Primary Productivity and Community Structure of an Estuarine Impoundment

An impounded estuary was employed to study primary productivity, community respiration, and community structure as they related to seasonal and temporal succession, salinity, and water temperature. Metabolism of plankton was studied by the light— and dark—bottle technique; that of the benthic community was determined by using the "diurnal oxygen curve" method. Four different physical environments developed owing to procedures required to control the water in the management of the impoundment. One environment was saline, two were brackish, and one was fresh water. Distinct benthic plant communities developed in each of these environments, and these communities were named according to the dominant plants. An Enteromorpha—Melosira community developed in the saline environment and accounted for the highest metabolic rates of the entire study. A photosynthesis to respiration ((P/R) ratio of 1.36 resulted in the development of a large standing crop which dramatically became senescent during late fall and formed organic ooze on the bottom as well as contributing dissolved and suspended organic matter in the water. The Melosira—Enteromorpha community developed in brackish water and maintained a P/R of 0.76. The Melosira—Spirogyra community developed in the fresh—water environment and maintained a P/R of 0.78, and the Rhizoclonium—Melosira—Synedra community, which developed in brackish water, maintained a P/R of 0.77. The plankton flora was characteristically tychoplankton. The magnitude of the plankton metabolic rates was less than that of the benthic communities. The impoundment maintained a mean P/R of 1.02 over the entire study period, and was essentially autotrophic, primarily owing to the large standing crop developed by the Enteromorpha—Melosira community. Little exogenous organic material appeared to have been imported into the system.