External Nutrient Sources, Internal Nutrient Pools, and Phytoplankton Production in Chesapeake Bay

• Published in: Estuaries 1992-12, Vol.15 (4), p.497-516
• Main Authors: Magnien, Robert E., Summers, Robert M., Sellner, Kevin G.
• Format: Article
• Language: English
• Subjects: 540320 - Environment, Aquatic- Chemicals Monitoring & Transport- (1990-); 560300 - Chemicals Metabolism & Toxicology; AIR POLLUTION; Animal, plant and microbial ecology; Applied ecology; AQUATIC ORGANISMS; ATLANTIC OCEAN; BAYS; Biological and medical sciences; BIOMASS; CHESAPEAKE BAY; COASTAL WATERS; DILUTION; ECOLOGICAL CONCENTRATION; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; ELEMENTS; ENERGY SOURCES; ENVIRONMENTAL SCIENCES; ESTUARIES; Fundamental and applied biological sciences. Psychology; HYDROGEN COMPOUNDS; LIQUID WASTES; MANAGEMENT; NITROGEN; NONMETALS; NUTRIENTS; OXYGEN COMPOUNDS; Particulate matter; Phosphates; PHOSPHORUS; PHYTOPLANKTON; PLANKTON; PLANTS; POLLUTION; POTOMAC RIVER; PROCESSING; PRODUCTIVITY; Quaternary ammonium compounds; RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT; RENEWABLE ENERGY SOURCES; RIVERS; SALINITY; SEAS; SEASONAL VARIATIONS; SEDIMENTATION; Sediments; STREAMS; SURFACE WATERS; VARIATIONS; WASTE MANAGEMENT; WASTE PROCESSING; WASTE WATER; WASTES; WATER; WATER POLLUTION; Watersheds; ZONES
• ISSN: 0160-8347; 1559-2758
• DOI: 10.2307/1352393

External nutrient loadings, internal nutrient pools, and phytoplankton production were examined for three major subsystems of the Chesapeake Bay Estuary-the upper Mainstem, the Patuxent Estuary, and the Potomac Estuary-during 1985-1989. The atomic nitrogen to phosphorus ratios (TN:TP) of total loads to the Mainstem, Patuxent, and the Potomac were 51, 29 and 35, respectively. Most of these loads entered at the head of the estuaries from riverine sources and major wastewater treatment plants. Approximately 7-16% of the nitrogen load entered the head of each estuary as particulate matter in contrast to 48-69% for phosphorus. This difference is hypothesized to favor a greater loss of phosphorus than nitrogen through sedimentation and burial. This process could be important in driving estuarine nitrogen to phosphorus ratios above those of inputs. Water column TN:TP ratios in the tidal fresh, oligohaline, and mesohaline salinity zones of each estuary ranged from 56 to 82 in the Mainstem, 27 to 48 in the Patuxent, and 72 to 126 in the Potomac. A major storm event in the Potomac watershed was shown to greatly increase the particulate fraction of nitrogen and phosphorus and lower the TN:TP in the river-borne loads. The load during the month that contained this storm (November 1985) accounted for 11% of the nitrogen and 31% of the phosphorus that was delivered to the estuary by the Potomac River during the entire 60-month period examined here. Within the Mainstem estuary, salinity dilution plots revealed strong net sources of ammonium and phosphate in the oligohaline to upper mesohaline region, indicating that these areas were sites of considerable internal recycling of nutrients to surface waters. The sedimentation of particulate nutrient loads in the upper reaches of the estuary is probably a major source of these recycled nutrients. A net sink of nitrate was indicated during summer. A combination of inputs and these internal recycling processes caused dissolved inorganic N to P ratios to approach 16:1 in the mesohaline zone of the Mainstem during late summer; this ratio was much higher at other times and in the lower salinity zones. Phytoplankton biomass in the mesohaline Mainstem reached a peak in spring and was relatively constant throughout the other seasons. Productivity was highest in spring and summer, accounting for approximately 33% and 44%, respectively, of the total annual productivity in this region. In the Patuxent and Potomac, the TN:TP ratios of ext