The Delta Reform Act requires ‘taking into consideration the physical changes that have occurred in the past and the future impact of climate change and sea level rise’ for restoration planning. Re-establishment of tidal marsh is critical to restoring food web function and increasing the extent of habitat for fish and wildlife within the Delta and Suisun Marsh; however, land subsidence, sea level rise, and urbanization significantly constrain where tidal reconnection is possible in the future.
A team of Delta Stewardship Council staff, scientists, and consultants have been working for the last year on the effects of climate change on restoration projects in the Delta, and have been compiling information and putting together fundamental datasets to inform the ecosystem restoration amendment to the Delta plan, the development and refinement of performance measures, and to provide the foundation for a climate vulnerability assessment currently underway that will be completed in 2020. At the 2018 Bay Delta Science Conference, Ron Melcer, Senior Environmental Science Supervisor, gave a presentation on what the team has accomplished so far.
Mr. Melcer began by reminding that the Delta is the largest estuary on the West Coast of both North and South America. Within Western North America, the riparian, wetland, and estuarine ecosystems are both incredibly productive and support more than 80% of the biodiversity on the arid and semi-arid landscape. The Delta connects California’s largest river system from their montane headwaters to the ocean. It’s projected to be an important region for ecological adaptation to climate change, with its multitude of stream channels and marine influence causing cooler temperatures on the landscape.
The Delta is significantly impaired due to the disconnection of the land-water interface, significant loss of native vegetation and many other stressors. Currently there are well over 100 species of conservation concern; nearly half of these are endemic to the California floristic province. The Delta is one of the top 25 biodiversity hotspots in the world.
Mr. Melcer noted that there are at least 14 conservation and recovery plans that exist which provide ecological goals and objectives for the region. “And so given the level of scientific inquiry in our investments on the landscape within the Delta, it’s really hard to reconcile that we’re still in a very impaired state,” he said.
“A review that my coauthors and I undertook last year of conservation and restoration projects within the Delta indicate that there have been more than 170 physical projects within the legal Delta boundaries, including Suisun Marsh. So despite 170 conservation projects on the landscape, we found that less than a third of these carried out process-based restoration that reconnected either tidal or fluvial land-water interactions, and furthermore, more than 70% of those projects in the conservation lands within the Delta remain in agriculture, so not a big change from existing conditions. This has implications for ecological processes, like primary production and food web dynamics.”
Mr. Melcer noted that the Delta Plan provides a bold vision for the landscape: ‘A resilient functioning estuary and surrounding terrestrial landscape, capable of supporting viable populations of native resident migratory species with diverse biologically appropriate habitats, functional corridors, and ecosystem processes.’
Given the conservation and restoration to date has largely focused on protection of remnant habitats or the implementation of multi-benefit projects, such as vegetation on levees or wildlife friendly agriculture, they have been focusing on the elements of conservation that have yet to be implemented, such as reestablishing the physical and biological processes that support key ecosystem characteristics at multiple hierarchical scales.
“As species face a changing climate, they require ecosystems which are diverse and complex, provide space for evolutionary processes to play out, and support biodiversity and co-evolution,” said Mr. Melcer. “These are fundamental conservation biology principles, and I think it’s important that we don’t lose sight of these. They are not well achieved through static or synthetic approaches to restoration.”
Over the past year, the team has been acquiring, assessing, and updating models and datasets. They have focused on how to achieve two coarse outcomes on the landscape which tie back to the Delta Stewardship Council’s authorities related to land use and infrastructure throughout the Delta: the restoration of native vegetation communities and the concept of reconnecting tidal or fluvial land-water connections.
From a process-based restoration perspective, there are two key geomorphic drivers for the connection of the land-water interface: Landform and the flow of water. Elevation within the Delta presents significant constraints on the potential for restoration.
“Oxidation of peat soils within the region has resulted in 2.6 to 3.3 billion cubic yards of peaty soils to be lost, and that’s since the 1850s,” Mr. Melcer said. “A significant portion of the interior Delta now lies below sea level. The processes that have led to subsidence are still at play … These data depict organic content of the soils, and also the rate of subsidence within the Delta, which can exceed a half an inch per year in some of the worst locales within the region.”
The California Natural Resources Agency and the Ocean Protection Council released sea level rise guidance in 2018. The team is evaluating scenarios which include an optimistic, a likely, and an extreme scenarios for sea level rise, which correspond with 2.5, 7, and 10 feet of sea level rise at the Golden Gate respectively.
