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Effect of Discharge on the Chlorophyll a Distribution in the Tidally-Influenced Potomac River

James P. Bennett, Joan W. Woodward and David J. Shultz
Estuaries
Vol. 9, No. 4, Part A: River Input as a Cause of Estuarine Variability (Dec., 1986), pp. 250-260
Stable URL: http://www.jstor.org/stable/1352097
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Effect of Discharge on the Chlorophyll a Distribution in the Tidally-Influenced Potomac River
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Abstract

In the tidal Potomac River, high river discharges during the spring are associated with high chlorophyll a concentrations in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophyll a (less than 50 μ g l-1) occurred in the tidal river if average monthly discharge during July or August exceeded 200 m3 s-1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophyll a (greater than 100 μ g l-1) approximately one year out of four. Chlorophyll a maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m3 s-1, but sustained discharges greater than 1,100 m3 s-1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.

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