California WaterBlog

By Rosemary Hartman, Matt Young, Dylan Chapple, Stacy Sherman, Dave Ayers, Emma Mendonsa, Elizabeth Brusati, and Louise Conrad

Tidal wetlands in the Sacramento – San Joaquin Delta used to be vast. You may have seen artistic renditions of how the landscape may have looked with meandering channels weaving through a mosaic of land and water and with teaming wildlife.

In fact, prior to European colonization, the the Delta used to be a whole 95% tidal freshwater wetlands covered in tule and cattail vegetation, stewarded by a number of Indigenous Tribes. We know this historical landscape was forever changed when settlers forcibly removed Indigenous people and their stewardship practices from the landscape, and spent the subsequent hundred and fifty years diking and draining the wetlands to create farmland. In one of the most ambitious restoration efforts of the State, and to help reverse the ecological decline this transformation caused, a network of California State agencies, Federal agencies, private institutions, and non-governmental organizations have spent the last decade trying to restore some of these wetlands. The California Department of Water Resources is required to restore 8,396 acres of tidal wetlands to offset environmental impacts of the State Water Project, which exports water for municipal and agricultural use. About two thirds of this acreage has been completed, and several more restoration projects built for other programs also completed (Figure 2). An exciting aspect of these projects is that all of them have some level of environmental monitoring and research going on, ranging from the water quality to the fishes.

So, what have we learned? Well, because tidal wetlands have a rich and complex ecology and because hydrology in California is highly variable, we’re just beginning to understand how restored wetlands are functioning. A group of researchers got together this past fall to discuss what we’ve learned so far and identify major gaps in our understanding. The symposium “Delta-Suisun Tidal Wetland Restoration Symposium: State of the Science and Future Directions”, sponsored by the State Water Contractors and the Department of Water Resources, dove into the extensive research occurring in local estuarine wetlands and provided a discussion forum for development of a prioritized list of key next steps to support adaptive management. You may ask, what is there to adaptively manage about wetlands, and what does that mean, anyway? For this symposium, we mean that we wanted to look at our science and practices for how we design wetlands and identify tools or information we still need to do a better job with project design for future projects, or modify the existing ones. We also wanted to think about whether the environmental information that is being gathered now is putting us in a position to know whether restoration projects are fulfilling their intended purpose of providing food and habitat for native fishes. And, now that we’ve been building and monitoring wetlands for some time, we wanted to clearly identify science and management priorities based on what we know now.

When discussing the state of the science regarding fish use of restored tidal wetlands, it’s important to realize we are studying more than just fish. For one thing, it’s often very difficult to catch fish using the wetlands even when they are there – especially when they are the rare, endangered salmon and Delta Smelt.  Therefore, scientists conduct monitoring of, not only of the fish themselves, but also their habitat and food supply. This idea has been borrowed from restoration efforts on the Columbia River (Simenstad and Cordell 2000) and adopted by the IEP Tidal Wetlands Project Work Team (Sherman et al. 2017). 

Wetland scientists must act like forensic investigators. They can’t always catch salmon in the act of foraging in the wetland, but they can collect clues and decide if the salmon have the means, motive, and opportunity to use the restoration site. But instead of “means, motive, and opportunity” that you hear about in police procedurals, scientists talk about “capacity, opportunity, and realized function”.  We can measure the capacity of the habitat to support fish – meaning appropriate water quality, food supply, and physical habitat. We can also determine whether fish have the opportunity to access the site due to its location and physical attributes. Lastly, we can assess realized function by evaluating fish use of the habitat (Figure 3). Tidal wetlands are ephemeral habitats and notoriously difficult to sample for fishes, making realized function sometimes difficult to measure. We may not always be able to monitor realized function, but monitoring capacity and opportunity will tell you a lot about how fish might benefit from your site. 

Monitoring of restored tidal wetlands is ongoing, and our understanding of how they function as fish habitat is beginning to accumulate, and as the current restoration sites mature and continue to be studied, agency and academic scientists will be tracking and reporting on how they are performing. During the symposium, we learned that tidal wetland restoration sites have water that is often cooler than the surrounding environment, invertebrate production that is similar to established wetland reference sites, and many Longfin Smelt, Chinook Salmon, and other native species are using the sites. However, these restoration sites are still young and restoration can evolve slowly (see “Being Patient and Persistent with Nature”), so there is a lot left to be learned. Discussions at the symposium also identified current challenges that require attention from both scientists and managers: for example, to what extent do invasive aquatic weeds need to be controlled before they hinder the wetland function for native fish? If you are a juvenile salmon, will predator densities in wetlands make these places a dangerous place to be? 

