Goldilocks Plant Growth May Make River Deltas Resilient

Research by Indiana University geologists suggests that goldilocks plant growth - not too little and not too much - may make river deltas resilient to environmental factors that threaten their existence.

This "just right" amount of vegetation is the most effective way of stabilizing these freshwater areas, such as those near the mouth of the Mississippi River, which are under threat as sea levels rise.

Vegetation on marsh surfaces in river deltas can slow the flow of water and cause more sediment to be deposited, helping prevent sea-level rise from drowning marshlands. However, the study finds that vegetation that is too tall or dense can just as well divert water into the river channel, resulting in less sediment being deposited on the marsh.

"In river deltas the effect of vegetation on sedimentation seems to follow the Goldilocks principle," researcher Douglas A. Edmonds said in a statement. "You want the amount of vegetation that is just right - not too much, but also not too little."

The world's river deltas, which are home to about 10 percent of the world's population, are threatened by a variety of factors, including population growth, pollution, development and erosion, as well as sea-level rise associated with climate change.

But this new study suggests that vegetation could play a role in designing effective river delta restoration.

To figure out if vegetation can effectively increase sedimentation, researchers used computer modeling to create 75 simulations of varying scenarios of vegetation height and density and rates of water flow. They found that vegetation of intermediate height and density, or the "goldilocks" point, results in the greatest deposition of sand and mud.

One snag in this idea is that while "just right" plant growth may produce the optimal amount of sediment, the rate at which sediment is delivered to marshes in river deltas is strongly influenced by storms and flooding, which is often unpredictable.

"That unpredictability adds an interesting twist to the problem," Edmonds added.

The research was published in the journal Nature Geoscience.