Selected limnologic characteristics were examined at an east-central Indiana borrow pit lake to determine the role of submerged aquatic plants in water chemistry dynamics. During the summer of 1978 the lake was sampled at approximately weekly intervals in the evening and again the following morning in the shallow macrophyte area and the deeper open water control area void of macrophytes. Alkalinity, dissolved oxygen, and pH were evaluated for changes induced by macrophytes and Aufwuchs.Maximum macrophyte dry weight biomass was observed in the middle of July, after which the plants died off quickly. Potamogeton pusillus and P. pectinatus were the dominant species present.Dissolved oxygen levels were found to be higher in the evening and lower in the morning due to photosynthesis and respiration of aquatic plants at the macrophyte siteas compared to the control site. Daily variations in alkalinity at the macrophyte site were more intense than recorded at the control site. During the day, bicarbonate alkalinity was decreased and carbonate alkalinity increased at the macrophyte site. Diurnal fluctuation of hydrogen ion concentration was also greater at the macrophyte site than at the control site. Metabolism by macrophytes and Aufwuchs greatly influenced the water chemistry of Dumpert's Borrow Pit Lake.Laboratory studies have identified fluctuating levels of dissolved oxygen as a stress on fish resulting in reduced growth. A pilot experiment was conducted to determine the effects of macrophyte and Aufwuchs induced diurnal fluctuations of dissolved oxygen on growth, food consumption, and food conversion by adult bluegill fed mealworms ad libitum. Average growth, food consumption, and food conversion were lower for bluegill exposed to macrophyte-induced water quality changes. None of the differences were significant, however, due to variability and the small sample size.Ball State UniversityMuncie, IN 47306