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Study Addresses Need for Clean-Water Sediment Goals

By Luis Pons
December 4, 2003

When Agricultural Research Service scientists were called upon in 2002 to study sediment's effects on a Mississippi waterway, they took things a step further and tested techniques aimed at helping states comply with a key provision of the federal Clean Water Act.

In surveying James Creek in northwestern Mississippi, researchers from the ARS Channel Watershed and Processes Research Unit (CWPRU) coupled computer modeling with river-related geologic studies to determine how soil erosion and sediment loading within a watershed change over time. CWPRU is part of the ARS National Sedimentation Laboratory in Oxford, Miss.

According to research leader Carlos Alonso, his unit's work may help many states set and meet standards for the total maximum daily loads (TMDLs) of sediment their waterways can contain before being considered polluted.

The Clean Water Act requires states to identify pollution-impaired water bodies and develop plans for meeting TMDL requirements. TMDLs specify the amount of a pollutant a water body can receive and still meet quality standards set for its designated use by states, territories and tribes. Compliance is monitored by each state in concurrence with the U.S. Environmental Protection Agency.

Of all pollutants requiring TMDLs, none is as prevalent--or as potentially damaging--as sediment, which causes about $16 billion annually in damage to North American waterways, according to Alonso.

A 90-day analysis of the sediment-impaired creek was requested by Mississippi officials to develop the federally mandated water-quality targets there.

The ARS unit is already applying the integrated method of computer modeling coupled with geologic studies to projects in Alabama, California, Kansas, Michigan and elsewhere in Mississippi.

Citizen concern and court challenges have propelled recent action regarding TMDLs. A lack of proven methods for defining how much sediment constitutes pollution has contributed to past delays, according to Alonso.

Read more about this research in the December issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.