systems across the country, sediment is recognized as a pollutant, with significant federal and state program efforts in place to keep sediment out of streams, rivers, and lakes. Therefore, in considering actions to reintroduce sediment to the Missouri River, it is important to recognize the historic sediment volumes, sources and characteristics when defining water quality criteria and regulations for the Missouri River watershed.

In considering the full range of implications of the Corps of Engineers habitat projects along the Missouri River, it is therefore important to understand not only provisions of the Endangered Species Act, but also provisions of the Clean Water Act—especially setting water quality standards for sediment and phosphorus concentrations.

This chapter responds to two questions in this report’s statement of task:

  • What is the significance of the Missouri River sediments to the Gulf of Mexico Hypoxia problem? (Question 2), and

  • What are the key environmental and economic considerations regarding nutrient loads and/or contaminants in Missouri River sediment? To what extent can such issues be addressed with management strategies? (Question 4)

The first section of this chapter discusses potential effects of enhanced Missouri River sediment transport and associated phosphorus loads on hypoxia in the Gulf of Mexico. The following sections focus on setting water quality criteria for sediments and nutrients that will be protective of designated uses. The historical sediment and phosphorus loads in the basin and prior to the construction of the Pick-Sloan mainstem dams are discussed as context for setting nutrient (phosphorus) and sediment criteria as required by the Clean Water Act. The discussion provides a logic for setting of such criteria in ways that meet the requirements of the Clean Water Act and that can be compatible with ongoing and possible future Missouri River sediment management activities dictated in part by the Endangered Species Act. The chapter concludes with a discussion of the need for improved monitoring of sediments, nutrients, and other chemical constituents in sediments discharged into the river.

POTENTIAL WATER QUALITY EFFECTS IN THE GULF OF MEXICO

Northern Gulf of Mexico Hypoxia

Nitrogen and phosphorus delivered from the Atchafalaya and Mississippi rivers to the northern Gulf of Mexico combine with conditions of tempera-



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