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A partial reduction in the quantity of nutrients reaching the Gulf of Mexico, particularly nitrate–nitrogen, can be accomplished through several general approaches and specific techniques (Table 2). These include modification of agricultural practices, construction and restoration of riparian zones and wetlands as buffers between agricultural lands and waterways, control of urban and suburban nonpoint sources, use of environmental technologies such as tertiary treatment at point sources, and deployment of controls on atmospheric sources.

Precipitation has a great effect on the timing of nitrate–nitrogen exports from crop fields in the Mississippi River Basin, particularly in the case of nitrate–nitrogen that is discharged through subsurface drains. Dry years can result in very low levels of nitrate–nitrogen discharge. Wet years, particularly if they follow one or two dry years, can result in very large discharges of nitrate …