The research, led by Kyra Gmoser-Daskalakis of Utrecht University and the University of California, Davis, together with Mark Lubell and Gwen Arnold of UC Davis, examines barriers to wetland restoration across nine case study projects spanning San Francisco Bay and the Sacramento-San Joaquin Delta. The team conducted semi-structured interviews with 59 project developers, policymakers, funders, and program managers, generating 829 coded barrier statements that reveal where and when restoration efforts run into trouble. Their central argument is that existing frameworks for diagnosing barriers to climate adaptation are too abstract for the messy, site-specific work of putting a wetland back on the landscape, and that a new framework is needed to capture the physical and ecological realities that emerge only during implementation.

The stakes are enormous. The Bay-Delta Estuary has lost an estimated 85 to 90 percent of its historic wetlands to agriculture and development, and regional plans now call for restoring up to 187,000 acres: roughly 100,000 acres of tidal marsh in the Bay, 5,000 to 7,000 acres in Suisun Marsh, and 60,000 to 80,000 acres of habitat in the Delta. Progress has been far slower. Only about 16,400 acres of tidal restoration were completed in the Bay between 1998 and 2020, and roughly 13,758 acres of Delta wetland restoration were completed or in progress between 2007 and 2023. At that pace, the region’s climate adaptation goals, which depend on wetlands to protect communities from flooding and sea level rise, remain distant.

To understand the gap between ambition and achievement, the researchers built a diagnostic framework that integrates two influential climate adaptation barriers models: the five-category typology developed by Biesbroek and colleagues, which classifies barriers as cognitive, financial, informational, institutional, or social, and the spatial and temporal scaling approach of Moser and Ekstrom, which asks where and when in a process a barrier originates. Crucially, the team added two innovations tailored to restoration: a new physical and environmental barrier category, and a ‘future’ temporal origin to capture barriers stemming from anticipated conditions such as climate change impacts and shifting funding priorities. Each barrier statement from the interviews was coded by type, subtype, spatial origin, and temporal origin, then analyzed with descriptive statistics and non-parametric tests of association.

The single most common barrier type was physical and environmental, accounting for 26 percent of all reported barriers. Site elevation, water salinity, and precipitation variability led the list, followed by ecological problems such as invasive weeds. But a striking share of physical barriers came from the built environment: pipelines, high-voltage power lines, wastewater infrastructure, and railroad tracks crisscross the very parcels targeted for tidal marsh restoration. Interviewees described railroad lines encircling the Bay that sit directly in former tidal wetlands, preventing not only restoration but also the landward migration of wetlands as sea levels rise. In a developed estuary, ‘pristine’ sites free of infrastructure are rare, and participants warned that the acreage physically available to project developers does not match the acreage called for on paper in regional plans.

Institutional barriers ranked second at 20 percent, and within this category regulatory conflicts dominated overwhelmingly, with 143 of 163 institutional barriers falling into the regulatory subtype. Project developers described navigating overlapping state, federal, and local authorities with competing mandates, conflicting permit requirements, and jurisdictional disputes that can leave projects ‘frozen.’ Some requirements are internally contradictory: habitat protections for sensitive species can clash with public access mandates, and restoring tidal wetlands for endangered species such as the Salt Marsh Harvest Mouse and Ridgeway’s Rail may conflict with maintaining managed ponds that shelter protected birds like the Snowy Plover. Most paradoxically, some restoration projects must conduct environmental mitigation for their own habitat gains, for example when converting farmland removes foraging habitat used by certain protected species, driving up costs and, in some cases, making projects infeasible.

Resource barriers came third at 16 percent, and the pattern within them was consistent: money flows most readily to construction, not to stewardship. Of 136 resource barriers, 99 were financial rather than capacity-related, and participants repeatedly cited the absence of long-term monitoring and maintenance funding, restrictive timing of disbursements, expiring grants, and overall insufficiency. Funders, participants said, often want to ‘breach it to the tides and walk away,’ but restored wetlands in an already altered landscape require ongoing management of invasive weeds, water levels, and plant communities as climate and salinity conditions shift. Informational barriers accounted for 13 percent, social barriers 16 percent, and cognitive barriers 9 percent, the latter often reflecting a lack of motivation among funders and decision-makers to commit to decades-long stewardship.

The spatial and temporal analysis revealed a crucial insight: 53 percent of barriers were proximate, originating at the project site or with project partners, while 47 percent were remote, arising from regional governance, funding systems, or the wider ecological context. Temporally, 70 percent of barriers were contemporary, emerging during the project process itself, with only 16 percent legacy barriers and 14 percent future-oriented ones. Physical and environmental barriers were overwhelmingly proximate, while institutional barriers clustered at remote scales, suggesting that different barrier types demand interventions at different governance levels. Statistical comparisons showed that barrier profiles did not differ significantly between the Bay and the Delta, indicating these challenges are estuary-wide, though barrier types did differ significantly across individual projects and among participant roles, with policy actors reporting more remote resource barriers and project-level staff reporting more proximate, site-specific ones.

The authors propose solutions matched to their diagnosis. On regulation, California’s ‘Cutting Green Tape’ initiative and streamlined permitting have helped, but many streamlining options apply only to straightforward habitat projects, while modern restorations are increasingly multi-benefit undertakings that bundle flood protection, recreation, and transportation components. The researchers recommend expanding streamlining eligibility and shifting toward a landscape-scale regulatory vision in which requirements for public access, sensitive habitat, and other outcomes are met across a portfolio of projects rather than at every single site. They also call for systematic collaboration and training with local governments, city attorneys, utilities, and special districts, whose easement approvals and legal reviews often lack restoration expertise, pointing to organizations such as Resource Conservation Districts and Joint Ventures as trusted connectors. On funding, they urge private foundations and nonprofits to fill gaps across the full project cycle, especially long-term maintenance that public bond funds legally cannot cover.

The study’s framework is designed to travel. The authors argue it can be applied to other nature-based adaptation interventions, from green stormwater infrastructure to urban forestry, particularly in regions with heavy development and complex governance. They acknowledge limitations, including the absence of data on projects that failed outright and the inherent recall bias of interviews about past work. But the core message is clear: accelerating wetland restoration in developed coastal estuaries requires looking past high-level policy and confronting the on-the-ground frictions of permits, pipelines, and payrolls. As climate impacts intensify, the difference between a restoration target on paper and a functioning tidal marsh may come down to diagnosing precisely these barriers, and designing institutions flexible enough to overcome them.

Subject of Research: Barriers to implementing wetland restoration as a nature-based climate adaptation solution in the California Bay-Delta Estuary

Article Title: Diagnosing Barriers to California Bay-Delta Wetland Restoration Implementation: Extending the Adaptation Perspective

Article References: Gmoser-Daskalakis, K., Lubell, M., & Arnold, G. (2026). Diagnosing Barriers to California Bay-Delta Wetland Restoration Implementation: Extending the Adaptation Perspective. Environmental Management, 76(9), Article 308. https://doi.org/10.1007/s00267-026-02618-7

Image Credits: AI Generated

DOI: 10.1007/s00267-026-02618-7

Keywords: wetland restoration, climate adaptation, nature-based solutions, California Bay-Delta, tidal marsh, implementation barriers, regulatory conflicts, restoration funding, environmental management, social-ecological systems, permitting, long-term stewardship