Ecological parameters concerning the zooplankton community of the San Antonio estuarine system

Increasing urbanization and industrialization in coastal areas has resulted in the damming of many rivers leading into coastal estuaries, and the retardation of freshwater supply can have detrimental effects upon estuarine areas. Low flow augmentation of an estuary's fresh water supply causes a reduction in river material input and an increase in estuarine salinities. This often results in extensive qualitative changes in the biological characteristics of the estuarine ecosystem (Williams 1955; Copeland and Jones 1965; Copeland 1966). Quantitative characteristics may also be affected (Odum and Wilson 1962), especially in heterotrophic systems such as those involved in this study. The productivity of a heterotrophic estuarine ecosystem may not have an instantaneous response to decreased river flow, but on a long term basis most of the nutrient material deposited in the estuarine basin will be transported to the open sea. The purpose of this study is to determine the effects of environmental variations upon an estuarine zooplankton community, with special emphasis given to environmental conditions which would be appreciably altered by low flow augmentation. This is accomplished by analysis of field data obtained from the San Antonio estuarine system from April 1966 to May 1967. The sampling period traversed a term of naturally occurring low flow; the spring of 1966 had peak river flow rates, while the spring of 1967 was a virtual drought