To assess historical loads of nitrogen (N), phosphorus (P), and suspended sediment (SS) from the
nontidal Chesapeake Bay watershed (NTCBW), we analyzed decadal seasonal trends of flow-normalized loads at
the fall-line of nine major rivers that account for >90% of NTCBW flow. Evaluations of loads by season revealed
N, P, and SS load magnitudes have been highest in January-March and lowest in July-September, but the temporal
trends have followed similar decadal-scale patterns in all seasons, with notable exceptions. Generally, total
N (TN) load has dropped since the late 1980s, but particulate nutrients and SS have risen since the mid-1990s.
The majority of these rises were from Susquehanna River and relate to diminished net trapping at the Conowingo
Reservoir. Substantial rises in SS were also observed, however, in other rivers. Moreover, the summed rise
in particulate P load from other rivers is of similar magnitude as from Susquehanna. Dissolved nutrient loads
have dropped in the upland (Piedmont and above) rivers, but risen in two small rivers in the Coastal Plain
affected by lagged groundwater input. In addition, analysis of fractional contributions revealed consistent N
trends across the upland watersheds. Finally, total N:total P ratios have declined in most rivers, suggesting the
potential for changes in nutrient limitation. Overall, this integrated study of historical data highlights the value
of maintaining long-term monitoring at multiple watershed locations.
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION Vol. 51 No. 6 p 1535 - 1555