Soil type plays larger role in wetland erosion

New research could assist ecologists in managing erosion of coastal wetlands, but it bucks the theory that plants can directly mitigate soil loss during hurricanes and other natural disasters.

Dr. Rusty Feagin, a Texas AgriLife Research ecosystems management scientist, and a group of researchers discovered soil type plays a much larger role in preventing erosion along wetland edges rather than salt marsh plants.

“This study is part of a broader perspective in that the key is we can’t expect these plants to stop soil erosion during something like Hurricane Ike,” said Feagin, whose findings were published online in the Proceedings of the National Academy of Sciences.

“A lot of people are pushing this idea, but the research doesn’t show that," he said. "It shows (the plants) don’t even stop erosion on little waves, but we still need to keep these areas vegetated because wetlands, dunes and other coastal ecosystems build land, and those plants capture sediment in the long term.”

Wetlands have great value to Texas, Feagin said, attracting tourists for hunting and fishing, kayaking and other recreational activities.

One possible solution to protecting them is to build permeable barriers, he said.

“What has been done in the past is to build a non-permeable bulkhead or geotube, essentially a large sand sock. Nearly half of Galveston Island is ringed with these things,” he said. “That has stopped the waves from eroding the wetlands, but the problem is that we have essentially sealed off the open water connections with the bay. You’ve walled it off, it becomes sediment starved, it begins to drop in relative elevation, and there begins to be long-term sea level rise problems.”

A solution is to build many small gaps in the barrier that allow water to flow into the marsh, creating a more natural flow of water, sand and other nutrients, he said.

Feagin and the group of researchers challenged “the paradigm that saltmarsh (salt marsh) plants prevent lateral wave-induced erosion” along wetland edges by binding soil with live roots.

Observations were made that erosion appeared to be “most prominent during the draw-down (backwash) of the wave cycle, rather than during the swash of an oncoming wave,” according to the report.

In its summary, the researchers recommend that “efforts toward salt marsh restoration, a multi-billion dollar endeavor, should place the highest priority on obtaining the correct soil rather than on planting vegetation in areas that are subject to high-wave energy."

However, in the report the researchers also suggest vegetation should be used to modify the soil so it may become more resistant to erosion over the long term.

The work can be found at PNAS.

TAGS: Management
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