Levels of control in place in 1985 were applied to the year 2000 point source flows and land use. The linked models predict that in basins where atmospheric deposition of nitrate is highest, such as the Susquehanna and Potomac basins, reductions in nitrogen delivered to the Bay is greatest. In the case of the Susquehanna, nitrogen load reductions under implementation of the Clean Air Act are greater than the current limits of technology for point source and nonpoint source controls. Although the primary objective of the OTC is to reduce harmful levels of ozone in the mid-Atlantic and New England states, the nitrate emission controls called for under the OTC plan will also reduce nitrate loads delivered to the Bay by a further 9 million kilograms over an above the Bay Agreement reduction. A portion of all nonpoint source loads are due to atmospheric deposition.
Pasture receives no fertilizer input, but does receive manure inputs from pastured animals.
Forest inputs of nitrogen are solely from atmospheric sources. Thirty seven percent of the forest nonpoint source load is due to atmospheric deposition. Urban inputs of nitrogen include fertilizers, septic systems, and atmospheric deposition. Finally, direct deposition of atmospheric deposition to nontidal water surfaces are accounted for within the watershed. Conclusion Quantification of the total loads to the Chesapeake has changed the view that the watershed is the definitive source of nutrient loads.