“We know the guidance and modeling seem to be quickly out of date when it comes to sea level rise projections,” said Mr. Melcer. “What the new science consistently indicates is worsening conditions in terms of ice melting and the water surface elevation increases.”
Water surface elevation gradients within the Delta are complex. They have been working to refine the understanding of how river flows and tidal forcings interact within the estuary and they’ve undertaken a relatively static analysis which leverages more than 40 tidal datums across the estuary.
They have also been applying fragility and failure rate datasets from the Delta Risk Management Study and the Council’s Delta Levee Investment Strategy dataset, and they’ve recently received an empirical failure dataset for the region that they will utilizing.
They have also been working with the counties to compile a baseline understanding of the build landscape as of 2013 when the Delta Plan and its development policies were adopted. They have gathered existing local government plans and the existing land use for both the built working landscapes and natural lands. They are also currently in the process of supporting the Department of Fish and Wildlife and other organizations in the updating of the VegCAMP dataset based on 2016 NAP aerial imagery.
They have also been working hard to incorporate the social benefits of restoration and the vulnerability of human populations in the Delta. “Both Prop 84 and Prop 1 have given us priorities in terms of disadvantaged communities and issues that we should be targeting,” he said. “Public funding resources from the state’s cap and trade program has provided the Cal EnviroScreen tool which allows us to interact with GIS layers of similar issues. As we consider previously described subsidence, sea level rise, and level condition, it is clear that there are synergistic opportunities to provide both ecosystem and human benefits from restoration activities.”
Mr. Melcer also noted that they’ve been working with the San Francisco Estuary Institute in supporting the use of the resilient landscapes reports.
The team has begun exploring simple forecasting and scenario work. “Using the farmland mapping and monitoring program, we’ve really taken a look at the trajectory of land use in the Delta over the past 20 years,” he said. “We note that little change has occurred in overall land use within the Delta, despite major restoration investments. Agriculture is the dominant land use within the region, and of note, we see permanent crops taking hold in the Delta at a pretty significant rate. Since 2010, more than 27,000 acres have turned over to tree and vines. These tend to be of low value in terms of ecosystem services and benefiting wildlife.”
They have utilized terrain, subsidence, rate and water surface elevation data to parameterize relatively simple grid based models to forecast landform change within the estuary. “Currently every day, we lose 2 football fields of elevation to subtidal condition, and by 2100, much of the Delta and Suisun Marsh will be well below sea level under existing land use,” he said. “With subsidence reversal, it’s possible to recover a significant portion of the Delta from subsidence. Of course this is expensive and likely not feasible to apply at a broad scale.”
They have also worked with a colleague in Tacoma to develop grid-based forecasting models which evaluate both the changes in land elevation and water surface elevation while also considering changes in land use to give an understanding of potential future conditions within the Delta. The slide shows three scenarios: current conditions, business as usual scenario in the center, and the strategic levee maintenance and subsidence scenario on the right.
“We have varying opportunities to reconnect tidal or fluvial processes within these regions,” said Mr. Melcer. “The red indicates a series of islands that are relevant to tidal restoration and orange indicates where encroachment of urban development is occurring. Under that business as usual case, we see much less opportunity out into the future and if we were to apply subsidence reversal in a blanket way, the landscape looks a lot different, the opportunities look a lot different. This is the underpinning for more strategic analyses where we look at a subset of opportunities and how levee investments and subsidence reversal might be combined to really deliver restoration of those characteristics on the landscape.”
The work that the team is doing will inform the ecosystem amendment to the Delta Plan, which includes refinement of regulatory policies and recommendations that address considerations of climate change in restoration actions. He noted that the Delta Plan has a policy that requires restoration proponents in the Delta to place their projects in appropriate elevation zones. Some of the work they have been doing has been used to update this figure with a more nuanced look at those interactions between fluvial and tidal flows, with the new proposed figure shown on the right.
“We have an opportunity to refine how we are measuring success within the Delta in achieving the ecosystem vision of the Delta Plan, so these data and models provide a basis for the development of performance measures, both the baselines and the targets within the region,” he said. “These include assessing habitat restoration, fish passage improvements, reconnection of land-water interface, and the reversal of subsidence.
“The study seeks to balance society and equity, economy, the environment, and governance, and lots of technical work and stakeholder outreach ahead of us in relation to the study,” he said. “We look forward to building upon these data and analyses through the effort in developing a broadly supported understanding of the vulnerabilities facing the region and robust strategies to face these issues.”
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