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INPUTS, TRANSFORMATIONS, AND TRANSPORT OF NITROGEN AND PHOSPHORUS IN CHESAPEAKE BAY AND SELECTED TRIBUTARIES
Citation:
Boyton, W., J.H. Garber, R. Summers, AND W. Kemp. INPUTS, TRANSFORMATIONS, AND TRANSPORT OF NITROGEN AND PHOSPHORUS IN CHESAPEAKE BAY AND SELECTED TRIBUTARIES. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-95/426.
Description:
In this paper we assemble and analyze quantitative annual input-export budgets for total nitrogen (TN) and total phosphorus (TP) for Chesapeake Bay and three of its tributary estuaries (Potomac, Patuxent, and Choptank rivers). he budgets include estimates of TN and TP sources (point, diffuse, and atmospheric), internal losses (burial in sediments, fisheries yields, and denitrification), storage in the water column and sediments, internal cycling rates (zooplankton excretion and net sediment-water flux), and net downstream exchange. nnual terrestrial and atmospheric inputs (average of 1985 and 1986 data) of Tn and TP ranged from 4.3g TN M-2 yr-1 to 29.3g TN M-2 yr-1-2 -2 -1and 0.32g TP M yr-1 to 2.42g TP M yr , respectively. hese rates of TN and TP input represent 6-fold to 8-fold and 13-fold to 24-fold increases in loads to these systems since the precolonial period. ecent 11-yr record for the Susquehanna River indicates that annual loads of TN and TP have varied by about 2-fold and 4-fold, respectively. N inputs increased and TP inputs decreased during the 11-yr period. he relative importance of nutrient sources varied among these estuaries:point sources of nutrients delivered about half the annual TN and TP load to the Patuxent and nearly 60% of TP inputs to the Choptank; diffuse sources contributed 60-70% of the TN and TP inputs to the mainstream Chesapeake and Potomac River. he direct deposition of atmospheric wet-fall to the surface waters of these estuaries represented 12% or less annual TN and TP loads except in the Choptank River (37% of TN and 20% of TP). e found direct, although damped, relationships between annual rates of nutrient input, water-column and sediment nutrient stocks, and nutrient losses via burial in sediments and denitrification. ur budgets indicate that the annual mass balance of TN and TP is maintained by a net landward exchange of TP and, with one exception (Choptank River), a net seaward transport of TN. he budgets for all systems revealed that inorganic nutrients entering these estuaries from terrestrial and atmospheric sources are rapidly converted to particulate and organic forms. iscrepancies between our budgets and others in the literature were resolved by the inclusion of sediments derived from shoreline erosion. he greatest potential for errors in our budgets can be attributed to the absence of or uncertainties in estimates of atmospheric dryfall, contributions of nutrients via groundwater, and the sedimentation rates used to calculate nutrient burial rates.