THIS RESEARCH WAS DESIGNED TO PREDICT THE POTENTIAL RESPONSES OF GALVESTON BAY TO FRESHWATER INPUT REDUCTION WHICH WOULD INCREASE FRESHWATER RETENTION TIME, 15% OF HOUSTON SHIP CHANNEL EFFLUENT ENTERING CONTINUOUSLY INTO THE ESTUARINE HEADWATERS, AND SIMULTANEOUS APPLICATION OF BOTH STRESSES. SINCE THESE RESPONSES COULD NOT BE INVESTIGATED DIRECTLY, THE EFFECTS OF A SIMULATED FRESHWATER IMPOUNDMENT AND SIMULATED HOUSTON SHIP CHANNEL DIVERSIONS INTO ESTUARINE HEADWATERS WERE INVESTIGATED ON A GROUP OF SIX CONTINUOUS-CULTURE MICROECOSYSTEM SIMULATIONS OF GALVESTON BAY. THE EXPECTED GENERAL RESPONSES OF THE BAY ECOSYSTEM TO DAM CONSTRUCTION NEAR THE MOUTH OF THE TRINITY RIVER ARE INCREASING SALINITY, REDUCED IMPORT AND EXPORT OF ORGANIC CARBON, GREATER PROPORTION OF NUTRIENTS BOUND IN LIVING FORM, SHIFT IN COMMUNITY MET PRIMARY AND SECONDARY PRODUCTIVITY, AND REDUCTION IN THE ESTUARINE ECOSYSTEM'S EFFICIENCY AT CONVERTING INCOMING ENERGY INTO USEFUL WORK AND/OR PRODUCTS. SIMULTANEOUS DIVERSION OF HOUSTON SHIP CHANNEL EFFLUENT TO THE HEADWATERS OF GALVESTON BAY CAN BE EXPECTED TO BE ASSIMILATED PRIMARILY IN THE MOST IMPORTANT NURSERY AREAS OF THE BAY. PHYTOPLANKTON AND ZOOPLANKTON SPECIES DIVERSITY THROUGHOUT THE ESTUARY WILL BE REDUCED; THIS EFFECT WILL BE MOST INTENSE IN ESTUARINE HEADWATERS. (JONES-WISCONSIN)