The next highest 200 watersheds are shown with a slightly lighter color, and so on. Caveats Analyses do not show which watersheds will have water quality impairments related to agricultural production. The simulation models estimate soil loss, chemical loss, or vulnerability indexes for conditions at the edge of the field and the bottom of the root zone. Not included in the indicators are dynamics of fate and transport from the farm field to a water body. Dilution from runoff and recharge on noncropland areas in the watershed will also reduce the potential for actual water quality impairments.
Maps provide a relative ranking among watersheds.
It is not known how the class breaks relate to observed water quality problems. Farm management practices are not included in the determination of the indicators. Research has shown that soil, chemical, and water loss from farm fields can be substantially reduced by management practices. Where these practices are being used, the potential estimated by these indicators will be over-estimated. Where indicators are based only on the major crops, watersheds with large acreage of other crops may be mis-represented.