During the symposium, break-out groups discussed these management gaps and identified priority scientific studies needed to fill gaps. Communication among scientists, managers, and the larger community with an interest in restoration is a critical aspect of adaptive management. These breakout groups provided a critical opportunity to bring together state, federal, local, academic, non-profit, consultant, and community perspectives on the state of science and implementation. After the symposium, with the help of the Interagency Ecological Program Tidal Wetlands Monitoring Project Work Team, we distilled the management gaps into six priority action areas (Table 1). Each priority management action is accompanied by one or more scientific actions along with an example of what implementing the actions could look like. This is not an exhaustive list of all data gaps or management problems regarding wetland restoration in this region; instead, it prioritizes topics considered most important by a wide range of restoration practitioners and scientists.

Table 1. Priority management actions and science actions for improvements to adaptive management of tidal wetland restoration.

Management Priority	Science Priority	Example
1. Ensure that models used in design are validated, expanded, and updated for future use (including hydrodynamic models, sediment models, fish habitat models, productivity models, etc.).	Advance use of integrated models for design of restoration sites, including linking physical (e.g., hydrodynamic, sediment) models with ecological (e.g., productivity, fish habitat) models.	During the restoration design process, model potential primary production rates and hydrodynamic transport in wetland channels. After construction, monitor primary production to validate model and update model as needed.
2. Incorporate experimental design and opportunities for adaptive management in restoration planning.	Identify associations between desired tidal wetland functions and restoration site features that can be adaptively managed.	Divide a restoration site into parcels with different vegetation planting strategies. Monitor which planting strategy provides highest native species coverage.
3. Clearly define the adaptive management time frames for various performance metrics of tidal wetlands. When can we make a decision about adaptive management actions in tidal wetlands?	Determine appropriate monitoring time frames for each performance metric based on physical and biological processes, such as rates of tidal wetland evolution and generation times, to inform how much data is needed to make future management decisions.	Review existing literature and data to establish monitoring time frames. After this time frame, evaluate data to judge whether enough time has elapsed.
4. Identify pathways to take corrective action on existing sites (e.g., resizing breaches, treating weeds, dredging) if a site is not meeting ecological goals and objectives.	Identify metrics and thresholds which denote impaired ecological functions of a restored tidal wetland.	Link size and depth of channels to preferred depth for juvenile salmonid rearing. If the breach of the site fills in past preferred depth, re-excavate breach.
5. Invest in monitoring realized function to inform adaptive management.	Increase understanding of fish use of wetlands beyond occupancy – rearing, reproduction, foraging, and refuge.	Conduct field experiments of predation rates in different wetland sites.
	Understand associations between primary producers and invertebrates (especially non-zooplankton) with physical habitat features, and the role of different invertebrates as fish food.	Pair studies of fish diet with monitoring of epiphytic, epibenthic, and planktonic invertebrate communities across different tidal wetland habitat features
	Understand how constituents, including primary and secondary production, are transported into or out of wetlands, and how the spatiotemporal footprint of wetland production is affected by wetland size or geomorphology.	Conduct field experiments to measure primary and secondary production rates, rates of flux into and out of the site, and how these rates vary over space and time.
	Develop and validate new monitoring tools, including remote sensing, on-water platform-based mapping, in situ primary productivity measurement, phytoplankton species identification, and genetic tools (e.g., environmental DNA species identification).	Pair use of metabarcoding and imagery with traditional microscopy for identification of phytoplankton and zooplankton to determine if new tools can be more cost effective.
6. Connect outcome of scientific studies to the long-term management of the restoration site to increase resiliency to future change.	Develop science to predict future changes on restoration sites, including climate change, drought, and sea level rise.	Model expected rates of sediment accretion to see whether they are anticipated to keep pace with climate change. Measure rates of sediment accretion to validate the model.

We hope this list will help scientists prioritize which special studies to focus on, and will help funding agencies prioritize which project to support. However, this post is not a replacement for regular communication between researchers, restoration practitioners, policy makers, and managers. Even if all the actions in Table 1 are taken, tidal wetland restoration will not improve without wide sharing of new information, and dedicated attention to how to apply the lessons learned to project design or changes to existing projects. Therefore, the final priority action is to continue investment in regular communication between all interested parties to ensure the best available science reaches the people who can use it. Some of the most important communication venues (listed below in table 2), bring multi-disciplinary groups together to share the most recent results from restoration monitoring programs and use them to inform the next restoration projects. The venues listed in table 2 are all open to the interested public, so click on the links for more information and to receive updates.

With thousands of acres of wetland restoration projects currently being planned, learning from what we’ve done so far is more important than ever. 

Table 2. Communication venues to share science related to tidal wetland restoration, all of which are open to the public.

