Invasive aquatic vegetation in the Sacramento-San Joaquin Delta and Suisun Marsh: The history and science of control efforts and recommendations for the path forward

Authors: CONRAD, J - Delta Stewardship Council (A CALIFORNIA STATE AGENCY); THOMAS, MADISON - California Department Of Boating And Waterways; JETTER, KAREN - University Of California, Davis; Madsen, John; Pratt, Paul; Moran, Patrick; TAKEKAWA, JOHN - Suisun Resource Conservation District; DARIN, GINA - California Department Of Water Resources; KENISON, LYDIA - California Department Of Boating And Waterways

Submitted to: San Francisco Estuary and Watershed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2022
Publication Date: 2/1/2023
Citation: Conrad, J.L., Thomas, M., Jetter, K., Madsen, J.D., Pratt, P.D., Moran, P.J., Takekawa, J., Darin, G.S., Kenison, L. 2023. Invasive aquatic vegetation in the Sacramento-San Joaquin Delta and Suisun Marsh: The history and science of control efforts and recommendations for the path forward. San Francisco Estuary and Watershed Science. 20(4). Article 4. https://doi.org/10.15447/sfews.2023v20iss4art4.
DOI: https://doi.org/10.15447/sfews.2023v20iss4art4

Interpretive Summary: This manuscript reviews the history and issues surrounding aquatic weed management in the Sacramento-San Joaquin River Delta, and provides recommendations for future management, research, and monitoring.

Technical Abstract: Invasive aquatic vegetation (IAV) is a management challenge in the Sacramento-San Joaquin Delta and the Suisun Marsh that has triggered legislative mandates and commanded significant resource investment for four decades. We review the history of chemical, biological, and mechanical control in the Delta and Suisun Marsh as well as its supporting science. We find that outside of the system, while there is a significant history of research on IAV control in flowing water systems, there are few studies in tidal systems and we found no investigations at a spatial scale similar to the Delta. Within the system, the science of control efforts is nascent, with the first peer-reviewed study appearing in 2006, but with substantial growth in collaborative science over the recent decade. Since 1983, control of invasive submerged and floating species has been centralized within the California State Parks Division of Boating and Waterways (DBW). The program has relied primarily on herbicides, with an annual budget that has exceeded $12.5 Million since 2015. In parallel, biological control agents for water hyacinth (Pontedaria crassipes) and the giant reed (Arundo donax) have been identified and released. Despite this investment, outcomes of control efforts have had mixed results: herbicide applications, though more effective for floating species, are challenged by the tidally dynamic system. Five biological control agents have been established but offer no appreciable control benefit, likely because they are not matched to the temperate Delta climate. At the same time and during continued IAV spread, regulatory complexity has increased, hampering efforts to innovate alternative methods or respond quickly to new invaders. Control efforts for the giant reed and common reed (Phragmites australis), the main invasive emergent plants, have not been coordinated under a central program, and studies to investigate successful control strategies have only recently been permitted. As a result, there are no local studies published on control outcomes for these species, though there is a rich literature from other regions. Based on this history and our review of the general science, we develop recommendations for leadership and science actions needed in the Delta and Suisun Marsh for adopting a proactive approach to IAV management.