Inhibition of Metabolic Hydrogen Ion Flux Resulting from Cadmium Stress in Aquatic Microecosystems

Abstract

Periodic changes in pH were monitored at 30 s intervals in naturally-derived, aquatic microeco-systems. The pH of the system was controlled between two setpoints with a microcomputer. When the upper setpoint was reached a light bank was turned off until the pH dropped to the lower setpoint and the light was again turned on. The cycling of the pH in the microcosms was analyzed using time series analysis techniques. Each experiment resulted in a 24 hour control data set and a 24 hour experimental data set that began with the addition of an inhibitor or toxicant. EC50 values (effective concentration for 50% inhibition) of net photosynthesis and respiration of the community were calculated from slopes of the periodic response to cadmium and compared to literature values. The EC50 for dark induced pH change was 3.8 ppm while the EC50 for light induced pH change was 0.51 ppm. Increasing cadmium concentrations caused dominant peaks in the variance periodograms to be shifted to longer periods.