Marshes reduce storm flooding, filter contaminants out of water and provide habitat for birds, fish and other wildlife. However, these environmentally critical areas have decreased in extent along the coast in recent decades, and UD researchers are working to better understand the factors that affect marsh stability—especially in the face of sea level rise.
“The amount of space that’s available for marshes to survive is getting smaller and smaller,” says Christopher Sommerfield, associate professor of oceanography in the College of Earth, Ocean, and Environment (CEOE).
Tidal marshes exist in low-lying coastal areas between the low and high tide lines. On the landward edge, marshes often abut farms and developed properties. On the ocean side, they face increasingly higher sea levels—creating a “coastal squeeze” for space.
Too much water can drown out the tall grasses and other vegetation characteristic of marshes, potentially turning them into embayments and accelerating inundation.
Sommerfield is researching the critical role of sediment flow in tidal marsh health. Marshes grow vertically as muddy sediment is carried in from rivers and other sources, raising the landscape by a combination of sedimentation and plant growth. The process, called accretion, keeps marshes at or above sea level when undisturbed.
“The elevation of a marsh landscape relative to mean sea level is controlled by a balance between upward accretion at the surface and downward sinking of deeper strata,” Sommerfield explains.
Sommerfield is measuring accretion rates at coastal and estuarine marsh sites in the Mid-Atlantic region using radionuclides, or variants of elements emitting radiation, as a chronological tool.
Naturally occurring and manmade radionuclides enter estuaries through precipitation and other sources, attaching to particles