The study, “Optimum vegetation height and density for inorganic sedimentation in deltaic marshes,” reveals an intermediate amount of vegetation is the optimum level to stabilize river deltas.
The study’s authors are assistant professor Douglas A. Edmonds and former postdoctoral fellow William Nardin, both in the Department of Geological Sciences.
Nardin relocated to Boston four months ago, but said he is still working on vegetation and deltas.
Edmonds said the study was prompted by the recognition of endangered river deltas, which are landforms that form at the mouth of rivers where they empty into larger bodies of water.
“Sea level rise is threatening to drown the river delta,” he said.
Edmonds said the presence of sediment — sand and mud — in the endangered river deltas is critical to the delta’s preservation because it prevents their drowning in the sea water.
“Sediment is sort of the lifeblood of the river delta,” he said.
Edmonds explained that when sediment is delivered, the positive outcome is that it will be retained in the river delta, and the negative outcome is that it will go right through the delta and exit to the ocean.
“Anything we do to disrupt the natural environment limits the amount of sediment that gets down to the river delta,” he said.
River deltas often house large and complex ecosystems and are home to about 10 percent of the world’s population, according to a press release.
Edmonds said vegetation in the river deltas physically slows down the flow of water and increases the deposit of sediment.
According to a press release, Edmonds and Nardin conducted 75 simulations with varying combinations of vegetation height, density and water flow rates to see how exactly vegetation affects sediment transport and deposition.
Edmonds said the process took about a year and a half and the results were surprising, Edmonds said.
“You might predict that the more plants the better, but it actually doesn’t work that way,” he said.
Edmonds explained that if there is too much vegetation on the delta, the sediment bypasses the delta and stays in the river channels.
Edmonds said scientists call the kind of results revealed in his study the Goldilocks principle.
“You can’t have too much or too little,” he said. “It has to be just right.”
