Developing the capacity to monitor climate change impacts in Mediterranean estuaries

Background: Under predicted climate change scenarios, estuaries and deltas face increased threats to biological sustainability. The Sacramento-San Joaquin Delta in California, USA forms the upstream component of the largest estuary on the Pacific coast of the Americas. It is a Mediterranean system in steep ecological decline under threat from current and potential climate changes. Goal: Illustrate how climate change impacts on an already fragile system can be monitored with new, advanced remote sensing methods. Describe how remote sensing data can improve monitoring of ecosystem changes. Use examples from the Sacramento-San Joaquin Delta in California to illustrate some of the types of ecosystem changes that are expected with climate change, such as changing species composition and dominance, changes in environmental conditions like salinity, water and air temperatures, and precipitation patterns. Show how imaging spectroscopy can provide information about the dynamics of native and invasive estuarine plant communities. Data: Airborne HyMap imaging spectroscopy data of the Sacramento-San Joaquin Delta collected in June for the years 2004 through 2008. Approximately 65 flightlines covered the Delta each year with 3 ×3 m spatial resolution. Concurrent field data recorded geographical locations and phenology of different aquatic plant species. Airborne LiDAR data rasterized at 1 ×1 m, collected in winter 2007 for the entire Delta, was used to calculate light interception by riparian tree canopies. Analysis method: We used hyperspectral image analysis in various classification algorithms to perform vegetation type and species mapping, and estimate plant densities and functional traits. A radiative transfer model was applied to LiDAR data to estimate the effects of riparian tree canopies on the irradiance budget of the surface waters of the Sacramento-San Joaquin Delta as a surrogate for potential water temperature increases. Results: New remote sensing techniques and data detected and measured the density and other functional traits of plant communities and species in this delta. Examining the yearto-year locations of pixels containing invasive species shows that they have high rates of persistence, and that the predicted increases in water temperature may improve the habitat conditions for invasive aquatic plant species. Other changes, such as altered precipitation patterns, may affect the hydrograph of the Sacramento-San Joaquin Delta and its turbidity that could further improve the habitat for non-native species, although sea level rise and increasing upstream salinity might produce the opposite effect. Conclusions: The Sacramento-San Joaquin Delta and Estuary face ecosystem problems that are characteristic of most Mediterranean estuaries. Interactions between the biological and physical conditions in the Delta affect the trajectory of dominance by native and invasive aquatic plant species. Trends in growth and community characteristics associated with predicted impacts of climate change (sea level rise, warmer temperatures, changes in the hydrograph with high winter and low summer outflows) do not provide simple predictions. Individually, the impact of specific environmental changes on the biological components can be predicted, however it is the complex interactions of biological communities with the suite of physical changes that make predictions uncertain. Systematic monitoring of these estuarine environments is critical to achieving sustainable management of these ecosystems and providing the data needed to document and understand change and to identify successful adaptation strategies.