Salt marshes, critical buffers against coastal erosion, rely on a net gain of sediment to maintain their elevation and resilience as sea levels rise. A new study examines how two different sediment delivery routes—wave-battered marsh edges and meandering tidal creeks—combine to shape the future of these vital ecosystems.
By the USGS
Focusing on Whales Tail Marsh in South San Francisco Bay, which features both an eroding bay-facing edge and a major tidal creek, researchers deployed net-deposition tiles and oceanographic sensors to track when, where, and how sediment moved into and through the marsh.
The results show a seasonally split system:
- Summer: Strong daily sea breezes stirred up sediment in the bay shallows, driving wave-induced erosion and higher sediment concentrations in the water. This led to greater sediment import during summer months.
- Winter: Weaker winds dominated, punctuated by occasional storms, reducing overall sediment delivery and leading to net sediment export during this season.
While creek inflows supplied the bulk of sediment over time—feeding large portions of the marsh interior—the bay edge acted as a variable and sometimes intense sediment source, especially during windy periods. Sediment tended to erode near the bay edge, accumulate near creeks, and slowly migrate inland toward the marsh center.
Importantly, the study found that even though the marsh showed a net sediment gain on an annual scale, it was still experiencing rapid lateral erosion along its edges. In other words, higher sediment input doesn’t necessarily translate to a stable marsh; erosion at the edges can outpace sediment gains in the interior, leading to marsh loss despite a positive sediment budget.
The findings highlight the need to consider both tidal creeks and wave-exposed edges in models and management plans for marsh restoration. As sea-level rise and changing wind patterns reshape coastal dynamics, a better understanding of these sediment pathways will be key to sustaining marshes that protect shorelines, store carbon, and support wildlife.
Read the study, Comparison of creek and bay influences on salt marsh sediment budget and deposition patterns, in Earth Surface Processes and Landforms.
