Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2009
Publication Date: 9/1/2009
Citation: Santos, M.J., Khanna, S., Hestir, E.L., Andrew, M.E., Rajapakse, S.S., Greenberg, J., Anderson, L.W. 2009. Use of Hyperspectral Remote Sensing to Evaluate Efficacy of Aquatic Plant Management. Journal of Invasive Plant Science and Management. 2(3):216-229. Interpretive Summary: The Sacramento-San Joaquin Delta provides a potable water source for over 22 million Californians and irrigation water for multibillion-dollar crop production systems. Two non-native aquatic weeds, water hyacinth and Brazilian waterweed, greatly impair the transport, quality and uses of this vital resource. Multi-year aerial photography, coupled with digital analysis of reflectance called “hyperspectral imagery” has helped document the extent of aquatic weed infestations and the effectiveness of state-run programs aimed at managing these two invasive aquatic weeds. Delta-wide remote sensing showed that water hyacinth populations have been reduced over the past several years through the use foliar herbicide applications and that Brazilian waterweed continues to expand except where spring applications of a systemic herbicide, fluridone, were made in 3,000 acre area call Franks Tract. This remote sensing method will help provide large-scale, long-term monitoring information on location and cover of submersed, floating and shoreline plants and thus can be an essential part of overall Delta restoration efforts.
Technical Abstract: Invasive aquatic weeds negatively affect biodiversity, fluvial dynamics, water quality, and water storage and conveyance for a variety of human resource demands. In California’s Sacramento-San Joaquin River Delta one submersed species - Brazilian waterweed (Egeria densa) - and one floating species - water hyacinth (Eichhornia crassipes) - are actively managed to maintain navigable waterways. We monitored the spatial and temporal dynamics of submersed aquatic plant complexes, and floating and emergent plants in the Delta using airborne hyperspectral data and assessed the effect of herbicide treatments used to manage these species from 2003 to 2007. Each year, submersed aquatic plant species occupied about 12% of the surface area of the Sacramento-San Joaquin Delta in early summer and floating invasive plant species occupied 2-3%. Since 2003, the cover of submersed aquatic plants expanded about 500 ha in the Delta, whereas the cover of water hyacinth was reduced. Although local treatments have reduced areal extent of submersed aquatic plants, Delta-wide cover has not been significantly reduced within and across years. Locally, treating a site more that once (e.g. twice per week to sustain efficacious concentrations) could decrease submersed aquatic plants spread, given that no residual plants outside the treated area were present. In contrast, the spread of water hyacinth in the Delta has either been constant or has decreased over time. These results show that (1) the objectives of the Egeria densa Control Program (EDCP) have been hindered until 2007 by the restrictions imposed on the timing of herbicide applications; (2) repeated herbicide treatment of water hyacinth has resulted in control of the spread of this species and recent declines in areal cover, which also appears to have facilitated the spread of waterprimrose (Ludwigia spp.) and water pennywort (Hydrocotyle rannunculoides). Results suggest that management of the Delta aquatic macrophytes may benefit by an ecosystem level implementation of an Integrated Delta Vegetation Management and Monitoring Program rather than targeting only two initially problematic species.