Nitrogen dynamics in the tidal freshwater Potomac River, Maryland and Virginia, water years 1979-81: A water-quality study of the tidal Potomac River and estuary
On an annual basis, river supplied nitrate is the predominant form of N supplied to the tidal Potomac River from external sources. Much of the nitrate is associated with high flows that have rapid transit times through the tidal river. After the fall of 1980, initiation of advanced wastewater treatment at the Blue Plains Sewage Treatment Plant (STPP) reduced ammonia loading to the river by 90% and increased nitrate loading by a similar percentage. As a result, concentrations of ammonia during the 1981 low flow period were < 0.20 mg/L as N at alexandria, while nitrate concentrations were > 1.50 mg/L as N. Despite the reduced availability of ammonia, 15-N uptake studies showed that phytoplankton preferred ammonia to nitrate unless ammonia concentrations were < 0.10 mg/L as N. Nitrification studies during 1981 using a 14-C uptake technique indicate that rates did not vary with sample location, except for one sample from the head of the tidal river, where the rates were much higher. Process models were used in conjunction with mass-balance determinations and individual process studies to estimate rates of processes that were not directly measured. It is estimated that denitrification removed 10 times as much nitrate from the water column during the summer of 1981 as during the summer of 1980. Sedimentation of particulate N is estimated to be the largest sink for N from the water column and was approximately equal to the external annual loading of all N constituents on a daily basis. In summer, when river flows usually are low, the tidal Potomac River appears to be a partially closed system rather than one dominated by transport. Nitrogen constituents, primarily from point sources, are taken up by phytoplankton converted to organic matter, and sedimented from the water column. Some of this N eventually becomes available again by means of benthic exchange. Removal, by transport, out of the tidal river is significant only during winter. 70 refs., 20 figs., 10 tabs.
- OSTI ID:
- 7161205
- Country of Publication:
- United States
- Language:
- English
Similar Records
Water quality of the tidal Potomac River and Estuary: Hydrologic Data Reports supplement, 1979 through 1981 water years
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Related Subjects
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Aquatic-- Basic Studies-- Radiometric Techniques-- (1990-)
540320* -- Environment
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63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMMONIA
AQUATIC ORGANISMS
CARBON 14 COMPOUNDS
CARBON COMPOUNDS
CHEMICAL REACTIONS
DEVELOPED COUNTRIES
ECOLOGICAL CONCENTRATION
ESTUARIES
FRESH WATER
HYDRIDES
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
MARYLAND
MONITORING
NITRATES
NITRIFICATION
NITROGEN 15
NITROGEN COMPOUNDS
NITROGEN CYCLE
NITROGEN HYDRIDES
NITROGEN ISOTOPES
NORTH AMERICA
NUCLEI
ODD-EVEN NUCLEI
OXYGEN COMPOUNDS
PHYTOPLANKTON
PLANKTON
PLANTS
POLLUTION
POTOMAC RIVER
RIVERS
STABLE ISOTOPES
STREAMS
SURFACE WATERS
TRACER TECHNIQUES
USA
VIRGINIA
WATER
WATER POLLUTION