Article explores how marsh sediments shape and affect river deltas
River deltas and their adjacent wetlands are threatened by rising sea levels and decreasing river sediment loads. Better understanding how coastlines along river deltas are created and maintained will be key to preserving and even restoring them in the future.
A recent paper led by alumnus Kelly Sanks, a U of A geoscience PhD student at the time of writing, aimed to deepen our understanding of how marsh sediments shape and affect river deltas. Among its co-authors was U of A geoscience associate professor John Shaw.
River deltas like the Mississippi Delta are constructed by sediments in different ways. One of them is through the rivers, which form huge lobes of sand on which cities like New Orleans are built. Another way is through the swamps, where mud and organic detritus accumulate in wet, spongy sponges that cover thousands of square miles.
Although it is clear that both types of sediment accumulation are important, it was not known how these two types of accumulation interacted for thousands of years. To better understand, Sanks and his colleagues built an experimental river delta at Tulane University. Sediment Dynamics Laboratory. In the lab, they ran a small river of water and sediment in a science-grade tub that represented both river and swamp accumulation.
Surprisingly, the team found that a small addition of marsh sediment (about 8% of the mass of the system) nearly doubles the area of marsh on a river delta. This is because the accumulation of marshes tends to flatten the slopes of a river delta, leading to a larger area near sea level that can support marshes. The article argues that this feedback could explain the existence of the huge delta plains that exist on many river deltas around the world.
For example, the Mississippi Delta has more than 5,000 square miles within a few feet of sea level. These regions are susceptible to the adverse effects of sea level rise and decreased sediment input by due to dams and dykes. Since the marsh sedimentation experiment is a better representation of the world’s deltas, the results can help improve future coastal restoration and management plans that typically rely on the successful distribution and retention of river sediments.
“This project is a unique product of Kelly’s strong background in marsh science and my research program focused on river deltas,” Shaw said. “This would never have happened without the will to combine these complementary forces.”
The paper, titled “Marsh sedimentation controls the morphology, slope and mass balance of the top of the delta,” was published in the journal of the American Geophysical Union, Geophysical Research Letters. Sanks received the Distinguished Dissertation Award from the U of A in May 2022. The work of this paper was central to this dissertation and was funded by the National Science Foundation as part of a collaborative project between the University from Tulane and co-authors from the U of A. Sanks. also included SM Zapp, JR Silvestre, R.Dutt and KM Straub.
Sanks has completed his doctorate. in December 2021 and is now a postdoctoral researcher at Tulane University studying carbon accumulation in deltaic environments.
About the Department of Geosciences: The Department of Geosciences has its origins in 1873 when the first mineralogy course was offered at the University of Arkansas. Our faculty and students examine the processes that form and shape the Earth’s surface, the natural resources we use, how water and ecosystems are interconnected, variations in climate and paleoclimate, the use and development of geospatial methods and the human geography of ethnicity, gender, social class, social inequalities and religion. The department won $2 million in research grants in fiscal year 2020, and our students benefit from more than $3 million in scholarships donated by generous alumni and friends of the department. To learn more about the Department of Geosciences, please visit our website.