Reforestation Along Mississippi River Will Reduce Agricultural Runoff, Revive Gulf of Mexico

A proactive reforesting effort in the Lower Mississippi Alluvial Valley would lead to a significant reduction of agricultural runoff and sediment flowing into the area's streams, rivers and, ultimately, the Gulf of Mexico, according to new research by the US Forest Service.

The Lower Mississippi Alluvial Valley is one of the largest river basins in the world. The Lower Mississippi River runs more than 1,000 miles from its starting point in Cairo, Ill. southward to the Gulf of Mexico. The floodplain along the river has consistently been hit hard by erosion, sediment disposition and flooding, all of which have been tied to centuries of converting bottomland hardwood forests into agricultural lands.

These agricultural lands frequently flood, and the floodwater carries with it not only sediments from the land, but notable amounts of agricultural pesticides and fertilizers, which contribute to the formation of hypoxic regions - no oxygen "dead zones" - in the Gulf of Mexico.

The US Forest Service study, which is published in the journal Ecological Engineering, uses a model to show that reforesting the areas that lie between the Mississippi River and its levees, known as battures, would lead to a reduction in sediment load from flooded agricultural lands. The researchers behind the modeling study contend that the battures would be a prime site for a reforesting effort.

"Comparing simulation results with and without reforestation showed that converting agricultural lands close to streams into forests would greatly lessen water outflow and reduce the effects of sediment load as far as the Gulf of Mexico," said lead study author Ying Ouyang, who works as a research hydrologist at the SRS Center for Bottomland Hardwoods Research in Stoneville, Miss. 

For their study, the researchers focused on two Lower Mississippi Alluvial Valley watersheds: the large Lower Yazoo River Watershed and the smaller Peters Creek Watershed. The models charted the effects of reforestation in or near battures along the floodplains, focusing on water outflow and the amount of sediment carried by the the water, known as the sediment load.

The researchers modeled the water outflow and sediment load without reforestation, then re-ran the model over a 10-year period to test the potential impacts of reforestation at different levels. Reforestation along the battures was simulated in quartiles at 25 percent, 50 percent, 75 percent and 100 percent.

"In general, the larger the area converted, the greater the effect. For the Lower Yazoo River watershed, a two-fold increase in forest land area would result in approximately a two-fold reduction in the annual volume of water outflow and the mass of sediment load moving into the river."

"In general, the larger the area converted, the greater the effect," Ouyang said in a news release. "For the Lower Yazoo River watershed, a two-fold increase in forest land area would result in approximately a two-fold reduction in the annual volume of water outflow and the mass of sediment load moving into the river."

Carlton Owen, president and CEO of the US Endowment for Forestry and Communities - which is the organization that commissioned this study - said: "This study provides further evidence of the key role forests play in flood control and in reducing sediment flow from agricultural lands into our watersheds.

"The new forest areas would also provide regional economic and environmental benefits by not only improving water quality but also wildlife habitat and recreational opportunities."