GW - Yes. Addition of dissolved oxygen to water by phytoplankton, periphyton and rooted (submerged) plants is from photosythesis. Periphyton, FA, and submerged vascular plants add a big percentage but maybe not the largest percentage of the plant generated DO in the shallow and littoral zones. It depends. Phytoplankton can be very abundant in near-shore areas along with all the other plants. Light's penetration depth into the water plays a big role in this discussion. In open water (pelagic) zones (of primarily larger water bodies), phytoplankton for sure contributes the largest percentage of the plant produced DO. In small water and shallow water bodies, attached vegetation (algae and rooted) is often abundant and thus a big DO contributor. When estimating oxygen budgets of water, the proportion of littoral vs pelagic zones is important. Productivity (trophic status) and water transparency also play important roles in this topic because of the amount of plants present and ability of light to penetrate into the water.
GW asks- "How would this effect the efficiency of running aeration at night?" Surface disruption and bubbling activity is best at night because it does add some dissolved oxygen to the water. During night plant photosynthesis adds no oxygen to the water. Thus if one can add any extra DO, when photsynthesis is not occuring, it is good. Anytime you can add DO to the water of fish ponds it is good.
The main issue that I had with Sue's comment above of "the water is mostly reoxygenated by exposure to the air at the surface, not necessarily by phytoplankton" is primarily about which method adds the most DO to a pond or lake. I say phytoplankton (plants) and she says water's exposure to air at the surface (which has to be by diffusion). Do not take or use my discussion above as my answer to the debate.
Bruce asks "Do we have specific literature on what appears to be a "surface diffusion vs. phytoplankton delivery" issue that needs resolved?" There are no posts, discussions, or literature about which method adds the most DO to water or else they would have been referenced or cited. This thread may produce that info. I am waiting for Sue or someone to present her side of the debate.
