Sources of "new" mineral nutrients into Chesapeake Bay

Average rainfall year

Nitrogen Phosphorus

EPA Cor. EPA EPA EPA Cor. EPA EPA

1978 1987 1995 1999 1978 1987 1995 1999

point source 33% 25% 23% 22% 61% 73% 34% 25%

nonpoint source 67% 75% 77% 78% 39% 27% 66% 75%

atmosphere 9% 11% 21% 5% 6% 9%

land 65% 66% 57% 22% 60% 66%

atmos as a % of nps 12% 14% 27% 18% 9% 12%

land as a % of nps 87% 86% 73% 82% 91% 88%

ocean water no estimates no estimates

nitrogen fixation no estimates

Nonpoint sources of mineral nutrients into Chesapeake Bay

physiographic province area nitrogen phosphorus kg N/ha kg P/ha

(Correll, 1987) (EPA, 1995)

coastal plain 19% 13% 66% 2.6-3.8 0.79-0.91

piedmont/ridge 81% 87% 34% 5.2 0.1

and valley

land use (EPA, 1995) area, as % nitrogen, as a % of phosphorus, as a % of

of basin total new land nps total new land nps

agriculture 31% 39% 59% 49% 82%

forest 60% 18% 27% 3% 5%

urban/suburban 10% 9% 14% 8% 13%

land use (EPA, 1995) nitrogen phosphorus sediment

% of basin area lbs/ac/yr lbs/ac/yr lbs/ac/yr

forested 60% 3 0.1 50

pasture 9% 7 0.2 700

urban 10% 10 0.2 1300

cropland

/riparian 22% 16 1.7 3200

Point sources of mineral nutrients into Chesapeake Bay (EPA, 1978)

type of point source nitrogen phosphorus

publicly owned sewage

treatment works 80% 88%

industrial effluent 20% 12%

effect of amount of rainfall

dry year dry year

point 38% 69%

nonpoint 62% 31%

average year average year

point 33% 61%

nonpoint 67% 39%

wet year wet year

point 19% 36%

nonpoint 81% 64%