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First Place - Friends of Agua Caliente Award

The Relationship Between Photosynthesis, Cellular Respiration and Wet Biomass in Egeria densa

Earth and Environmental Sciences
Preston Stricker

Mr. Casey White

"Dissolved oxygen (DO) is an indicator of wetland health. Water plants both produce O2 and consume it. The rates of DO production and consumption were measured in eight flasks containing increasing masses of the water plant Egeria densa. Samples ranged from control (no E. densa), ~1/2 sprig (0.6 gm), ~ one sprig (0.9 gm) and up to ~ six sprigs (6.0 gm), floating in 230 ml of a 0.5% sodium bicarbonate-distilled water solution (to provide a CO2 source for photosynthesis). After determining the wet biomass of E. densa, the flasks were exposed to eight hours of 4,000-lumen LED light at one meter, and then to eight hours of complete darkness. DO was determined using a Milwaukee MW600 electronic DO meter before and after each experiment, and the change in DO was graphed against E. densa wet biomass. Regression analysis was used to determine the strength of relationship for the light and for the dark experiments. In darkness, the reduction of DO was linear and highly correlated with wet biomass down to <1.0 PPM (R2 x 100 = 98.9). When exposed to light, the relationship between change in DO and wet biomass was linear to about eight PPM and then showed a plateau with a weak correlation (R2 x 100 = 44.4). At the highest ratio of E. densa to water, DO consumption exceeded DO production. The optimal level for wetland health is below that point. The results of this study are limited to E. densa and to eight hours of light and dark. Future projects should study other aquatic plant species and investigate to effects of longer or shorter light-dark cycles."

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