In situ Measurement of Macrophyte Photosynthesis and Respiration in Shallow Lakes

A method using a specially designed apparatus is presented for obtaining in situ measurements of macrophytic photosynthesis and respiration in shallow lakes. While the measurement of suspended algal photosynthesis and respiration is relatively straightforward using conventional light bottle/dark bottle techniques, macrophytic photosynthesis and respiration is difficult. Indeed, these processes are often neglected in some dissolved oxygen dynamic models, including QUAL2E. This is problematic in some systems where macrophytes may dominate. The procedure presented herein utilizes an apparatus consisting of light (clear) and dark (opaque) tubes in which commercially available dissolved oxygen probes are inserted. Results are presented and discussed from two different New Jersey lakes.