Nutrient-Dissolved Oxygen Dynamics In Chesapeake Bay
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Date
1985
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Abstract
This study focused on the relationships of phytoplankton and microheterotrophs
to the development and maintenance of anoxia in the mesohaline
region of Chesapeake Bay. A series of 14 cruises were made from February to
October, 1985, on which water quality, nutrient concentrations, phytoplankton
production, and microheterotroph production and metabolism were
assessed. Phytoplankton production from February to May generates a quantity of
organic matter more than adequate to cause oxygen decline in mid-Bay deep
waters. The development of the summer mazimum in phytoplankton productivity
appears to depend upon the regeneration of nutrients from phytoplankton
carbon produced in the spring which sinks into deep water and is remineralized
by bacteria. These nutrients are recycled into the euphotic zone via
vertical mixing and oscillations of the pycnocline. Bacterial biomass, production, and metabolism are tightly coupled to
phytoplankton production during the spring and summer. Phytodetritus is the
source of carbon fueling bacterial oxygen consumption in deep waters. A
relationship for predicting oxygen consumption rates from bacterial abundance
estimates has been developed. Water column oxygen consumption by
microheterotrophs is a major contributor to the development of anoxia during
the spring and early summer. Microbial sulfur cycling then becomes an important mechanism for maintaining anoxia. The potential for the establishment of anoxia is greatest in the northern regions of the mesohaline Chesapeake Bay.
greater variation over shorter distances in an east to west direction.
However, phytoplankton and bacteria parameters exhibit greater variatin over shorter distances in an east to west direction.
Comparisons of biological measurements made in the summer of 1984, a
high flow year in which anoxia was widespread, with measurements made in
1985, a low flow year in which anoxia was limited and of short duration,
suggest that fundamental changes have occurred in the ecosystem of mid-
Chesapeake Bay such that a significant portion of primary production is
channeled into bacterial production. Thus, the severity of anoxic conditions depends upon climatic differences regulating freshwater flow, pycnocline
tilting, and wind mixing rather than upon changes in biological parameters.
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Keywords
Phytoplankton, Micro-Heterotrophs, Summer Conditions 1985