By the USGS Pacific Coastal and Marine Science Center
Erosion of marsh boundaries by waves is a major cause of marsh loss, but little research has captured the effect of seasonal differences on marsh-edge retreat. A new study conducted by scientists at the United States Geological Survey (USGS) and the University of California, Berkeley, shows how seasonal climate variations influence the rate of marshland erosion due to wind-driven wave activity.
The study, published in the Journal of Geophysical Research: Earth Surface, focused on Whale’s Tail Marsh South in South San Francisco Bay. The researchers constructed five detailed 3D models of the marsh surface using aerial photos collected with a fixed-wing aircraft and photogrammetry techniques, capturing its state during summer, fall, winter, and spring over a single year. By comparing these models, they observed distinct variations in marsh loss depending on the season:
- Spring and Summer: The rate of marsh loss was notably high during these seasons, characterized by strong daily winds. The constant wave action generated by these winds led to accelerated erosion at the marsh boundaries.
- Fall and Winter: In contrast, during the stormier fall and winter months, the rate of marsh loss was considerably slower. Despite the presence of storms, the absence of persistent daily winds resulted in less erosive wave activity.
Interestingly, the researchers also detected some positive changes during the fall and winter, with minor additions to the nearby mudflats. This suggests that under certain conditions, sediment deposition can occur, partially offsetting erosional losses.
When comparing the annual marsh loss data to historical data from 2004 to 2019, the researchers found a consistent pattern, indicating that their one-year study accurately reflected long-term marsh dynamics.
As climate change continues to impact coastal regions worldwide, understanding these seasonal variations will be essential for safeguarding marshland ecosystems, which are vital for coastal protection, biodiversity, and carbon sequestration.
