it would be setting minimum and maximum ranges of what our ecosystem can or cannot tolerate or requires.

Jessie- We need indicators- what spatial areas are we trying to address? How useful is it to have an average residence time for the slough?

Josh- Management can be driven by extreme conditions or average conditions. The thresholds depend on what our priorities are.

Kerstin- Perhaps we could agree on what is totally unacceptable, we can set red flags.

Presenter: Joanna Nelson

Salt marsh and nitrogen interactions

Does salt marsh function as a coastal filter for nutrient additions from land?

A literature review was presented on nutrient removal by salt marsh and mudflat microbes. The primary mechanisms for retaining or transforming nitrogen and P are denitrification, benthic…. Denitrification rates depend on nitrate loading- some literature shows proportional changes up to a threshold, others show other responses…

The mechanisms of nitrogen retention or transformation: vegetation slows water down and traps sedimentand carbon rich compounds. Physical plant tissues take up N.

Comparing percent reduction in nutrients- vegetated usually slowed a greater removal than mudflats, but not always. Relatively few studies were reviewed.

Jim- In Elkhorn Slough we don’t have much filtered runoff. It seems increased nitrogen goes into Ulva and then it goes out. Elkhorn Sloughworks differently than the typical system.

Joanna- Perspectives on values of estuaries in terms of nitrogen have changed over time. Export used to be favored, and now we value retention ofnitrogen.

Kerstin- Could we compare what’s coming in and going out of a place like Parsons, with little marsh, to a place with extensive marsh?

Ken- It’s not so easy-Ulva covers the mooring.

Discussion: Is salt marsh more valuable than other habitats for water quality?

Key Points

  • Historic conditions are often a target, but they aren’t necessarily the most appropriate target.
  • The value of marsh habitat compared to others isn’t straightforward, and depends on several parameters, but salt marsh clearly filters sediment.

Bryan- Wetlands are valued for their contributions to water quality. We want to be sure we are considering this appropriately. Is salt marsh more valuable or functional than other habitats?

Kerstin- There are reasons to compare with, and aim for, historic conditions, and reasons not to. But historic conditions may not necessarily be the best target.

Josh- It can be a mixed story, depending on several parameters, but marshes do filter sediment.

Peter- The Monterey Bay National Marine Sanctuary includes the main channel of Elkhorn Slough. They will have an interest in this.

Discussion: Should reducing nitrate input in the slough be an objective?

Key Points

  • It would be an amazing experiment to collect nitrogen and oxygen data and other data with the flow in the OldSalinasRiver channel reversed.
  • The rates of nitrate uptake by macroalgae relative to denitrification have not been determined.
  • We should have target maximum loading rates and threshold concentrations for nitrate, as it is a stressor affecting the slough in a number of ways. The objective should be to reduce the input.

Mike- Is the objective to reduce nitrate input in slough?

Bryan- Should it be?

Ken- Nitrate goes too high during rain events. Denitrification rates would have to be real high to sustain a balance. I am not sure if anyone is looking at the fraction of nitrate that goes to algae vs. denitrification.

Joanna- It varies for vegetated vs. non-vegetated habitats. Could we measure particle export?

Joanna- (On biological processing and thresholds) - The more eutrophic, the more phytoplankton, the more shading. Eel grass is a sink. Rather than thinking about thresholds, maybe think more about nitrate as a stressor and reducing it. There is a paper on nitrate as a toxin to Zostera. Eventually they take up too much.

Ken-If we could keep OldSalinasRiver mouth open and run it backwards for a while, that would be informative. That would be much cheaper to do than solve the source in the watershed.

Jim- That was seriously considered at one point, when DDT was a big problem in the harbor.

Discussion: What should the objectives be related to anoxia?

Key Points

  • In order to understand effects of hypoxia on various species, additional questions need to be asked. For example, “What is the effect of limiting leopard shark habitat extent during periods of anoxia?”

Bryan- One endpoint is to avoid hypoxic conditions that limit abundance and diversity of species.

Jessie- Is hypoxia a problem?

Kerstin- It gets low enough to cause observableimpacts on growth rates, but it is not a

cause of major die-offs, as far as we know.

Ken- What are the impacts to fish populations?

Josh/Ken- What other things do we measure? That’s the question. For example, what is the effect of limiting the habitat of leopard sharks, combined withthe effects of the sharks not coming in the summer due to anoxic conditions?

Bryan- Nick Welschmeyeris unable to speak today about the delicately poised phytoplankton balance in slough. [This was the result of our scheduling error-Editor]

Presenter: Bryan Largay

Water quality regulation and water quality objectives for the Slough.

Water quality regulations define criteria for various parameters such as dissolved oxygen based on the beneficial use assigned to the water body. Elkhorn Slough has many beneficial uses, and the most restricted with respect to water quality is Marine Habitat. A project that negatively impacts water quality– that violates those standards - would notbe permitted unless the net benefit exceeds the negative effects. The Marine Habitat standard indicates that dissolved oxygen concentrations should not drop below 7 mg/L. The slough presently violates that standard on a daily basis for several months each year.