Climate change is expected to pose a significant threat to coastal ecosystems worldwide. How salt marshes will respond to climate change depends on local environmental drivers and plant-mediated biogeomorphic feedbacks, but these factors are highly variable in time and space. A salt marsh’s ability to maintain equilibrium by actively building elevation largely depends on plant productivity, which enables the creation of biomass that contributes to organic matter accretion and sediment trapping. Yet, salt marsh productivity and biomass are not well-characterized across broad spatial scales or continuously in time. We combined field surveys, high-resolution unmanned aerial vehicle (UAV) multispectral imagery and Landsat satellite data to investigate the patterns and drivers of salt marsh biomass in the southern California region. Our approach utilizes innovative UAV technology to characterize the relationship between salt marsh biomass and remotely-sensed vegetation indices, which can improve our ability to investigate long-term biomass dynamics in wetlands across broad spatial scales using Landsat satellite imagery.
Results/Conclusions
Seasonal collections of salt marsh biomass and UAV imagery revealed intra-annual variations in productivity, with winter showing a weak correlation between live biomass and NDVI. Consideration of broad cover classes improves the relationship between in situ biomass and NDVI, as evidenced by significant differences in aboveground biomass among green vegetation, non-photosynthetic vegetation, soil and water. Remotely-derived estimates of NDVI were consistent between the UAV and Landsat imagery, supporting the application of a biomass estimation model to the Landsat archive. We assessed long-term biomass dynamics in several salt marshes in Southern California, where we found a strong seasonal pattern in NDVI. Sea levels and drought were identified as key drivers throughout the region, indicating that regional environmental variability, i.e., the Moran effect, was the dominant process affecting synchrony at larger spatial scales. However, some sites exhibited variable response to these drivers over time, suggesting the importance of local factors in determining marsh biomass and productivity. As rising seas and a warmer, drier climate threaten many coastal areas worldwide, these insights into the spatial synchrony of regional salt marsh biomass are valuable indicators of future resilience to climate change.