DELTA LEAD SCIENTIST REPORT: Primary production in the Delta

At the June meeting of the Delta Stewardship Council, Delta Lead Scientist Dr. Laurel Larsen spotlighted recent research on the Delta’s food web, noted a paper on preparing for rapid changes expected from climate change, and updated the Council on the Delta Lead Scientist Office Hours and the upcoming Science Action Agenda workshop.

Dr. Laurel Larsen began by asking everyone to imagine what the Delta might have looked like before colonization by the European settlers.  If you see a lot of green swampy land, you probably have a pretty accurate picture in mind, she said.

Coming out of the late Holocene period, the Delta had experienced relatively steady sea levels, rising only slightly over time. These conditions were conducive to the formation of an extensive marshland through the whole Delta area.  The modern Delta is very different than the extensive marshlands of the past. However, one of the things that scientists still don’t have a good handle on is how these extensive changes to the landscape structure have affected functions.

For example, how much of the decline of the species that we manage for like fish species in particular, is due to this broad-scale landscape conversion versus other factors such as diversions and nutrients, and to what extent are those negative impacts reversible by, for example, restoring wetlands?” said Dr. Larsen.  “These questions are particularly difficult to answer in the Delta. Because unlike counterpart ecosystems in the Everglades, Chesapeake Bay, and southern Louisiana, such a tremendous fraction of the original wetlands have been lost.”

It might be that the benefits of wetlands for many of the species we’re managing for might not be apparent until a threshold coverage of wetlands is reached, and we may still be far from that threshold. As a result, the value of wetland restoration has been a bit difficult to demonstrate, which has led to a lot of uncertainty and debate about the role of wetland restoration in the ongoing voluntary agreements negotiations.”

Recently, in a synthesis study funded jointly by the Delta Science Program and the US Geological Survey, former ISB member Jim Cloern and his coauthors set out to quantify how the loss of these historic wetlands influenced the Delta’s total primary production, and specifically the infusion of fuel into the base of the food web.

In the paper, On the human appropriation of wetland primary production, the authors first synthesized data from the scientific literature to quantify average rates of primary production in five communities: phytoplankton, attached microalgae, aquatic plants, marsh plants, and woody riparian vegetation.  They did this separately for wet years and dry years. Then, based on this information and the distribution of these communities among five habitat types, they constructed a model of primary production and applied that model to the historic landscape, which was reconstructed based on available historical maps to give them a historical baseline. Finally, they developed estimates for habitat coverage in the Delta if all restoration targets specified in the Delta plan had been met. And they applied their model to that hypothetical landscape to evaluate how the targeted amount of wetland restoration could improve fuel supply to Delta food webs.

Dr. Larsen then gave the highlights of their results. “First of all, based on their historical landscape reconstruction, they found that the Delta has lost 77% of its hydrologically connected habitat, with more than 98% of its title and non-tidal marsh area lost between today and the early 19th century. Unfortunately, marsh plants produced an order of magnitude more carbon in the historic landscape than any other community groups examined. So this 77% loss of marshland translated into a 94% loss in primary productivity across the Delta, and specifically, an 89% loss of food supply to herbivores at the base of the food chain.  This represents a tremendous hit to the food web, which surely has had major negative consequences for native consumer fish.”

Can wetland restoration reverse these consequences? “The authors of this paper suggest that we can begin to if all of the habitat targets for Marsh and riparian restoration in the Delta plan are met, they estimate that we would recover 12% of the deltas historical primary production,” said Dr. Larsen.  “That doesn’t sound like a lot – 12%. But considering that this number nearly triples the fuel currently available to the food web, it could potentially make huge gains for the ecosystem relative to its current state.” 

Dr. Larsen also noted that the paper makes another interesting point relevant to the current drought situation: the portions of the landscape that contribute the most to primary productivity have been substantially reconfigured, which has significant consequences for the year-to-year variability of food supply.

Historically, primary production was primarily sourced from plants and marshes and attached algae, and these landscapes were inundated during most years,” she said.  “Now, that is mostly gone, but woody plants are a relatively large contributor behind open water, which was the smallest contributor historically. This means that the difference in the provisioning of food to the food chain now, unlike in the past swings drastically between wet years and dry years, is governed by the inundation of woody riparian zones and their reconnection to fish habitat. In other words, wetlands could provide food security to Delta food chains, making them more resilient to drought.”

These results really could be a game-changer when it comes to agencies taking the charge seriously to restore wetlands and implement nature-based solutions to management challenges. So let’s share them widely among our colleagues and continue to get the word out.

Councilmember Virginia Madueño asked Dr. Larsen what would be a reasonable timeline for wetland restoration.

I believe the timeline that is written into the Delta plan is reasonable,” said Dr. Larsen.  “When it comes to restoration of wetlands, the sooner we can get a start on restoring these landscapes, the better. A number of our listed fish species are in a period of precipitous decline. We’re likely to see additional, really drastic declines of these native fishes, particularly during a drought year.  So anything that we can do in the near future to produce habitat connected to where the fish are and is known to produce relatively large amounts of phytoplankton and zooplankton that really supplies that food chain, the better off we are in this rapidly changing situation. But we need to get started now, especially if we want to avoid extinctions or further endangerment of listed species.”

Paper: Preparing Scientists, Policy-Makers, and Managers for a Fast-Forward Future

The Delta Independent Science Board’s paper, Preparing Scientists, Policy-Makers, and Managers for a Fast-Forward Future, has been published in the current issue of San Francisco Estuary and Watershed Sciences.  The article is the call to action that underlay the science needs assessment efforts.  The Journal is an open-source publication partially funded by the Delta Stewardship Council, so all articles are free to access.

Delta Lead Scientist Office Hours

The third episode of the Delta Lead Scientist’s Office Hours was recently held as an Instagram live chat.  Program Manager Dylan Stern within the Delta science program was the cohost.  They discussed funding that is provided for different types of science by the Delta Stewardship Council and other agencies, as well as upcoming opportunities within the Delta science program to get the most exciting work funded.   

The next session will be on July 15 at noon, which will again focus on funding.  To attend the office hours event, log in to the Delta Stewardship Council’s Instagram page (@deltastewardshipcouncil).

Science Action Agenda and Workshop

The Science Action Agenda is one element of a three-fold science strategy; the other elements are the Delta Science Plan and the State of Bay-Delta Science. The Science Action Agenda aligns science needs with management priorities and sets the priorities for funding science within the Delta.

The current Science Action Agenda is expiring at the end of this year, so the 2022-2026 update to the Science Action Agenda is underway.  Through an ongoing collaborative process and a series of workshops in 2020, a set of management questions has been developed.  A progress summary on the last Science Action Agenda was recently completed. In addition, there have been a series of stakeholder engagement surveys to rank, merge, group, and prioritize management questions.   

In late May, the Delta science program circulated the draft management needs for the 2022 to 2026 Science Action Agenda for public review to ensure that those needs accurately reflected overarching and pressing gaps and management. The final list of management needs is available.  It will shape the science actions workshop in July because those science actions will be crafted directly in response to those management needs.

The Science Actions Workshop will be held July 13-14 in a fully virtual format.  Workshop participants will consider the top 65 Delta management questions grouped within the management needs to develop priority science actions and then rank them. Registration just recently closed, with over 100 participants expected.

Click here for more information on the Science Action Agenda.

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