Soil Management Strategies Mitigate Extreme Weather

Can Soil Management Strategies Mitigate Extreme Weather?

mississippi floodsWritten just 2 years after Hurricane Katrina hit, Manale (2007) describes the importance of soil carbon in flood control:

What does soil carbon have in common with Hurricane Katrina, ….the Great Upper Mississippi Flood of 1993, and the Red River Flood of 1997?  For each of these extreme weather and flooding events, substantial investments in soil carbon, and thus soil organic matter in upland and coastal soils, could have saved the public both trouble and money.”

As I watch the floods currently unfolding in Missouri, I couldn’t help thinking that we continue to fail to grasp the link between landscape processes and ecosystem services.   Put simply, an ecosystem service is the process of valuing an ecosystem asset by the services provided by the ecosystem.  In this case, it is the value of soil carbon to flood mitigation.  We cannot prevent extreme weather events from occurring, but we can mitigate their social and environmental impacts but increasing the carbon content of agricultural soils.

Soil carbon, and resultant soil organic matter, acts a sponge by absorbing up to six times it’s weight in water, and functions like a glue that causes soil to clump and form aggregates improving soil structure and permeability. As such, a greater proportion of precipitation is retained in the soil with less runoff contributing to down-stream flow.

The modification of landscape by human activity results in a large loss of soil carbon.  Lands in areas with recurrent flooding often have lost the ability to manage extreme weather events – an important ecosystem service.  This decline in natural resilience can lead to greater and more costly impacts on society.  Conversely, watersheds containing large portions of land with carbon-rich soils (e.g. wetlands) have the lowest flood risk, higher quality resources and higher levels of biodiversity (NRC, 2005).

red river basinManale (2007) calculated that for the loamy, relatively poorly drained soils of the Red River Basin of North Dakota and Minnesota, increasing soil organic matter by 1% results in a 2.5% increase in volume of water retained in the soil.  Extending to a depth of 6 inches, this translate to a 0.03 acre-foot per acre increase (37.5 cubic meters per hectare for my metric friends).  Based on numbers reported by Manale (2007) there are 14,803,260 acres of cultivated soils in the North Dakota and Minnesota portions of the watershed – this equates to a lot of additional water storage.

Soil Carbon and Water Storage (Manale, 2007)

Additional Soil Organic Matter

Additional Soil Carbon Acre-feet of Water per Acre Cubic Meters of Water per Hectare

1%

0.57% 0.03

37.5

2%

1.14% 0.06

75

3% 1.71% 0.09

112.5

With respect to Hurricane Katrina, storm surges overwhelmed the dyke and levee system of New Orleans.  Over one million acres (as of 2007) of coastal wetlands have been lost since the 1930s.  A mile of restored coastal wetland could have reduced the storm surge by between 1 and 3 inches.  Assuming a 100 miles of coastline to protect with a 16-mile-wide buffer could provide between 4 and 16 feet of surge protection.

Managing agricultural landscapes to maintain and restore soil carbon provides multiple benefits to both the environment and society, including temporary storage for flood mitigation.  The technologies and systems for protecting and enhancing soil carbon are known and feasible.  What is needed are the policies that lead to their adoption.

References

Manale, A., 2007, Soil Carbon and the Mitigation of the Risks of Flooding, in J. Kimble, C. Rice, D. Reed, S. Mooney, R. Follett, and R. Lal, eds., Soil Carbon Management and Societal Benefits: Boca Raton, CRC Press, p. 199-207.

NRC, 2005, Valuing Ecosystem Services, Washington, DC, National Research Council, p. 290.

 

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