Assessing ecological change with 20+ years of high spatial resolution airborne imaging spectroscopy data in a highly invaded/modified inland delta

Estuaries serve a critical ecological role bridging between ocean and land environments. The Sacramento-San Joaquin River delta in California, the largest on the west coast of the Americas, is a unique inverted freshwater tidal delta of 2,990 km² that drains into San Francisco Bay.  It has undergone extensive hydrological modification with ~1800 km of levees. One of the most invaded estuaries in the world, it is also a biodiversity hotspot, supporting 750 plant and wildlife species. Invasive aquatic macrophytes have significantly impacted endangered pelagic fish and native plant species, water temperatures and flow rates, sediment deposition and water clarity in this ecosystem.  The system is highly dynamic; canopy cover by invasive macrophytes, composition and dominance vary significantly on an annual timescale with weather, hydrology, nutrient inputs, and management actions.

Since 2004, we have acquired annual high spatial resolution (1-5m) airborne imaging spectrometer (IS): AVIRIS, AVIRIS-ng, AVIRIS-3, HyMap, SpecTIR, with a gap (2009-2012) filled by commercial satellite data. Supporting datasets include annual vegetation species surveys, weather, hydrology, water quality, and herbicide application data.  Using IS data we have developed species and guild class maps, demonstrated high rates of turnover, changing successional pathways, and system functionality over this 21-year record. Invasive and native macrophytes are functionally different at metabolic, physiological, morphological levels that can be distinguished by spectrally significant differences, which change in association with changing environmental characteristics. Submerged aquatic vegetation (SAV), accounts for 40-60% of annual new growth, with about 50% surviving over winter.  Early in the study, Eichhornia crassipes (water hyacinth) was the dominant floating invasive species (FAV), but in 2014, it began being replaced by Ludwigia spp. (water primrose) that has also invaded the emergent tule marsh, growing over and killing it, causing about half of all marsh erosion. Finally, we also show that the 3-dimensional structure of communities within the water column and distance to shore leads to competitive interactions between SAV and FAV. The maps and research emerging from this extended monitoring project have expanded understanding of ecosystem functionality and directly informed management actions and policy, and restoration recommendations.