Water quality monitoring in major watersheds — the Susquehanna, Potomac, James, Rappahannock, Appomattox, York, Patuxent and Choptank — generally found no nutrient trends in nutrient loads between 1985 and 1998. The exception was that nitrogen was up in the Choptank and down in the Patuxent. Also, phosphorus was down in both the Patuxent and the Susquehanna.
When the effects of flow were factored out, the data suggested a downward nitrogen trend in six of nine major basins: the Susquehanna, Patuxent, Rappahannock, Mattaponi (a tributary of the York), James and Appomattox. Phosphorus trends were down in seven of nine basins: the Susquehanna, Choptank, Patuxent, Potomac, Rappahannock, Mattaponi, and James.