Nutrient Budgets and Management Actions in the Patuxent River Estuary,Maryland |
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Authors: | W R Boynton J D Hagy J C Cornwell W M Kemp S M Greene M S Owens J E Baker R K Larsen |
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Institution: | (1) Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Box 38, Solomons, MD 20688, USA;(2) Environmental Protection Agency Laboratory, 1 Sabine Island Drive, Gulf Breeze, FL 32561, USA;(3) Horn Point Environmental Laboratory, University of Maryland Center for Environmental Science, Box 775, Cambridge, MD 21613, USA;(4) Department of Chemistry and Biochemistry, St. Mary’s College of Maryland, St. Mary’s City, MD 20686, USA |
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Abstract: | Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified
and moderately eutrophic tributary of Chesapeake Bay. Major inputs (point, diffuse, septic, and direct atmospheric) were measured
for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment
plant improvements. Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in
tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and
biota. Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated
using a salt and water balance model. Several major nutrient recycling terms were directly and indirectly evaluated and compared
to new N and P inputs on seasonal and annual time-scales. Major findings included: (1) average terrestrial and atmospheric
inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured
in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that
expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline
estuary, which by area comprised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and
P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons
and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded
rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought
periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore
water quality conditions to pre-eutrophic levels. |
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