Primary reproduction studies in shallow aquatic environments of Southern Illinois

Summary

An investigation of photosynthetic and respiratory rates for natural communities found in shallow aquatic environments (∼1 decimeter) revealed significant differences for communities dominated by different species. The lowest rates (70 micromoles/gram dry weight of algae per hour) were observed for communities dominated by Cladophora. Highest rates (580) were associated with communities dominated by blue-green algae. A pronounced diurnal trend was established with highest rates in the morning and declines to rates one-half so high or less in the late afternoon. Respiration rates were one-fourth to one-sixth as high as gross photosynthesis, and did not show consistent diurnal trends. Experiments utilizing CO₂-fertilized waters revealed enhanced photosynthetic rates in communities dominated by filamentous algae, but not in the blue-green communities. In all communities so investigated an interesting phenomenon of CO₂-uptake was encountered in the dark bottles, exhibiting dark CO₂-absorption similar to that attributable to photosynthesis. Photosynthetic rates under completely natural conditions average 8 micromoles per liter of water per hour, agreeing closely with data for less shallow environments reported in the literature.