Sep 03, 2008

Harnessing the Power of Nature

One of the best ways to help control what Mother Nature throws at us is using what Mother Nature has made, thus harnessing her power and using it for a greater purpose.

Stabilized organic matter, such as compost, has been used for millions of years as one of nature’s principle measures to filter rain and storm water in the world’s soil and terrestrial ecosystems. Compost and composted mulch are mostly organic matter, and approximately 60 percent to 80 percent of the stable organic matter content in compost is in the form of humus. Humus, organic matter and compost have each been well documented in scientific research literature as effective pollutant filtration devices, evaluated by sediment reduction and absorption of contaminants in soil and storm water.

Compost wood chips and socks stabilize a steep, eroding slope.

Soluble Pollutants

Vegetation and topsoil are the skin of the earth; when they are removed through construction activities, the exposed earth bleeds sediment every time it rains. In 1998, the U.S. Environmental Protection Agency (EPA) national water quality assessment stated that 35 percent of streams were found to be severely impaired, while nearly 75 percent of the U.S. population lives within 10 miles of an impaired water body. Since 1995, pathogens, metals and nutrients have been the three most frequently cited total maximum daily load (TMDL) water-impairing pollutants, respectively, and also are the first, fourth and fifth leading causes of impaired water quality, according to the EPA. These pollutants are often attached to sediment; however, research has indicated that sediment-bound pollutants can quickly become desorbed, therefore transforming into soluble pollutant forms.

Where sedimentation is minimal because of effective erosion control or stabilized post-construction surfaces, soluble pollutants can be more than 80 percent of the total pollutant load, according to researchers. In order to protect and improve receiving water quality, BMPs need to reduce soluble pollutant loading. This is particularly important around soils where fertilizers have been applied for vegetation establishment, around impervious surfaces that typically transport metals, hydrocarbons and harmful bacteria in storm water and where water bodies have been designated to meet TMDL requirements.

Compost Filter Media

Filtrexx Intl., Grafton, Ohio, produces a line of netting products that can be used with certified compost filter media for erosion and sediment control. Scientific evidence is showing that the benefit of using certified compost filter media goes far beyond simple sediment control. Recent research is showing that this eco-friendly technology has the ability to filter soluble pollutants, typically found in storm water flows originating from urban and suburban post-construction surfaces, such as roadways, parking lots and rooftops. The humus fraction of the certified compost filter media has the ability to chemically absorb free ions, such as soluble phosphorus (P) and ammonium nitrogen (N).

A compost-filled sock protects an inlet.

The U.S. Department of Agriculture Agricultural Research Service recently reported removal efficiencies for compost-filled sock tubes between 14 percent and 28 percent for soluble P, and between 1 percent and 17 percent for nitrite-nitrate N. Researchers have also reported minor removal concentrations between 1 and 7 mg L-1 for nitrate-N and total P, and motor oil removal efficiencies between 85 percent and 99 percent when initial runoff concentrations of motor oil ranged between 1,000 and 10,000 mg L-1.

Dioten Engineering, Rapid City, S.D., uses Filtrexx’s sediment control devices exclusively. There is a great need for erosion and sediment control devices that capture sediment but are also eco-friendly. The compost inside the socks effectively stops the sediment, and all other soluble pollutants the compost captures will become more important as regulations tighten. Most other sediment control devices being used are concrete, man-made alternatives that could not be further from mimicking nature. The old, dilapidated silt fences often seen sticking out of fully vegetated fields or lots are hardly an effective way to harness and use nature’s power.

Compost use helps to mimic nature, minimize the impacts of man-made activities and return sites to preconstruction hydrologic conditions. It minimizes negative impacts from human activities while bandaging and repairing the earth. There is great power to be harnessed from a pile of composted leaves, grass and brush. What greater purpose is there for compost than using what Mother Nature has already given us to protect natural resources?

About the author

Dion Lowe, P.E., is president of Dioten Engineering Inc. Lowe can be reached at 605.430.7213 or by e-mail at [email protected].

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