These are average nutrient “loads” from various sources to local streams as estimated by the Watershed Model, except for point sources, which are based on discharge data, For land uses, two key factors affect runoff amounts: the amount of nutrient runoff per acre and the number of acres. Forests generate less nutrients per acre than other uses, but cover more area, making them a relatively large nutrient source. Other land uses contribute more per acre, but cover less area. Pounds per acre changes reflect improved runoff control efforts or improved estimates.

Forest/Wooded

Any woodlot larger than 28-by-28 meters, including forests, parks, and even trees in a highway median strip. A large part of forest nitrogen runoff is thought to stem from air pollution.

Nitrogen (pounds per acre):

1985: 1.69
2003: 1.75

Change: 4.06%

Phosphorus (pounds per acre):

1985: 0.02
2003: 0.02

Change: 4.25%

Total Acres:

1985: 22,970,000
2003: 23,495,000

Change in acres: 2.29%

Crop

All cropland, including corn, soybeans, small grains, hay, and lands using conservation and conventional tillage.

Nitrogen (pounds per acre):

1985: 15.93
2003: 13.22

Change: -17.01%

Phosphorus (pounds per acre):

1985: 1.04
2003: 0.88

Change: -15.77%

Total Acres:

1985: 7,018,000
2003: 6,304,000

Change in acres: -10.17%

Other Agriculture

This includes everything related to animal agricultural activities, from low-runoff pasture land to high-runoff feedlots.

Nitrogen (pounds per acre):

1985: 10.41
2003: 8.56

Change: -17.75%

Phosphorus (pounds per acre):

1985: 1.18
2003: 1.13

Change: -4.62%

Total Acres:

1985: 3,609,000
2003: 2,906,000

Change in acres: -19.47%

Septic

Buildings not hooked into sewer systems typically have septic systems. Traditional systems do little to remove nitrogen. Phosphorus from septic systems does not reach waterways.

Nitrogen (total pounds basinwide):

1985: 10,108,000
2003: 12,220,000

Change: 20.90%

Urban

An average of all runoff from developed areas, including suburban, urban, industrial and commercial land uses, and roads.

Nitrogen (pounds per acre):

1985: 9.69
2003: 7.98

Change: -17.66%

Phosphorus (pounds per acre):

1985: 1.18
2003: 0.82

Change: -30.37%

Total Acres:

1985: 3,152,000
2003: 3,825,000

Change in acres: 21.34%

Point Sources

Point sources are discharges delivered directly to streams from the end of a pipe. Most are from wastewater treatment plants, some are from industrial activity.

Nitrogen (total pounds basinwide):

1985: 87,721,000
2002: 61,156,000

Change: -30.28%

Phosphorus (total pounds basinwide):

1985: 9,173,000
2002: 4,518,000

Change: -50.75%

Mixed Open

This includes land with low levels of development and low population densities that are not in agricultural use.

Nitrogen (pounds per acre):

1985: 4.47
2002: 4.39

Change: -1.77%

Phosphorus (pounds per acre):

1985: 0.54
2002: 0.54

Change: 1.03%

Total Acres:

1985: 3,937,000
2002: 4,155,000

Change in acres: 5.55%

Air to Water

Most air pollution is included in the land use category where it comes down. But some lands directly on rivers, lakes and reservoirs and has its own category.

Nitrogen (pounds per acre):

1985: 8.23
2002: 8.36

Change: 1.67%

Phosphorus (pounds per acre):

1985: 0.37
2002: 0.38

Change: 4.10%

Total Acres: 424,000