Venue	Scope	Participants
IEP Tidal Wetlands Monitoring PWT	Effectiveness monitoring of tidal wetland restoration sites for at-risk fishes.	Wetland scientists and restoration practitioners.
Delta Science Program’s Adaptive Management Forums	Promoting dialogue and information exchange related to adaptive management in the Delta	Wetland scientists and restoration practitioners.
CA Monitoring Council’s Estuary Monitoring Work Group	California-wide monitoring of estuaries for a variety of purposes	Wetland scientists and restoration practitioners.
Bay-Delta Science Conference	All aspects of science in the estuary, including wetlands and restoration.	Scientists working on all aspects of the San Fransisco Bay, Suisun, and the Delta
State of the Estuary Conference	Management, Science, and policy, focusing mostly on the San Fransisco Bay with some information on the Delta too.	Resource managers and scientists working on all aspects of the San Fransisco Bay, Suisun, and the Delta
Interagency Ecological Program annual workshop	Work conducted by IEP and associated groups, including wetland studies.	Scientists working within the auspices of the IEP.
San Francisco Estuary and Watershed Sciences (journal)	All aspects of science in the estuary, including wetlands and restoration.	Scientists working on all aspects of the San Fransisco Bay, Suisun, and the Delta

About the authors

Rosemary Hartman is an aquatic community ecologist for the Department of Water Resources where she leads the Interagency Ecological Program Synthesis Team. Website: https://iep.ca.gov/Science-Synthesis-Service/Directed-Studies-Synthesis. Email: Rosemary.Hartman@water.ca.gov

Matt Young is a research fish biologist with the US Geological Survey California Water Science Center. His research is focused on interactions of native and non-native fishes with their environment, including novel ecosystem elements such as altered hydrology and proliferating non-native habitat engineers such as submersed aquatic vegetation. https://www.usgs.gov/staff-profiles/matthew-j-young

Stacy Sherman is an environmental program manager for the California Department of Fish and Wildlife where she leads the Fish Restoration Program Monitoring Team. Website: https://iep.ca.gov/Science-Synthesis-Service/Monitoring-Programs/Tidal-Wetland

David Ayers is a PhD candidate at UC Davis interested in understanding how aquatic habitats structure ecological processes and influence fish distribution. Website: https://watershed.ucdavis.edu/people/dave-ayers

Dylan Chapple is an environmental program manager with the Delta Science Program where he leads the Adaptive management unit. https://www.deltacouncil.ca.gov/delta-science-program/adaptive-management

Elizabeth Brusati is a senior environmental scientist with the Delta Science Program working on adaptive management of restoration projects in the Delta. 

Emma Mendonsa is a senior environmental scientist with the California Department of Water Resources where she works on monitoring water quality at Fish Restoration Program tidal wetland restoration sites.

Louise Conrad is the lead scientist of the Department of Water Resources with a background in the aquatic community ecology of the Sacramento San Joaquin Delta. Previous research includes interactions between invasive predatory fish and aquatic weeds, impacts of drought on fish in the Delta, floodplain ecology, and efficacy and impacts of aquatic weed control.

Further Reading

Brown, L. R. 2003. Will tidal wetland restoration enhance populations of native fishes? San Francisco Estuary and Watershed Science. [accessed 2024 Apr 18].  1 (1):43 pages. https://doi.org/10.15447/sfews.2003v1iss1art2

Durand, J., and P. Moyle. 2017. Blacklock Marsh: tidal habitat no panacea for thoughtful restoration. https://californiawaterblog.com/2017/06/04/blacklock-marsh-tidal-habitat-no-panacea-for-thoughtful-restoration/

Herbold, B., D. M. Baltz, L. Brown, R. Grossinger, W. Kimmerer, P. Lehman, C. S. Simenstad, C. Wilcox, and M. Nobriga. 2014. The role of tidal marsh restoration in fish management in the San Francisco Estuary. San Francisco Estuary and Watershed Science. [accessed 2024 Apr 18].  12 (1). https://doi.org/10.15447/sfews.2014v12iss1art1

Rypel, A.L. 2022. Being Patient and Persistent with Nature. https://californiawaterblog.com/2022/10/16/being-patient-and-persistent-with-nature/

Rypel, A.L. 2023. Wetlands on the edge. https://californiawaterblog.com/2023/09/03/wetlands-on-the-edge/

Sherman, S., R. Hartman, and D. Contreras. 2017. Effects of Tidal Wetland Restoration on Fish: A Suite of Conceptual Models. Interagency Ecological Program Technical Report 91. Department of Water Resources, Sacramento, CA. [accessed 2024 Apr 18]. https://cadwr.app.box.com/v/InteragencyEcologicalProgram/file/571038692179

Simenstad, C. A., and J. R. Cordell. 2000. Ecological assessment criteria for restoring anadromous salmonid habitat in Pacific Northwest estuaries. Ecological Engineering. [accessed 2024 Apr 18].  15 (3–4):283-302. http://dx.doi.org/10.1016/S0925-8574(00)00082-3