|Manure Nitrogen Runoff Vulnerability Index|
|Source: Natural Resources Conservation Service|
A watershed index score for the runoff potential for manure nitrogen was calculated by multiplying the total manure nitrogen estimate for the watershed times the average 12-month runoff factor for the watershed. The average runoff factor was based on values for all non-Federal rural land.
A variety of algorithms were used to create watershed values, generating a variety of units (pounds per watershed, index scores per watershed, etc.). To facilitate comparisons among the maps, the classes shown in each map were based on a consistent set of watershed rankings. The 200 watersheds with the highest scores are shown with the darkest color. The next highest 200 watersheds are shown with a slightly lighter color, and so on.
Taken from a poster presentation at the 52nd Annual SWCS Conference (July 1997), "Potential Priority Watersheds for Protection of Water Quality from Nonpoint Sources Related to Agriculture" by R.L. Kellogg, S. Wallace, K. Alt, and D.W. Goss. Revised October 1997.Cautions for this Product:
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. For Further Information: