Initial Measurements of Benthic Photosynthesis and Respiration in Lake Erie

The first reported in situ measurements of benthic primary production in Lake Erie were made on rocky substrata using oxygen and dissolved inorganic carbon change in 1997 and 1998. The productivity quotient for net benthic algal growth was determined to be 1.1 based on contemporaneous measurement of oxygen production and carbon uptake. Highest rates of gross photosynthesis were > 300 mg O2/m2/h on rocky substrata with mixed stands of Cladophora and dreissenid mussels. These stands also exhibited the greatest rates of oxygen consumption in the dark. Bare rock substrata had lower rates of gross photosynthesis than rock occupied by mussels or Cladophora, but even these habitats had rates that would place them among the highest rates measured in fresh water. Areal benthic photosynthetic rates would greatly exceed areal pelagic photosynthesis in depths shallower than 5 m depth in the eastern basin; and, at greater depths, the importance of declining benthic areal photosynthesis relative to generally increasing integral pelagic production with depth would depend on substratum type and water clarity. Dreissenid mussels had a positive effect on benthic photosynthesis that was especially evident in stimulating Cladophora growth over the course of the 1998 season.