Invasive Aquatic Weeds in the Sacramento-San Joaquin Delta
Sacramento–San Joaquin River Delta of northern California is the largest freshwater estuary on the western coast of the United States. The Delta provides irrigation water for over $30 billion in crops in the Delta and Central Valley and drinking water for 27 million people, supports $300 million in recreational boating, and includes the ports of West Sacramento and Stockton. The Delta’s sloughs, wetlands and riparian habitats host 56 threatened or endangered species. Invasions by nonnative aquatic weeds constitute a major environmental challenge. Invasive aquatic vegetation incurs billions of dollars in direct control costs and lost economic opportunity while causing significant environmental damage and adversely affecting water use. Aquatic invasive plants have no known natural controls. Continued warm temperatures help the plants grow at high rates. Plants are also known to form dense mats of vegetation creating safety hazards for boaters, obstructing navigation channels, marinas and irrigation systems.
- Invasive aquatic weeds – such as submerged Brazilian waterweed, floating water hyacinth, and emergent giant reed – are some of the most prolific and damaging invasive plants in the Delta, which threaten our environment and economy.
Floating and submerged aquatic weeds alter water velocity causing degradation of water quality and quantity including reduced dissolved oxygen, increased temperature and sedimentation, displace native plants, and reduce habitat for native fish and other animal species. Major impacts on human activities include impairment of water conveyance and diversions and damage to infrastructure, obstruct navigation resulting in loss of access to water for boating, commercial shipping and transportation, and increases in disease-vectoring organisms such as mosquitos contributing to concerns of the potential for increased incidents of West Nile Virus and Zika Virus.
- Past solutions were ineffective. Local control measures are limited to mechanical removal of aquatic weeds, which is labor intensive, costly, and only effective in relatively small critical areas.
Spraying can be effective, but the size and scope of the problem is too large for the Department of Boating and Waterways to handle given the immediate relief needed from these weeds and the regulatory backlog. Additionally, as large mats of aquatic weeds decay post-spraying, dissolved oxygen in the water column can potentially become depleted, which is harmful for fish. Biological Opinions from USFWS and NMFS were granted annually for herbicide use for each aquatic weed species and restricted seasonal applications. These restrictions have reduced the overall effectiveness of herbicide usage needed to maintain aquatic weed control.
- Beginning in 2014, USDA spearheaded a comprehensive and sustainable invasive weeds strategy for the Delta. The Delta Region Areawide Aquatic Weed Project (DRAAWP) was funded from 2014 to 2018 to improve control of floating water hyacinth [Eichhornia crassipes (Mart.) Solms], submersed Brazilian waterweed (Egeria densa Planch.), and riparian arundo (Arundo donax L.) in the Delta. Outputs from the DRAAWP are now informing control of nine aquatic weedsand arundo using adaptive, integrated chemical, mechanical, and biological approaches and all available tools, including herbicides, mechanical control, and biological control with insects. Satellite-based remote sensing and new knowledge on aquatic weed growth, dispersal, and environmental and economic impacts in the Delta are being used to inform decision-support tools to prioritize control sites and select optimal combinations of control methods at each site. Modeling and monitoring of control outcomes (i.e. the effect of healthy weeds in relation to sprayed weeds on dissolved oxygen) is a critical component of this effort to restore habitats with beneficial plant species to limit weed reinvasion.
- More remains to be done. Successful control of aquatic weeds in these ecosystems requires integration of financial and logistical support, in-depth knowledge of weed invasions and impacts, and a range of control tools extending beyond the capacity of one agency or organization. This calls for adoption of integrated management tools and strategies to substantially reduce weed populations while also reducing herbicide use. Improved water availability and quality resulting from improved aquatic weed control is expected to increase habitat suitability. Funding for the Division of Boating and Waterway’s Aquatic Invasive Plant Control Program comes from the Harbors and Watercraft Revolving Fund, which receives revenues from boaters’ registration fees and gasoline taxes.
Additional funding will be needed in FY2022/23 and beyond to continue this important work. Without the continued investment, the prior investments will have been wasted and the promising progress will halt.
- Federal Support. Section 104 of the River and Harbor Act of 1958, as amended (33 U.S.C. §610), authorizes the Aquatic Plant Control Program, a program for the prevention, control, and progressive eradication of noxious aquatic plant growths and aquatic invasive species in U.S. waters. The USACE generally undertakes efforts to prevent or reduce the introduction and establishment of invasive species at its projects, pursuant to its nationwide invasive species policy, engineering regulations, and project and programmatic authorizations (some of which authorize specific invasive species control and eradication activities). USACE typically funds invasive species work for individual projects through the Operation and Maintenance (O&M) account; project planning documents address the nature of work at the project level. USACE also pursues invasive species research that may involve field studies at USACE projects For FY2021, Congress appropriated $25 million for the Aquatic Plant Control Program. The WRDA act of 2020 included provisions related to USACE invasive species efforts and called for periodic updates on invasive species policy and provided annual authorizations to $50M from FY2021 through FY2024. However, these appropriations are to be shared nationwide in regions.
We would also ask that the Delta be added to the list of locales authorized by Sections 129 and 501 of WRDA 2020 as those where the Corps may consider invasive species specific efforts and provide updates on invasive species policy for the Sacramento-San Joaquin Delta.